Dietary stress increases the total opportunity for sexual selection and modifies selection on condition‐dependent traits

Abstract

Although it is often expected that adverse environmental conditions depress the expression of condition-dependent sexually selected traits, the full consequences of environmental change for the action of sexual selection, in terms of the opportunity for total sexual selection and patterns of phenotypic selection, are unknown. Here we show that dietary stress in guppies, Poecilia reticulata, reduces the expression of several sexually selected traits and increases the opportunity for total sexual selection (standardized variance in reproductive success) in males. Furthermore, our results show that dietary stress modulates the relative importance of precopulatory (mating success) and postcopulatory (relative fertilization success) sexual selection, and that the form of multivariate sexual selection (linear vs. nonlinear) depends on dietary regime. Overall, our results are consistent with a pattern of heightened directional selection on condition-dependent sexually selected traits under environmental stress, and underscore the importance of sexual selection in shaping adaptation in a changing world. LETTEREnvironmental-dependent sexual selection 449

Imminent risk of predation reduces the relative strength of postcopulatory sexual selection in the guppy

“…By contrast, the presence of a predator is expected to favour males that invested relatively more in mate acquisition traits, at the expense of sperm production traits. A multivariate selection analysis of pre-and postcopulatory traits under contrasting gradients of predation risk will allow us to test this prediction [27,50].…”

“…Because of logistic problems (second day's observations were missing), one C replicate was excluded from shoaling data analyses. During the same observation sessions, for each male, individually recognizable from colour patterns [27,50], we recorded the number of courtship displays (sigmoid displays, SD), coercive mating attempts (gonopodial thrusts, GT) and the number of successful copulations (hereafter male copulation success, MCS), i.e. copulations followed by postcopulatory jerks performed by the male [61].…”

“…For each male in each treatment, we determined male mating success (MMS) as the number of females with which a given male produced offspring divided by the number of females that produced a brood in each female set (genetic MMS, sensu [63]); male reproductive success (MRS), as the number of offspring sired by a given male divided by the number of offspring produced by the set of females; postcopulatory success (PCS), as the mean paternity share of offspring produced by the females successfully inseminated by a male, corrected by the number of males that fertilized the eggs of a given female [50]; and fecundity of mates (FEC), as the average fecundity of females with which a given male produced offspring divided by the average number of offspring produced within the female set [27].…”

“…Recently, it has been shown that the relative importance of pre-and postcopulatory sexual selection (and their interaction) can fluctuate significantly under variable environmental conditions [21]. For example, population density [22][23][24][25] or short-term food limitation [26,27] can significantly alter sexual © 2020 The Author(s) Published by the Royal Society. All rights reserved.…”

Differential gene regulation in selected lines for high and low sperm production in male guppies

“…As predicted by theoretical models, the number of sperm transferred during mating is the most important indicator of fertilization success in this species (Boschetto, Gasparini, & Pilastro, 2011). However, males are limited in their sperm investment because sperm are costly to produce as suggested by diet manipulation experiments (Cattelan, Evans, Garcia‐Gonzalez, Morbiato, & Pilastro, 2019; Devigili, Kelley, Pilastro, & Evans, 2013; Gasparini et al, 2013). The upregulation of the immune system negatively affects sperm production, as well as other costly sexually‐selected traits (Devigili, Di Nisio, Grapputo, & Pilastro, 2016; Kolluru, Grether, Dunlop, & South, 2009), suggesting the existence of trade‐offs between sperm investment and immune response.…”