An experimental test for body size‐dependent effects of male harassment and an elevated copulation rate on female lifetime fecundity and offspring performance

Abstract

Many studies investigate the benefits of polyandry, but repeated interactions with males can lower female reproductive success. Interacting with males might even decrease offspring performance if it reduces a female's ability to transfer maternal resources. Male presence can be detrimental for females in two ways: by forcing females to mate at a higher rate and through costs associated with resisting male mating attempts. Teasing apart the relative costs of elevated mating rates from those of greater male harassment is critical to understand the evolution of mating strategies. Furthermore, it is important to test whether a male's phenotype, notably body size, has differential effects on female reproductive success versus the performance of offspring, and whether this is due to male body size affecting the costs of harassment or the actual mating rate. In the eastern mosquitofish Gambusia holbrooki, males vary greatly in body size and continually attempt to inseminate females. We experimentally manipulated male presence (i.e., harassment), male body size and whether males could copulate. Exposure to males had strong detrimental effects on female reproductive output, growth and immune response, independent of male size or whether males could copulate. In contrast, there was a little evidence of a cross‐generational effect of male harassment or mating rate on offspring performance. Our results suggest that females housed with males pay direct costs due to reduced condition and offspring production and that these costs are not a consequence of increased mating rates. Furthermore, exposure to males does not affect offspring reproductive traits.

Stress in the city: meta-analysis indicates no overall evidence for stress in urban vertebrates

“…They are only one component of a suite of physiological and behavioural responses to stress [91]. For example, chronic stress increases glucose levels [92] and oxidative stress [93], and reduces immune responses [94,95], body condition [12], and reproductive output [21,22]. Each of these responses could have negative consequences for an individual's reproductive output and, by extension, population viability.…”

“…Both increases and reductions in glucocorticoid levels after repeated or prolonged exposure to stressors can result in the maladaptive allocation of energy to certain biological processes, resulting in a range of detrimental effects (e.g. impaired immune response [19], reduced lifetime reproduction [21,22] and lower survival [23]). If urban environments present stressful, novel challenges then wild animals could maladaptively respond to chronic stress which might, in turn, lower population growth and threaten the persistence of wild populations in urban areas.…”

Condition-transfer maternal effects modulate sexual conflict

“…Thus, the mere existence of male harassment and/or coercion is far from a litmus test for male harm. Different forms of sexual harassment and/or coercion to females have been reported for a number of vertebrates (and are probably common 42 ), but direct evidence that such harassment reduces female fitness is limited [43][44][45] . In short, there does seem to be a relationship between the overall scope for maternal effects within broad taxonomic groups and reports of male harm.…”

Male size and reproductive performance in three species of livebearing fishes (Gambusia spp.): a systematic review and meta-analysis

“…'gonopodial thrusting'; Itzkowitz, 1971;Martin, 1975;McPeek, 1992;Bisazza, 1993;. Males can perform about one gonopodial thrust per minute (Wilson, 2005), and this incessant male harassment seemingly lowers female fitness by reducing foraging efficiency as well as increasing predation risk and energy expenditure (Dadda et al, 2005;Iglesias-Carrasco et al, 2019). Gambusia shows considerable inter-and intraspecific male size variation, making them an often-used model to study male body size selection (Zulian et al, 1995;Deaton, 2008).…”