Sexual selection protects against extinction

Abstract

SUMMARY 19"Reproduction through sex carries substantial costs, mainly because only half of sexual 20" adults produce offspring 1 . It has been theorised that these costs could be countered if 21" sex allows sexual selection to clear the universal fitness constraint of mutation load 2-4 . 22"Under sexual selection, competition between (usually) males, and mate choice by 23" (usually) females create important intraspecific filters for reproductive success, so that 24" only a subset of males gains paternity. If reproductive success under sexual selection is 25" dependent on individual condition, which depends on mutation load, then sexually 26" selected filtering through 'genic capture' 5 could offset the costs of sex because it 27" provides genetic benefits to populations. Here, we test this theory experimentally by 28" comparing whether populations with histories of strong versus weak sexual selection 29" purge mutation load and resist extinction differently. After evolving replicate 30" populations of the flour beetle Tribolium castaneum for ~7 years under conditions that 31" differed solely in the strengths of sexual selection, we revealed mutation load using 32" inbreeding. Lineages from populations that had previously experienced strong sexual 33" selection were resilient to extinction and maintained fitness under inbreeding, with 34" some families continuing to survive after 20 generations of sib × sib mating. By contrast, 35" lineages derived from populations that experienced weak or non-existent sexual 36" selection showed rapid fitness declines under inbreeding, and all were extinct after 37" generation 10. Multiple mutations across the genome with individually small effects can 38" be difficult to clear, yet sum to a significant fitness load; our findings reveal that sexual 39" selection reduces this load, improving population viability in the face of genetic stress. 40"3"Sexual selection is a widespread evolutionary force giving rise to a striking diversity of sights, 41" sounds and smells that filter reproductive success away from less competitive or attractive 42" individuals, frequently at the expense of survival 6 . Sexual selection will operate to varying 43" degrees whenever sexual reproduction exists, and its significance as a potent force 44" profoundly influencing reproductive fitness of individuals is long established 6 . In contrast, 45"limited empirical work has been directed at measuring the consequences of sexual selection 46" for the fitness of populations. This lack of attention is surprising for two reasons: first, 47"because population viability is vital for biodiversity maintenance and ecosystem stability, 48"especially under modern anthropogenic stress 7,8 ; and second, because it is predicted that the allows sexual selection to operate, reducing the universal handicap of mutation load 3,4 .51" 52"Population or lineage health will always suffer at some level from mutation load -the 53"difference in fitness betw...

Simultaneous exposure to estrogen and androgen resulted in feminization and endocrine disruption

“…One is that androgen receptors are expressed in XX gonads at a time critical for sex determination in tilapia (Tao et al 2013); the other is that androgens probably act as an inhibitor of female pathway and E 2 synthesis (Bhandari et al 2006, Vizziano et al 2008. The male's main role is the production of sperm, which is critical for improving population viability via sexual selection in the face of genetic stress as demonstrated recently in the flour beetle (Lumley et al 2015). It is well documented that androgen is essential for spermatogenesis (Billard et al 1982, Ruwanpura et al 2010.…”

Intralocus Sexual Conflict and the Tragedy of the Commons in Seed Beetles

“…The population-level consequences of sexual selection should represent a balance between the opposing forces of IeSC inducing male harm on females, on one hand, and purging generally deleterious mutations, on the other (e.g., Chenoweth et al 2015;Lumley et al 2015). Recent studies have pointed to the importance of ecology and genetic architecture in determining the efficacy of the second mechanism and, therefore, the overall effect of sexual selection (e.g., Long et al 2012;Arbuthnott et al 2014;Berger et al 2014a;Bonduriansky 2014;Connallon and Clark 2014;Connallon 2015).…”

“…Today, the question of whether sexual selection renders net costs or benefits to the population as a whole remains open and a matter of considerable debate (e.g., Hunt and Hosken 2014; Rice and Gavrilets 2014;Schwander et al 2014;Shuker and Simmons 2014;Chenoweth et al 2015;Lumley et al 2015).…”

“…Within this framework, numerous studies have tested the efficacy of sexual selection in aiding adaptation by modifying the strength of sexual selection to study evolutionary responses from standing genetic variation (e.g., Holland and Rice 1999;Holland 2002;Martin and Hosken 2003;Rundle et al 2006;Fricke and Arnqvist 2007;Morrow et al 2008;Jarzebowska and Radwan 2010;Maklakov et al 2010;Plesnar-Bielak et al 2012;Chenoweth et al 2015;Lumley et al 2015) or purging naturally accumulated (e.g., Radwan et al 2004;Rundle et al 2006;Mallet et al 2011;McGuigan et al 2011;Sharp and Agrawal 2013) or artificially induced/introduced deleterious mutations (e.g., Radwan 2004;Sharp and Agrawal 2008;Hollis and Houle 2011;Plesnar et al 2011;Arbuthnott and Rundle 2012;Clark et al 2012;Almbro and Simmons 2013;Power and Holman 2015;Grieshop et al 2016). The results of these studies have been inconsistent, which allows several insights.…”

What can we infer about the origin of sex in early eukaryotes?

“…Surprisingly, we need a rather late development in the sexual saga, the process of sexual selection, to demonstrate that efficiently purging mutational load is what sex is all about. Let us briefly look at a recent study of a 'recent' mechanism [32].…”