Plasticity in immune responses in a model insect

Abstract

In order to understand how the environment, parental environment and inbreeding influence immune function and life history traits, I carried out a series of experiments using the Indian meal moth, Plodia interpunctella, as a model organism. Past studies have focused mainly on one aspect of environmental fluctuation at a time, so, to study the nature of the interactions between environmental variables in determining immunity, temperature, food quality and density were all varied together. There were interaction effects on immunity between all three environmental variables. The effect of density, for example, can be reversed if diet is changed from high- to low-quality. Diet quality has been shown to affect many life-history traits and an interesting question arising from this is whether these effects carry on to the next generation. I showed that the negative effects of a poor diet can be seen in the offspring of those affected but that a good quality diet given to the offspring goes some way to ameliorate these effects. Some of these effects on offspring could be mediated by maternal investment in their eggs; for example, when females were mated to a male that had received a poor quality diet, egg sized showed a strong effect of maternal size, with smaller females laying smaller eggs. Finally, I addressed the question of how inbreeding affects immune function using P. interpunctella derived from Australian stocks as well as a UK culture and I showed that there are some high costs to be paid in terms of larval size, egg size, larval survival, protein content of the haemolymph and immune function. There were also strong effects of origin, for example Australian males showed a very marked reduction in PO activity with inbreeding, but Australian females and both sexes from the UK lines did not show a great reduction with inbreeding.