Question

Draw the phylogenetic tree that shows that understanding of the evolutionary relationships of all invertebrates among the major phyla of metazoans. What are the major clades shown on the tree? Why are the phyla grouped together in the specific clades that you have drawn? What are the synapomorphies that define each of the clades and the different phyla within them? What sources of evidence were used to reconstruct the phylogeny that you have drawn? Are certain sources of evidence more reliable than others? Explain and provide examples. Do you think that there are someareas of the tree that seem uncertain and are likely to be revised by additional study?

Answer 1

Why are the phyla grouped together in the specific clades that you have drawn?

Key Points

• Phylogenetic trees are constructed using various data derived from studies on homologous traits, analagous traits, and molecular evidence that can be used to establish relationships using polymeric molecules ( DNA, RNA, and proteins ).
• Evolutionary relationships between animal phyla, or Metazoa, are based on the the presence or absence of differentiated tissues, referred to as Eumetazoa or Parazoa, respectively.
• Eumetazoa can be further classified into categories that are based on whether they have radial or bilateral symmetry, referred to as Radiata or Bilateria, respectively.

Key Terms

• orthologous: having been separated by a speciation event
• homoplasy: a correspondence between the parts or organs of different species acquired as the result of parallel evolution or convergence

• Phylogenetic trees represent hypotheses about the evolutionary relationships among a group of organisms.

• A phylogenetic tree may be built using morphological (body shape), biochemical, behavioral, or molecular features of species or other groups.

• In building a tree, we organize species into nested groups based on shared derived traits (traits different from those of the group's ancestor).

• The sequences of genes or proteins can be compared among species and used to build phylogenetic trees. Closely related species typically have few sequence differences, while less related species tend to have more.