Abstract
Social organization in highly eusocial bees relies upon two important processes: caste differentiation in female larvae, and age polyethism in adult workers. Juvenile Hormone (JH) is a key regulator of both processes. Here we investigated the expression of two genes involved in JH metabolism - mfe (biosynthesis) and jhe (degradation) - in the context of social organization in the stingless bee Melipona interrupta. We found evidence that the expression of mfe and jhe genes is related to changes in JH levels during late larval development, where caste determination occurs. Also, both mfe and jhe were upregulated when workers engage in intranidal tasks, but only jhe expression was downregulated at the transition from nursing to foraging activities. This relation is different than expected, considering recent reports of lower JH levels in foragers than nurses in the closely related species Melipona scutellaris. Our findings suggest that highly eusocial bees have different mechanisms to regulate JH and, thus, to maintain their level of social organization.
Highlights
Juvenile Hormone (JH) is an isoprenoid compound that plays a remarkable role in the development, reproduction and regulation of distinct morphologies and behaviors of insect species (Hartfelder, 2000; Truman and Riddiford, 2002)
We found that expression levels of both mfe and jhe varied significantly among the larval stages (ANOVA for mfe: F = 3.35, p = 0.02; Analysis of Variance (ANOVA) for jhe: F = 8.67, p = 8.3x10-5)
We observed that the patterns of variation in gene expression throughout late larval instars were distinct between mfe and jhe genes in M. interrupta
Summary
Juvenile Hormone (JH) is an isoprenoid compound that plays a remarkable role in the development (including metamorphosis), reproduction and regulation of distinct morphologies and behaviors of insect species (Hartfelder, 2000; Truman and Riddiford, 2002). JH is synthetized in the corpora allata (CA), which are endocrine glands located in the posterior regions of the insect head, and transported through the hemolymph to its site of action in target cells (Tobe and Stay, 1985; Gilbert et al, 2000). JH levels are regulated by two biochemical processes: JH biosynthesis and JH degradation (Gilbert et al, 2000). The final and critical step of JH biosynthesis is catalyzed by the enzyme Methyl Farnesoate Epoxidase (MFE) (Bellés et al, 2005). JH degradation, on the other hand, is catalyzed primarily by one of two enzymes: JH Esterase (JHE) or JH Epoxide Hydrolase (JHEH)
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