What are parental condition‐transfer effects and how can they be detected?

While it has been recognized for many years that parental condition can influence offspring performance, recent research on adaptive parental effects has focused primarily on anticipatory effects, whereby parents adjust the phenotype of their offspring for the anticipated environment. Here, we make the case that condition transfer is a widespread and important type of adaptive parental effect, and endeavour to clarify how such effects should be interpreted and studied. Some authors have suggested that condition‐transfer effects result simply from resource limitation constraints (passive condition transfer, or transmissive effects). However, condition transfer can also reflect evolved parental investment strategies (active condition‐transfer effects). In some species, such strategies can involve cryptic mechanisms such as epigenetic inheritance. As recently shown in this journal by Engqvist and Reinhold, condition‐transfer effects can be obscured by anticipatory effects and interactions between the effects of parental and offspring environments. Nonetheless, we argue that these complications can be largely overcome by examining a broad range of ecologically relevant environments in both parental and offspring generations. This can be accomplished by adapting a powerful methodology from the nutritional sciences—the geometric framework—to research on parental effects.