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This document contains Chapters 10 to 11 CHAPTER 10 Taxonomy and Phylogeny of Animals CHAPTER OUTLINE 10.1. Order in Diversity A. History 1. All cultures classify or group animals by patterns in animal diversity. 2. Systematic zoologists have three goals: a. to discover all species of animals, b. to reconstruct their evolutionary relationships, and c. to communication those relationships via an informative taxonomic system. 3. Taxonomy produces a formal system for naming and classifying species. 4. Systematics is the broader science of studying variation among animal populations used to understand their evolutionary relationships.. 5. Adjusting taxonomy to accommodate evolution has produced several problems and controversies. B. Linnaeus and Taxonomy 1. The Greek philosopher Aristotle was the first to classify organisms according to their structural similarities 2. Carolus Linnaeus invented the current system of classification. (Figure 10.1) a. Linnaeus was a Swedish botanist with extensive experience classifying flowers. b. He used morphology to develop a classification of animals and plants in his Systema Naturae. 3. A hierarchy of taxa is one major concept Linnaeus introduced. (Table 10.1) a. His hierarchy contains 7 major ranks: kingdom, phylum, class, order, family, genus and species. b. All animals are classified in kingdom Animalia, each species has its own name; the names of animal groups at each rank in the hierarchy are called taxa (singular: taxon). c. Each rank can be subdivided into additional levels of taxa, as in subfamily, superorder, etc. d. For large and complex groups, such as fishes and insects, up to 30 levels may be used. 4. Systematization versus Classification a. Taxonomists’ role has changed from classification of organisms to systemization with the introduction of evolutionary theory. b. Taxonomists now group organisms according to their evolutionary lineage. 5. Binomial Species Nomenclature a. Linnaeus introduced binomial nomenclature. b. A scientific name of an animal consists of two words (binomial) as in Turdus migratorius. The first word is the genus and is capitalized; the second is the specific epithet and is in lower case. To separate from common text, a scientific name is always written in italics or underlined. c. The specific epithet is never used; the genus must be used to form the scientific name. d. A specific epithet may be used in many names; animal genera must always be different. e. Ranks above species are single names written capital initial letter (e.g., Reptilia and Cnidaria). f. Geographic subspecies are trinomials; all three terms are in italics, and the subspecies is in lower case. (Figure 10.2) g. A polytypic species contains one subspecies whose subspecific name is a repetition of the species epithet and one or more additional subspecies whose names differ. 10.2. Species A. Criteria for Recognition of Species 1. Huxley was among the first to ask, “What is a species?” 2. “Species” is easy to use, but the term “species” has been hard to define. 3. Certain criteria for identifying species has been used. a. Common descent—members of a species must trace their ancestry to a common ancestral population. b. Smallest distinct grouping—members share similar characteristics different from those in higher taxa. These may consist of morphological, chromosomal, and molecular characters. c. Reproductive community—members must form a reproductive community that excludes members of other species. 4. A species has a geographic range and evolutionary duration, which defines its distribution through space and time. Geographic ranges may be large or worldwide distributions, cosmopolitan, or restricted ranges, endemic. A species geographic range can change over its evolutionary duration. B. Typological Species Concept (Figure 10.3) 1. Before Darwin, species were considered fixed and with essential and immutable features. 2. Typological species concept centered on an ideal form for the species; variations were “imperfect.” 3. A type specimen was labeled and deposited in a museum to represent this “standard” specimen; today the practice continues, but as a name-bearer to compare with potentially new species. 4. Variation in a population is now recognized as normal. C. Biological Species Concept 1. Theodosius Dobzhansky and Ernst Mayr formulated this during the evolutionary synthesis. 2. A species is a reproductive community of populations (reproductively isolated from others) that occupies a specific niche in nature. 3. The ability to successfully interbreed is central to the concept. 4. The criteria of “niche” tie in ecological properties. 5. However, controlled breeding experiments can be difficult to conduct. Molecular and other studies may detect sibling species with similar morphology. The biological species concept lacks an explicit temporal dimension and gives little guidance regarding the species status of ancestral populations relative to their evolutionary descendants. Proponents of the biological species concept often disagree on the degree of reproductive isolation necessary for the determination of distinct species. 9. The biological species concept has received strong criticism for a number of reasons: a. A species has limits in space and time; boundaries between species may be difficult to locate. b. Species are both a unit of evolution and a rank in taxonomic hierarchy. c. Interbreeding is not an operational definition in asexual organisms. D. Evolutionary and Cohesion Species Concepts 1. Where do we set the species boundary in a lineage leading back to a fossil form? 2. Simpson provided the evolutionary species concept in the 1940s; it persists with modification. (Figure 10.4) 3. An evolutionary species is a single lineage of ancestor-descendant populations that maintains its identity from other such lineages and that has its own evolutionary tendencies and historical fate. 4. This definition accommodates both sexual and asexual forms as well as fossils. 5. The cohesion species concept is as follows: the most inclusive population of individual shaving the potential for phenotypic cohesion through intrinsic cohesion mechanisms. E. Phylogenetic Species Concept 1. The phylogenetic species is an irreducible (basal) grouping of organisms diagnosably distinct from other such groupings and within which there is a parental pattern of ancestry and descent. 2. This is a monophyletic unit that recognizes the smallest groupings that undergo evolutionary change. 3. It discerns the greatest number of species but may be impractical. 4. This system disregards details of evolutionary process. F. Dynamism of Species Concepts 1. The various competing concepts of species have a common underlying principle, that a species constitutes a segment of a population-level lineage—the general lineage concept of species. 2. Disagreement is a sign of dynamic research and argument. 3. We cannot predict which species concepts will remain useful in the future. 4. It is possible that disagreements regarding species boundaries may identify interesting cases of evolution in action. 5. No one concept is comprehensive or final; all need to be understood to understand future concepts. G. DNA Barcoding of Species 1. DNA barcoding is a technique for identifying organisms to species using sequence information from a standard gene present in all animals. 2. This method can be used for specimens in nature as well as natural-hisotry museums, zoos, aquaria, and frozen-tissue collections. 3. DNA barcoding often permits the origin of a specimen to be identified to a particular local population. 10.3. Taxonomic Characters and Phylogenetic Inference A. Homology 1. A phylogeny or evolutionary tree is based on the study of characters that vary among species. 2. Character similarity that results from common ancestry is called homology. 3. Different lineages may develop similar features independently; this is convergent evolution. 4. Characters that are similar but misrepresent common descent are nonhomologous or homoplastic. B. Using Character Variation to Reconstruct Phylogeny (Figure 10.5) 1. Reconstructing phylogeny requires determining ancestors and descendants. 2. The form that was present in the common ancestor is ancestral. 3. Characters that arose later are derived character states. 4. An outgroup shows if a character occurred both within and outside the common ancestor. 5. A series of species that share derived characters form a subset called a clade. 6. The derived character shared by members of a clade is called a synapomorphy of that clade. 7. By identifying the nested hierarchy of clades or branches, we can form patterns of common descent. 8. Character states ancestral for a taxon are plesiomorphic for that taxon; sharing of ancestral states is termed symplesiomorphy. 9. Identifying the level at which a character state is a synapomorphy may identify a clade. 10. A cladogram is a nested hierarchy of clades. 11. To obtain a phylogenetic tree, we must add important information on ancestors, duration of lineages, and amount of change. C. Sources of Phylogenetic Information (Figure 10.6) 1. Comparative morphology examines shapes, sizes and development of organisms. a. Skull bones, limb bones, scales, hair and feathers are important morphological characteristics. b. Both living specimens and fossils are used as phylogenetic information. 2. Comparative biochemistry analyzes amino acid sequences in proteins and nucleic acid sequences in nucleotides. a. Direct sequencing of DNA and indirect comparisons of proteins sequences are comparative methods. b. Some recent studies use biochemical techniques to analyze fossils. 3. Comparative cytology (karyology) examines variation in number, shape and size of chromosomes in living organisms. 4. Fossils can provide information on the relative time of evolution; radioactive dating can confirm age. 5. Some protein and DNA sequences undergo linear rates of divergence; this allows us to calculate the time of the most recent common ancestors. 10.4. Theories of Taxonomy A. Phyletic Relationships (Figure 10.7) 1. Based upon phylogenetic tree or cladogram, a taxonomic group and can be one of three forms. a. Monophyly—a monophyletic taxon includes the most recent common ancestor and all descendants of that ancestor. The terms “monophyletic group” and “clade” are synonymous. b. Paraphyly—a taxon is paraphyletic if it includes the most recent common ancestor of all members of a group but not all descendants of that ancestor. c. Polyphyly—a taxon is polyphyletic if it does not include the most recent common ancestor of members of that group; the group has at least two separate evolutionary origins. 2. Monophyletic and paraphyletic groups share the property of convexity; a group is a convex if you can trace a path between any two members of the group on a cladogram or phylogenetic tree without leaving the group. 3. Both evolutionary and cladistic taxonomy accepts monophyletic and rejects polyphyletic groups; they differ on accepting paraphyletic groups. B. Evolutionary Taxonomy (Figures 10.8-10.9) 1. The two main principles are common descent and amount of adaptive evolutionary change. 2. A branch on a family tree represents a distinct adaptive zone; a distinct “way of life.” 3. A taxon that represents an adaptive zone is a grade; modifications of the penguin branch to swimming are an example. 4. Evolutionary taxa may be either monophyletic or paraphyletic; chimpanzees and gorillas share a more recent ancestor with man than with orangutans, but are in a family separate from humans. 5. By accommodating adaptive zones, nomenclature reflecting common descent is not as clear. 6. Phenetic taxonomy was another school of classification that abandoned producing phylogenetic trees in favor of measuring overall similarity; but it has little support today. C. Phylogenetic Systematics/Cladistics (Figure 10.10) 1. Willi Hennig first proposed cladistics or phylogenetic systematics in 1950. 2. It emphasizes common descent and cladograms. 3. For example, chimpanzees, gorillas and orangutans are included in Hominidae with humans. 4. Cladists do not assert that amphibians evolved from fish or birds from reptiles; they contend that a monophyletic group descending from a paraphyletic group contains no useful information. 5. Likewise, extinct ancestral groups are always paraphyletic since they exclude a descendant that shares their most recent common ancestor. 6. Some cladists indicate that primitive and advanced are relic ideas derived from a pre-Darwinian “scale of nature” leading to humans near the top; groups were defined based on “higher” features they lacked. 7. Cladists avoid paraphyletic groups by defining a list of sister groups to each more inclusive taxon. D. Current State of Animal Taxonomy 1. Modern animal taxonomy was established using evolutionary systematics and cladistic revisions. 2. Total use of cladistic principles would require abandonment of Linnaean ranks. 3. A new taxonomic system called Phylocode is being developed as alternative to Linnean taxonomy. 4. This system replaces Linnean ranks with codes that denote the nested hierarchy conveyed by cladograms. 5. Sister groups relationships are clear descriptions that will replace “mammals evolved from reptiles” paraphyletic statements that are problematic. 6. The terms “primitive,” “advanced,” “specialized” and “generalized” are used for specific characteristics and not for groups as a whole. 7. Likewise, avoid calling a living species of group of living species “basal”; rather, the term is best reserved for describing branch ponts on phylogenetic tries. 8. Cladistics causes confusion by using “bony fishes” to also include amphibians and amniotes, reptiles to include birds, but not some fossil forms, etc. 10.5. Major Divisions of Life 1. Aristotle’s two kingdom system included plants and animals; one-celled organisms became a problem. 2. Haeckel proposed Protista for single-celled organisms in 1866. 3. In 1969, R.H. Whittaker proposed a five-kingdom system to distinguish prokaryotes and fungi. 4. Woese, Kandler and Wheelis proposed three monophyletic domains above kingdom level—Eucarya, Bacteria and Archaea—based on ribosomal RNA sequences. 5. Retaining Whittaker’s five kingdoms, the Eucarya are paraphyletic unless Protists are broken up into Ciliata, Flagellata and Microsporidia, etc. (Figures 10.11) 6. More revisions are necessary to clarify taxonomic kingdoms based on monophyly. 7. “Protozoa” are neither animals nor a valid monophyletic taxon. 8. “Protista” is not a monophyletic kingdom but is most likely composed of seven or more phyla. 10.6. Major Subdivisions of the Animal Kingdom 1. Phylogenetic relationships among animal phyla have been difficult to resolve by morphological and molecular characters. 2. Animal phyla have been informally grouped based on embryological and anatomical traits. 3. Protozoa constitute many phyla and none of them belong within the animal kingdom. 4. Eumetazoa include all animal phyla except Porifera and Placozoa and is divided into Radiata and Bilateria. 5. Bilateral animals are divided into deuterostomes and protostomes based on their embryological development, with further division of Protostomia into taxa Lophotrochozoa and Ecdysozoa. Lecture Enrichment 1. Describing the problems with Aristotle’s land air sea classification provides students with an idea of the limitations of some classification schemes logical for their time. 2. One effective but time-consuming method to understand traditional, phenistic and cladistic classification is to work through one simple set of animals or plants by developing a table of traits and a similarity matrix. For instance, ask for six common animals, form a chart of features they share then build a phylogeny on number of shared traits. 3. Ask students why drug research proceeds first to rats, then to monkeys, and then moves to human trials. Ask for applications of the predictive power of a phylogeny that more closely matches evolutionary history. 4. Several decades ago, some scientists predicted numerical taxonomy would make classification a technician’s job. A decade ago, molecular systematists proclaimed they would provide the ultimate key to objective classification. Students who fully comprehend the work of systematics will understand this is a field that integrates all of biology. Commentary/Lesson Plan Background: Most students will have used high school textbooks that addressed classification in a classical manner and assume it is a matter of memorizing the hierarchy of names. Most secondary biology teachers lack coursework in systematics and therefore student misconceptions are likely. Misconceptions: Many students have been confused by biology teachers holding up a specimen and asking students to “name” (only one scientist gets to “name” a species), “classify,” (group a species with its closest relatives) or “identify” it, this final word being the correct usage. Identifying an organism by name is not classifying it; “classifying” is grouping and it takes three organisms to classify so that two are more closely related than they are to a third. In common life, these terms are used interchangeably, but biology majors must be more careful in their use of these terms, the process starts now. Students may assume that the number of species to be named is finite, as are the contents of an auto parts store or a grocery store; the continual evolutionary change dimension will not be evident. Both cladograms and phylogenies will be assumed to lead to “higher” forms on the right hand side. In practice, each branching of a phylogeny or node of a cladogram can rotate like an inverted mobile and more recent derived forms can be placed to the left or right at each branch. Schedule: If you intend to work through the concepts of “synapomorphy,” “clade,” “monophyly,” etc. and provide detailed examples of the schools of systematics, add another hour. HOUR 1 10.1. Order in Diversity A. History B. Linnaeus and Taxonomy 10.2. Species A. Criteria for Recognition of Species B. Typological Species Concept C. Biological Species Concept D. Alternatives to the Biological Species Concept E. Dynamism of Species Concepts 10.3. Taxonomic Characters and Phylogenetic Recognition A. Homology B. Using Character Variation to Reconstruct Phylogeny C. Sources of Phylogenetic Information HOUR 2 10.4.Theories of Taxonomy A. Phyletic Relationships B. Traditional Evolutionary Taxonomy C. Phylogenetic Systematics/Cladistics D. Current State of Animal Taxonomy 10.5. Major Divisions of Life 10.6. Major Subdivisions of the Animal Kingdom ADVANCED CLASS QUESTIONS: 1. Why can’t scientists arrive at one stable classification system where the taxa names no longer change? Answer: Scientists cannot arrive at one stable classification system where taxa names no longer change due to several reasons: 1. New Discoveries: • New species are constantly being discovered, particularly in less-explored regions and in microscopic habitats. • These new discoveries may necessitate the creation of new taxa or the reclassification of existing ones. 2. Advancements in Taxonomy: • Taxonomy is not a static field; it evolves with advances in technology, such as DNA sequencing and phylogenetic analysis. • New techniques and methodologies often lead to changes in our understanding of evolutionary relationships and genetic diversity. 3. Revisions and Refinements: • As scientific knowledge expands, taxonomic relationships may need to be revised or refined based on new evidence. • Taxonomists continually evaluate and update classification systems to reflect the most current understanding of evolutionary relationships. 4. International Collaboration: • Taxonomy is an international endeavor, and different taxonomists may have different interpretations of the evidence. • International bodies such as the International Commission on Zoological Nomenclature (ICZN) and the International Code of Nomenclature for algae, fungi, and plants (ICNafp) provide guidelines for naming and classifying organisms, but individual taxonomists may still interpret these guidelines differently. 2. In some states, you must have a fishing license to hunt frogs. Many stores post a sign that reads “No animals allowed,” but you are technically an animal. Such regulations are often written into state laws. Why can’t science use common names rather than scientific names? Answer: Science cannot rely solely on common names rather than scientific names due to the following reasons: 1. Ambiguity of Common Names: • Common names vary from region to region and language to language, leading to confusion and miscommunication. • The same common name may refer to different species, and different common names may refer to the same species. 2. Precision and Clarity: • Scientific names provide a precise and universally accepted way to identify and classify organisms. • Each species is assigned a unique binomial name (genus + species), ensuring clarity and eliminating ambiguity. 3. Consistency and Stability: • Scientific names follow standardized rules and conventions outlined by international codes of nomenclature. • Unlike common names, scientific names are stable and do not change over time, providing consistency in communication among scientists worldwide. 4. Legal and Regulatory Considerations: • Scientific names are essential for legal and regulatory purposes, such as wildlife conservation, trade regulations, and enforcement of hunting and fishing laws. • Common names are often insufficient for accurately identifying species in legal and regulatory contexts. 3. If organisms exist and live and die as individual organisms, why are species defined at the population level? Answer: Species are defined at the population level rather than the individual level because: 1. Genetic Variation: • Within a species, individuals exhibit genetic variation due to mutations, genetic recombination, and gene flow. • Species are defined based on shared genetic characteristics and the ability to interbreed and produce fertile offspring. 2. Reproductive Isolation: • Members of the same species can interbreed and produce viable, fertile offspring, whereas individuals from different species cannot. • Species are reproductively isolated from each other, meaning they do not interbreed in nature. 3. Evolutionary Processes: • Species are considered fundamental units of evolution, representing populations of interbreeding individuals with a common evolutionary history. • Evolutionary changes occur at the population level, leading to the divergence of populations into distinct species over time. 4. Why do cladists believe that traditional systematists are being subjective? Answer: Cladists believe that traditional systematists are being subjective because: 1. Subjectivity in Morphological Characters: • Traditional systematists often rely on subjective interpretations of morphological characters to classify organisms. • Different taxonomists may prioritize different morphological characters or interpret them differently, leading to inconsistencies in classification. 2. Lack of Objectivity in Taxonomy: • Traditional taxonomy historically relied on subjective judgments and intuition rather than objective, data-driven methods. • Cladists advocate for a more rigorous and objective approach to taxonomy, focusing on phylogenetic analysis and objective criteria for classification. 3. Focus on Phylogeny: • Cladistics emphasizes the importance of phylogenetic relationships in classification, based on shared evolutionary history and ancestry. • Traditional systematics may prioritize other criteria, such as overall similarity or ecological characteristics, which can be more subjective. 5. A phenistics movement called “numerical taxonomy” concluded that technicians taking measurements and computers calculating similarities could do all classification. Australia and the United States both have dog-like, cat-like, and rabbit-like animals but the Australia versions of these mammals have pouches (they are marsupials) while the U.S. counterparts are placental. Why is the concept of homology important here? Answer: The concept of homology is important for understanding evolutionary relationships and classifying organisms accurately: 1. Homology vs. Analogy: • Homologous structures are similar in structure and origin but may have different functions, indicating a common evolutionary origin. • Analogous structures have similar functions but different evolutionary origins and structures. 2. Evolutionary Relationships: • Homologous structures provide evidence of common ancestry and shared evolutionary history. • The presence of pouches in Australian marsupials and their absence in placental mammals is a homologous trait, indicating a shared evolutionary origin. 3. Classification and Phylogeny: • Phylogenetic classification relies on homologous characters to infer evolutionary relationships and construct phylogenetic trees. • Numerical taxonomy, based solely on similarities calculated by computers, may not distinguish between homologous and analogous traits, leading to inaccurate classifications. 4. Evolutionary Convergence: • Analogous structures, such as pouches in marsupials and placental mammals, can result from convergent evolution rather than shared ancestry. • Homology allows scientists to distinguish between traits that evolved independently (analogous) and those that share a common evolutionary origin (homologous). CHAPTER 11 Unicellular Eukaryotes: Protozoan Groups CHAPTER OUTLINE 11.1. Emergence of Eukaryotes A. Cellular Symbiosis 1. The first evidence of life dates to 3.5 billion years ago; these first cells were bacteria-like. 2. The origin of complex eukaryote cells was most likely symbiosis among prokaryotic cells. 3. Aerobic bacteria engulfed by bacteria unable to tolerate the increasing oxygen may have become mitochondria found in most modern eukaryotic cells. 4. Engulfed photosynthetic bacteria evolved into chloroplasts; descendants in the green algae lineage gave rise to multicellular plants. 5. The modification of an engulfed prokaryote into an organelle is referred to as primary endosymbiosis. 6. Protozoa are a diverse assemblage with mixed affinities. a. They lack a cell wall. b. They have at least one motile stage in the life cycle. Most ingest their food. 7. Other groups apparently originated by the secondary endosymbiosis in which one eukaryotic cell engulfed another eukaryotic cell, and the latter became transformed into an organelle. 8. Protozoans carry on all life activities inside a single plasma membrane. 9. Protozoa can live successfully only within narrow environmental ranges. 10. Protozoa are very important ecologically. 11. At least 10,000 species of protozoa are symbiotic in or on other plants or animals. 12. These relationships may be mutualistic, commensalistic, or parasitic. B. Naming and Identifying Unicellular Eukaryotic Taxa (Figure 11.1) 1. Protozoa were considered one phylum; recent work shows there are at least seven or more phyla. 2. There may be more than 60 monophyletic eukaryotic clades. 3. The term “protozoa” is now used informally without implying phyletic relationship. 4. Plants are autotrophic, while heterotroph protozoa obtain organic molecules synthesized by other organisms. 5. Heterotrophs that feed on visible particles are phagotrophs, or holozoic feeders. (Figure 11.2) 6. Those that feed on soluble food are osmotrophs, or saprozoic feeders. 7. Nutritional distinctions work well for multicellular forms, but are less distinct for unicells. 8. The mode of nutrition employed by unicellular organisms is often variable and opportunistic. 9. Originally, the mode of locomotion was used to distinguish three of the four classes of the phylum Protozoa. (Figures 11.3 − 11.7). 10. Molecular analyses have revolutionized our concepts of phylogenetic affinities in protozoans. 11. Although there is now a far better understanding of the relationships among unicellular or microbial eukaryotes, these relationships can be difficult to convey because of the proliferation of new clade names arising from each new analysis. 12. Some workers estimate there may be 250,000 protozoan species 11.2. Form and Function A. Locomotion 1. Cilia and flagella are morphologically the same and may both be called undulipodia. 2. Cilia propel water parallel to the cell surface; flagella propel water parallel to the flagellum axis. (Figure 11.4) 3. The Axoneme (Figure 11.8) a. Each contains a “9 + 2” pattern of paired microtubules, the axoneme. b. A membrane continuous with the cell membrane covers the axoneme. c. The center pair of tubules end at a small plate. d. The kinetosome, a short tube of nine triplet microtubules joins at the base of the axoneme. e. The kinetosome is the same in structure as the centriole and therefore they may give rise to each other. 4. Both protozoan and metazoan flagella and cilia have kinetosomes at their bases. 5. The sliding microtubule hypothesis explains the movement of cilia and flagella. a. Chemical bond energy in ATP propels the action. b. Release of ATP energy causes filaments to “walk along” an adjacent filament. c. Shear resistance causes the axoneme to bend. 6. Pseudopodia (Figures 11.9) a. This is the chief means of locomotion in Sarcodina, many flagellates and ameboid cells of many invertebrates and vertebrates. b. Lobopodia are large blunt extensions of the cell body containing both endoplasm and ectoplasm. c. In the limax form, the whole body moves rather than sending out arms. d. Filopodia are thin extensions containing only ectoplasm; these are seen in class Filosea. e. Reticulopodia repeatedly rejoin to form a netlike mesh. f. Axopodia occur in Actinopoda. (Figure 11.10) 1) Axial rods of microtubules support these long thin pseudopodia. 2) They form a geometrical array, which is the axonome of the axopod. 3) Addition and removal of microtubular material extends and retracts the axopod. 4) Cytoplasm flows away from the body on one side and toward the body on the other. g. How Pseudopodia Work (Figure 11.11) 1) A lobopodium forms by extending ectoplasm as a hyaline cap; endoplasm flows into it. 2) Flowing endoplasm contains actin subunits with proteins that prevent actin from polymerizing. 3) Endoplasm flows into the hyaline cap; lipids release the actin to polymerize. 4) The actin filaments cross-link by another actin-binding protein to form semisolid gel. 5) At the trailing edge of the gel, calcium ions activate actin-severing protein. 6) Filaments are released from gel and myosin associates and pulls them to contract. 7) This contraction at trailing edge forces fluid endoplasm back towards the hyaline cap. B. Functional Components of Cells of Unicellular Eukaryotes 1. Nucleus (Figures 11.12) a. The nucleus is membrane bound and contains DNA in the form of chromosomes. b. Chromatin often lumps irregularly leaving clear areas; this provides a vesicular appearance. c. Nucleoli are often present inside the nucleus. (Figures 11.12, 11.20) d. Ciliates possess two kinds of nuclei: micronucleus and macronucleus. e, Macronuclei of ciliates are compact or condensed with no clear areas. 2. Mitochondria a. Mitochondria are used in energy production. b. In cells without mitochondria, hydrogenosomes may be present. c. Hydrogenosomes are assumed to have evolved from mitochondria. d. Kinetoplasts are also assumed to be mitochondrial derivatives, and work in association with a kinetosome. 3 Golgi Complex a. The Golgi complex is part of the endomembrane system that participates in cellular secretory processes. b. They are called dictyosomes. c. Parabasal bodies are similar structures. 4. Plastids (Figure 11.13) a. Plastids are organelles containing a variety of pigments. b. Chloroplasts contain different types of chlorophylls. 5. Extrusomes a. Extrusosomes function to extrude something from the cell. b. Ciliate trichocysts are a type of extrusosome. C. Nutrition (Figure 11.14) 1. Phagotrophs or holozoic feeders ingest food particles while saprozoic feeders ingest soluble food. 2. Holozoic nutrition uses phagocytosis; the membrane invaginates around a food particle. 3. An enclosed food particle is a food vacuole or phagosome. 4. Lysomes fuse with phagosomes and dump enzymes to digest the contents. 5. As digested food is absorbed, the phagosome becomes smaller. 6. In ciliates, the site of phagocytosis is a stable cytostome. 7. Many ciliates have a point for expulsion of wastes, the cytopyge or cytoproct. 8. Saprozoic feeding may be by pinocytosis; diffusion is of little importance in protozoan nutrition. D. Excretion and Osmoregulation (Figure 11.15) 1. Excretion of metabolic wastes is by diffusion. 2. The main end product of nitrogen metabolism is ammonia that diffuses out of small protozoa. 3. Contractile vacuoles fill and empty to maintain osmotic balance. a. There is no known lipid bilayer that retains water against a gradient. b. A proton pump may actively transport H+ ions and cotransport bicarbonate; this would draw across water. c. Paramecium has complex contractile vacuoles located in one place and with an “excretory” pore surrounded by ampullae of six feeder canals. E. Reproduction 1. Asexual Processes a. Fission produces more individuals than other forms of reproduction; binary fission is most common and produces two identical copies. (Figure 11.16) b. Budding occurs small progeny cells pinch-off from a parent cell, as seen in some ciliates. c. Multiple fission, or schizogony, undergoes several nuclear divisions followed by cytokinesis, causing many simultaneous individuals to form at once; common in Sporozoea and Sarcodina. d. If union of gametes precedes multiple fission, it is sporogony. e. Mitosis in protozoa divisions varies from metazoan mitosis. 1) The nuclear membrane often persists. 2) The microtubular spindle may be formed within the nuclear membrane. 3) Centrioles are not observed in ciliates. 4) The macronucleus of ciliates simply elongates, constricts and divides without mitosis (amitosis). 2. Sexual Processes a. Although some exclusively asexual, sex is widespread and an important source of genetic variation. b. Isogametes look alike; anisogametes, the egg and sperm, are dissimilar. c. Like metazoa, some protozoa undergo gametic meiosis: meiosis occurs before gamete formation. d. In some flagellates and Sporozoea, the first divisions after fertilization are zygotic meiosis; all individuals produced up to the next zygote are haploid. e. Most protozoa that do not reproduce sexually are probably haploid; this is difficult to detect without meiosis occurring. f. Some foraminiferans show an alternation of haploid and diploid generations or intermediary meiosis, as in many plants. g. Fertilization of one gamete by another is syngamy; this is the standard form of sexual reproduction. h. Autogamy is when gametic nuclei arise by meiosis and fuse to form a zygote inside the parent organism. i. Conjugation is exchange of gametic nuclei between paired organisms, common in Paramecium. 3. Encystment and Excystment a. Protected only by a delicate membrane, protozoa are successful in changing and harsh environments. b. Cysts are dormant forms that shut down metabolism and have a resistant material covering. c. Encystment is not found in Paramecium, some parasitic forms and some marine forms. d. Cysts often resist cold or hot temperatures; some tolerate acidity but not sunlight. e. Some protozoa form cysts as a stage in a regular life cycle; most form cysts due to a change in environment. f. During encystment, cilia or flagella are resorbed; the Golgi apparatus secretes the cyst wall. g. Under favorable conditions, the organism escapes from the cyst, excystment; parasitic forms cue on host stimuli. Major Protozoan Taxa (Figure 11.17) A. Phyla Retortamonada and Diplomonada (Figure 11.18) Retortamonds include commensal and parasitic unicells. Lack mitochondria and Golgi bodies. Diplomonads, once a subgroup of retortamonds, also lack mitochondria. Recent work has shown that mitochondrial genes are present in the cell nucleus. Absence of mitochondria may be a secondary derivation. The diplomonad Giardia live in the digestive tract of humans, birds, and amphibians. B. Parabasalids (Figure 11.19) 1. The parabasalid clade contains about 400 species from the phylum Axostylata 2. Members of this phylum have a stiffening rod composed of microtubules, the axostyle. 3. Parabasalids possess a modified region of the Golgi apparatus called a parabasal body. 4. Much of the work on parabasalid structure has been done on species of Trichomonas. 5. Trichomonas vaginalis infects the urogenital tract of humans and is sexually transmitted. C. Heterolobosea 1. Heteroloboseans are naked amembas whose pseudopodia form abruptly. 2. The lifecycle includes both amebic and flagellated stages. D. Phylum Euglenozoa (Figure 11.20) 1. Generally considered as monophyletic. 2. Have a series of longitudinal microtubules that help stiffen the cell membrane into a pellicle. 3. Subphylum Euglenida a. Have chloroplasts surrounded by a double membrane. b. Euglena viridis is a representative flagellate. (Figure 11.13) 1) Found in freshwater with abundant vegetation. 2) Flagellum extends from reservoir on the anterior end. 3) Kinetosome is located at the base of the flagellum. 5) Cytoplasm contains oval chloroplasts. 4) A stigma functions in orientation to light. 5) Nutrition is normally autotrophic, but Euglena can make use of saprozoic nutrition. 4. Subphylum Kinetoplasta (Figure 11.20) a. Zooflagellates lack chromoplasts and have holozoic or saprozoic nutrition; most are symbiotic. b. Trypanosoma is an important genus of protozoan parasites; some are not pathogenic. 1) Trypanosoma brucei gambiense and T. b. rhodesiense cause African sleeping sickness in humans. 2) T. brucei brucei causes a related disease in domestic animals. 3) These trypanosomas are transmitted by tsetse flies; natural reservoirs include antelope and other wild mammals. 4) Half of the 10,000 new cases each year are fatal; the remainder may suffer brain damage. 5) Trypanosoma cruzi causes Chagas disease in Central and South America; this parasite is carried by a bug and causes nervous system problems. c. Leishmania species cause visceral diseases in humans; they are transmitted by sand flies. E. Stramenophiles 1. Members of this clade have tubular mitochondrial cristae. 2. Stramenophiles are heterokont flagellates. 3. Have two different flagella, both inserted in the anterior end of the cell. 4. Contains plant-like brown algae, yellow algae, and diatoms. 5. Also contains opalinids, a group of animal parasites. 6. Includes slime nets, Actinophyidas, and Oomycetes (once considered a fungi). F. Alveolata: This clade, sometimes called a superphylum, contains three traditional phyla united by the shared presence of alveoli. G. Phylum Ciliophora (Figures 11.21-23) 1. Ciliates are the most diverse and specialized of the protozoans. 2. Ciliate Structures a. They are always multinucleate with at least one macronucleus and a micronucleus. 1) Macronuclei are responsible for metabolic and developmental functions. 2) Micronuclei participate in sexual reproduction; give rise to macronuclei afterwards. 3) Micronuclei divide mitotically and macronuclei divide amitotically. b. The pellicle varies from a simple membrane to thickened armor. c. Cilia 1) Cilia are short and often arranged in longitudinal or diagonal rows. 2) Cilia may be fused into a sheet, an undulating membrane, or smaller membranelles to propel food to the cytopharynx. 3) Fused cilia form stiffened tufts called cirri, used in locomotion. 4) A structural system of fibers, the infraciliature, is beneath the pellicle. 5) Cilia, kinetosomes and fibrils form a “kinety” but it does not coordinate movement. 6) Movement appears coordinated due to waves of depolarization of the cell membrane. 7) Most ciliates are holozoic; they have a mouth (cytostome) sometimes with specializations for feeding. d. Trichocysts and toxicysts are small structures expelled when stimulated; thought to be defensive, their mechanism is unknown. e. Other common ciliates include Stentor, Vorticella and Euplotes. 3. Reprentative ciliate groups: a. Suctorians: ciliates that possess cilia and are free-swimming when young; they grow a stalk and attach as adults. 1) Capture paralyze their prey and ingest contents through tube-like tentacles; the prey cytoplasm flows to the suctorian. 2) Found on turtles and on freshwater and saltwater algae. b. Symbiotic Ciliates (Figure 11.23) 1) Balantidium coli lives in intestines of humans, pigs, rats, etc.; not usually pathogenic. 2) Entodinium and Nyctotherus live in frogs and toads, respectively. 3) Ichthyophirius causes the fish disease “ick.” c. Free-living ciliates 1) Stentor is trumpet shaped and solitary, with a bead-like macronucleus. 2) Vorticella is bell shaped and attached by a contractile stalk. 3) Euplotes has a flattened body and groups of fused cilia. 4) Paramecium may be studied as a typical free-living ciliate. (Figures 11.24 − 11.26) i. Paramecium caudatum is common; demonstrates slipper-shape of paramecia. ii. Its asymmetrical appearance is caused by oral groove. iii. Structures a. Surface pellicle may be ornamented, have ridges or papillalike projections. b. Clear ectoplasm is just below the surface. c. The interior is granular endoplasm. d. Trichocysts are spindle-shaped and just below the surface. e. Cytostome at the end of the oral groove leads to a tubular cytopharynx. f. Fecal material is discharged from the cytoproct. g. 2 contractile vacuoles have radiating canals and serve in osmoregulation. h. Kidney-shaped macronucleus has smaller micronucleus alongside; some species have up to seven micronuclei. iv. Paramecia are holozoic, eating bacteria, algae, etc.; vacuoles carry particles from ingestion to ejection. v. The body is elastic; it can bend and squeeze through spaces. vi. Cilia can beat forward, backward or obliquely: oral groove cilia are more vigorous, all causing rotation. vii. It can exhibit an avoiding reaction to noxious substances, and keep itself near an attractant. viii. Changing the electrical potential across the cell membrane is the cells way of “knowing” stimuli. ix. Taxic movements orient it to stimuli: kineses merely slow or speed up movement. x. Reproduction 1. Binary fission (Figure 11.25) occurs across kineties (ciliary rows); the micronucleus divides mitotically; the macronucleus elongates and divides amitotically. 2. Conjugation (Figure 11.26) is temporary union of two individuals; the macronucleus disintegrates and the micronucleus undergoes meiosis where one of four haploid micronuclei divides and one is exchanged. 3. Autogamy is self-fertilization similar to conjugation but with no exchange of nuclei; meiotic divisions of the micronucleus fuse to form a synkaryon that is homozygous. H. Phylum Dinoflagellata (Figures 11.27 and 11.28) 1. Another group formerly included with the Phytomastigophorea. 2. About half are photoautotrophic; it is believed that chloroplasts were acquired by endosymbiosis. 3. Some species are among the most important primary producers in marine environments. 4. Commonly have an equatorial flagellum and a longitudinal flagellum. 5. Body may be naked or covered by cellulose plates. 6. Many species have a mouth region through which they can ingest prey. 7. Many species are bioluminescent. 8. Zooxanthellae are dinoflagellates that live mutually with corals and other invertebrates. 9. Pfiesteria piscicada can affect fish in brackish waters of the Atlantic coast. I. Phylum Apicomplexa (Figures 11.29 and 11.30) 1. All are endoparasites; hosts are in many animal phyla. 2. An apical complex is a feature of this phylum; it is present only in certain stages. 3. Rhoptries and micronemes help it penetrate the host’s cells. 4. Pseudopodia occur in some stages; gametes may be flagellated and contractile fibrils may form waves to propel it through liquid. 5. The life cycle usually includes both sexual and asexual stages; an invertebrate may be an intermediate host. 6. At some point, they form a spore (oocyst) that is infective in the next host and protects the sporozoan. 7. Class Coccidea a. Coccidia are intracellular parasites in invertebrates and vertebrates, and include species of great medical and veterinary importance. b. Eimeria is a genus (along with Isospora) that causes coccidiosis. 1) Isospora infections are mild unless the immune system is weak, as in AIDS patients. 2) Eimeria tenela is often fatal to young fowl. 3) Organisms undergo schizogony in intestinal cells; the zygote forms an oocyst that exits via the feces and releases eight sporozoites when ingested by the next host. c. Toxoplasma gondii is a parasite of cats. 1) Rodents, cattle, sheep, birds and humans can ingest sporozoites. 2) They cross the intestine and asexually reproduce in tissues. 3) As the host builds immunity, zoites enclose in tough tissue cysts called bradyzoites. 4) Up to half of the U.S. population carries tissue cysts from eating undercooked meat. 5) Toxoplasmosis is a serious threat during pregnancy; 2% of the cases of mental retardation may be due to congenital toxoplasmosis. d. Plasmodium: The Malarial Organism (Figure 11.30) 1) Malaria is the most important infectious disease of humans. 2) Four species infect humans; each produces different clinical symptoms. 3) Anopheles mosquitoes carry all forms; female injects the Plasmodium in her saliva. 4) Sporozoites penetrate liver cells and initiate schizogony. 5) Products of this stage penetrate more liver cells; in P. falciparum they penetrate red blood cells (RBCs). 6) The period while parasites are in the liver (6–15 days) is the incubation period. 7) Liver releases merozoites to enter RBCs where they begin schizogonous cycles. 8) When they enter RBCs, they are ameboid trophozoites that feed on hemoglobin. 9) The parasites digest hemoglobin into hemozoin; this is released as the next generation of merozoites is produced and accumulates in the liver, etc. 10) The trophozoite in a red blood cell undergoes schizogony, producing 6–36 merozoites that burst forth to infect more RBCs. 11) This cyclic release of foreign substances produces the chills and fever of malaria: i. -Plasmodium vivax (benign tertian) and P. ovalae: every 48 hours ii. -P. malariae (quartan): every 72 hours iii. -P. falciparum (malignant tertian): about every 48 hours 12) P. falciparum is the most common (50%) and most fatal, leading to cerebral malaria. 13) After some cycles of schizogony, some merozoites produce microgametocytes and macrogametocytes. 14) Gametocytes in blood are ingested by mosquitoes and mature into gametes that fertilize in the insect gut. 15) The zygote becomes a motile ookinete that penetrates the stomach wall of the mosquito and becomes an oocyst. 16) The oocyst undergoes sporogony and thousands of sporozoites are produced; these migrate to the mosquito’s salivary gland where they are injected into a human host. 17) Development in the mosquito may take 7–18 days. 18) Elimination of mosquitoes and breeding places is difficult; insecticide resistance by mosquitoes and drug resistance by Plasmodium will allow this to be a serious disease for a long time. 19) Culex mosquitoes transmit bird malaria. J. Cercozoa 1. Members of the Phylum Cercozoa do not share a common body plan, as there are both flagellated and amoeboid members. 2. Representatives a. Phaeodarians 1) Formerly considered Radiolarians; have amorphous skeleton with additions of magnesium, calcium, and copper. b. Desmothoracids. Foraminifera (Figure 11.31) a. Have slender pseudopodia extending through openings in the test. Most reticulopods are foraminiferans. 1) An ancient group of shelled amebas found in all oceans. 2) Most live on the ocean floor; perhaps the largest biomass of any animal group. 3) Most tests are many-chambered and made of calcium carbonate. Complex life cycles, with multiple fission and alternation of haploid and diploid generations. Forams have existed since Precambrian times and have left good fossil record. Some were among largest protozoa that ever lived (100 mm diameter). About 1/3 of sea bottom is covered with foraminiferous ooze. Limestone and chalk deposits have been laid down by foram accumulations. Chalk deposits of many areas of England, including White Cliffs of Dover, were formed in this way. Fossil foram identification is important to oil geologists for identifying rock strata. L. Radiolaria 1. Marine testate amebase with axopodia 2. Body divided by central test (Figure 11.32), or central capsule, that separates inner and outer zones of cytoplsm. 3. Sticky axopodia arise from test; axopodia capture prey items and bring in through protoplasm. 4. Chemical composition and complexity of radiolarian test varies with species. M. Clade Plantae 1. Includes 3 photosynthetic lineages: glaucophytes, rhodophytes (red algae) and phylum Viridiplantae 2. Phylum Viridiplantae (Figures 11.33 and 11.34) a. Contains unicellular and multicellular photoautotrophs with chlorophyll a and b. 1) Contains autotrophic, single-celled algae such as Chlamydomonas, as well as colonial forms like Gonium and Volvox (Figure 11.34). 2) Molecular evidence clearly indicates that neither of these taxa is acceptable. 3) Single-celled (and multicellular) green algae (Chlorophyta) form a clade with “higher” plants (bryophytes and vascular plants). 4) Flagellated, single-celled algae (such as Chlamydomonas and colonial forms such as Gonium and Volvox belong to this group, and have chloroplasts. 5) The mode of development of Volvox is somewhat similar to embryonic development of some metazoans. a) Each cell resembles a euglenid, including a nucleus, pair of flagella, chloroplast and stigma. b) Cytoplasmic strands connect cells; the stigma of “front” cells is larger as coordinated flagella move the ball in one direction. c) Most cells are somatic; a few germ cells in the posterior reproduce asexually or sexually. d) In development, the sphere must turn itself inside out to get flagella on the outside. e) Asexual reproduction involves repeated mitotic division and formation of daughter colonies that eventually invert. f) For sexual reproduction, zooids differentiate into macrogametes and microgametes. g) Macrogametes are larger and store food; microgametes are smaller and form bundles of flagellated sperm that swim freely until they find an ovum. h) The zygote secretes a hard, spiny, protective shell and overwinters. i) In spring, repeated divisions allow it to break out; asexual generations occur in the summer. N. Centrohelida 1. Large group of testate amebas forming axopodia O. Amoebazoa 1. Include both naked and testate amebas, as well as amebas with flagellated stages in life cycle. 2 Representatives: a. Plasmodial and cellular slime molds. b. Testate amebas with lobose pseudopodia. c. Naked amebas, such as those commonly used in school laboratories and those that can be human parasites, such as those that can kill human cornea cells and can be transmitted by improper cleaning of contact lenses (Figure 11.35) P. Opisthokonta (Figure 11.36) 1. Have flattened mitochondrial cristae and posterior flagellum on flagellated cells, if present. 2. Contains metazoans, fungi, and previously considered protozoans. 3. Best known unicells in this group are microsporidians and choanoflagellates. 11.4. Phylogeny and Adaptive Diversification A. Phylogeny 1. Molecular evidence has greatly changed phylogeny of unicellular eukaryotes. 2. It seems the ancestral eukaryote diversified into many morphologically distinct clades. 3. It is now assumed that all amitochondriate protozoans had ancestors with mitochondria. 4. Plastids were transferred among eukaryotic lineages by primary, secondary and tertiary endosymbiotic events. 5. This explains why particular plastids are found among a wide variety of seemingly unrelated single and multicellular eukaryotes. 6. Using molecular data sets and the pathway of endosymbiont transfers, eukaryotic lineages can be combined into a few eukaryotic supergroups. (Figures 11.1 and 11.17) B. Adaptive Diversification 1. Ameboid forms have radiated into a wide range of environments and have become morphologically diverse. 2. Flagellated forms have adapted to a wide range of habitats and have great variation. Specialization is most advanced in ciliates and intracellular parasitism in Apicomplexa and Microspora. C. Classification: Phylum Retortamonada Phylum Diplomonada Phylum Parabasala Order Trichomonadida Phylum Heterolobosea Phylum Euglenozoa Subphylum Euglenida Class Euglenoidea Subphylum Kinetoplasta Class Trypanosomatidea Phylum Stramenopiles Phylum Ciliophora Phylum Dinoflagellata Phylum Apicomplexa Class Gregarinea Class Coccidea Phylum Cercozoa Phylum Foraminifera Phylum “Radiolaria” Phylum Viridiplantae Phylum Centrohelida Phylum Amoebozoa Phylum Opisthokonta Lecture Enrichment 1. Unlike the following chapters in this book, this is a diverse and non-monophyletic group. Keeping this “disjointedness” in front of students as you cover these groups while trying to present unifying features is not easy. There will always be a problem with the large number of taxa that are correctly represented but are difficult to hold in memory. 2. Slides, overheads and videos will be useful to show students the appearance of protists and how they move and reproduce. 3. Today, Americans are unfamiliar with the ravages of malaria, amebic dysentery, etc. Actually, malaria was a major problem in our early history. Excerpts from Robert Desowitz’s Malaria Capers, Who Put the Pinta in the Santa Maria and other narratives, can help make these major world diseases relevant. 4. Emphasize the importance of many of the protozoan groups in the food chain, especially in freshwater and marine environments. Commentary/Lesson Plan Background: Fewer and fewer students have woodland and stream experiences; more may have a home aquarium and have seen water mold on tropical fish. Visuals are therefore critical to illustrate most groups. The diversity and variation in life cycles will also require diagrams. Misconceptions: All of us have the tendency to think that microscopic things, because of their small size, are unimportant. Students will tend to think that all evolution of protozoans took place at an early stage. However, the evolution of protozoa continued, and the evolution of parasitic forms that are today restricted to birds or mammals had to occur with the emergence of these more modern groups. Students and non-systematist biology colleagues who do not understand why zoologists can’t “just decide once and for all on one classification and stick to it” would find this section a good overall explication of the problems of discerning phylogeny based on evolutionary similarities. Earlier textbook terms for protozoan anatomy that reflected multicellular tissues have now been replaced with terminology specific to one-celled organisms: cytoproct rather than anal pore, cytopharynx, etc. Newspapers and even science journals have been promising a malaria cure “just around the corner” for decades; the text is accurate in its pessimism and Desowitz’s Malaria Capers will provide more background. Students assume that any question that has been around for long will be answered; the detailed explanation of pseudopodia flow has just been discovered but the function of trichocysts has yet to be conclusively defined. Schedule: For extensive coverage and illustration of all diseases discussed in the text, add an additional class day. HOUR 1 11.1. Emergence of Eukaryotes A. Cellular Symbiosis B. Ancestry C. Biological Contributions D. 1980 Publication of New Classification E. General Features 11.2. Form and Function A. Characteristics of Protozoan Phyla B. Nucleus and Cytoplasm C. Locomotor Organelles D. Excretion and Osmoregulation E. Nutrition F. Reproduction HOUR 2 11.3. Representative Types A. Phylum Sarcomastigophora B. Phylum Apicomplexa HOUR 3 C. Phylum Ciliophora 11.4. Phylogeny and Adaptive Diversification A. Phylogeny B. Adaptive Diversification C. Classification ADVANCED CLASS QUESTIONS 1. If Euglena have chloroplasts, why are they not grouped with green algae? Answer: Although Euglena have chloroplasts and are capable of photosynthesis, they are not grouped with green algae due to the following reasons: 1. Lack of Cell Wall: • Euglena lack a cell wall, a characteristic shared by most green algae. • Green algae typically possess a cell wall composed of cellulose, while Euglena have a pellicle, which is a proteinaceous layer that provides structural support. 2. Flagellar Structure: • Euglena have a single emergent flagellum, while most green algae have two flagella of equal length. • The structure and arrangement of flagella in Euglena are more similar to those of other flagellated protists than to green algae. 3. Mixotrophic Lifestyle: • While Euglena are capable of photosynthesis in the presence of light, they can also feed on organic matter in the absence of light. • This mixotrophic lifestyle distinguishes Euglena from most green algae, which are primarily photosynthetic. 4. Phylogenetic Relationships: • Molecular phylogenetic studies have revealed that Euglena are more closely related to other flagellated protists, such as kinetoplastids and trypanosomes, than to green algae. • Based on molecular data, Euglena are classified within the phylum Euglenozoa, separate from green algae. 2. Compared to other groups in the animal kingdom, the protozoan groups are very tentative and likely to undergo major higher systematic revision. Why? Answer: Protozoan groups are more tentative and likely to undergo major higher systematic revision compared to other groups in the animal kingdom due to the following reasons: 1. Morphological Diversity: • Protozoans exhibit tremendous morphological diversity, with a wide range of body forms, locomotion mechanisms, and feeding strategies. • This diversity makes classification challenging and often requires the use of complex morphological criteria. 2. Phylogenetic Uncertainty: • The phylogenetic relationships among protozoan groups are often poorly resolved and subject to ongoing debate. • Molecular phylogenetic studies have revealed unexpected relationships and necessitated revisions to traditional taxonomic schemes. 3. Polyphyly and Paraphyly: • Many traditional protozoan groups, such as the "flagellates" and "amoebae," are polyphyletic or paraphyletic. • These groups do not represent natural evolutionary clades and require reevaluation based on molecular data and phylogenetic analysis. 4. Technological Advances: • Advances in molecular techniques, such as DNA sequencing and phylogenetic analysis, have provided new insights into the evolutionary relationships among protozoans. • These advances have revealed cryptic diversity and necessitated revisions to existing classification schemes. 3. Organisms such as the causative agent of “ick” (water “molds”) were classified as fungi until recently. Why are they no longer classified with fungi when they look fungus-like? Answer: Organisms such as the causative agent of "ick" (water "molds") were traditionally classified as fungi due to their fungus-like appearance and lifestyle. However, they are no longer classified with fungi due to the following reasons: 1. Cell Wall Composition: • Water molds, including the causative agent of "ick" (Ichthyophthirius multifiliis), have cell walls composed of cellulose. • Fungi have cell walls composed of chitin, a different type of polysaccharide. 2. Mode of Nutrition: • Water molds are heterotrophic, absorbing nutrients from their environment, similar to fungi. • However, water molds lack true hyphae and do not form mycelium, which are characteristic features of fungi. 3. Phylogenetic Relationships: • Molecular phylogenetic studies have revealed that water molds belong to the kingdom Stramenopila, specifically within the phylum Oomycota. • Stramenopiles are a distinct group of protists and are not closely related to fungi. 4. Ecological and Morphological Differences: • Water molds exhibit ecological and morphological differences from true fungi, including reproductive structures and life cycles. • Water molds typically produce motile spores (zoospores) with two flagella, whereas fungi produce non-motile spores. In summary, although water molds share some superficial similarities with fungi, molecular and morphological evidence supports their classification within the kingdom Stramenopila, separate from true fungi. 4. Most plants and animals have very defined stages where they are haploid or diploid. But among protozoan groups, there is much variation in the occurrence of haploid and diploid phases. Why is this found among protozoan groups while the metazoa and plants are more stable in their phases? Answer: The variation in the occurrence of haploid and diploid phases among protozoan groups is due to the following reasons: 1. Life Cycle Complexity: • Protozoans exhibit a wide range of life cycles, with varying degrees of complexity. • Unlike plants and metazoans, protozoans often have life cycles that involve multiple stages and modes of reproduction. 2. Adaptation to Environmental Conditions: • Protozoans have evolved diverse life cycle strategies to adapt to different environmental conditions and ecological niches. • Variations in haploid and diploid phases allow protozoans to exploit different reproductive strategies and life history traits. 3. Asexual Reproduction: • Many protozoans are capable of asexual reproduction, where haploid or diploid stages predominate depending on environmental conditions. • Asexual reproduction allows for rapid population growth and adaptation to changing environmental conditions. 4. Environmental Stressors: • Protozoans often inhabit diverse and unpredictable environments, leading to the evolution of flexible life cycle strategies. • Variations in the occurrence of haploid and diploid phases may be advantageous in response to environmental stressors such as predation, competition, and resource availability. 5. The pronuclei of the micronucleus of a Paramecium are exchanged during conjugation, but the macronucleus that is not exchanged is the center of genetic control of the Paramecium’s traits. If the value of sexual conjugation is more genetic diversity, how does this exchange of pronuclei result in diversity that can be subject to natural selection? Answer: Although the macronucleus of Paramecium is not exchanged during conjugation, the exchange of pronuclei from the micronucleus results in genetic diversity that can be subject to natural selection due to the following reasons: 1. Genetic Recombination: • During conjugation, genetic recombination occurs between the exchanged micronuclei, leading to the formation of new genetic combinations. • This genetic recombination increases genetic diversity within the Paramecium population, providing raw material for natural selection. 2. Variation in Offspring: • The genetic diversity generated by conjugation results in variation among offspring, with different combinations of alleles and traits. • Offspring with advantageous traits are more likely to survive and reproduce, leading to the differential transmission of alleles and the operation of natural selection. 3. Adaptive Evolution: • Natural selection acts on the variation generated by conjugation, favoring individuals with traits that enhance their survival and reproductive success. • Over time, the frequency of advantageous alleles increases in the population, leading to adaptive evolution. 6. In Sporozoea, meiotic division occurs after fertilization. This contradicts the paradigm in biology where meiosis is merely used to produce haploid gametes before fertilization, which then restores the diploid state. This makes the main part of the organism’s life cycle, between reproductive events, haploid. What implications does this have for genetics and natural selection? Answer: The occurrence of meiotic division after fertilization in Sporozoea has several implications for genetics and natural selection: 1. Haploid-Dominant Life Cycle: • The haploid-dominant life cycle between reproductive events in Sporozoea differs from the typical diploid-dominant life cycle observed in most eukaryotes. • This life cycle variation affects the genetic composition of the population and the operation of natural selection. 2. Genetic Diversity: • Meiotic division after fertilization results in the production of haploid spores with unique genetic combinations. • This genetic diversity increases the adaptive potential of the population and provides raw material for natural selection. 3. Selective Pressures: • Natural selection acts on the genetic variation generated by meiosis, favoring individuals with traits that enhance their survival and reproductive success. • Selective pressures may vary depending on environmental conditions and ecological interactions, shaping the genetic composition of Sporozoea populations over time. 7. We mistakenly tend to think that all protozoan evolution occurred early and all evolution of derived organisms occurs later. Consider the many parasitic forms among protozoans that today live only in bird or mammal hosts. How did they exist before birds and mammals evolved? Answer: Parasitic protozoans that today live only in bird or mammal hosts existed before birds and mammals evolved due to the following reasons: 1. Host Specificity: • Many parasitic protozoans exhibit a high degree of host specificity, with adaptations to particular host species. • Protozoans may have initially evolved as parasites of other ancestral organisms, with subsequent host shifts to birds and mammals. 2. Ancient Host-Parasite Interactions: • Parasitic protozoans may have coevolved with their hosts over millions of years, undergoing adaptive radiation and diversification. • Protozoans may have initially parasitized early vertebrates or invertebrates, with subsequent diversification and specialization to birds and mammals. 3. Vertical Transmission: • Some parasitic protozoans are transmitted vertically from parent to offspring, ensuring their survival and persistence in host populations. • These protozoans may have persisted in ancestral host populations, with subsequent host shifts and adaptations to birds and mammals. 4. Environmental Reservoirs: • Parasitic protozoans may have persisted in environmental reservoirs, such as soil, water, or other organisms, during periods when suitable hosts were scarce. • Protozoans may have opportunistically infected birds and mammals when they evolved, leading to the establishment of new host-parasite relationships. Instructor Manual for Integrated Principles of Zoology Cleveland Hickman, Jr., Susan Keen, Allan Larson, David Eisenhour, Helen I'Anson, Larry Roberts 9780073524214
