Data from: Social density, but not sex ratio, drives ecdysteroid hormone provisioning to eggs by female house crickets (Acheta domesticus)

Social environment profoundly influences the fitness of animals, affecting their probability of survival to adulthood, longevity, and reproductive output. The social conditions experienced by parents at the time of reproduction predict the social environments that offspring will face. Despite clear challenges in predicting future environmental conditions, adaptive maternal effects provide a mechanism of passing environmental information from parent to offspring, and are now considered pervasive in natural systems. Maternal effects have been widely studied in vertebrates, especially in the context of social environment, and are often mediated by steroid hormone (SH) deposition to eggs. In insects, although many species dramatically alter phenotype and life history traits in response to social density, the mechanisms of these alterations, and the role of hormone deposition by insect mothers into their eggs, remains unknown. In the experiments described here, we assess the effects of social environment on maternal hormone deposition to eggs in house crickets (Acheta domesticus). Specifically, we tested the hypotheses that variable deposition of ecdysteroid hormones (ESH) to eggs is affected by both maternal (1) social density and (2) social composition. We found that while maternal hormone deposition to eggs does not respond to social composition (sex ratio), it does reflect social density; females provision their eggs with higher ESH concentrations under low density conditions. This finding is consistent with the interpretation that variable ESH provisioning is an adaptive maternal response to social environment, and congruent with similar patterns of variable maternal provisioning across the tree of life. Moreover, our results confirm that maternal hormone provisioning may mediate delayed density dependence by introducing a time lag in the response of offspring phenotype to population size.

社会环境对动物的适合度具有深远影响，可作用于其成年存活率、寿命及繁殖产出。亲本在繁殖阶段所经历的社会环境，可预判子代将面临的社会环境。尽管预测未来环境条件存在明确挑战，但适应性母性效应为环境信息从亲本向子代传递提供了机制，如今该效应被认为在自然系统中普遍存在。适应性母性效应在脊椎动物中已得到广泛研究，尤其围绕社会环境展开，且通常通过类固醇激素（steroid hormone, SH）向卵内的沉积来实现介导。在昆虫类群中，尽管诸多物种会响应社会密度而显著改变自身表型与生活史性状，但此类改变的内在机制，以及昆虫母本向卵内沉积激素所发挥的作用仍未明确。在本文所述的实验中，我们以家蟋蟀（Acheta domesticus）为研究对象，评估了社会环境对母本向卵内沉积激素的影响。具体而言，我们检验了两个假说：一是蜕皮类固醇激素（ecdysteroid hormones, ESH）向卵内的可变沉积会受到母本（1）社会密度的影响，以及（2）社会组成的影响。研究结果显示，尽管母本向卵内的激素沉积不受社会组成（性比）的调控，但会随社会密度发生显著变化：雌性个体在低密度条件下会为卵提供更高浓度的蜕皮类固醇激素。这一发现与“可变的蜕皮类固醇激素供给是母本对社会环境的适应性响应”这一解释相符，同时也与整个生命树中各类群存在的可变母本供给模式一致。此外，我们的研究结果证实，母本激素供给可通过使后代表型对种群大小的响应产生时滞，从而介导延迟密度依赖效应。