Abstract
Sexual selection results from variation in success at multiple stages in the mating process, including competition before and after mating. The relationship between these forms of competition, such as whether they trade-off or reinforce one another, influences the role of sexual selection in evolution. However, the relationship between these 2 forms of competition is rarely quantified in the wild. We used video cameras to observe competition among male field crickets and their matings in the wild. We characterized pre- and post-copulatory competition as 2 networks of competing individuals. Social network analysis then allowed us to determine 1) the effectiveness of precopulatory competition for avoiding postcopulatory competition, 2) the potential for divergent mating strategies, and 3) whether increased postcopulatory competition reduces the apparent reproductive benefits of male promiscuity. We found 1) limited effectiveness of precopulatory competition for avoiding postcopulatory competition; 2) males do not specifically engage in only 1 type of competition; and 3) promiscuous individuals tend to mate with each other, which will tend to reduce variance in reproductive success in the population and highlights the trade-off inherent in mate guarding. Our results provide novel insights into the works of sexual competition in the wild. Furthermore, our study demonstrates the utility of using network analyses to study competitive interactions, even in species lacking obvious social structure.
Highlights
Competition for mates has a potent influence on evolution
In 2006, there were 35 males that never used the same burrow as another male, and 23 such males in 2013. These isolated individuals were not considered for the analyses of interactions, as they could not contribute to sexual selection through fighting and were unlikely to contribute through sperm competition
We found that 1) males were in stronger sperm competition with the males they fought more; 2) males that fought with many different males were in sperm competition with many different males; and 3) there is a positive relationship between the promiscuity of (b)
Summary
Females may prefer particular males and dominant individuals can monopolize access to females (Birkhead and Pizzari 2002; Andersson and Simmons 2006), leading to variance in fitness that drives selection In both internally and externally fertilizing species, once matings are achieved there is still room for further sexual selection through processes such as sperm competition (Parker 1970) and cryptic female choice (Thornhill 1983). This divides sexual selection into 2 arenas of competition: precopulatory and postcopulatory (“episodes of selection” according to Pizzari et al 2002). A number of studies have identified negative associations across species between sexual dimorphism in body size (an indicator of males’ ability to monopolize access to females) and relative testes size (an indicator of the strength of postcopulatory selection)
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