Abstract
We tested whether the early‐life environment can influence the extent of individual plasticity in a life‐history trait. We asked: can the early‐life environment explain why, in response to the same adult environmental cue, some individuals invest more than others in current reproduction? Moreover, can it additionally explain why investment in current reproduction trades off against survival in some individuals, but is positively correlated with survival in others? We addressed these questions using the burying beetle, which breeds on small carcasses and sometimes carries phoretic mites. These mites breed alongside the beetle, on the same resource, and are a key component of the beetle's early‐life environment. We exposed female beetles to mites twice during their lives: during their development as larvae and again as adults during their first reproductive event. We measured investment in current reproduction by quantifying average larval mass and recorded the female's life span after breeding to quantify survival. We found no effect of either developing or breeding alongside mites on female reproductive investment, nor on her life span, nor did developing alongside mites influence her size. In post hoc analyses, where we considered the effect of mite number (rather than their mere presence/absence) during the female's adult breeding event, we found that females invested more in current reproduction when exposed to greater mite densities during reproduction, but only if they had been exposed to mites during development as well. Otherwise, they invested less in larvae at greater mite densities. Furthermore, females that had developed with mites exhibited a trade‐off between investment in current reproduction and future survival, whereas these traits were positively correlated in females that had developed without mites. The early‐life environment thus generates individual variation in life‐history plasticity. We discuss whether this is because mites influence the resources available to developing young or serve as important environmental cues.
Highlights
Phenotypic plasticity is classically defined as variation in the phenotype that is induced when a single genotype is exposed to different environments (Pigliucci, 2001; West‐Eberhard, 2003)
Our goal was to understand the role of the early‐life environment in explaining plasticity in a life‐history trait
We found no evidence for our a priori expectation that the mere presence or absence of mites at either life stage would explain cur‐ rent levels of investment in reproduction (Table 1)
Summary
Phenotypic plasticity is classically defined as variation in the phenotype that is induced when a single genotype is exposed to different environments (Pigliucci, 2001; West‐Eberhard, 2003). The variation seen in adult life (illustrated in Figure 1a) can be explained by the cues perceived during development If these cues match the cues perceived in adulthood, for example, it might yield increased invest‐ ment in current reproduction—because an individual has greater certainty that environmental conditions will yield high fitness re‐ turns on greater investment in current reproduction (English et al, 2016; Frankenhuis & Panchanathan, 2011; Stamps & Frankenhuis, 2016). Again in keeping with the informational models, individual beetles can be exposed to mites as larvae during develop‐ ment and again as adults when they breed This means individuals can repeatedly sample this environmental cue before deciding how to invest in current reproduction. We tested whether the informational models could apply to burying beetles and their mites, by assessing whether (c) mite density per beetle provides a reliable cue of burying beetle population density
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