REPRODUCTIVE PATTERNS AND RESOURCE-ALLOCATION IN TROPICAL BUTTERFLIES - INFLUENCE OF ADULT DIET AND SEASONAL PHENOTYPE ON FECUNDITY, LONGEVITY AND EGG SIZE

The reproductive patterns and resource allocation strategies of three closely related tropical satyrine butterflies, Mycalesis terminus, M. sirius and M. perseus, were studied under laboratory and semi-laboratory conditions. We first examined the influence of two adult food sources, sugar (25% honey solution) and rotting fruit, on the oviposition pattern, fecundity, longevity, egg size and reproductive effort in the west-season forms of M. terminus and M. sirius. We then compared the reproductive traits between the two seasonal phenotypes (wet- and dry-season form) of M. perseus fed only on the rotting fruit diet. In this species females of the dry-season form diapause as adults whereas those of the wet-season form usually reproduce directly. Availability of sugar or rotting fruit in the adult diet of M. sirius had no significant effect on any of the reproductive traits. However, in M. terminus diet had two major effects: availability of sugar increased longevity, while females fed on rotting fruit tended to maintain constant egg weight over time. Differences in response to adult diet in these two species correspond with their behaviour in the field: M. sirius adults rarely feed at nectar sources or on rotting fruit, whereas those of M. terminus readily feed on rotting fruits. Hence, availability of rotting fruits to adult M. terminus may enhance reproductive success since females appear to produce better quality offspring (i.e. lay larger eggs over time). In M. perseus, post-diapausing females of the dry-season form had reduced realised and potential fecundity, laid proportionally fewer eggs, and had a shorter oviposition period compared with the wet-season form. Egg weight increased with female age in the wet-season form but declined in the dry-season form. Although the dry-season form laid larger eggs it still had a much lower reproductive effort, indicating that diapause imposes a substantial cost to reproduction. We tentatively conclude that this cost is the result of an adjustment in resource allocation between soma (body size and structure to increase longevity) and reproductive reserves acquired during the larval feeding period. Comparison of the reproductive patterns between the three species (i.e. when both seasonal form and adult diet are standardised) revealed striking similarities in many traits, including oviposition pattern, potential fecundity, reproductive effort and survival. However, there were substantial differences in allocation strategies, with M. perseus partitioning its reproductive effort into many smaller eggs. Differences in these reproductive strategies are associated with the preferred habitats of each, and we suggest that habitat uncertainty and limited breeding opportunities may have selected for higher fecundity in M. perseus.