The Roles of Natural and Sexual Selection During Adaptation to a Novel Environment

Abstract

Abstract. The net effect of sexual selection on nonsexual fitness is controversial. On one side, elaborate display traits and preferences for them can be costly, reducing the nonsexual fitness of individuals possessing them, as well as their offspring. In contrast, sexual selection may reinforce nonsexual fitness if an individual's attractiveness and quality are genetically correlated. According to recent models, such good-genes mate choice should increase both the extent and rate of adaptation. We evolved 12 replicate populations of Drosophila serrata in a powerful two-way factorial experimental design to test the separate and combined contributions of natural and sexual selection to adaptation to a novel larval food resource. Populations evolving in the presence of natural selection had significantly higher mean nonsexual fitness when measured over three generations (13-15) during the course of experimental evolution (16-23% increase). The effect of natural selection was even more substantial when measured in a standardized, monogamous mating environment at the end of the experiment (generation 16; 52% increase). In contrast, and despite strong sexual selection on display traits, there was no evidence from any of the four replicate fitness measures that sexual selection promoted adaptation. In addition, a comparison of fitness measures conducted under different mating environments demonstrated a significant direct cost of sexual selection to females, likely arising from some form of male-induced harm. Indirect benefits of sexual selection in promoting adaptation to this novel resource environment therefore appear to be absent in this species, despite prior evidence suggesting the operation of good-genes mate choice in their ancestral environment. How novel environments affect the operation of good-genes mate choice is a fundamental question for future sexual selection research.

Maintenance of genetic variation in sexual ornaments: a review of the mechanisms

“…No such promotion was detected. The same was true for Drosophila serrata selected for adaptation to novel food (Rundle et al 2006). However, Dolgin et al (2006) have recently found that adaptation to thermal environment did increase male mating success.…”

“…One-way to test whether sexual selection increases population fitness is experimental evolution under varying opportunities for sexual selection (e.g. Holland 2002; Radwan et al 2004;Rundle et al 2006;Fricke and Arnqvist 2007). …”

Genomic Evidence that Sexual Selection Impedes Adaptation to a Novel Environment

“…Several experiments have manipulated the opportunity for sexual selection and then measured the consequences for population mean fitness or components thereof, beginning either from standing genetic variance [4,[15][16][17][18][19][20][21][22][23][24] or from novel mutational variance [25][26][27]. This approach integrates genetic effects across much of the genome, meaning the net effect on fitness may be dominated by sets of segregating alleles with opposing effects on sexual versus nonsexual fitness, obscuring underlying patterns at individual loci.…”

“…To provide insight into the impact of sexual selection on naturally segregating polymorphisms across the genome, we previously evolved 12 populations of Drosophila serrata in a novel environment employing a factorial manipulation of the opportunities for natural and sexual selection [4]. Here, we genotype more than 1,400 SNPs in the evolved populations and reveal that sexual selection affected many of the same genomic regions as natural selection, aligning with it as often as opposing it.…”

Time flies: time of day and social environment affect cuticular hydrocarbon sexual displays in Drosophila serrata

“…Sexual conflict has been extensively studied in D. melanogaster [49,58,59] and D. serrata males are likewise also known to be harmful to females [43]. Reduced attractiveness of females when mating activity is highest may therefore be an adaptive response in females to ongoing interlocus conflict, allowing them to reduce costly male harassment and/or to avoid possibly harmful matings.…”