Dung beetle populations's morphology show evidence of isolation in southern Brazil islands

Abstract

Insects in islands may undergo morphological variations related to the geographic isolation faced by their populations. This isolation on insular biota can vary according to the history and characteristics of the islands, as well as the dispersal ability of each species. We investigated the existence of morphological variations in the populations of the Canthon rutilans cyanescens dung beetle from the southern Brazil islands and the nearby mainland. Dung beetles were sampled from December/2020 to April/2021 from five Islands in the Santa Catarina Archipelago and on the mainland through samplings with baited live traps. With geometric morphometry analyses and individuals from each population we compared the body size using an Analysis of Variance and body shape using a Discriminant Analysis with cross-validation test, followed by a Canonical Variable Analysis to visualize the populations in morphometric space. We found a significant difference in the body length: the population of Ratones Grande Island has smaller individuals than the populations of the mainland, Dona Francisca Island, and Peri on Santa Catarina Island. We also observed that the body shape of the population of Campeche Island differs from the populations of Arvoredo Island and Dona Francisca Island, with a slightly oval body, a larger dorsal region, and a retracted abdomen. These results are consistent with the hypothesis that the populations found on the islands may have remained there since their formation after the Last Glacial Maximum. The isolation and the absence of connectivity between the populations would explain why some islands have populations with distinct morphology.

Abstract in Portuguese is available with online material.