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Belostoma is the most diverse genus of Belostomatidae, comprising 74 species. The small Belostoma species are challenging to identify mainly due to the presence of cryptic species. As DNA barcoding has been a crucial tool to solve the taxonomic impediment associated with many taxa, we compared species delimitations obtained by morphological and molecular approaches, in order to help to disentangle the taxonomy of Belostoma. We sampled 192 specimens of Belostoma across the Rio Grande do Sul Brazilian Coastal Plain. Specimens were first identified with the use of morphological markers and then characterized for two mitochondrial markers: cytochrome C oxidase subunit I (COI) and 16S rRNA genes, generating 181 and 164 sequences, respectively. These were complemented with Belostoma sequences downloaded from NCBI/BOLD (101 for COI & 13 for 16S). Thus, matrixes including 282, 177 and 299 sequences for COI, 16S and the concatenated data set, respectively, were analysed through phylogenetic, phylogeographic and distance approaches. The initial morphological evaluation allowed the identification of 14 male genitalia morphotypes, whose sequences were added to a preliminary matrix containing ​NCBI/BOLD sequences of five other described species, allowing us to recover 10 clades in the molecular analyses. Patterns of reciprocal monophyly were confirmed for only six of the studied species: Belostoma angustum, Belostoma cummingsi, Belostoma dentatum, Belostoma noualhieri, Belostoma orbiculatum and Belostomaribeiroi. Belostoma candidulum, Belostoma horvathi and Belostoma sanctulum appeared intermingled in a single clade. The grouping of these with the other five distinct (male genital) morphotypes reveals a clade with high levels of morphological polymorphism or phenotypic plasticity. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Recent investigations into relationships among the cosmopolitan Belostomatidae have led to recognition of the Belostomatinae, Horvathiniinae and Lethocerinae clades. Here we investigate the relationships among the genera of this family (with Appasus, Benacus and Kirkaldyia now resurrected, and three fossils: Cratonepa, Iberonepa and Lethocerus vetus) by including modifications or clarifications of both somatic and genitalic characters (including some spermatheca traits), as well as multiple genes (COI, 18S rDNA and 16S rDNA). A comparative study of these genera yielded putative homology hypotheses coded as 104 morphological characters and 1829 aligned characters. A majority-rule tree utilizing the Bayesian method [the 'master' tree with highlighted clades estimated by maximum parsimony and maximum likelihood (ML)] is as follows: (Cratonepa, Iberonepa, (Benacus, Kirkaldyia, Lethocerus), (((Horvathinia, Hydrocyrius), Limnogeton), (((Abedus, Weberiella), Belostoma), (Appasus, Diplonychus))))). Lethocerinae and Belostomatinae (now with Horvathinia included) form two monophyletic groups. Weberiella appears as the sister group of Abedus, and Belostomatini had to be reformulated. In all trees, the monophyly of Diplonychini trib. nov. (Appasus+Diplonychus) was recovered with high support indices. This study highlights a global tree based on combining the molecular and morphological data representing topologies from separate analyses, irrespective of the existence of missing data and the type of dataset. [ABSTRACT FROM AUTHOR]