Meeting Abstract
Elucidating the physiological mechanisms that link environmental conditions to the development of alternative phenotypes is a central question in developmental plasticity research. In insects, studies have traditionally focused on the role of ecdysteroids and juvenile hormone in the specification of environmentally-cued alternative phenotypes, yet more recent work has examined additional classes of signaling molecules such as the biogenic amines. Here we investigate the role of the biogenic amine serotonin in regulating the ontogeny and evolution of polyphenism in the horned beetle, Onthophagus taurus. In this species, males exhibit a nutrition-sensitive dimorphism, developing into either hornless sneaker (low nutrition) or horned fighter (high nutrition) adult morphs. Transcriptomic data show that serotonin receptors are differentially expressed among i) the putative horn tissue of adult morphs and ii) recently established populations of O. taurus that are rapidly diverging in relative horn investment. To assess the role of serotonin in the development and evolution of morph specification, we use a pharmacological approach to manipulate systemic levels of serotonin in the final larval stage of O. taurus. We find that increasing serotonin signaling suppresses larval growth and delays pupation, whereas decreasing serotonin signaling has the opposite effect, consistent with findings in Drosophila. Results to date additionally suggest that serotonin signaling shapes the highly sigmoidal body size-horn length allometry of this species. Specifically, decreasing serotonin signaling appears to lower the threshold body size at which horns are expressed, but does not appear to alter the scaling relationships of additional traits. Here we present our latest results and discuss them within the context of developmental plasticity and population divergence.
