The mechanisms of parental effects, and their intergenerational impact on life history traits and population dynamics
Intergenerational effects occur when a parent’s experiences impact upon the reproduction of their offspring, and potentially subsequent generations. Models indicate that intergenerational effects can have important implications for the evolution of life-history traits and for patterns of population dynamics, although these will necessarily depend upon the nature and duration of such effects. Experiments in soil mites have shown that manipulating both parental food environments and maternal age, generate context-dependent maternal effects, which are still detectable in the life histories of descendants several generations later.
Here we use a population-level study of the soil mite Sancassania berlesei, coupled with nutritional assays of egg contents and characterisation of DNA methylation patterns (i.e. epigenetic variation) to address some of the key areas of parental effects that are currently poorly understood. Firstly, what mechanisms give rise to different forms of parental effects – do they typically arise from differential egg provisioning, or from epigenetic effects, or from a combination of the two? Secondly, how are different causes of parental effects integrated into offspring phenotype – do different mechanisms affect traits in the same way and do different factors (e.g. maternal and paternal condition) produce the same effects?
Preliminary analyses of life history data indicate that manipulation of parental food environment, maternal age and paternal age all produced parental effects at the population level, with an impact on life history traits still detectable after two or three generations. Furthermore, interactions occurred between different factors; e.g. the impact of maternal age was dependent upon paternal age, and vice versa.
Additionally, we report evidence that successive generations are able to “compensate” for poor environmental conditions experienced by their ancestors. Limiting parental food led to reduced egg size and subsequent size at maturity for the F2 generation. However, these effects were reduced in the F3 generation and either undetectable or reversed by the F4 generation.
Preliminary biochemistry data show that eggs produced in a restricted food environment may have a different protein composition to those produced when food is unlimited. We combine the data from the life history and nutritional assays with estimates of epigenetic variation across generations, in order to investigate the contributions of the different mechanisms to parental effects. Unravelling the complex interactions between different factors and mechanisms of parental effects is critical to our understanding of the extent to which parental effects contribute to population dynamics.