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Molecular Evolution of Seminal Proteins in Field Crickets Jose A. Andres,* Luana S. Maroja,* Steven M. Bogdanowicz,* Willie J. Swanson, and
 

Summary: Molecular Evolution of Seminal Proteins in Field Crickets
Jose´ A. Andre´s,* Luana S. Maroja,* Steven M. Bogdanowicz,* Willie J. Swanson, and
Richard G. Harrison*
*Department of Ecology and Evolutionary Biology, Cornell University; and Department of Genome Sciences,
University of Washington
In sexually reproducing organisms, male ejaculates are complex traits that are potentially subject to many different se-
lection pressures. Recent experimental evidence supports the hypothesis that postmating sexual selection, and particularly
sexual conflict, may play a key role in the evolution of the proteinaceous components of ejaculates. However, this evidence
is based almost entirely on the study of Drosophila, a species with a mating system characterized by a high cost of mating
for females. In this paper, we broaden our understanding of the role of selection on the evolution of seminal proteins by
characterizing these proteins in field crickets, a group of insects in which females appear to benefit from mating multiply.
We have used an experimental protocol that can be applied to other organisms for which complete genome sequences are
not yet available. By combining an evolutionary expressed sequence tag screen of the male accessory gland in 2 focal
species (Gryllus firmus and Gryllus pennsylvanicus) with a bioinformatics approach, we have been able to identify as many
as 30 seminal proteins. Evolutionary analyses among 5 species of the genus Gryllus suggest that seminal protein genes
evolve more rapidly than genes encoding proteins that are not involved with reproduction. The rates of synonymous sub-
stitution (dS) are similar in genes encoding seminal proteins and genes encoding ``housekeeping'' proteins. For the same
comparison, the rate of fixation of nonsynonymous substitutions (dN) is 3 times higher in genes encoding seminal proteins,
suggesting that the divergence of seminal proteins in field crickets has been accelerated by positive Darwinian selection. In
spite of the contrasting characteristics of the Drosophila and Gryllus mating systems, the mean selection parameter x and

  

Source: Andrés, José - Department of Biology, University of Saskatchewan

 

Collections: Biology and Medicine