Aerial Predation and Butterfly Design: How Palatability, Mimicry, and the Need for Evasive Flight Constrain Mass Allocation

Abstract

Certain components of flight performance, particularly acceleration, are strongly affected by the ratio of flight-muscle mass to body mass. Thus, flying animals should vary in their "design" according to their need for high-performance flight, and capacities other than flight may be affected as a result of constraints on the distribution of body mass. Here we examine that hypothesis by comparing design of butterflies and diurnal moths that vary in their need to evade aerial predators. Among 124 Neotropical species, allocation of body mass to flight muscle and other tissues varied according to palatability and mimicry status. Unpalatable and mimetic species had proportionally less flight muscle and had larger guts and ovaries, which may allow greater fecundity. Nearly all palatable and nonmimetic species had enough flight muscle to enable greater acceleration than avian insectivores, but at the cost of having smaller guts and ovaries. These patterns were highly significant after removal of statistical nonindependence due to phylogenetic association. Thus, the need for evasive flight imposes constraints on body design that have potentially far-reaching effects on butterfly biology.