Ornaments indicate parasite load only if they are dynamic or parasites are contagious

Abstract

Choosing to mate with an infected partner has several potential fitness costs, including disease transmission and infection-induced reductions in fecundity and parental care. By instead choosing a mate with no, or few, parasites, animals avoid these costs and may also obtain resistance genes for offspring. Within a population, then, the quality of sexually selected ornaments on which mate choice is based should correlate negatively with the number of parasites with which a host is infected (“parasite load”). However, the hundreds of tests of this prediction yield positive, negative, or no correlation between parasite load and ornament quality. Here, we use phylogenetically controlled meta-analysis of 424 correlations from 142 studies on a wide range of host and parasite taxa to evaluate explanations for this ambiguity. We found that ornament quality is weakly negatively correlated with parasite load overall, but the relationship is more strongly negative among ornaments that can dynamically change in quality, such as behavioral displays and skin pigmentation, and thus can accurately reflect current parasite load. The relationship was also more strongly negative among parasites that can transmit during sex. Thus, the direct benefit of avoiding parasite transmission may be a key driver of parasite-mediated sexual selection. No other moderators, including methodological details and whether males exhibit parental care, explained the substantial heterogeneity in our data set. We hope to stimulate research that more inclusively considers the many and varied ways in which parasites, sexual selection, and epidemiology intersect.

Infection‐related sexual conflict in mating behaviors of wolf spiders

“…Alternatively, a recent paper by Dougherty et al (2023) conducted a meta-analysis from studies investigating infection stress, parasitism, mate choice and ornamentation, finding that parasite load may not warrant discrimination if virulence is not high enough, or if ornamentation is static (Dougherty et al, 2023). The spiders used in this study were infected with the pathogen as adults, after the critical and energetic last molt to maturity.…”

A reformulation of Fisher's runaway identifies the heritability of mate choices as a key parameter and highlights limitations of the hypothesis

“…In spite of the profusion of papers showing that Fisher's runaway is a mathematical possibility, or otherwise arguing in favour of the hypothesis [22][23][24], the vast majority of empirical work on the evolution of mate choice has focused on testing predictions of the first class of hypotheses, for example the prediction that preferred traits should be indicators of health or condition [25][26][27][28]. Although several authors have tested what is sometimes regarded as a key prediction of the runaway-that preference is genetically correlated with the trait that is the target of preference (reviewed in [29,30])-this approach has three important limitations.…”

Effects of an entomopathogenic fungus on the reproductive potential of Drosophila males

“…Studies on pathogen virulence on host reproduction have primarily focused on females (Chadwick & Little, 2005 ; Hudson et al., 2020 ; Rose et al., 2022 ). Several studies have looked into the effects of infection on various aspects of male's reproductive biology (e.g., courtship (Kennedy et al., 1987 ; Pélabon et al., 2005 ), sexual ornaments (Dougherty et al., 2023 ; Longo et al., 2020 ), and sperm quality (Pham et al., 2022 )). Yet, only limited number of studies investigated how infection affects males' mating success or overall reproductive success in the absence of mortality (De Lisle & Bolnick, 2021 ; Imroze & Prasad, 2011 ; Khan & Herberstein, 2022 ; Lehmann & Lehmann, 2000 ; Rittschof et al., 2013 ) and to what extent sexual selection contributes to the selection for resistance.…”