Allopatric vs. Sympatric Speciation

My AP Biology ThoughtsEpisode #9

Welcome to My AP Biology Thoughts podcast, my name is Adrienne and I am your host for episode 9 called Unit 7 Evolution: Allopatric vs. Sympatric Speciation. Today we will be discussing the differences between allopatric and sympatric speciation and I will provide examples for each.

Segment 1: Introduction to Allopatric & Sympatric Speciation

• Speciation: formation of a new species, occurs when a group of organisms isn’t capable of interbreeding and producing viable offspring anymore
• Allopatric speciation: occurs through geographical isolation like a physical geographic barrier
• Sympatric speciation: occurs without a geographical barrier
• Driven by other factors: habitat differentiation and sexual selection.

Segment 2: Example of Allopatric & Sympatric Speciation

Allopatric speciation

• Ex. Isthmus of Panama: narrow strip of land that causes a geographical barrier between Caribbean sea and Pacific ocean
• Two species of porkfish have emerged

Sympatric speciation: 2 types (prezygotic and postzygotic barriers)

• Prezygotic barriers: before the sperm and egg
• Habitat: different times of year organisms reproduce
• Ex. 2 related frog species, Rona aurora breeds earlier in the year than Roma poyilil making them unavailable for each other
• Behavioral: set of certain behaviors that must be executed to reproduce
• Ex. New Birds of Paradise and Birds of Paradise have different courtship characteristics
• Mechanical: the sexual parts must fit like a “lock” and “key”
• Ex. 20 different species of Bush Babies, different sexual parts won’t fit and allow reproduction
• Gametic isolation: if the gametes are incompatible, the organisms won’t reproduce
• Ex. Cells of red and purple sea urchins are genetically incompatible, fertilization is impossible
• Postzygotic barrier: after sperm and egg
• Inviability: organism dies before reproduction
• Infertility: organisms can’t form gametes
• Breakdown: F2 generation doesn’t sexually develop properly
• Ex. Horses and donkeys