Abstract
BackgroundThe number of partners that individuals mate with over their lifetime is a defining feature of mating systems, and variation in mate number is thought to be a major driver of sexual evolution. Although previous research has investigated the evolutionary consequences of reductions in the number of mates, we know little about the costs and benefits of increased numbers of mates. Here, we use a genetic manipulation of mating frequency in Drosophila melanogaster to create a novel, highly promiscuous mating system. We generated D. melanogaster populations in which flies were deficient for the sex peptide receptor (SPR) gene – resulting in SPR- females that mated more frequently – and genetically-matched control populations, and allowed them to evolve for 55 generations. At several time-points during this experimental evolution, we assayed behavioural, morphological and transcriptional reproductive phenotypes expected to evolve in response to increased population mating frequencies.ResultsWe found that males from the high mating frequency SPR- populations evolved decreased ability to inhibit the receptivity of their mates and decreased copulation duration, in line with predictions of decreased per-mating investment with increased sperm competition. Unexpectedly, SPR- population males also evolved weakly increased sex peptide (SP) gene expression. Males from SPR- populations initially (i.e., before experimental evolution) exhibited more frequent courtship and faster time until mating relative to controls, but over evolutionary time these differences diminished or reversed.ConclusionsIn response to experimentally increased mating frequency, SPR- males evolved behavioural responses consistent with decreased male post-copulatory investment at each mating and decreased overall pre-copulatory performance. The trend towards increased SP gene expression might plausibly relate to functional differences in the two domains of the SP protein. Our study highlights the utility of genetic manipulations of animal social and sexual environments coupled with experimental evolution.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0699-8) contains supplementary material, which is available to authorized users.
Highlights
The number of partners that individuals mate with over their lifetime is a defining feature of mating systems, and variation in mate number is thought to be a major driver of sexual evolution
Each generation began with 100 adult males and 100 adult females, which were permitted to interact in chambers for 9 days before progeny were collected for the generation
Initial tests of male courtship behaviour revealed that sex peptide receptor (SPR)- and white-eyed control males had comparable courtship rates, whereas wild-type males courted females significantly more (>50 % more frequently) than both SPR- and whiteeyed males
Summary
The number of partners that individuals mate with over their lifetime is a defining feature of mating systems, and variation in mate number is thought to be a major driver of sexual evolution. Several studies have adopted this approach by evolving populations at natural or restricted numbers of partners These studies have revealed that variation in mating frequency can drive the evolution of a wide range of phenotypes, including mating behaviour [9,10,11,12], sperm competitiveness [9, 13], genital and gonad size [14,15,16], cuticular hydrocarbons [17], mate harming and resistance to harm [18, 19], cognitive function [20], and sex-specific transcription [21]. The evolutionary consequences of increases in mating frequency that are driven by changes in mating behaviour, independent of environmental variation, remain unknown
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