SCOTT, M.P.; University of New Hampshire: Resource defense and juvenile hormone: The challenge hypothesis extended to insects

As predicted for vertebrates by the challenge hypothesis, the endocrine system of invertebrates can respond to social stimuli to modulate aggression. Vertebrate aggression is promoted by testosterone; juvenile hormone (JH) serves an analogous function in burying beetles. Hemolymph titers of JH increase significantly in Nicrophorus orbicollis, a species with facultative biparental care, when challenged by an intruder to defend their resource. For the first 12 hours after the discovery of a carcass, the necessary breeding resource, there is intraspecific competition for its possession; during this period JH of males responds only to a challenge by males and that of females only to female intruders. After this period, JH increases significantly in both males and females challenged by an intruder of either sex. In contrast, JH titers in a nonparental species of burying beetle are much higher throughout the breeding season and neither males nor females respond hormonally to an intruder. These finding support the challenge hypothesis and suggest that mating systems and breeding strategies can promote plastic responses in insect, as well as vertebrate, endocrine systems.