NEW SEXUALLY DIMORPHIC CHARACTERS OF THE BEETLE Erioscelis emarginata (MANNERHEIM, 1929) (Scarabaeidae; Dynastinae)
Keywords:
Protibial shape, Protibial tooth, Geometric morphometry, CyclocephaliniAbstract
Erioscelis emarginata is a Cyclocephalini beetle known for pollinating various Araceae species. Recent observations revealed a significant variation in form among specimens, especially between males and females, which exceeds previously known characteristics — particularly concerning the protibia. This study aimed to assess sexually dimorphic traits in E. emarginata, focusing on protibial shape and body size. A total of 57 specimens from Brasilia (Brazil) were selected for analysis. Photographs (n = 51) of the left protibia were taken using an Axiocam 105 color camera mounted on a Leica MZ6 stereomicroscope, and 17 landmarks and semi-landmarks were digitized using the software TPSdig2 v. 2.32. A Generalized Procrustes Alignment was performed to standardize the size and position of the images, and the resulting shapes were analyzed using MorphoJ v. 1.07, applying Procrustes ANOVA and PCA. Additionally, total length, pronotum width, and protibia length were measured and analyzed by one-tailed Welch t-tests. The analyses revealed clear dimorphisms, with distinct protibia shape and the presence of a third tooth only in females. This contradicts the species' original description but is consistent with other species of the genus, which possess three protibial teeth in both sexes. Furthermore, males exhibited greater body length and longer protibiae. Significant protibial wear was also observed on these beetles, supporting the hypothesis that E. emarginata has soil-dwelling habits. In conclusion, we believe this study contributes to the current taxonomic delimitation of E. emarginata and enhances the understanding of the its biology.
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