Meeting Abstract
Locusts are grasshoppers (Acrididae) that form large migratory swarms or marching bands, and show density-dependent phase polyphenism. This polyphenism consists of two phases, solitarious and gregarious, that manifest in response to low and high population density, respectively. The two phases differ in several traits, including but not limited to behavior, morphology, nymphal coloration, physiology and reproduction. From a phylogenetic perspective, locusts are rare among grasshoppers, representing only 19 out of about 6700 grasshopper species. They are a phylogenetically heterogenous group, strongly suggesting that density-dependent phase polyphenism in locusts convergently evolved multiple times. The genus Schistocerca contains three locust species and more than 40 non-swarming sedentary species, and the phylogeny of the genus is well understood. In this study, we focus on the Central American locust (S. piceifrons) and three closely related non-swarming grasshoppers that, together, are expected to form a spectrum in the degree of density-dependent phenotypic plasticity. We reared S. piceifrons and these three related species in isolated and crowded conditions, and subsequently quantified density-dependent reaction norms at a behavioral and a molecular level. We establish that there is indeed a spectrum of density-dependent phenotypic plasticity in this clade at both tested levels. We subsequently discovered clear correlations between gene expression patterns in our study system and behavioral traits using a weighted gene co-expression analysis. This represents the first study of locusts in a phylogenetic framework, and extends our understanding about the evolution of the density-dependent phase polyphenism.
