International Union for the Study of Social Insects (IUSSI2018), August 5-10, 2018 in Guarujá, Brazil.

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Comparing male and worker body sizes in the Common Eastern Bumble Bee to examine the benefit of diversity in social systems

Author(s):
Alaina Hope Michaels, Alaina Hope Michaels , Evan Kelemen , Anna Dornhaus
Institution(s):
University of Arizona; Ecology and Evolutionary Biology Department, University of Arizona, Tucson, AZ, United States ; Ecology and Evolutionary Biology Department, University of Arizona, Tucson, AZ, United States ; Ecology and Evolutionary Biology Department, University of Arizona, Tucson, AZ, United States
In the bumble bee, Bombus impatiens, body size is highly variable among individual workers. Typical of social insects, workers perform different tasks in the colony such as foraging and caring for brood. However, morphological differences in body size do not necessarily dictate specialization of a task. Instead, a range of sizes participate in a variety of tasks during their lifetime.  On the other hand, male bees spend much less time in the colony after emerging. Before leaving the nest to find potential mates, males participate briefly in brood care.  However, there is no other evidence that males contribute to the colony after leaving the nest.  This leads to the question of whether or not variation in worker body size serves a function or benefit to the colony as a whole. The purpose of this research is to examine the potential for selection to be driving highly variable body sizes among bumble bee workers by comparing the differences in thorax widths between males and workers produced within the same week. The variance between male and worker body size was significant.  Additionally, it was found that male bees had significantly smaller thorax widths than female workers.  This supports the hypothesis that variation in worker body size is beneficial in this social structure rather than it being attributed to biological noise.  It can be concluded that selective forces are driving highly variable, relatively larger body sizes in female workers and that diversity in social systems is advantageous.
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