The giant water bug fauna from tropical South America remains poorly known. Three species of Belostoma Latreille (Belostoma fittkaui De Carlo, B. sayagoi De Carlo and B. hirsutum Roback & Nieser) have been cited only a few times in the literature. These three species are remarkable since they represent an extreme variation for the genus, with article II of the labium distinctly shorter than article III. Here, the synonymy of B. hirsutum with B. sayagoi is proposed based on examination of type material and additional specimens. Further, B. fittkaui and B. sayagoi are redescribed, including discussion about comparative morphology with congeners. A new species group is proposed for these species and a key to the Belostoma species groups is provided. Distribution records are also updated.
The genus Belostoma comprises about 70 species classified in sixteen species groups. Here, the remarkable Belostoma triangulum group sensu Lauck, 1964, is revised. Belostoma bicavum Lauck, 1964 is proposed as a junior synonym of B. bachmanni De Carlo, 1957, which is added to this group. Thus, the rearranged group is now composed of two species: Belostoma bachmanni and B. triangulum Lauck, 1964. Redescriptions of these species are presented including a discussion about comparative morphology with other species of the genus. The geographic distributions of the species in the B. triangulum group are also updated.
The structures involved in parental care are often dimorphic. Female Belostoma angustum water bugs lay eggs on the hemelytra of their mates, where the eggs are brooded until hatching. Males use their hind legs to carry, aerate and protect the eggs. After controlling for covariance between variables, we fitted a series of structural equation models (SEMs) and evaluated the existence of sexual dimorphism in the size of the body and hind legs, in the shape and centroid size of the hemelytrum, and among the static allometry slopes of the size-related differences. Landmarks were used to capture phenotypic variation, by eliminating all non-shape variations with a Procrustes superimposition. Neither the shape of the hemelytrum nor its centroid size was related significantly to the aforementioned linear body measurements. Instead, the differences in the size of the hind legs were mediated by body dimensions only in males. We also found that males were wider and had longer heads than females, according to the SEM intercept values. Our findings suggest that sexual dimorphism in B. angustum may be related to a balance between sexual role reversal and viability costs.
The population dynamics of freshwater organisms are expected to be related to the connectivity among comparable streams, ponds, or rivers in a patchy habitat. Here, we investigated the population dynamics of the giant water bug, Belostoma angustum Lauck 1964 (Hemiptera: Belostomatidae), in a fine-scale spatial sampling, and evaluated which gene flow model previously described for freshwater organisms could explain the genetic–morphological variation in this species. For these purposes, we evaluated genetic and morphological variations, as well as the demographic history of this freshwater insect. Our genetic analyses showed a lack of geographical structure within B. angustum populations across the evaluated range, concordant with widespread gene flow model. Our findings of the demographic history of B. angustum suggest recent and rapid expansion beginning during the late Pleistocene after the Last Glacial Maximum. Likewise, we did not find geographically structured morphological variation in B. angustum, except for body size. The lack of structure of genetic–morphological variation in B. angustum could be explained by a stepping ponds system resulting in the widespread gene flow detected among populations of this species. The warmer and wetter climatic conditions after the last glacial period may have favored the demographic expansion of B. angustum populations due to the increasing of potential freshwater habitats and food resources. This favorable habitat probably allowed the stepping ponds dispersal mode resulting in the verified geographically unstructured genetic–morphological variation.
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