Developmental plasticity in response to early-life conditions affects male sexual traits in guppies

Early environmental conditions play an important role in animal development. Lack of sufficient food early in life can lead to impaired growth and long-term fitness consequences. To avoid that, many animal species compensate during a period of low food availability by increasing their growth rate when food becomes abundant again, ie compensatory growth. However, compensatory growth during development may divert resources away from the ontogeny of reproductive and somatic functions, imposing hidden costs that are only apparent later in life. For ectotherms, these trade-offs are expected to be exacerbated by increased temperatures due to the high energetic demands of increased metabolism. We test if diet restriction during early development has long-term effects on the reproductive traits of male Trinidadian guppies (Poecilia reticulata), and, if so, whether such effects are exacerbated in warmer temperatures. Previously, we have shown that diet-restricted guppies exhibit compensatory growth. Here, we found that diet restriction during early development had no effect on the expression of sexual traits later in life. In contrast, males experiencing elevated temperatures throughout life exhibited a reduction in both black body coloration and dominance behaviors and died younger. Surprisingly, temperature did not mediate the effects of early-life diet on male sexual traits. However, temperature did mediate the effects of diet on adult growth, with diet-restricted males showing impaired growth later in life but only when they experienced elevated temperatures. Our results highlight the developmental plasticity of sexual traits and suggest that future climate predictions have the potential to negatively affect fish reproduction.