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)

Systematics Develop an understanding of patterns of diversity in the context of evolutionary and ecological theory.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

Systematics Sample questions:Sample questions: What has favored/allowed greater diversity of fishes on coral reefs than in lakes?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 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 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?What is the evolutionary (phylogenetic) relationship between salmon and pike?

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

Focus of Systematics on Species Historically, much of emphasis has been at the species level of classification: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?)Today, emphasis is below species level (why?) –Endangered Species Act: applies to distinct population segment of a species which interbreeds when matureapplies to distinct population segment of a species which interbreeds when mature

Species Concepts Morphological (Linnaeus): the smallest group of individuals that are distinct and distinguishable from all othersMorphological (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

Species Concepts Biological (Mayr): group of populations of individuals that are similar in form and function and that are reproductively isolated from other populationsBiological (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

Species Concepts Evolutionary: a population or group of populations that shares a common evolutionary fate and historical tendenciesEvolutionary: 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?

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)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

Species Concepts Usefulness of each concept depends on the use - for Endangered Species Act, use as much evidence as possible: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

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

Determining Relationships Between Taxa Phenetics: multivariate statistical approach: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)

Determining Relationships Between Taxa Phylogenetic (cladistic):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:

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

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

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

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 lineagesHow 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)

Speciation Allopatric (with geographic isolation) 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

Speciation Non-allopatric (without geographic isolation)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

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