Variation in the post-mating fitness landscape in fruit flies.

C Fricke,T Chapman

doi:10.1111/jeb.13090

Abstract

Sperm competition is pervasive and fundamental to determining a male's overall fitness. Sperm traits and seminal fluid proteins (Sfps) are key factors. However, studies of sperm competition may often exclude females that fail to remate during a defined period. Hence, the resulting data sets contain fewer data from the potentially fittest males that have most success in preventing female remating. It is also important to consider a male's reproductive success before entering sperm competition, which is a major contributor to fitness. The exclusion of these data can both hinder our understanding of the complete fitness landscapes of competing males and lessen our ability to assess the contribution of different determinants of reproductive success to male fitness. We addressed this here, using the Drosophila melanogaster model system, by (i) capturing a comprehensive range of intermating intervals that define the fitness of interacting wild‐type males and (ii) analysing outcomes of sperm competition using selection analyses. We conducted additional tests using males lacking the sex peptide (SP) ejaculate component vs. genetically matched (SP +) controls. This allowed us to assess the comprehensive fitness effects of this important Sfp on sperm competition. The results showed a signature of positive, linear selection in wild‐type and SP + control males on the length of the intermating interval and on male sperm competition defence. However, the fitness surface for males lacking SP was distinct, with local fitness peaks depending on contrasting combinations of remating intervals and offspring numbers. The results suggest that there are alternative routes to success in sperm competition and provide an explanation for the maintenance of variation in sperm competition traits.

Highlights

Post-copulatory male–male contests in the form of sperm competition were first described by Parker (1970) and, since huge research effort has been dedicated to understanding and identifying the underlying mechanisms involved
Sperm competition occurs after a female has remated and both first and second male ejaculates are simultaneously present to compete for fertilizations
We estimated the natural length of the intermating interval in twice-mated females and found that about half of the females remated within 6 h after their first mating

Summary

Introduction

Post-copulatory male–male contests in the form of sperm competition were first described by Parker (1970) and, since huge research effort has been dedicated to understanding and identifying the underlying mechanisms involved (reviewed in Simmons, 2001). Studies conducted on diverse vertebrates, and controlled laboratory experiments in invertebrate systems, have highlighted the importance to success in sperm competition of the timing of matings, reproductive trait morphology, differential sperm. Last male sperm precedence dominates, and data from Drosophila melanogaster suggest that the degree of second male sperm precedence is associated with male lifetime reproductive success (Fricke et al, 2010). Sperm competition occurs after a female has remated and both first and second male ejaculates are simultaneously present to compete for fertilizations. Male sperm ‘offence’ is one of two contrasting roles males can adopt and occurs when a male encounters a mated female and has to gain a remating in a 2017 THE AUTHORS.

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