Are parental condition transfer effects more widespread than is currently appreciated?

It has long been recognized that the environment experienced by parents can influence the traits of offspring (i.e. 'parental effects'). Much research has explored whether mothers respond to predictable shifts in environmental signals by modifying offspring phenotypes to best match future conditions. Many organisms experience conditions that theory predicts should favor the evolution of such 'anticipatory parental effects', but such predictions have received limited empirical support. 'Condition transfer effects' are an alternative to anticipatory effects that occur when the environment experienced by parents during development influences offspring fitness. Condition transfer effects occur when parents that experience high-quality conditions produce offspring that exhibit higher fitness irrespective of the environmental conditions in the offspring generation. Condition transfer effects are not driven by external signals but are instead a byproduct of past environmental quality. They are also likely adaptive but have received far less attention than anticipatory effects. Here, we review the generality of condition transfer effects and show that they are much more widespread than is currently appreciated. Condition transfer effects are observed across taxa and are commonly associated with experimental manipulations of resource conditions experienced by parents. Our Review calls for increased research into condition transfer effects when considering the role of parental effects in ecology and evolution.