BIOL 3542 Lecture Notes - Species, Species Complex, Reproductive Isolation

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Species Concepts
Species is the smallest evolutionarily independent unit
Evolutionary independence occurs when mutation, selection, gene flow, and drift operate on
populations separately
Evolution consists of changes in allele frequencies, and species form a boundary for the spread
of alleles
oAs a result, different species follow different evolutionary trajectories
oThe essence of speciation is lack of gene flow
Species consist of interbreeding populations that evolve independently of other populations
The three most important “species concepts”:
oMorphospecies Concept
oBiological Species Concept
oPhylogenetic Species Concept
Each of the three agrees that species are evolutionarily independent units that are
isolated by lack of gene flow, but each employs a different criterion for the
determining that independence is actually in effect
The Morphospecies Concept
In traditional cultures, people name species based on morphological similarities and differences
In biology, careful analyses of phenotypic differences are the basis of identifying morphospecies
Morphospecies can be identified in species that are extinct or living, and in species that
reproduce sexually or asexually
Fossil species that differed in color or the anatomy of soft tissues cannot be distinguished
Neither can populations that are similar in morphology but were strongly divergent in traits like
songs, temperature, or drought tolerance, habitat use, or courtship displays
oSpecies like these are called cryptic species
Species that are indistinguishable morphologically, but divergent in songs, calls,
odor, or other traits
The Biological Species Concept
Under this concept, criterion for identifying evolutionary independence is reproductive isolation
If populations of organisms do not hybridize regularly in nature, or if they fail to produce fertile
offspring when they do, then they are reproductively isolated and considered good species
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