Tropical dry and wet season polyphenism in the butterfly Melanitis leda (Satyrinae): Phenotypic plasticity and climatic correlates

Abstract

Changes in wing pattern, colour, shape and size associated with seasonal polyphenism in Melanitis leda were quantified using a series of 155 butterflies collected by N. Manders on Mauritius in 1905. Butterflies of the wetter period were predominantly of the wet season form with large, well differentiated eyespots, short tails, smaller wings and a characteristic background colour. The dry season form occurred only in the drier period and has much smaller eyespots, longer tails, larger wings and a variable background. Many intermediates occurred, mainly in the drier period. These are associated with an absence of extreme seasonal change in Mauritius. The first principal component (PCI) describing the morphometric and colour data is closely related to the wing form (r = 0.80). Regression analyses using temperature and rainfall data for the 8 weeks before each capture showed that about 40% of variation in PCI could be accounted for by temperature in weeks 2–3 before capture. Many of the characters measured are redundant; a subset of seven morphometric characters yields a closely similar PCI. Analysis of is subset in an additional sample of 70 M. leda from Kenya showed that the seasonal polyphenism overrides a small degree of sexual dimorphism. The results are discussed with regard to seasonal changes in adult activity, resting backgrounds and visual predation. Wing phenotype characters are part of an array of coordinated morphological and life history traits which include ovarian dormancy and fat body development in dry season adults. A partial independence occurs in the proximal control of these traits as indicated, for example, by the larger wing and tail size, and smaller eyespots of the small number of the wet season form captured in the drier period in comparison to those of the wetter months.