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

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. Os insetos em ilhas podem sofrer varia & ccedil;& otilde;es morfol & oacute;gicas relacionadas ao isolamento geogr & aacute;fico enfrentado por suas popula & ccedil;& otilde;es. Este isolamento pode variar de acordo com a hist & oacute;ria e caracter & iacute;sticas das ilhas, bem como com a capacidade de dispers & atilde;o de cada esp & eacute;cie. N & oacute;s investigamos a exist & ecirc;ncia de varia & ccedil;& otilde;es morfol & oacute;gicas nas popula & ccedil;& otilde;es do besouro rola-bosta Canthon rutilans cyanescens em ilhas do sul do Brasil e do continente pr & oacute;ximo. Os besouros foram amostrados de dezembro/2020 a abril/2021 em cinco ilhas do Arquip & eacute;lago de Santa Catarina e no continente por meio de armadilhas iscadas para captura de insetos vivos. Comparamos os indiv & iacute;duos de cada popula & ccedil;& atilde;o por meio de an & aacute;lises de morfometria geom & eacute;trica, onde testamos o tamanho do corpo atrav & eacute;s de uma An & aacute;lise de Vari & acirc;ncia e a forma do corpo atrav & eacute;s uma An & aacute;lise Discriminante com teste de valida & ccedil;& atilde;o cruzada, seguida de uma An & aacute;lise de Vari & aacute;veis Can & ocirc;nicas para visualizar as popula & ccedil;& otilde;es no espa & ccedil;o morfom & eacute;trico. Encontramos diferen & ccedil;a significativa no tamanho corporal: a popula & ccedil;& atilde;o da Ilha Ratones Grande possui indiv & iacute;duos menores que as popula & ccedil;& otilde;es do continente, Ilha Dona Francisca, e Peri na Ilha de Santa Catarina. Observamos tamb & eacute;m que a forma corporal da popula & ccedil;& atilde;o da Ilha do Campeche difere das popula & ccedil;& otilde;es da Ilha do Arvoredo e da Ilha Dona Francisca, com o corpo levemente ovalado, uma regi & atilde;o dorsal maior e o abd & ocirc;men retra & iacute;do. Estes resultados s & atilde;o consistentes com a hip & oacute;tese de que as popula & ccedil;& otilde;es encontradas nas ilhas podem ter permanecido ali desde a sua forma & ccedil;& atilde;o ap & oacute;s o & Uacute;ltimo M & aacute;ximo Glacial. O isolamento e a aus & ecirc;ncia de conectividade entre as popula & ccedil;& otilde;es explicariam por que algumas ilhas apresentam popula & ccedil;& otilde;es com morfologia distinta. We investigated the existence of morphological variations in the populations of Canthon rutilans cyanescens dung beetle from the southern Brazil islands and the nearby mainland. With geometric morphometry analyses and individuals from five islands and on the mainland, we confirm differences in body size and body shape in isolated populations. The isolation and the absence of connectivity between the populations since the formation of the islands after the Last Glacial Maximum would explain the distinct morphologies.image