Little evidence for intralocus sexual conflict over the optimal intake of nutrients for life span and reproduction in the black field cricketTeleogryllus commodus

Abstract

There is often large divergence in the effects of key nutrients on life span (LS) and reproduction in the sexes, yet nutrient intake is regulated in the same way in males and females given dietary choice. This suggests that the sexes are constrained from feeding to their sex‐specific nutritional optima for these traits. Here, we examine the potential for intralocus sexual conflict (IASC) over optimal protein and carbohydrate intake for LS and reproduction to constrain the evolution of sex‐specific nutrient regulation in the field cricket, Teleogryllus commodus. We show clear sex differences in the effects of protein and carbohydrate intake on LS and reproduction and strong positive genetic correlations between the sexes for the regulated intake of these nutrients. However, the between‐sex additive genetic covariance matrix had very little effect on the predicted evolutionary response of nutrient regulation in the sexes. Thus, IASC appears unlikely to act as an evolutionary constraint on sex‐specific nutrient regulation in T. commodus. This finding is supported by clear sexual dimorphism in the regulated intake of these nutrients under dietary choice. However, nutrient regulation did not coincide with the nutritional optima for LS or reproduction in either sex, suggesting that IASC is not completely resolved in T. commodus.

Macronutrients and micronutrients drive trade‐offs between male pre‐ and postmating sexual traits

“…Moreover, T. oceanicus are known to be plastic in their trait expression under different environmental pressures, as they are able to adjust the contribution to postmating traits according to the number of competitors in their environment (Gray & Simmons, 2013;Simmons & Lovegrove, 2017;Sloan, Lovegrove, & Simmons, 2018;Thomas & Simmons, 2009a. Rapkin et al (2017) have demonstrated that the regulated intake of protein and carbohydrate is heritable in T. commodus and that the regulation of protein intake is under stronger genetic control than carbohydrate intake; likewise, we observed a smaller variance on protein intake than carbohydrate intake in T. oceanicus ( Figure 5). It will be interesting to determine whether male crickets adjust the ratio of protein and carbohydrate intake in response to their social environment to optimize the expression of pre-and postmating sexual traits.…”

Genotype-by-sex-by-diet interactions for nutritional preference, dietary consumption, and lipid deposition in a field cricket

“…Examples of active nutrient regulation can be found in a diversity of insect species, including predatory ground beetles (Anchomenus dorsalis; Jensen et al 2015), fruit flies (Drosophila melanogaster; Lee et al 2008;Jensen et al 2015), speckled roaches (Nauphoeta cinerea; South et al 2011;Bunning et al 2015Bunning et al , 2016, and field crickets (Teleogryllus commodus; Maklakov et al 2008;Rapkin et al 2017;Gryllus veletis, Harrison et al 2014). However, with the exception A. dorsalis, nutrient regulation in these species does not appear optimal for the expression of important phenotypic traits, such as reproduction (Lee et al 2008;Maklakov et al 2008;South et al 2011;Bunning et al 2015Bunning et al , 2016Jensen et al 2015;Rapkin et al 2017) and lifespan (Lee et al 2008;Maklakov et al 2008;Jensen et al 2015;Rapkin et al 2017). As traits frequently have different nutritional optima (e.g., Lee et al 2008;Maklakov et al 2008;Jensen et al 2015), it has been argued that this sub-optimal nutrient regulation may represent an attempt by individuals to balance the expression of multiple traits (Lihoreau et al 2015;Bunning et al 2016).…”

“…One source of variation in nutrient intake that is likely to be important is the genotype of an individual. Indeed, studies on humans (e.g., Tanaka 2014), rats (e.g., Liu and Lloyd 2013), mice (e.g., Smith et al 2000), fruit flies (Reddiex et al 2013), and field crickets (Rapkin et al 2017) all indicate that the intake of macronutrients has a genetic basis. The predisposition to the deleterious effects of dietary overconsumption also appears to have a genetic basis that varies with the nutritional environment (van der Klaauw and Farooqi 2015), with genotype-by-diet interactions for weight gain and obesity being demonstrated in mice (Sutton et al 2006;Gordon et al 2008), D. melanogaster (Reed et al 2010), and humans (Qi and Cho 2008;Heianza and Qi 2017).…”

Digest: Does intralocus sexual conflict affect cricket nutrition?*

“…In this issue, Rapkin et al. () used quantitative genetics and dietary choice experiments utilizing the geometric framework to show that intralocus sexual conflict is likely not responsible for suboptimal nutrient regulation in T. commodus . The authors showed that protein and carbohydrate intake are highly heritable but differentially affect lifespan and reproductive output of the two sexes.…”

“…The difference between preferred and optimal diet in T. commodus could also serve as a mechanism for reducing the fitness costs in offspring that Pischedda and Chippindale () reported. Rapkin et al.’s () findings show that much remains unknown about the underlying mechanisms of and interactions between IASC and sexual dimorphism.…”