Morphological and molecular evidence for considering Xylocopa nigrocincta as the senior synonym of Xylocopa suspecta (Apidae: Xylocopini)

Abstract

Xylocopa nigrocincta Smith, 1854, and Xylocopa suspecta Moure & Camargo, 1988, are two nominal species within the subgenus Neoxylocopa and have a sympatric geographic distribution in South America. While X. nigrocincta is recognized by the presence of reddish metasomatic bands, X. suspecta is entirely black. Although morphologically distinct in terms of metasomal band colour, other morphological characters suggest that both species could be the same evolutionary entity and therefore synonymous. The aim of this research was to review both nigrocincta and suspecta morphotypes using an integrative approach (morphological and molecular) to evaluate if they are truly two different evolutionary lineages. Females of both species were obtained from field collections and museums, representing a large part of their morphotype distribution. Additional diagnostic characters of the external morphology were investigated, such as metasomal band colour, metasomal punctuation, wing colours, and apical regions of the basitibial plate. Mitochondrial gene sequences (COI and CytB) were used for phylogenetic reconstructions. Our results showed that both nigrocincta and suspecta morphotypes are undistinguished based on morphology, although the metasomal band colour, together with the geographic distribution, revealed the presence of three distinct morphogroups, including an intermediate one with a variable number of reddish bands. Nonetheless, the three morphogroups are not supported by molecular data and therefore represent intra-specific variations. In conclusion, our results do not support the hypothesis that the two nominal species are distinct evolutionary lineages, and we propose a synonym between X. nigrocincta and X. suspecta.