Landmark-based morphometric analysis of two sibling species of the genus Asida (Coleoptera, Tenebrionidae)

The case described here analyses morphological change at the boundary between ecological and evolutionary scales. The size and shape of 8 populations of two sibling species of tenebrionid beetles (Asida planipennis and A. moraguesi) are analysed using landmark-based methods. The two species differ in size, shape and in allometric trajectory. Thin-Plate Spline Analysis (TPSA) combined with Canonical Variate Analysis (CVA) reveal the specific shape changes that allow the best inter-species discrimination. These changes involve the outline of the posterior margin of the pronotum. Moreover, the landmark-based method provides useful tools for interpreting the intraspecies variability of some continuously varying morphological characters. In the case of A. planipennis, size and shape are correlated at the inter-population level, but are independent at the intra-population level. Moreover, size and shape do not reflect any spatial (i.e., geographical) structure or phylogenetic inertia at the inter-population level. These facts favour site-specific environmental conditions as the main cause of shape and size variability in this species. One environmental variable is suggested to be the cause of the inter-population morphological differences detected.