ABSTRACT

Butterflies display a variety of sexual differences in size and morphology beyond those found in the gonads and genitalia. The size and nature of such differences can be explained as (1) the result of selection pressures acting on one or both sexes that are a function of these differences, or (2) as the incidental consequence of selection acting independently on each sex. This chapter reviews various attempts to relate mating–system structure and ecology to these explanations for sexual dimorphism in butterflies. Females are usually larger than males in butterflies; although there are positive size–fecundity relationships in females, the patterns of selection on male size are not understood well enough to explain this pattern. Body and wing shape reflect male mate–locating tactics, but selection pressures shaping female wing and body shape characteristics are poorly known. Sexual selection still appears to be a likely explanation for the elaborate colorations, scent–pro – ducing, and sensory structures in males, although there is clearly more work to be done. These sexual differences all appear to be the products of selection acting independently on the sexes, whereas sexual differences in eclosion patterns might be explained by selection for specific sexual differences in eclosion dates.

INTRODUCTION

A variety of sexual differences in morphology, beyond the gonads and genitalia, are common in butterflies. These include differences in wing color, wing shape, body size, body proportions, sensory structures, foreleg development, and signal–producing structures (Fig. 15–1).