Allometric relationships shape foreleg evolution of long-legged oil bees (Melittidae: Rediviva)

Species circumscription within the Rediviva neliana group (Hymenoptera: Melittidae), with the description of the new species Rediviva vogeli sp. nov. Melin & Colville

Rediviva neliana Cockerell 1931 has been considered to be widely distributed along the southeastern and eastern Escarpment of South Africa and Lesotho, with high variation in foreleg length recorded across populations. A recent analysis of the allometric relationship between foreleg length and body size for the oil-collecting species of Rediviva revealed that R. neliana is a notable 'outlier', suggesting that it represented a group of species and not a single taxon. This hypothesis necessitates a critical review of the taxonomy of R. neliana. Here, we examined a large amount of old (n = 1228) material as well as more recent material collected from 23 different sites across the Great Escarpment, including the resurveying of type localities. Based on this, we (i) redescribe the male of R. neliana and the previously unknown female; (ii) reinstate R. politissima (Cockerell 1934) stat. rev. from synonymy with R. neliana, and redescribe both the male and female; (iii) reassign the male of R. whiteheadi Kuhlmann 2012 to R. autumnalis Whitehead & Steiner 2008, and include the female of R. whiteheadi syn. nov. into synonymy with R. neliana; (iv) reassign 242 specimens of R. neliana to R. steineri Kuhlmann 2012, thus vastly expanding the known distribution of the latter taxon; (v) describe both sexes of the new species R. vogeli Melin & Colville sp. nov.; and (vi) provide a revised key to the species of Rediviva occurring in the southern African summer-rainfall region based on the shape of the galea and male genitalia. Detailed images of genitalia and hidden sterna are also provided for all species of Rediviva in the summer-rainfall region for which males are known. We conclude that the R. neliana group comprises four species. Understanding their geographic distributions is relevant to assessing their conservation status and understanding their coevolution with host plants.

Sexual size and shape dimorphism, and allometric scaling in the pupal and adult traits of Eristalis tenax

The patterns and amount of variation in size, shape, and/or life history traits between females and males are fundamentally important to gain the comprehensive understanding of the evolution of phenotypic diversity. In addition, the covariation of phenotypic traits can significantly contribute to morphological diversification and sexual dimorphism (SD). Using linear and geometric morphometrics, 237 Eristalis tenax specimens sampled from five populations were, therefore, comparatively assessed for the variation in sexual size dimorphism (SSD), sexual shape dimorphism (SShD), and life history traits, as well as for trait covariation (ontogenetic and static allometry). Pupal body, adult wing, and body mass traits were analyzed. Female-biased SSD was observed for pupal length, width, and centroid size, adult wing centroid size, mass, wing loading, and wing area. Conversely, pupal length/width ratio, developmental time, and mass were not found to be sexually dimorphic. Next, wing SShD, but not pupal body SShD was revealed, while allometry was found to be an important "determinant of SD" at the adult stage, with only a minor impact at the pupal stage. By comparing the patterns of covariance (based on allometric slope and intercept) between respective body mass and morphometric traits of pupae and adults, greater variation in allometric slopes was found in adult traits, while static allometries of the two stages significantly differed, as well. Finally, the results indicate that changes in the allometric intercept could be an important source of intraspecific variation and SD in drone fly adults.