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Readings 13 notes

Biological Sciences
Course Code
Maydianne Andrade

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Readings 13
Pgs. 605-633 (refer to Figure 16.7)
-a species is the smallest evolutionary independent unit
-evolutionary independence occurs when mutation, selection, gene flow, and drift operate on
populations separately
-speciation is caused by lack of gene flow
-there are three important species concepts, which all agree that species are evolutionary
independent units that are isolated by lack of gene flow
-each concept employs a different criterion for determining that independence is in effect
-the morphospecies concept involves people naming species based on morphological
similarities and differences (widely applicable concept)
-morphospecies can be identified in species that are extinct or living and in species that
reproduce sexually or asexually
-the disadvantage of the morphospecies concept is that when it is not applied carefully,
species definitions can be arbitrary
-cryptic species }µo]}vZZÀÀÇo]u]((vÁvZ}ZZv[
be distinguished
-cryptic species are considered the same based on morphological similarity
-under the biological species concept, the criterion for identifying evolutionary independence
is reproductive isolation
-the advantage of the BSC is that reproductive isolation confirms the lack of gene flow in
overlap may or may not be reproductively isolated
-the biological species concept can never be tested in fossil forms and is irrelevant to asexual
-the phylogenetic species concept (also known as the genealogical species concept) focuses
on a criterion for identifying species called monophyly
-under the PSC, species are identified by estimating the phylogeny of closely related
populations and finding the smallest monophyletic groups
-the rationale behind the phylogenetic species concept is that traits can only distinguish
populations on a phylogeny if the populations have been isolated in terms of gene and
diverged genetically and possibly morphologically as well
-populations within species have shared derived traits that distinguish them from populations
of other species
-this concept can be applied to any type of organism because species are named on the basis of
difference in traits used to estimate phylogeny
-speciation has been hypothesized to be a three stage process involving (1) isolating
populations (2) divergence in traits (3) reproductive isolation
-the final phase was hypothesized to occur when these diverged populations came back into
physical contact, which is referred to as secondary contact
-gene flow tends to homogenize gene frequencies and reduce the differentiation of populations
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