BIOL 112 Lecture 8

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Chapter 24: The Origin of Species

${\mbox{Macroevolution}}=\sum {\mbox{microevolution}}$

Ultimately resulting in two separate species.

Morphological Species Concept

similar appearance

originally used by Linneaus (father of taxonomy)

Problems

different species can look similar or same species could have different variants (e.g. sexual dimorphism)

Biological Species Concept

species should be able to interbreed, so different species become genetically isolated

Pre-zygotic barriers that prevent interbreeding:

• Habitat: living in different environments
• Temporal: mating season is different between two species
• Behavioral: courtship cues differ between species
• (Mating attempt might occur) ... Mechanical: "they just can't get it together"
• Gametic: gametes can't fuse; species-specific receptors ensure con-specific fusion (esp. in aquatic environments)

Post-zygotic: a hybrid organism develops, but chromosome incompatibility (diff. number or incompatible loci) might cause a breakdown

• Reduced hybrid viability: organism may not survive or be sickly
• Reduced hybrid fertility: organism will be sterile
• Hybrid breakdown: successor to hybrid organism will be sterile

Problems

Only applies to species in the same geographical location (sympatric). If different areas, one can't say whether mating would occur

Only applies to species that reproduce sexually

Doesn't apply to fossils / extinct species