Rapid elevation of juvenile hormone titer during behavioral assessment of the breeding resource by the burying beetle, Nicrophorus orbicollis

Abstract

Female burying beetles ( Nicrophorus orbicollis) rapidly complete ovarian maturation upon discovering a suitable carrion resource for breeding. In this study, we examined changes in hemolymph titers of juvenile hormone (JH) over the first 30 days of adult female life, and in response to the discovery of a mouse carcass. Levels of JH were found to increase gradually over the first 20 days, and then increased abruptly within 24 h of discovery of a carcass. Changes in JH titer were correlated with increases in ovarian mass and length of terminal oocytes. To more precisely determine the timing of the endocrine response to a carcass, hemolymph titers of JH were measured 2, 10, 20 and 60 min after carcass discovery. Titers of JH were significantly elevated (112% over controls) in just 10 min. To confirm this resource discovery-related increase in JH, hemolymph samples were taken from the same individuals both 2 days before, and 10 min after, discovery of a carcass. Again, JH titers rose significantly (170%) in beetles 10 min after carcass discovery. Prominent behaviors observed during the 10-min period following discovery included palpating, lifting, walking around the carcass and making forays into the surrounding soil. Feeding did not occur. These results suggest that the rapid JH surge in female burying beetles is triggered by information obtained during behavioral assessment of a breeding resource, and not by mating or feeding cues. The association between ovarian development and JH titer further suggests a role for JH in co-ordinating reproduction in a temporally and spatially unpredictable environment.