Abstract
BackgroundDespite the common assumption that multiple mating should in general be favored in males, but not in females, to date there is no consensus on the general impact of multiple mating on female fitness. Notably, very little is known about the genetic and physiological features underlying the female response to sexual selection pressures. By combining an experimental evolution approach with genomic techniques, we investigated the effects of single and multiple matings on female fecundity and gene expression. We experimentally manipulated the opportunity for mating in replicate populations of Drosophila melanogaster by removing components of sexual selection, with the aim of testing differences in short term post-mating effects of females evolved under different mating strategies.ResultsWe show that monogamous females suffer decreased fecundity, a decrease that was partially recovered by experimentally reversing the selection pressure back to the ancestral state. The post-mating gene expression profiles of monogamous females differ significantly from promiscuous females, involving 9% of the genes tested (approximately 6% of total genes in D. melanogaster). These transcripts are active in several tissues, mainly ovaries, neural tissues and midgut, and are involved in metabolic processes, reproduction and signaling pathways.ConclusionsOur results demonstrate how the female post-mating response can evolve under different mating systems, and provide novel insights into the genes targeted by sexual selection in females, by identifying a list of candidate genes responsible for the decrease in female fecundity in the absence of promiscuity.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-014-0239-3) contains supplementary material, which is available to authorized users.
Highlights
Despite the common assumption that multiple mating should in general be favored in males, but not in females, to date there is no consensus on the general impact of multiple mating on female fitness
When measured as number of adult progeny emerging from eggs laid during a period of 4 days, this difference was significant only after a single mating (F1,13 = 6.06, P = 0.029), again regardless of the male partner, but not when females where continuously exposed to males (F1,13 = 2.93, P = 0.110), the effect sizes were comparable for direction and magnitude (Table 1)
The phenotypic change in reproductive output of females from the MP populations following 25 generations of reversed selection was smaller and non-significant. It did indicate a reversal in reproductive output had occurred; posthoc tests showed that the reproductive output of females from the MP treatment was intermediate to both monogamous and promiscuous treatments (Tukey Honest significant difference (HSD): M vs MP, t = 0.913, P = 0.6365; MP vs P, t =1.804, P = 0.1850; Figure 3)
Summary
Despite the common assumption that multiple mating should in general be favored in males, but not in females, to date there is no consensus on the general impact of multiple mating on female fitness. Female polyandry can be promoted by selection if males provide resource benefits, through the ejaculate [10,11,12] or through additional paternal care [13,14], or if some males do not provide viable sperm or insufficient ejaculate to fertilize the ova [15,16]. It has be proposed as a strategy to reduce sexual harassment [17]. Multiple mating can be non-adaptive for females in the presence of strong selection for multiple mating on males coupled with a strong intersexual genetic correlation for mating propensity [19]
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