Geographic variation in body size and tegmen shape of the grasshopper Dichroplus elongatus (Orthoptera: Acrididae) from Central-West Argentina: morphological trait variation along environmental gradients.

How phenotype varies across geographic space constitutes a key question in current evolutionary biology. Species with widespread geographic ranges are helpful models for examining phenotype variation patterns. Here we examined body size and tegmen shape variation in 12 populations of widespread agricultural pest Dichroplus elongatus collected in Central-West Argentina. D. elongatus showed significant phenotypic variation. Combining linear and geometric morphometric techniques reveals differences in body size and tegmen shape between sexes. General linear mixed models (GLMMs) analyses showed that body size is mainly associated with variables related to temperature of the warmest trimester and temperature annual range along a latitudinal gradient. Individuals achieve larger body sizes at colder areas with lower thermal amplitude. The GLMMs procedures to test allometries demonstrated that most of the analyzed traits scaled isometrically in both sexes indicating that the shape of the individual will not modify with changes in body size. Thorax length is the only trait that scaled hypoallometrically although there were sex-specific differences. Climatic conditions, mainly temperature and precipitations, molded isometric and allometric trait patterns. The detected clinal patterns of phenotypic variation of D. elongatus from Central-West Argentina is likely to be the result of local adaptation to temperature and phenotype plasticity along climatic gradients, and identify geographic areas in where this species showed bigger body size and would undergo greater dispersal capacity. Finally, our results offer insights into how environmental changes may impact the species dispersal and adaptability, advising targeted control and management strategies for this agricultural pest.