Meeting Abstract

3.1  Monday, Jan. 4  Age, but not task-specialization, is associated with differences in brain structure in bumblebee, Bombus huntii, workers HANNAFORD, S.J.*; FOSTER, R.L.; BOSSART, C.; Univ. of Puget Sound; Univ. of Puget Sound; Univ. of Puget Sound shannaford@ups.edu

Social insects vary tremendously in colony size, with some as small as 10 individuals and others with more than 100,000. Polymorphisms among individuals covary with colony size. These include greater physical and behavioral differences between queen and worker castes and even within worker castes for large colony species. Most studies of neural correlates of social behavior have been done in insects characterized by large colony size (i.e. honeybees, ants). In this study we measured the volumes of several regions in the brains of worker bumblebees, Bombus huntii , whose colonies typically range in size from 10 to 100 individuals. Worker bumblebees carry out a diversity of tasks, including those that occur in the hive (e.g. brood care and nest maintenance) and foraging for pollen and nectar outside the hive. Previous studies on the highly eusocial insects have linked differences in brain structure to task specialization. In contrast, our results from bumblebees showed no significant differences in the volumes of structures associated with smell (antennal lobes), vision (optic lobes), or learning and memory (mushroom bodies) between the brains of workers specializing in in-hive versus foraging tasks. We did, however, observe striking differences in the brains of mature workers versus newly emerged worker bees. Within the mushroom bodies, the brains of newly emerged bumblebee workers showed distinctly smaller neuropil regions and larger Kenyon cell regions relative to their older nestmates. These age-related differences are comparable to those seen in highly eusocial insects.