Maternal age interacts with environmental conditions in shaping of offspring phenotype in an annual fish species.

Abstract

Annual populations of animals express all of their reproductive effort in a single year only, with some of them producing offspring across a series of reproductive attempts (e.g. clutches) within the same breeding season. In such organisms, the timing of a reproductive attempt correlates with maternal age (so that offspring produced late in the breeding season are mothered by older females), and thus the phenotype of the offspring may differ between reproductive attempts of the same female. Moreover, environmental conditions experienced by the mother during that breeding season may further modify the phenotypic effects of maternal age. In this study, I investigated the effects of the interaction between maternal age and maternal environment on offspring phenotype using an annual population of three-spined stickleback (Gasterosteus aculeatus). I compared the phenotype of offspring from the early, mid- and late clutches of females, half of which were exposed to environmental stressors across their breeding season. Older females produced heavier eggs and fry that were larger at hatching, regardless of environmental stressors. Offspring of both stressed and non-stressed older mothers showed increased hormonal response to an acute stressor, but their survival patterns showed a complex relationship with both maternal age and stress exposure. Moreover, I observed a positive effect of maternal age on their daughters’ reproductive investment, but only if the mothers experienced stressful conditions during the breeding season. I thus show that annual females nearing the end of their reproductive lifespan increase their reproductive investment, with a potentially intergenerational effect. In addition, maternal age influences offspring phenotype, but this influence is moderated by the environmental conditions the mothers experience during the reproductive period.