The aim of this thesis was to investigate whether physiological and performance-related parameters in two species of gammarid amphipod with differing abilities to osmoregulate were affected by reduced salinity within a generation, and across generations as a consequence of parental and grandparental environments. This was achieved using a fully factorial reciprocal exposure experiment manipulating salinity across three generations. Overall, this study demonstrates that trans-generational effects of salinity differed depending on the species and on the level of biological organisation. Both species were able to adjust their physiology over the generations, but the influence of parental or grandparental salinity appeared stronger in the stronger osmoregulator, Gammarus duebeni compared with the weak osmoregulator, Echinogammarus marinus. Life-history effects were limited to those affecting age at reproduction and reproductive output.
Low salinity exposure in both the strong osmoregulator and the weak osmoregulator led to an increase in the activities of the key enzymes underpinning osmoregulation, Na+/K+-ATPase and H+-ATPase. This response was associated with an elevation in rates of oxygen uptake and a decline in cellular energy budgets. This had negative implications for individual and reproductive performance, with decreases in rates of protein synthesis, growth rates, reproductive output and survival.
Environmental matching between generations provided an advantage for offspring in freshwater, where metabolic adjustments improved energy budgets and rates of protein synthesis to some extent. However, the only life history trait to be affected across the generations in G. duebeni was female age at reproduction. In E. marinus environmental matching between generations provided an advantage and alleviated the negative effects of low salinity on rates of protein synthesis, but the only life history trait to be affected by trans-generational effects of salinity was fecundity. When environments were matched between generations in the favourable environmental condition of full strength seawater, fecundity increased. However, this species shows adjustments over 3 generations, with rates of oxygen uptake, energy budgets and growth becoming independent of the effects of salinity.
This thesis broadens our understanding of how trans-generational responses can alter the capacity of aquatic invertebrate species to respond to environmental change. Moreover, it supports the need to study species-specific responses to environmental change that are associated with the conditions normally experienced by species and their populations on the shore.