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)

Why Systematics?OrganizationBasis for identificationDiscriminationUnderstanding relationshipsCommon language!

SystematicsUnderstand patterns of diversityHow? ...in the context of evolutionary and ecological theory.trends in where fish groups are found (spatial distribution)trends in emergence/extinction of evolutionary groups

SystematicsSample 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?

Subdisciplines in SystematicsTaxonomy - the theory and practice of describing, identifying and classifying taxa (groups of phylogenetically related organisms)Taxonomy can be predictive!!

Nomenclature - the naming of taxonomic groups

Classification - organizing taxa into like groupings

What is a Species?C. Tate. Regan (1926) (20th Century)A community, or a number of related communities whose distinctive morphological characters are, in the opinion of a competent systematist, sufficiently definite to entitle it, or them to a specific name.

Focus of Systematics on SpeciesHistorically, understanding species* most common:*group of organisms that can reproduce and generate viable offspringToday, emphasis is below species level (why?)Endangered Species Act:applies to distinct population segment of a species which interbreeds when mature

Species ConceptsMorphological (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 differencesinbreeding

Species ConceptsBiological (Mayr): group of populations of individuals that are similar in form and function and that are reproductively isolated from other populationsconventional definition until late 1980sincludes genetic informationignores hybridizationdependent on geographic isolation to achieve species status

Species ConceptsEvolutionary (Wiley): a population or group of populations that shares a common evolutionary fate and historical tendenciesrecognizes more than just genetic and morphological differencesdifficult to determine evolutionary fatehow much diversity is allowed within a common evolutionary fate? Nelson 1999 Reviews in Fish Biology and Fisheries

Species ConceptsPhylogenetic: the smallest biological unit appropriate for phylogenetic analysis (process that rates traits as ancestral (plesiomorphes) or derived (apomorphies) and then looks for groupings based on similarities (shared)depends on thorough phylogenetic analysis

Species ConceptsUsefulness of each concept depends on the use - for Endangered Species Act, use as much evidence as possible:morphological, physiological, behavioralgeographiclife history & developmenthabitat & feeding ecologyphylogeneticsevolutionary fate

Determining Relationships Between TaxaTraditional: examine and list primitive to advanced, link groups based on a few arbitrary traits, generate lineage model based on these limited data

Determining Relationships Between TaxaPhylogenetic (cladistic):assemble a list of traitsclassify each taxonomic group on basis of presence or absence of each traitdetermine degree of similarity among groups based on shared and unique traits:

Determining Relationships Between TaxaPhylogenetic (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 (group of 2 or more taxa derived from evolution from common ancestor)monophyletic group of taxa (common origin) = clade

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

Constructing a CladogramListing of traitsCoding of each taxon by presence/absence of each traitAssemble groupings based on trait conditionsUse the simplest branching structure possible: principle of parsimony

More on traits...Meritic-count it!Morphometric-measurable shape fin lengtheye shape head lengthratios between such measures...anatomical characteristicsmolecular characteristics

Which traits do I use?

SpeciationHow do populations become distinct species? - the process whereby gene flow is reduced sufficiently between sister populations to allow each to become different evolutionary lineagesAllopatric (with geographic isolation)Non-allopatric (without geographic isolation)

SpeciationAllopatric (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 (Gilligans Island)Reinforcement - early isolation followed by sympatry, (other species came but show now aggression) but selection against hybrids

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

Final synthesis on speciesGroupings that are different from each other:morphology, behavior, physiology, ecologyReproduction is isolated in practiceMating systems and mate-recognition systems are important enforcers of isolation

*