Dopamine has diverse roles in the regulation of reproduction and social behaviors in insects. In the burying beetle, Nicrophorus orbicollis, a species with extended care, our previous work has shown that brain dopamine levels increase significantly after 24 h of care. It is not known, however, whether this increase arises from changes in the expression of genes responsible for dopamine biosynthesis and/or degradation. To that end, we quantified transcript levels of tyrosine hydroxylase (Noth); aromatic amino acid decarboxylase (Noaadc), and dopamine N-acetyltransferase (Nodnat) in head tissue of female burying beetles across four developmental and parental stages: newly-emerged, sexually mature, 1-day parental, and 6-day parental. Surprisingly, transcript levels of Noth, encoding the rate-limiting enzyme, did not increase after 24 h of care relative to non-breeding controls. Moreover, expression of Noaadc, encoding the enzyme involved in the final step of dopamine synthesis, showed a striking, albeit not statistically significant, reduction in actively parenting females at 24 h of care, with transcript levels returning to pre-breeding levels by 6 days of care. In contrast, expression of both Noth and Nodnat was significantly elevated in newly emerged females compared with reproductively mature and parental stages, revealing a pattern of transcriptional upregulation associated with early development, rather than active parenting. The previously observed increase in dopamine during early parenting is thus unlikely to be driven by transcriptional upregulation of biosynthetic genes; post-transcriptional mechanisms, including altered release, turnover, or synaptic signaling, may instead contribute to neuromodulatory changes associated with parental care in burying beetles.
Panaitof et al. (Mon,) studied this question.