Meeting Abstract
The insect body size model hypothesizes that larval growth and metamorphosis are the developmental basis for adult size variation. Recent studies have suggested that these mechanisms may hold common elements among different taxa, while also diversifying as life histories evolve. However, the mechanisms must be characterized at different levels to model body size variation for each species. Recently, metamorphosis in the blue orchard bee, Osmia lignaria, was observed to undergo metamorphosis in response to food absence; however, the physiological and molecular mechanisms that regulate metamorphosis have not been described. We characterized hemolymph titers of juvenile hormone III (JH III) in developing O. lignaria using HPLC-MSMS from larvae that were feeding (days 5-12) and from larvae that had food removed (0-96 hrs, 8 time points). Gene expression of hormone synthesis and receptivity genes were characterized using qPCR. Hemolymph JHIII concentration decreased following food removal, although remained detectable for up to 72 hrs following food removal. Gene expression overall showed a significant shift between 12-24 hrs following food removal. In particular, JHIII genes (met, jhamt), ecdysone genes (ecr, shadow), and downstream transducers of hormonal signals (krh1, brc) were upregulated. These responses provide evidence that food removal induces metamorphosis in O. lignaria. However, JH synthesis and receptivity genes were upregulated following food removal as JHIII titers declined, which suggests that the relationship between physiological and molecular regulators are more complex than JHIII titer alone.
