PATTERNS OF EVOLUTION OF WARM-UP RATES AND BODY TEMPERATURES IN-FLIGHT IN SOLITARY BEES OF THE GENUS ANTHOPHORA

1. Energetic considerations of preflight warm-up in bees predict that bees should warm-up as fast as they can and that larger species should be able to warm-up more rapidly. Larger species should also be able t o maintain higher thoracic temperatures during flight. These predictio ns are examined for 19 species in the solitary bee genus Anthopora (Hy menoptera; Apoidea; Anthophoridae). 2. The genus Anthophora has unifor mly high warm-up rates and body temperatures in flight, and the highes t warm-up rates measured in any heterotherm. 3. Under standard conditi ons, both warm-up rates and thoracic temperatures during flight increa se with body mass in Anthophora, in keeping with the prediction that h eterotherms should minimize the energetic cost of warm-up. 4. Having c ontrolled for body mass effects, Anthophora species able to maintain f light activity at lower ambient temperatures have higher warm-up rates and body temperatures in flight, showing that even in the smallest en dotherms there may still be room for selective modification within the limits imposed by body size. 5. Differences in warm-up rates between subgenera within Anthophora suggest that endothermic abilities have di verged in response to differences in the thermal environments which ar e the centres of diversity for the subgenera. 6. Similar importance of both body mass and the thermal environment in which the species is ac tive is demonstrated over 40 bee species in six families. Because spec ies over a wide taxonomic range do not constitute independent data poi nts, phylogenetic effects in these analyses are controlled for using G rafen's phylogenetic regression. 7. The evolution of high levels of en dothermy in Anthophora is discussed with reference to patterns of nect ar secretion found in the arid environments which are current centres of diversity for the genus.