PREDATION AND THE ELEVATION OF THORACIC TEMPERATURE IN BRIGHTLY COLORED NEOTROPICAL BUTTERFLIES

Notes a positive partial correlation between 1) mean thoracic temperatures of 55 brightly colored Neotropical butterfly species and 2) their palatabilities to rufous-tailed jacamars Galbula ruficauda melanogenia (a specialized insectivorous bird) following adjustment for mean ambient temperature and lineage membership. The higher thoracic temperature of palatable butterflies suggests that predation is a strong selective force on the thermal physiology of these butterflies. Palatable butterflies were active (and were captured) toward late morning, during sunny weather, and in open microhabitats; unpalatable butterflies were not so constrained and were captured more evenly across time and microhabitat categories. Within the same microhabitat, palatable butterflies have a higher mean thermal excess than unpalatble species. The higher thermal excess of palatable species could result from 1) greater net influx of radiative energy, 2) greater production of metabolic heat or 3) lower conductive and convective heat loss. The ambient radiation in which the butterflies are active tends to be maximum when and where the palatable species are active. Palatable butterflies tend to fly more quickly and erratically (which may mean that they require more metabolic energy to fly the same distance than do unpalatable ones) but may suffer greater convective heat loss. They also posses wider thoraxes, which may retain more metabolic heat. Palatability is associated with divergences within phylogenetic lineages of the flight temperatures of brightly colored palatable and unpalatable species. As a result of its association with coloration and flight mimicry, palatability is also associated with convergences in flight temperatures of distantly related lineages. -from Authors