Evolution Lecture No. 9: Speciation
Friday September 28 , 2012
Speciation – Defining The Undefinable:
-When examining different species of the globe, each should:
Reflect morphological distinctiveness (have different or unique phenotypic qualities).
Reflect evolutionary independence (be able to survive successfully).
Be objective (and not subjective).
Be testable (in the field of its natural setting).
Be applicable to sexual and asexual forms, cryptic species (morphologically similar), fossils, etc.
Make identification easy.
The Three Species Concepts:
-It is quite difficult to accurately define the parameters for a species, but three concepts exist to
alleviate this difficulty:
-Morphological Species Concept (MSC): groups of populations with distinct morphological differences;
incredibly identifiable in the field.
-Biological Species Concept (BSC): groups of potentially or actively interbreeding natural populations
which are reproductively isolated from other groups.
-Phylogenetic Species Concept (PSC): the smallest group whose members descend from a common
ancestor and who possess defining (derived) characteristics that distinguish them from other groups;
shows the evolutionary relationships among different species.
-In an example featuring the phylogenetic tree of various species of Eurytemora offinis around the
world, they would all be part of one species according to the MSC (as they more or less resemble each
other) and eight distinct species (due to 8 different nodes) according to the PSC.
The Processes Of Separation:
-There are three processes of evolution:
-Isolating Barrier: geographic/allopatric (different place) or reproductive/sympatric (same place).
-Divergence: mutation, genetic drift or selection; describes the evolutionary portion of separation.
-Secondary Contact: The reinforcement of evolved differences between newly-formed species. Dispersal As A Geographic Isolating Barrier:
-Dispersal represents when certain members of a species will