BLG 144 Lecture Notes - Lecture 5: Species Complex, Reproductive Isolation, Phylogenetics

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5 May 2015

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Speciation occurs when populations of the same species become genetically isolated by lack
of gene flow and then diverge from each other due to selection, genetic drift or mutation
Creates two or more distinct species from a single ancestral group
Species: evolutionary independent population or group of populations
Anagenesis (phyletic evolution): changes that gradually change a species into one with
different characteristics
Cladogenesis (branching evolution): splitting the population (gene pool) into 2 or more
separate pools, giving rise to new species, promotes biological diversity by increasing # of
Four Criteria to identify a species:
1. Biological species concept
2. Morphospecies concept
3. Ecological species concept
4. Phylogenetic species concept
Biological Species Concept
– analyze reproductive isolation because no gene flow occurs between populations
- if populations cannot interbreed or produce viable offspring = distinct species
- if they can ^ = species (therefore, compatible)
Prezygotic Isolation – prevents individuals of different species from mating
Temporal = populations are isolated because they breed at different times
Habitat = populations are isolated because they breed in different habitats
Behavioral = Do not interbreed because they don’t display courtship
Gametic Barrier = incompatibility of egg and sperm
Mehanical = reproductive structures are incompatible
Postzygotic – offspring of the species does not survive
Hybrid viability – hybrid offspring do not develop normally and die as embryos
Hybrid sterility – hybrid offspring mature but are sterile
Morphospecies Concept
- Identify differences in size, shape or other morphological features –
Disadvantages of this concept
1. Cannot identify cryptic species – looks the same by morphological traits
2. Subjective morphological traits – disagree on what distinguishes a trait
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