Limited sex differences in plastic responses suggest evolutionary conservatism of thermal reaction norms: A meta-analysis in insects

Abstract

Temperature has a profound effect on the growth and development of ectothermic animals. However, the extent to which ecologically driven selection pressures can adjust thermal plastic responses in growth schedules is not well understood. Comparing temperature‐induced plastic responses between sexes provides a promising but underexploited approach to evaluating the evolvability of thermal reaction norms: males and females share largely the same genes and immature environments but typically experience different ecological selection pressures. We proceed from the idea that substantial sex differences in plastic responses could be interpreted as resulting from sex‐specific life‐history optimization, whereas similarity among the sexes should rather be seen as evidence of an essential role of physiological constraints. In this study, we performed a meta‐analysis of sex‐specific thermal responses in insect development times, using data on 161 species with comprehensive phylogenetic and ecological coverage. As a reference for judging the magnitude of sex specificity in thermal plasticity, we compared the magnitude of sex differences in plastic responses to temperature with those in response to diet. We show that sex‐specific responses of development times to temperature variation are broadly similar. We also found no strong evidence for sex specificity in thermal responses to depend on the magnitude or direction of sex differences in development time. Sex differences in temperature‐induced plastic responses were systematically less pronounced than sex differences in responses induced by variations in larval diet. Our results point to the existence of substantial constraints on the evolvability of thermal reaction norms in insects as the most likely explanation. If confirmed, the low evolvability of thermal response is an essential aspect to consider in predicting evolutionary responses to climate warming.

Does What You Eat Affect How You Mate? Disentangling the Interactions Between Diet-Induced Phenotypic Plasticity and Adult Reproductive Strategies in Black Soldier Flies

“…Females are often more sensitive to nutritional stress during the larval stage than males (Teder and Kaasik 2023). This is reflected in our study, where the allometric scaling of female reproductive organs showed more significant plasticity, suggesting that the female reproductive organ development is particularly sensitive to nutritional variations experienced during the larval stages.…”

Speciation and development

“…Theory provides multiple nonmutually exclusive explanations to account for Haldane's rule, including dominance theory (unmasked recessive DMIs linked to the hemizygous sex chromosome), faster male theory (production of DMIs from more rapid molecular evolution of genes with male‐biased expression, potentially due to sexual selection), fragile male theory (greater sensitivity of male developmental programs to generate DMIs), faster X theory (DMIs arising from potentially quicker molecular evolution of X‐linked genes), and genomic conflict theory (DMIs arising from cyto‐nuclear divergence or divergence in sex‐linked genetic drive elements) (Cowell, 2023; Hurst & Pomiankowski, 1991; Presgraves, 2010a; Turelli & Orr, 1995; Turelli & Orr, 2000; Wu & Davis, 1993; Wu & Davis, 1993). The fragile male hypothesis perhaps has the strongest implicit roots in development in that it supposes that there is something about the architecture of genetic networks that control development of male‐specific traits (such as gametogenesis) that are particularly sensitive to perturbation (Hunt & Hassold, 2002; Sage et al, 2015; Sharp & Agrawal, 2013; Yeh et al, 2018, but see Teder & Kaasik, 2023). However, the developmental causes for why, in general, the sexes differ in the sensitivity of traits to perturbation remain to be characterized.…”

A future food boom rescues the negative effects of early-life adversity on adult lifespan in a small mammal

“…Sex-specific susceptibility to early-life adversity has been demonstrated in some species, with negative associations between harsh developmental conditions and later-life phenotypes apparent in only one sex [24–28]. When longevity differs between the sexes (e.g.…”