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 where fish groups are found (spatial distribution)
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, understanding species* most common:
*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 look different from each other.
can misclassify based on differences that can be maintained within an interbreeding group
depends only 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 (Wiley): 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: examine and list 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. Which traits do I use?

20. 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)

21. 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

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

23. 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