Landmark-based geometric morphometrics as a tool for the characterization of biogeographically isolated populations of the pollinator scarab beetle Erioscelis emarginata (Coleoptera: Melolonthidae)

Abstract

Erioscelis emarginata is a species of pollinator scarab beetle whose adults are predominantly associated with night-blooming aroid inflorescences (Araceae) of the Neotropical genus Thaumatophyllum, towards which they are attracted by volatile organic compounds (VOCs). It is assumed that olfactory preferences towards species-specific floral VOCs emitted by different plant hosts, as well as geographical segregation of natural populations of E. emarginata, might reinforce their reproductive isolation and differentiation, but external morphological dissimilarities between them are not evident. In the present work, body shapes of geographically isolated populations of E. emarginata associated with different species of Thaumatophyllum were compared using landmark-based geometric morphometrics. A total of 86 adult specimens of E. emarginata were analyzed, collected in inflorescences of Thaumatophyllum spp. at four locations in Brazil distant 333–912 km from one another. Eighteen landmarks and semi-landmarks were digitized to capture the shapes of the elytra and pronotum separately, and landmarks configurations were compared through Canonical Variates and pairwise Discriminant Function Analyses. There were significant shape differences between specimens from the four different populations of E. emarginata (p < 0.05) in all paired comparisons, for both the shape of the elytra and pronotum and correct classification levels were high for most pairwise comparisons. Further investigations on the morphological variation across these populations and assessments of the specificity of their olfactory-oriented relationship with host plants are important next steps in understanding the full scenario of the segregation and diversification of E. emarginata. In addition, a lectotype male of Apogonia emarginata (ZIN) was designated to fix the identity of E. emarginata.