Student Activities 2008-2009

Emmanuel Rodriguez

Geographic Variation in M7 Lysin Allele Frequency: A Test of the Hypothesis of Reinforcement in the Rapid Evolution of a Reproductive Protein

Activity:
Annual Benthic Ecology Meeting

Abstract:
Speciation in broadcast spawning organisms is believed to be driven by differences in gamete binding proteins, which tend to evolve quickly. One of the hypotheses proposed to explain the rapid evolution of gamete binding proteins is reinforcement. Reinforcement is the process by which the evolution of pre-zygotic barriers is favored because they limit the production of lower fitness hybrids. This mechanism tends to show greater differences in reproductive characters in areas of sympatry than in areas of allopatry. There are known sympatric and allopatric populations of M.  edulis and M. galloprovinciallis along the coast of Western Europe and this organism also has a divergent allele of the sperm protein M7 lysin found in M.galloprovinciallis called GD. One study found GD to have a higher frequency in areas of sympatry, which is a pattern indicative of reinforcement. A different study did not find any geographical pattern of GD allele frequency. This study was aimed at expanding on these studies by collecting a larger sample size from more closely related collection sites. Individuals from 14 sites along the Western coast of Europe and the Mediterranean were collected from areas of sympatry and areas of allopatry. These individuals were genotyped at the M7 locus, and the GD allele frequency was calculated. Our results showed that there is no difference in GD allele frequency in areas of sympatry versus areas of allopatry, and there was no correlation between distance from a sympatric population and the frequency of the GD allele. Both of these findings reject reinforcement. Further studies will need to be performed to test other hypothesis as an explanation of the rapid evolution of these proteins.