Testing the migration syndrome : Comparative fecundity of migratory and non-migratory nymphaline butterflies

Empirical studies have shown a positive relationship between migration and fecundity, suggesting a ‘migration syndrome’ that also includes delayed reproduction and an extended reproductive lifespan. At the same time, life history theory predicts that the cost of migration should result in lower fecundity because both traits draw from a common resource. We test whether migration is associated with higher fecundity and delayed reproduction in five closely related butterfly species in the Nymphalini tribe. Two of these are migratory, Vanessa cardui and Vanessa atalanta, and three are non-migratory, Aglais urticae, Aglais io, and Polygonia c-album, which appears in a diapausing and a non-diapausing generation. Laboratory experiment of this study demonstrated a higher lifetime fecundity in the non-migratory species A. urticae and A. io, compared with the migratory species. When reproductive output was measured in terms of egg mass over adult female mass, also the non-migratory species P. c-album had a higher reproductive investment than the two migratory species, and the non-diapausing generation had a higher reproductive output than the diapausing generation. All species but P. c-album delayed reproduction until 5–7 days after eclosion/emergence. These results indicate that a migratory lifestyle carries a reproductive cost and suggests that the migratory habit has not resulted in selection for higher fecundity. However, the migratory species are highly fecund in a wider phylogenetic perspective, which leads to the conclusion that rather than selection having selected for high fecundity and delayed reproduction, these traits may be prerequisites for evolving a migratory lifestyle