Fish Systematics: How does this stuff work??

1. Fish Systematics:How does this stuff work?? Study of fish diversity and the evolutionary relationships among populations, species and higher taxa Chapter 2 (Helfman, Collette & Facey)

2. Systematics • Develop an understanding of patterns of diversity in the context of evolutionary and ecological theory. • trends in spatial distribution of species • trends in emergence/extinction of evolutionary groups

3. Systematics • Sample questions: • What has favored/allowed greater diversity of fishes on coral reefs than in lakes? • What has allowed/favored cypriniforms, siluriforms and characiforms to become so diverse? • What factors have allowed/favored the persistence of ancient taxa in the Mississippi River basin (bowfin, gar, paddlefish, etc.)? • What is the evolutionary (phylogenetic) relationship between salmon and pike?

4. Subdisciplines in Systematics • Taxonomy - the theory and practice of describing, identifying and classifying taxa (groups of phylogenetically related organisms) • Nomenclature - the naming of taxonomic groups • Classification - organizing taxa into like groupings

5. Focus of Systematics on Species • Historically, much of emphasis has been at the species level of classification: • group of organisms that can reproduce and generate viable offspring • Today, emphasis is below species level (why?) • Endangered Species Act: • applies to distinct population segment of a species which interbreeds when mature

6. Species Concepts • Morphological (Linnaeus): the smallest group of individuals that are distinct and distinguishable from all others • can misclassify based on differences that can be maintained within an interbreeding group • depends solely on observable morphological differences

7. Species Concepts • Biological(Mayr): group of populations of individuals that are similar in form and function and that are reproductively isolated from other populations • conventional definition until late 1980’s • includes genetic information • ignores hybridization • dependent on geographic isolation to achieve species status

8. Species Concepts • Evolutionary: a population or group of populations that shares a common evolutionary fate and historical tendencies • recognizes more than just genetic and morphological differences • difficult to determine “evolutionary fate” • how much diversity is allowed within a common evolutionary fate?

9. Species Concepts • Phylogenetic: the smallest biological unit appropriate for phylogenetic analysis (process that rates traits as ancestral or derived and then looks for groupings based on similarities) • does not infer modes of speciation • nothing is arbitrary • depends on thorough phylogenetic analysis first

10. Species Concepts • Usefulness of each concept depends on the use - for Endangered Species Act, use as much evidence as possible: • morphological, physiological, behavioral • geographic • life history & development • habitat & feeding ecology • phylogenetics • evolutionary fate

11. Determining Relationships Between Taxa • Traditional: grade primitive to advanced, link groups based on a few arbitrary traits, generate lineage model based on these limited data

12. Determining Relationships Between Taxa • Phenetics: multivariate statistical approach: • assemble list of traits • determine degree of similarity among groups based on number of similar traits • ignores evolutionary linkage of groups (convergence could put evolutionarily distinct lines into a single taxon)

13. Determining Relationships Between Taxa • Phylogenetic (cladistic): • assemble a list of traits • classify each taxonomic group on basis of presence or absence of each trait • determine degree of similarity among groups based on shared and unique traits:

14. Determining Relationships Between Taxa • Phylogenetic (cladistic), continued: • determine degree of similarity among groups based on shared and unique traits: • shared traits = plesiomorphic traits (ancestral) • unique traits = apomorphic traits (derived) • shared unique traits = synapomorphic traits • monophyletic group of taxa (common origin) = clade

15. Cladograms • Phylogenetic relationships expressed in cladograms - branching representation of the evolutionary relationships among taxa based on shared common traits and shared unique traits

16. Constructing a Cladogram • Listing of traits • Coding of each taxon by presence or absence of each trait • Assemble groupings based on trait conditions • Use the simplest branching structure possible: principle of parsimony

17. Speciation • How do populations become distinct species? - the process whereby gene flow is reduced sufficiently between sister populations to allow each to become different evolutionary lineages • Allopatric (with geographic isolation) • Non-allopatric (without geographic isolation)

18. Speciation • Allopatric (with geographic isolation) speciation: • Vicariant - large populations geographically isolated (little inbreeding) (United States) • Founder - small population becomes geographically isolated and then reproductively isolated via inbreeding, selection, drift (Gilligan’s Island) • Reinforcement - early isolation followed by sympatry, but selection against hybrids

19. Speciation • Non-allopatric (without geographic isolation) • Sympatric - sister species evolve within the dispersal range of each other, but adapt to different habitats - habitat-dependent assortative mating • Parapatric - sister species evolve in segregated habitats across a narrow contact zone - little mixing in spite of proximity

20. Final synthesis on “species” • Groupings that are different from each other: • morphology, behavior, physiology, ecology • Reproduction is isolated in practice • Mating systems and mate-recognition systems are important enforcers of isolation