There has been an explosion of recent evidence that environments experienced by fathers or their ejaculates can influence offspring phenotypes (paternal effects). However, little is known about whether such effects are adaptive, which would have far-reaching implications for the many species facing rapidly changing environments. For example, some arguments suggest paternal effects might be a source of cross-generational plasticity, preparing offspring to face similar conditions to their father (anticipatory hypothesis). Alternatively, ejaculate-mediated effects on offspring may be non-adaptive by-products of stress. Here, we conduct an experiment to distinguish between these predictions, exposing ejaculates of the externally fertilizing mussel Mytilus galloprovincialis to ambient (19°C) and high (24°C) temperatures, then rearing offspring groups in temperatures that match and mismatch those of sperm. We find that, overall, high temperature-treated sperm induced higher rates of normal offspring development and higher success in transitioning to second-stage larvae, which may represent adaptive epigenetic changes or selection on sperm haplotypes. However, the progeny of high temperature-treated sperm did not perform better than those of ambient temperature-treated sperm when rearing temperatures were high. Overall, these findings offer little support for the anticipatory hypothesis and suggest instead that beneficial paternal effects may be eroded when offspring develop under stressful conditions.

最近有大量证据表明，父亲经历的环境或其射精会影响后代的表型（父本效应）。然而，人们对这种效应是否具有适应性知之甚少，这对面临快速变化环境的许多物种产生深远影响。例如，一些论点表明，父亲效应可能是跨代可塑性的一个来源，让后代做好准备面对与父亲类似的条件（预期假设）。或者，射精介导的对后代的影响可能是压力的非适应性副产品。在这里，我们进行了一项实验来区分这些预测，将外部受精贻贝的射精暴露在环境温度（19°C）和高温（24°C）下，然后在与精子匹配和不匹配的温度下饲养后代群体。我们发现，总体而言，高温处理的精子诱导了更高的正常后代发育率和向第二阶段幼虫过渡的更高成功率，这可能代表了精子单倍型的适应性表观遗传变化或选择。然而，当饲养温度较高时，高温处理的精子的后代表现并不比环境温度处理的精子更好。总体而言，这些发现几乎没有为预期假设提供支持，反而表明，当后代在压力条件下发育时，有益的父系效应可能会受到削弱。