Intraspecific variation of reproductive traits between migratory and resident populations of the rice plant skipper Parnara guttata guttata

Abstract

Much empirical data obtained across taxa is necessary to evaluate how variation in migratory costs and benefits can play a role in shaping the phenotypic and genetic patterns of reproductive investment between populations. Reproductive resources are allocated to both the size and number of eggs, and females may vary their allocation to each of these traits in response to increased movement capacity. In central regions of Japan, the rice plant skipper Parnara guttata guttata migrates in a southwesterly direction every year during late summer and early autumn (‘migratory’ population), but this migration is not observed in populations in southern or parts of western Japan (‘resident’ population). If migratory costs and benefits vary between these populations, they may cause their reproductive strategies to differ. Moreover, migration combined with a shift of reproductive allocation that evolved in one generation may influence the flight ability and patterns of reproductive allocation in the other generation in which migration has not evolved. In this study, a common-garden experiment was conducted to compare reproductive traits (egg size and number of eggs), flight ability and body size between these populations under two daylength regimes, at which different forms of adult P. g. guttata emerge. Under both daylength regimes the female adults of migratory populations had greater flight ability and tended to lay a greater number of eggs, which were on average smaller than the eggs laid by resident population females. A population-level difference in reaction norm elevation for flight ability and number of eggs was detected, but no interactions between population and daylength. The effects of the energetic cost of flight, adaptive constraints (e.g., genetic correlations and trade-offs), and the optimal strategy may explain the difference between populations of this species in the patterns of reproductive allocation to egg size and number of eggs.