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doi:10.1534/genetics.105.045591
A more recent version of this article appeared on October 1, 2005.
REGULAR RESEARCH PAPERS |
Pre-mating, not post-mating, barriers drive genetic dynamics in experimental hybrid populations of the endangered Sonoran topminnow
Carla R. Hurt 1*, Manoush Farzin 2 and Philip W. Hedrick 2
1 Naos Marine Lab
2 Arizona State University
* To whom correspondence should be addressed. E-mail: carla_asu{at}yahoo.com.
Submitted on May 12, 2005
Revised on June 14, 2005
Accepted on 14 June 2005
The timing and pattern of reproductive barrier formation in allopatric populations has received much less attention than the accumulation of reproductive barriers in sympatry. The theory of allopatric speciation suggests that reproductive barriers evolve simply as byproducts of overall genetic divergence. However, observations of enhanced pre-mating barriers in allopatric populations suggest that sexual selection driven by intraspecific competition for mates may enhance species-specific signals and accelerate the speciation process. In a previous series of laboratory trials, we examined the strength of pre-mating and post-mating barriers in an allopatric species pair of the endangered Sonoran topminnow, Poeciliopsis occidentalis and P. sonoriensis. Behavioral observations provided evidence of asymmetrical assortative mating, while reduced brood sizes and male biased F1 sex ratios suggest post-mating incompatibilities. Here we examine the combined effects of pre-mating and post-mating barriers on the genetic makeup of mixed populations using cytonuclear genotype frequencies of first- and second-generation offspring. Observed genotype frequencies strongly reflect the directional assortative mating observed in behavioral trials, illustrating how isolating barriers that act earlier in the reproductive cycle will have a greater affect on total reproductive isolation and may be more important to speciation than subsequent post-mating reproductive barriers.
Key Words: Poeciliopsis, allopatric speciation, cytonuclear disequilibrium, microsatellite loci, mtDNA
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