Meeting Abstract
Miniaturization, a pervasive condition in the Animal Kingdom, occurs when species evolve extremely small body size with respect to ancestral species. Stingless bees, Meliponini, are a tropical group that evolved miniaturization in 11 separate genera with species ranging in size across three orders of magnitude. To explore how these bees might be affected by small size, we examined scaling of flight metabolic rate, wing beat frequency, body temperature, and wing area of foragers in 13 Panamanian stingless bee species with masses from 1.5-115mg. We compared our results to prior studies of Eugolossine bees that ranged in size from 47-1065mg. In Meliponini, flight metabolic rates scaled hypermetrically and wing beat frequency did not vary with size, contrasting with Euglossines, in which flight metabolic rate scaled hypometrically and wingbeat frequency declined with size. Thorax mass scaled isometrically with body mass while abdomen mass scaled slightly hypermetrically and head mass scaled hypometrically. Thus all bees had roughly the same relative investment in flight muscles while small bees had relatively large heads and less investment in abdominal tissues. Bees heavier than 70mg (roughly ancestral size of stingless bees) had thorax temperatures more than 10°C above air temperature, while bees less than 20 mg had thoraxes only 1-2°C above air. Together, these observations suggest that increased heat loss rates cause reductions in flight muscle temperatures in miniaturized bees, causing them to have reduced wing beat frequencies and mass-specific metabolic rates, and likely lower power output in flight compared to the expected pattern based on changes in body size alone. While these cooler body temperatures may have performance costs, they will also reduce energetic requirements of the colonies. We thank W. Wcislo, D.Roubik, Smithsonian Tropical Research Institute, and NSF IOS 1122157 for help and funding.
