Adaptive maternal and paternal effects: gamete plasticity in response to parental stress

Recently, the adaptive significance of maternal effects has been increasingly recognized. No longer are maternal effects relegated as simple `troublesome sources of environmental resemblance' that confound our ability to estimate accurately the genetic basis of traits of interest. Rather, it has become evident that many maternal effects have been shaped by the action of natural selection to act as a mechanism for adaptive phenotypic response to environmental heterogeneity. Consequently, maternal experience is translated into variation in offspring fitness.

The female reproductive tract is where competition between the sperm of different males takes place, aided and abetted by the female herself. Intense postcopulatory sexual selection fosters inter-sexual conflict and drives rapid evolutionary change to generate a startling diversity of morphological, behavioural and physiological adaptations. We identify three main issues that should be resolved to advance our understanding of postcopulatory sexual selection. We need to determine the genetic basis of different male fertility traits and female traits that mediate sperm selection; identify the genes or genomic regions that control these traits; and establish the coevolutionary trajectory of sexes.

One of the outstanding challenges for evolutionary biologists is to understand how developmental plasticity can influence the evolutionary process. Developmental plasticity frequently involves parental effects, which might enable adaptive and context-dependent transgenerational transmission of phenotypic strategies. However, parent-offspring conflict will frequently result in parental effects that are suboptimal for parents, offspring or both. The fitness consequences of parental effects at evolutionary equilibrium will depend on how conflicts can be resolved by modifications of developmental processes, suggesting that proximate studies of development can inform ultimate questions. Furthermore, recent studies of plants and animals show how studies of parental effects in an ecological context provide important insights into the origin and evolution of adaptation under variable environmental conditions.