SPECIES CONCEPTS

SPECIES ASSIGNMENTS
1. WHY?
  1. sp is a fundamental units of analysis in bio sciences
2. e.g. African Elephant
  1. - traditionally believed to be a single sp.
  2. new evidence of new sp (forest and savannah) -
  3. - possibly a 3rd sp (West African) + hybrid btwn forest and savannah
  4. recognition of multiple sp may leave the hybrids in an uncertain conservation status
ARE SP. REAL? (for human convenience or for a fundamental evolutionary unit?)
1. evidence for...
  1. widely believed that ind' and popn are partitioned into discrete grps that are objective & most ppl equate w sp.
  2. good concordance btwn scientific and folk sp
  3. scientific evidence of the presence of discrete groups in sympatry in some cases
2. evidence against...
  1. the development of a universally applicable sp. definition has proved elusive
SPECIES CONCEPTS
1. theoretical definition of a species
  1. 1) Phenetic (a set of orgnsms that are SIMILAR to each other & distinct from those in other sets)
  2. 2) Ecological ( a set of orgnsms that are ADAPTED to a particular discrete set of resources)
  3. 3) Evolutionary ( a lineage (ancestor-descendant seq) of orgnsms that maintains its IDENTITY frm other such lineages & has its own evolutionary tendencies and fate)
BIOLOGICAL SPECIES CONCEPTS (BSC)
1. Sp: a set of interbreeding orgnsms that are reproductively isolated frm those in other such sp.
2. exhange => cohesion & no gene exchange => divergence
3. Strengths
  1. attempt to define sp in terms of neo-Darwinian theory
  2. replaced typological sp concept
    1. Typological sp. concept
      1. biodiversity consists of a fixed # of types
      2. all indv' of a sp are of the same basic type
      3. sp x change through time & variation is an aberration
  3. precise & mechanistic
4. Limitations
  1. Theoretical a) 'Interspecific' gene exchange b) Asexual reproduction c)Is gene flow enough?
    1. Interspecific Gene Exchange
      1. BSC- difft sp x exchange genes (challenged by interspecific gene exchange)
      2. Intersp hybridisation = reproduction indv' of difft sp.
      3. Introgression = permanent incorporation of the genes of 1 sp into the genome of another (backcross)
      4. how widespread, common & significant?
        e.g. Birds (% in orders & sp. frm 1992 - 2006 that are involved in interspecific incidence) - good biological sp. - low but widespread
        e.g. Flowering plants
        Annotations:
        Eucalyptus - >700 sp - Some subgroups are characterised by interspecific hybridisation, introgression & convergent evolution
        in 1996 - 6-16% of genera contain at least 1 sp that regularly hybridizes (intersp. gene exchange)
        include syngameons (reticulate networks of gene exchange among closely related morphosp)
        fossil evidence indicates that some syngameons are stable over evolutionary time
    2. Asexual Reproduction
      1. BSC- sp can be defined by intraspecific gene exchange (challenged by obligate asexual orgnsm)
      2. How widespread & common are obligate asexual?
        Eubacteria & Archaea
        reproduction is strictly asexual (binary fission)
        however, unilateral exchange of genes occur via several processes
        gene exchange may occur btw divergent forms (up to 16%)
        gene exchange are less frequent but more promiscuous than in eukaryotes
        Animals (production of embryo without fertilisation (parthenogenesis))
        rare, wide range of taxa and common in certain groups (e.g. 400/1000 species of non-marine ostracod)
        Flowering plants (agamospermy)
        Annotations:
        agamospermy - formation of seeds without fertilisation
        overall rare, common in a few grps (grasses, roses)
      3. Obligate Asexual
        display patterns of phenotypic cohesion similar to sexual species
        can be ancient (e.g. Ostracod Darwinula stevensoni ca 20myo)
        BSC x apply to obligate asexuals. The phenotype cohesion displayed by ancient asexuals raises questions about the importance of gene flow in maintaining phenotypic cohesion within a species.
    3. Is Gene Flow Enough?
      1. BSC- species gene flow promotes phenotypic cohesion. (challenged by observations that the amount of gene flow among the populations of many species is very small. )
      2. e.g. European Land Snail Cepaea nemoralis
        Map of the Pyrenees – Cepaea inhabit river valleys separated by high ground
        indicates that gene exchange between them is limited that gene flow is limited
        The proportion of colour morphs in each population is generally very similar, despite the lack of gene flow
        Shell type can vary according to microhabitat
        How they maintain a range of similar colour morphs over broad spatial scales, despite negligible gene flow? - SELECTION
  2. practical
CONCLUSION
1. strength & limitations associated w BSC
2. numerous alternative proposed (none has universal support)
3. pluralistic species concept (multiple sp concepts)
4. unclear

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SPECIES CONCEPTS

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	Created by chaz_id89 about 11 years ago