Abstract
In this project we will investigate the evolutionary significance of egg size variation and its functional relations with other life history traits in the seasonal tropical butterfly Bicyclus anynana. Egg size determines by a large extent the initial size and growth of the progeny and its effects may persist through to the adult stage. The size of the egg and its relation to egg number is determined by genetic, Maternal and environmental factors, and hence all play a role in the species-specific evolution of egg size. Environmental and Maternal factors are especially important in species that encounter (predictabIe) temporal and spatial seasonal variation because it provides the opportunity for adaptive phenotypic plasticity to evolve. This certainly applies to ectotherms because they are most amenable to environmental variance in life history traits. Given the importance of egg size for the fitness of parents and offspring, it is surprising that few studies have attempted to uncover causal relationships using a combined genetic and experimental approach. The biology of Bicyclus anynana butterflies exhibits exciting properties to allow such an approach. The butterfly lives in tropical seasonal environments with starkly different ecological demands on the phenotype. The morphology of the wing patterns is strikingly different between the two seasonal forms. This plasticity in wing pattern is thought to be an adaptive response to the seasonal changes in climate and resting background. In concordance, the life history shows a remarkable contrast between the seasons for traits including, weight, fecundity , fat content, longevity and developmental time. This must occur, however, within the limits set by development and physiology that have to integrate the two phenotypes in one single gene pool. In this project we select for lines differing in egg size and study the direct and correlated responses along a temperature gradient. Using existing selection lines for eyespot plasticity, developmental time and pupal size will allow us to identify the causal relations between egg size and the general life history and its likely evolution using path analysis. Crosses between lines differing in egg size win allow the analysis and quantification of Maternal effects. We will also begin the molecular quantitative analysis and functional genomics of egg size by using our growing expertise in gene mapping in this species.
Netherlands