Consequences of population structure for sex allocation and sexual conflict

Abstract

Both sex allocation and sexual conflict can be modulated by spatial structure. However, how the interplay between the type of dispersal and the scale of competition simultaneously affects these traits in sub‐divided populations is rarely considered. We investigated sex allocation and sexual conflict evolution in meta‐populations of the spider mite Tetranychus urticae evolving under budding (pairing females from the same patch) or random (pairing females from different patches) dispersal and either local (fixed sampling from each subpopulation) or global (sampling as a function of subpopulation productivity) competition. Females evolving under budding dispersal produced less female‐biased offspring sex ratios than those from the random dispersal selection regimes, contradicting theoretical predictions. In contrast, the scale of competition did not strongly affect sex allocation. Offspring sex ratio and female fecundity were unaffected by the number of mates, but female fecundity was highest when their mates evolved under budding dispersal, suggesting these males inflict less harm than those evolving under random dispersal. This work highlights that population structure can impact the evolution of sex allocation and sexual conflict. Moreover, selection on either trait may reciprocally affect the evolution of the other, for example via effects on fecundity.

Sex-biased demography modulates male harm across the genome

“…In addition to studies of natural populations, experimental evolution offers ways to artificially generate particular population structures and thereby investigate their effects on male harm. Previously, such approaches have been used in bulb mites [ 17 ], spider mites [ 18 ] and seed beetles [ 20 , 23 ]. While spider mites are arrhenotokous and lack sex chromosomes, both bulb mites (XO) and seed beetles (XY) have sex chromosomes and therefore may be systems in which the predictions we have outlined could be most effectively tested.…”

“…Male harming traits have been described across a wide range of taxa [4], from traumatic insemination of bed bugs [54], and grasping appendages of water striders [55,56], to proteins in the ejaculates of flatworms [57], and tomiodonts of painted turtles [58]. Recent theory has shown how kin selection may curb the worst excesses of such male harm [24][25][26][27]29] and has been supported empirically in a growing range of taxa, including arachnids, birds and insects [12][13][14][15][16][17][18][19][20][21]23,30]. We have built upon this theory to show how aspects of demography may shape the potential for male harm differently across different parts of the genome, yielding novel predictions as to how intragenomic conflicts may emerge over such traits, where male harm loci are likely to be enriched, and how these patterns are expected to vary across different populations and species.…”

“…traits that increase a male's mating success at the expense of the females with whom he interacts) may be curbed by relatedness between mates and between mate competitors, in a range of ecologically and demographically explicit population settings [24][25][26][27][28][29]. These theoretical predictions have motivated a growing body of empirical work on a diversity of organisms including flies [12][13][14][15]30], chickens [16], mites [17,18] and beetles [19][20][21]23].…”

No evidence that relatedness or familiarity modulate male harm in wild Drosophila melanogaster

“…Such evidence includes proof of male plastic responses to relatedness reliant on kin discrimination (i.e. in flies, seed beetles and red junglefowl; (Carazo et al, 2014;Le Page et al, 2017;Lymbery & Simmons, 2017Rosher et al, 2017;Tan et al, 2016), as well as non-plastic responses to experimental evolution under increased local relatedness (i.e., in mites; (Lukasiewicz et al, 2017;Rodrigues et al, 2021). There is thus accumulating evidence that the evolutionary interplay between kin selection and sexual conflict is an emerging research area with the potential to advance our understanding of female harm, sexual cooperation, intra-genomic conflict, and male and female co-evolution at large.…”

“…Empirical studies have followed suit over the past few years, with reports congruent with the idea that relatedness modulates male harm accumulating in flies (Drosophila melanogaster ; (Carazo et al, 2014(Carazo et al, , 2015Hollis et al, 2015;Le Page et al, 2017)), seed beetles (Callosobruchus maculatus ; (Lymbery & Simmons, 2017; but see (Berg et al, 2019)), bulb mites (Rhizoglyphus robini ; (Lukasiewicz et al, 2017), spider mites (Tetranychus urticae ; (Rodrigues et al, 2021)), red junglefowl (Gallus gallus ; (Rosher et al, 2017;Tan et al, 2016) and least killifish (Heterandria formosa ; (Ala-Honkola et al, 2011, p.). Such evidence includes proof of male plastic responses to relatedness reliant on kin discrimination (i.e.…”