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.

Allopatric Speciation bydispersal

Representative HawaiianDrosophila diversity

Aspidosceliscarmenensis

A. picta

A. danheimae

A. franciscensis

A. espiritensis

A speciation problem

Unresolved: maybe not species?

Grismer, L. Lee. 1999. Phylogeny, taxonomy, and biogeography of Cnemidophorus hyperythrus and C. ceralbensis (Squamata: Teiidae)In Baja California, Mexico