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United States Department of Agriculture

Agricultural Research Service

Research Project: Sustainable Pest Management Strategies for Arid-land Crops

Location: Pest Management and Biocontrol Research

Title: Juvenile hormone titres reflect social opportunities in the facultatively eusocial bee Megalopta genalis (Hymenoptera:Halictidae)

Authors
item Smith, Adam -
item Kapheim, Karen -
item Perez-Ortega, Betsy -
item Brent, Colin
item Wcislo, William -

Submitted to: Hormones and Behavior
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 30, 2012
Publication Date: September 8, 2012
Citation: Smith, A.R., Kapheim, K.M., Perez-Ortega, B., Brent, C.S., Wcislo, W.T. 2012. Juvenile hormone titres reflect social opportunities in the facultatively eusocial bee Megalopta genalis (Hymenoptera:Halictidae). Hormones and Behavior. 63:1-4.

Interpretive Summary: The evolution of eusociality is believed to have involved a separation of parental care behaviour from actual reproduction, both of which are controlled by endocrine processes. While data for insects that are obliged to be eusocial are consistent with this hypothesis, we lack information from species representative of the transition from solitary reproduction to eusociality. Here we report the first evidence for a link between endocrine processes and social behaviour in a bee, Megalopta genalis (Halictidae), which can readily transition between solitary and social states. Using females that varied in social, reproductive, and ecological context, we measured juvenile hormone (JH), a major regulator of colony caste dynamics in other eusocial species. JH was low when bees first matured to adulthood, but after 10 days was elevated in non-reproductive workers and highest in reproductive foundresses, suggesting JH plays a role in regulating egg production. In similarly-aged, cage-reared females, JH never rose, highlighting the importance of nesting opportunity. Among females in established nests, JH was elevated in queens relative to workers and solitary reproductives, suggesting a role for JH in social dominance. The lack of significant differences in JH between solitary reproductive females and workers suggests that JH content reflects more than reproductive status. Our data support the hypothesis that endocrine modifications are involved in the evolutionary decoupling of reproductive from other bodily processes in social insects.

Technical Abstract: The evolution of eusociality is hypothesized to have involved de-coupling parental care from reproduction mediated by changes in endocrine regulation. While data for obligately eusocial insects are consistent with this hypothesis, we lack information from species representative of the transition from solitary reproduction to eusociality. Here we report the first evidence for a link between endocrine processes and social behaviour in a facultatively eusocial bee, Megalopta genalis (Halictidae). Using females that varied in social, reproductive, and ecological context, we measured juvenile hormone (JH), a major regulator of colony caste dynamics in other eusocial species. JH was low at adult emergence, but elevated after 10 days in all nesting females. Females reared in cages with ad lib nutrition, however, did not elevate JH levels after 10 days. All reproductive females had significantly more JH than all age-matched non-reproductive females, suggesting a gonadotropic function. Among females in established nests, JH was higer in queens than workers and solitary reproductives, suggesting a role for JH in social dominance. A lack of significant differences in JH between solitary reproductives and non-reproductive workers suggests that JH content reflects more than reproductive status. Our data support the hypothesis that endocrine modifications are involved in the evolutionary decoupling of reproductive and somatic effort in social insects. These are the first measurements of JH in a solitary-nesting hymenopteran, and the first to compare eusocial and solitary nesting individuals of the same species.

Last Modified: 9/21/2014
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