Shorter effective lifespan in laboratory populations of D. melanogaster might reduce sexual selection

Abstract

The role of sexual selection in mediating levels of sexual conflict has been demonstrated in many experimental evolution studies on Drosophila spp. where competition among males for mating was the target of selection. Sexual selection has also been shown to affect the evolution of life-histories. However, the influence of divergent life-histories on reproductive strategies and, therefore, sexual selection and possibly sexual conflict has been less well studied. We examined D. melanogaster populations selected for a short development time and early age at reproduction for changes in reproductive behavior and traits that are proxies of sexual selection. We report a large reduction in reproductive competition experienced by the males of these populations, compared to ancestral populations that are not consciously selected for rapid development or early reproduction, potentially leading to reduced sexual selection. We show that rapidly developing and early reproducing populations have very low levels of mating in their lifetime (females are more or less monandrous), low courtship levels, shorter copulation duration, and longer time from eclosion to first mating, compared to the controls. These results are discussed in the context of the previously demonstrated reduction of inter-locus sexual conflict in these populations. We show that life-history strategies might have a large and significant impact on sexual selection, with each influencing the other and contributing to the complexities of adaptation. Significance statement Sexual conflict, often manifested as an arms-race between males and females trying to enhance their own reproductive success at some cost to the other, is of great evolutionary interest because it can maintain genetic variation in populations, prevent the independent optimization of male and female traits, and also promote speciation. Sexual selection, or variation in mating success, is well known to affect levels of sexual conflict. However, it is not so clear whether, and how, the regular evolution of life-histories also affects sexual selection. Here, we show that life-history evolution in fruit fly populations selected for traits not directly related to sexual conflict might, nevertheless, mediate the possible evolution of altered sexual conflict levels through effects on sexual selection. Populations that evolved to develop to adulthood fast, and reproduce relatively early in life, are shown to potentially experience less sexual selection, which can explain the low sexual conflict levels earlier observed in them.

Evolution of mate harm resistance in females fromDrosophila melanogasterpopulations selected for faster development and early reproduction

“…However, if expression of MHR leads to reduction in reproductive cost in general, detecting cost of MHR per se might be difficult. Alternatively, cost of MHR can be indirectly inferred from the evolutionary reduction in MHR when selection on such traits is removed (11,24) (25,26). In a similar study, we showed reduction in mate mating behaviour, including mate harming ability (27).…”

“…Several experimental evolution studies have shown the evolution of MHR (2,(10)(11)(12)(13)(14)16,17,24,38). Of these, only two have directly connected evolution of conflict related traits to life history traits such as, condition, adult lifespan, development time, and size (17,39). Though evolution of MHR is important for a population's survival (40), continuation of sexual selection (41), and maintenance of genetic variation (42), it cannot evolve in the vacuum of sexually antagonistic traits only.…”

“…Mital et al (2021) reported a reduction in MHR in females in populations of D. melanogaster experimentally evolved for faster development and early reproduction, possibly due to a change in breeding system to near-monogamy (25,26). In a similar study, we showed reduction in mate mating behaviour, including mate harming ability (27).…”

Evolution of reduced mate harming tendency of males in Drosophila melanogaster populations selected for faster life history

“…In an independent investigation on a similar set of experimentally evolved populations (Ghosh and Joshi 2012;Mital et al 2021Mital et al , 2022 found that the intensity of sexual selection and the degree of interlocus sexual conflict to be lower in populations selected for faster development and early reproduction. The parallel between our results and those of Ghosh and Joshi (2012) and Mital et al (2021Mital et al ( , 2022 is somewhat expected, and is a robust proof in support of our theory. However, even more interesting is the difference.…”

“…Secondly, traits that inflict mate harm, i.e., the sexually antagonistic male traits, are energetically expensive to express and hence, increase in such traits is constrained by trade-offs involving costly life history traits (Wedell et al 2006;Bonduriansky et al 2008;Adler and Bonduriansky 2014;Lemaître et al 2020). Thirdly, survivorship pattern and scheduling of reproduction can also put additional constraints on the evolution of mate harm, for example by restricting mating system and breeding ecology (Mital et al 2021(Mital et al , 2022. The latter two theories are a more recent development in the field and we focus on them in the present investigation.…”