Intergenerational responses to a changing environment: maternal and paternal early life shape fitness components in the bank vole

Abstract

An individual’s early life environment can have a significant influence over the adult phenotype, and these effects can potentially extend to their offspring. From an eco-evolutionary standpoint, the question arises whether these intergenerational effects can be adaptive i.e. increase offspring fitness. As most mammals lack paternal care, the most likely pathway for intergenerational effects is through the maternal line, as the mother provides the intrauterine environment but is also responsible for the post-natal environment. However, there is increasing evidence for paternal environment-dependent effects. In this thesis, it was explored how the early life environment of a wild rodent can have intra- and intergenerational effects, both through the maternal and paternal line. Bank voles (Myodes glareolus) were used to explore early life intergenerational effects by receiving high population density cues during their pre- and postnatal life and their growth and reproductive success were measured. Both in the maternal and paternal experiment, intergenerational effects and offspring fitness were assessed in semi-natural outdoor enclosures. Through the maternal line, the adaptive value was investigated by placing the offspring in different population densities. Through the paternal line, the focus was to determine if there is evidence for paternal intergenerational effects on offspring. The results showed significant effects on offspring fitness through the maternal and paternal line, with maternal effects being potentially adaptive. Additionally, two molecular mechanisms were explored, gene methylation and ribosomal RNA gene copy number. While no clear relationship between the early life and gene methylation was found, ribosomal RNA gene copy number was significantly related to early life protein diet. This thesis provides concrete evidence that the environment in which an individual is born directly affects the fitness of their offspring, and these effects can potentially be adaptive, at least through the maternal line.