Fish Systematics:Fish Systematics:How does this stuff work??How does this stuff work??

Study of fish Study of fish diversitydiversity and the and the evolutionary evolutionary relationshipsrelationships among populations, species and among populations, species and

higher taxahigher taxa

Chapter 2Chapter 2(Helfman, Collette & Facey)(Helfman, Collette & Facey)

SystematicsSystematics

• Develop an understanding of patterns of Develop an understanding of patterns of diversity in the context of evolutionary and diversity in the context of evolutionary and ecological theory.ecological theory.– trends in where fish groups are found (spatial trends in where fish groups are found (spatial

distribution)distribution)– trends in emergence/extinction of evolutionary trends in emergence/extinction of evolutionary

groupsgroups

SystematicsSystematics

• Sample questions:Sample questions:• What has favored/allowed greater diversity of fishes What has favored/allowed greater diversity of fishes

on coral reefs than in lakes?on coral reefs than in lakes?

• What has allowed/favored cypriniforms, siluriforms What has allowed/favored cypriniforms, siluriforms and characiforms to become so diverse?and characiforms to become so diverse?

• What factors have allowed/favored the persistence What factors have allowed/favored the persistence of ancient taxa in the Mississippi River basin of ancient taxa in the Mississippi River basin (bowfin, gar, paddlefish, etc.)?(bowfin, gar, paddlefish, etc.)?

• What is the evolutionary (phylogenetic) relationship What is the evolutionary (phylogenetic) relationship between salmon and pike?between salmon and pike?

Subdisciplines in SystematicsSubdisciplines in Systematics

• Taxonomy Taxonomy - the theory and practice of describing, - the theory and practice of describing, identifying and classifying taxa (groups of identifying and classifying taxa (groups of phylogenetically related organisms)phylogenetically related organisms)

• NomenclatureNomenclature - the naming of taxonomic groups - the naming of taxonomic groups

• ClassificationClassification - organizing taxa into like groupings - organizing taxa into like groupings

Focus of Systematics on SpeciesFocus of Systematics on Species

• Historically, understanding Historically, understanding species*species* most most common:common:*group of organisms that can reproduce and generate *group of organisms that can reproduce and generate

viable offspringviable offspring

• Today, emphasis is below species level (why?)Today, emphasis is below species level (why?)– Endangered Species Act:Endangered Species Act:

• applies to applies to distinct population segmentdistinct population segment of a species which of a species which interbreeds when matureinterbreeds when mature

Species ConceptsSpecies Concepts

• MorphologicalMorphological (Linnaeus): the smallest (Linnaeus): the smallest group of individuals that look different group of individuals that look different from each other.from each other.– can misclassify based on differences that can be can misclassify based on differences that can be

maintained within an interbreeding groupmaintained within an interbreeding group– depends only on observable morphological depends only on observable morphological

differencesdifferences

Species ConceptsSpecies Concepts

• BiologicalBiological (Mayr): group of populations of (Mayr): group of populations of individuals that are similar in individuals that are similar in formform and and function function and that are and that are reproductively isolated reproductively isolated from other from other populationspopulations– conventional definition until late 1980’sconventional definition until late 1980’s– includes genetic informationincludes genetic information– ignores hybridizationignores hybridization– dependent on dependent on geographic isolation geographic isolation to achieve to achieve

species statusspecies status

Species ConceptsSpecies Concepts

• Evolutionary (Wiley)Evolutionary (Wiley): a population or : a population or group of populations that shares a common group of populations that shares a common evolutionary fate and historical tendenciesevolutionary fate and historical tendencies– recognizes more than just genetic and recognizes more than just genetic and

morphological differencesmorphological differences– difficult to determine “evolutionary fate”difficult to determine “evolutionary fate”– how much diversity is allowed within a how much diversity is allowed within a

common evolutionary fate?common evolutionary fate?

Species ConceptsSpecies Concepts

• PhylogeneticPhylogenetic: the smallest biological unit : the smallest biological unit appropriate for phylogenetic analysis appropriate for phylogenetic analysis (process that rates traits as (process that rates traits as ancestralancestral or or derivedderived and then looks for groupings based and then looks for groupings based on similarities)on similarities)– does not infer modes of speciationdoes not infer modes of speciation– nothing is arbitrarynothing is arbitrary– depends on thorough phylogenetic analysis firstdepends on thorough phylogenetic analysis first

Species ConceptsSpecies Concepts

• Usefulness of each concept depends on the use - Usefulness of each concept depends on the use - for Endangered Species Act, use as much for Endangered Species Act, use as much evidence as possible:evidence as possible:– morphological, physiological, behavioralmorphological, physiological, behavioral

– geographicgeographic

– life history & developmentlife history & development

– habitat & feeding ecologyhabitat & feeding ecology

– phylogeneticsphylogenetics

– evolutionary fateevolutionary fate

Determining Relationships Determining Relationships Between TaxaBetween Taxa

• TraditionalTraditional: examine and list primitive to : examine and list primitive to advanced, link groups based on a few advanced, link groups based on a few arbitrary traits, generate lineage model arbitrary traits, generate lineage model based on these limited databased on these limited data

Determining Relationships Determining Relationships Between TaxaBetween Taxa

• PheneticsPhenetics: multivariate statistical approach:: multivariate statistical approach:– assemble list of traitsassemble list of traits– determine degree of similarity among groups determine degree of similarity among groups

based on number of similar traitsbased on number of similar traits– ignores evolutionary linkage of groups ignores evolutionary linkage of groups

(convergence could put evolutionarily distinct (convergence could put evolutionarily distinct lines into a single taxon)lines into a single taxon)

Determining Relationships Determining Relationships Between TaxaBetween Taxa

• PhylogeneticPhylogenetic (cladistic): (cladistic):– assemble a list of traitsassemble a list of traits– classify each taxonomic group on basis of classify each taxonomic group on basis of

presence or absence of each traitpresence or absence of each trait– determine degree of similarity among groups determine degree of similarity among groups

based on shared and unique traits:based on shared and unique traits:

Determining Relationships Determining Relationships Between TaxaBetween Taxa

• Phylogenetic Phylogenetic (cladistic), (cladistic), continuedcontinued::– determine degree of similarity among groups determine degree of similarity among groups

based on shared and unique traits:based on shared and unique traits:• shared traits = shared traits = plesiomorphicplesiomorphic traits (ancestral) traits (ancestral)

• unique traits = unique traits = apomorphicapomorphic traits (derived) traits (derived)

• shared unique traits = shared unique traits = synapomorphicsynapomorphic traits traits

– monophyletic group of taxa (common origin) = monophyletic group of taxa (common origin) = cladeclade

CladogramsCladograms

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

Constructing a CladogramConstructing a Cladogram

• Listing of traitsListing of traits

• Coding of each taxon by presence or Coding of each taxon by presence or absence of each traitabsence of each trait

• Assemble groupings based on trait Assemble groupings based on trait conditionsconditions

• Use the simplest branching structure Use the simplest branching structure possible: principle of parsimonypossible: principle of parsimony

Which traits do I use?Which traits do I use?

SpeciationSpeciation

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

SpeciationSpeciation• Allopatric (with geographic isolation) Allopatric (with geographic isolation)

speciation:speciation:– VicariantVicariant - large populations geographically - large populations geographically

isolated (little inbreeding) (United States)isolated (little inbreeding) (United States)– FounderFounder - small population becomes geographically - small population becomes geographically

isolated and then reproductively isolated via isolated and then reproductively isolated via inbreeding, selection, drift (Gilligan’s Island)inbreeding, selection, drift (Gilligan’s Island)

– ReinforcementReinforcement - early isolation followed by - early isolation followed by sympatrysympatry, but selection against hybrids, but selection against hybrids

SpeciationSpeciation

• Non-allopatric (without geographic Non-allopatric (without geographic isolation)isolation)– SympatricSympatric - sister species evolve within the - sister species evolve within the

dispersal range of each other, but adapt to dispersal range of each other, but adapt to different habitats - habitat-dependent assortive different habitats - habitat-dependent assortive matingmating

– ParapatricParapatric - sister species evolve in segregated - sister species evolve in segregated habitats across a narrow contact zone - little habitats across a narrow contact zone - little mixing in spite of proximitymixing in spite of proximity

Final synthesis on “species”Final synthesis on “species”

• Groupings that are different from each Groupings that are different from each other:other:– morphology, behavior, physiology, ecologymorphology, behavior, physiology, ecology

• Reproduction is isolated in practiceReproduction is isolated in practice

• Mating systems and mate-recognition Mating systems and mate-recognition systems are important enforcers of isolationsystems are important enforcers of isolation