Experimental evidence for stronger impacts of larval but not adult rearing temperature on female fertility and lifespan in a seed beetle

Temperature impacts behaviour, physiology and life-history of many life forms. In many ectotherms, phenotypic plasticity within reproductive traits could act as a buffer allowing adaptation to continued global warming within biological limits. But there could be costs involved, potentially affecting adult reproductive performance and population growth. Empirical data on the expression of reproductive plasticity when different life stages are exposed is still lacking. Plasticity in key components of fitness (e.g., reproduction) can impose life-history trade-offs. Ectotherms are sensitive to temperature variation and the resulting thermal stress is known to impact reproduction. So far, research on reproductive plasticity to temperature variation in this species has focused on males. Here, I explore how rearing temperature impacted female reproduction and lifespan in the bruchid beetle Callosobruchus maculatus by exposing them to four constant temperatures (17 °C, 25 °C, 27 °C and 33 °C) during larval or adult stages. In these experiments, larval rearing cohorts (exposed to 17 °C, 25 °C, 27 °C and 33 °C, from egg to adulthood) were tested in a common garden setting at 27 °C and adult rearing cohorts, after having developed entirely at 27 °C, were exposed to four constant rearing temperatures (17 °C, 25 °C, 27 °C and 33 °C). I found stage-specific plasticity in all the traits measured here: fecundity, egg morphological dimensions (length and width), lifespan and egg hatching success (female fertility). Under different larval rearing conditions, fecundity and fertility was drastically reduced (by 51% and 42%) at 17 °C compared to controls (27 °C). Female lifespan was longest at 17 °C across both larval and adult rearing: by 36% and 55% compared to controls. Collectively, these results indicate that larval rearing temperature had greater reproductive impacts. Integrating both larval and adult rearing effects, I present evidence that female fertility is more sensitive during larval development compared to adult rearing temperature in this system.

温度对众多生命形式的行为了解、生理机能以及生命周期产生显著影响。在众多变温动物中，繁殖性状的表型可塑性可能作为一种缓冲机制，使得生物在生物适应范围内应对持续的全球变暖。然而，这种适应可能伴随着代价，进而影响成年个体的繁殖表现和种群增长。当不同生命阶段暴露于不同环境时，关于繁殖可塑性表达的经验数据仍然匮乏。在适应力关键组成部分（如繁殖）中的可塑性，可能对生命周期产生权衡。变温动物对温度变化敏感，由此产生的热应激已证实会影响到繁殖。迄今为止，关于该物种对温度变化的繁殖可塑性研究主要集中于雄性个体。本研究中，我探讨了养殖温度如何影响豆象Callosobruchus maculatus的雌性繁殖和寿命，通过在幼虫或成虫阶段暴露于四种恒定温度（17°C、25°C、27°C和33°C）进行探究。在这些实验中，幼虫养殖群体（从卵至成虫，暴露于17°C、25°C、27°C和33°C）在27°C的共生环境中进行测试，而成虫养殖群体，在完全发育于27°C后，被暴露于四种恒定养殖温度（17°C、25°C、27°C和33°C）。研究发现，所测量的所有性状均表现出特定阶段的可塑性：繁殖力、卵的形态特征（长度和宽度）、寿命以及卵孵化成功率（雌性繁殖力）。在不同的幼虫养殖条件下，与对照（27°C）相比，在17°C下繁殖力和繁殖力显著降低（降低51%和42%）。雌性寿命在幼虫和成虫养殖阶段均以17°C为最长，分别比对照提高36%和55%。综合这些结果，表明幼虫养殖温度对繁殖的影响更为显著。整合幼虫和成虫养殖效果，本研究提供了证据，表明在该系统中，雌性繁殖力在幼虫发育阶段相对于成虫养殖温度更为敏感。