Animal Classification, Phylogeny, and Organization Chapter 7 Animal Classification, Phylogeny, and Organization

Classification of Organisms Systematics or taxonomy Study of the kinds and diversity of organisms and of the evolutionary relationships among them

A Taxonomic Hierarchy Taxon Taxonomic categories Any grouping of animals that shares a particular set of characteristics Taxonomic categories Hierarchically arranged (broader to specific) Domain, kingdom, phylum, class, order, family, genus, species Above species level there are no definitions for each category

Table 7.1

Nomenclature Binomial system of nomenclature International Code of Zoological Nomenclature Homo sapiens (H. sapiens) Other naming rules See General Zoology Laboratory Manual (Exercise 6).

Molecular Approaches to Animal Systematics Relatedness of animals reflected in proteins and DNA. Nuclear and mitochondrial DNA Ribosomal RNA

Domains and Kingdoms Ribosomal RNA studies Distant evolutionary relationships Evolutionary conservation results in slow rates of change. Three major lineages (Domains) Eubacteria Bacteria Archaea Extremophile microbes Eukarya Organisms with compartmentalized cells Nuclear membranes mitochondrial and chloroplast membranes Horizontal gene transfer (HGT) common in early history of life and makes base of tree net-like

Figure 7.2 Three lineages of life.

Animal Systematics Goal Groupings reflecting insufficient knowledge Arrange animals into MONOPHYLETIC GROUPS using traits having a genetic basis and that can be measured (characters). Single ancestral species and all descendants Groupings reflecting insufficient knowledge Members of a lineage found to have separate ancestry Polyphyletic groups Some, but not all, members of a lineage included Paraphyletic group

Figure 7.3 Evolutionary groups.

Approaches to Animal Systematics Evolutionary systematics Traditional approach Homologies useful in classification Phylogenetic trees depict relationships, time, and abundance.

Figure 7.4 Phylogenetic tree showing vertebrate phylogeny.

Approaches to Animal Systematics Phylogenetic systematics (cladistics) Homologies of recent origin are most useful. Ancestral characters Common to all members of a group Symplesiomorphies Outgroup Related group not included in study group Used to help decide whether or not a character is ancestral or more recently derived

Approaches to Animal Systematics Phylogenetic systematics (continued) Derived characters Arisen since common ancestry with the outgroup Synapomorphies Clade Related subset within a lineage Cladogram Depicts a hypothesis regarding monophyletic lineage

Figure 7.5 This hypothetical cladogram shows five taxa (1-5) and characters (A-H) used in deriving taxonomic relationships.

Approaches to Animal Systematics Phylogenetic species concept Group of populations that have evolved independently of other groups of populations Monophyletic Share one or more synapomorphies Hierarchical nesting Cladograms represent nested groups that share synapomorphic characters. Less inclusive nests contain closely related organisms.

Figure 7.6 Cladogram showing vertebrate phylogeny.

Compare figures 7.4 and 7.6 What kind of information is common to both representations? What kind of information is present in figure 7.4 that is not in figure 7.6? What kind of information is present in figure 7.6 that is not in figure 7.4? How are the relationships between reptiles, birds, and mammals represented differently in the two figures? How do the differences in question 4 reflect differing approaches of evolutionary systematics and phylogenetic systematics?

Table 7.2 Symmetry describes how parts of an animal are arranged around a point or axis.

Figure 7.7 Sponges display cell-aggregate organization and some sponges are asymmetrical (Monochora barbadensis).

Figure 7.8 This coral polyp (Tubastraea sp.) is radially symmetrical.

Figure 7.9 Bilateral symmetry is accompanied by the formation of a distinct head (cephalization).

Table 7.3

Other Patterns of Organization Unicellular (cytoplasmic) level of organization Protists (unicellular) Sponges (cell aggregate) Diploblastic organization Ectoderm (outer cellular layer) Endoderm (inner cellular layer) Mesoglea (noncellular)

Other Patterns of Organization Triploblastic Organization Mesoderm Third tissue later sandwiched between ectoderm and endoderm Supportive, contractile, and blood cells Body cavities often present Organ development Exchanges by diffusion Storage Hydrostatic skeletons Elimination of wastes and reproductive products Facilitate increased body size

Figure 7.11 Triploblastic Organization. Triploblastic acoelomate Mesoderm forms solid mass. Triploblastic pseudocoelomate Body cavity not entirely lined by mesoderm. Gut is not associated with muscle or connective tissue. Triploblastic coelomate Body cavity completely surrounded by mesoderm. Mesenteries suspend visceral structures in body cavity.

Higher Animal Taxonomy Animalia is monophyletic Molecular and embryological evidence Four phyla originated independently Bilaterally symmetrical phyla Protostome phyla Spiral, determinate cleavage Trochophore larval stage Ecdysozoa Molt a cuticle Lophotrochozoa Deuterostome phyla Radial, indeterminate cleavage

Figure 7.12 Animal taxonomy.

Figure 7.13 Developmental characteristics of protostomes and deuterostomes.