Post on 21-Dec-2015
Sympatric Speciation
• Flies (Rhagoletis pomonella)• (1) Larvae develop in hawthorns (Crataegus)• Native to NE U.S.• (2) Larvae develop in apples (Pyrus)• Apples introduced c. 300 ya; apple flies became a pest c.• 150 ya.• H0: The flies belong to the same species; there is
phenotypic plasticity in use of hosts.• H1: Speciation has occurred; each species of fly adapted to
one host species.• Since hawthorns and apples are both within the range of
Rhagoletis, this would represent an example of sympatric speciation.
• Flies using the two types of fruit cannot be distinguished morphologically (cryptic).
• But, evidence of lineage splitting:
• 1. Allele frequency differs for 6 different proteins; therefore can be distinguished genetically.
• 2. Flies imprint on fruit from which they developed.
– Mating takes place on the fruit.
– Provides some degree of physical segregation.
– Only c. 2% of matings are between misimprinted flies.
• Flies are diverging because of natural selection
• Selective agent = timing of fruit ripening.
• Apples ripen “early.”
• Larvae in apples
– Selected to develop slowly (present in some Mexican fly populations).
– Prevents emergence of adults prior to winter.
• Hawthorns ripen ca. 3 weeks later than apples.
• Larvae in hawthorn fruit
– Selected to develop rapidly.
– Enables pupation prior to winter.
• A few mistakes are made: speciation nearing completion.