Abstract
Understanding the effects of male and female age on reproductive success is vital to explain the evolution of life history traits and sex‐specific aging. A general prediction is that pre‐/postmeiotic aging processes will lead to a decline in the pre‐ and postcopulatory abilities of both males and females. However, in as much the sexes have different strategies to optimize their fitness, the decline of reproductive success late in life can be modulated by social context, such as sex ratio, in a sex‐specific manner. In this study, we used Drosophila melanogaster to investigate whether sex ratio at mating modulates age effects on male and female reproductive success. As expected, male and female age caused a decrease in reproductive success across male‐biased and female‐biased social contexts but, contrary to previous findings, social context did not modulate age‐related fitness decline in either of the two sexes. We discuss these results in the light of how sex ratio might modulate pre‐/postcopulatory abilities and the opportunity for inter‐ and intrasexual competition in D. melanogaster, and generally suggest that social context effects on these processes are likely to be species specific.
Highlights
Exploring the effects of male and female age on reproductive success is vital to understand life history evolution and sex‐spe‐ cific aging (Bonduriansky, Maklakov, Zajitschek, & Brooks, 2008; Flatt & Heyland, 2011; Maklakov & Lummaa, 2013; Zajitschek, Bonduriansky, Zajitschek, & Brooks, 2009)
We predicted that male age would decrease reproductive success rela‐ tively more in a MB social context, because we expected old males to have a higher disadvantage under intense male–male competi‐ tion
D. melano‐ gaster males exhibit a marked preference for young females (Cook & Cook, 1975; Lüpold, Manier, Ala‐Honkola, Belote, & Pitnick, 2011), so we predicted female age to decrease reproductive success more in a FB social context, where there is a potentially higher opportu‐ nity for males to choose young females over the old ones
Summary
Exploring the effects of male and female age on reproductive success is vital to understand life history evolution and sex‐spe‐ cific aging (Bonduriansky, Maklakov, Zajitschek, & Brooks, 2008; Flatt & Heyland, 2011; Maklakov & Lummaa, 2013; Zajitschek, Bonduriansky, Zajitschek, & Brooks, 2009). Intrasex‐ ual competition is mostly observed in males, aggression between females is present, mainly when food sources are scarce (Bath et al, 2017; Bath, Morimoto, & Wigby, 2018; Ueda & Kidokoro, 2002) Both males and females of this species ex‐ hibit mate choice but the degree and direction of these choices can differ depending on the population of origin and the social en‐ vironment (Byrne & Rice, 2006; Edward & Chapman, 2012, 2013; Gowaty, Steinichen, & Anderson, 2003; Monier, Nöbel, Isabel, & Danchin, 2018). We predicted that male age would decrease reproductive success rela‐ tively more in a MB social context, because we expected old males to have a higher disadvantage under intense male–male competi‐ tion In this species female intrasexual competition ap‐ pears to be less important than intersexual selection (Gowaty et al, 2003), so we did not predict a similar outcome. D. melano‐ gaster males exhibit a marked preference for young females (Cook & Cook, 1975; Lüpold, Manier, Ala‐Honkola, Belote, & Pitnick, 2011), so we predicted female age to decrease reproductive success more in a FB social context, where there is a potentially higher opportu‐ nity for males to choose young females over the old ones
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