Abstract
An account is given of the karyotypes of five species and one additional subspecies of Deronectes Sharp, 1882, three species of Stictotarsus Zimmermann, 1919, one species of Trichonectes Guignot, 1941, four species of Scarodytes Gozis, 1914 and 17 species of Nebrioporus Régimbart, 1906. Deronectes species are characterised by a neo-Xy system of sex chromosomes and autosome numbers ranging from 60 (Deronectes ferrugineus Fery et Brancucci, 1987 and Deronectes wewalkai Fery et Fresneda, 1988) through 48 (Deronectes latus (Stephens, 1829), Deronectes angusi Fery et Brancucci, 1990) to 28 (Deronectes costipennis Brancucci, 1983, Deronectes costipennis gignouxi Fery et Brancucci, 1989 and Deronectes platynotus (Germar, 1834)). The three species of Stictotarsus, Stictotarsus duodecimpustulatus (Fabricius, 1792), Stictotarsus procerus (Aubé, 1838) and Stictotarsus bertrandi (Legros, 1956), all belonging to the Stictotarsus duodecimpustulatus group of species, have karyotypes comprising 54 autosomes and neo-Xy sex chromosomes. Trichonectes otini Guignot, 1941 has 48 autosomes and an X0 system of sex chromosomes, an arrangement shared with the 17 species of Nebrioporus Régimbart. The four Scarodytes species, Scarodytes halensis (Fabricius, 1787), Scarodytes nigriventris (Zimmermann, 1919), Scarodytes fuscitarsis (Aubé, 1838) and Scarodytes malickyi Wewalka, 1997, all have 54 autosomes and X0 sex chromosomes. The karyotypes of the various species are found to be distinctive and to support separation of these species from one another. In two cases (Nebrioporus martinii (Fairmaire, 1858) and Nebrioporus sardus (Gemminger et Harold, 1868), and Scarodytes halensis and Scarodytes fuscitarsis) the karyotypes require the recognition of the taxa as full species, not subspecies. The implications of these data for the generic classification are considered. The data are found to be compatible with the DNA-based phylogeny proposed by Ribera (2003), where the enlarged Stictotarsus proposed by Nilsson and Angus (1992) is found to be unsatisfactory.
Highlights
The Deronectes group of genera comprise small diving beetles (Dytiscidae) which belong to the subfamily Hydroporinae, tribe Hydroporini
The species that possessed hooked parameres were placed in the genera Nebrioporus Regimbart, 1906 and Scarodytes Gozis, 1914, while those without them were placed in an expanded Stictotarsus Zimmermann, 1919
The genus Trichonectes Guignot, 1941, which was included in Stictotarsus by Nilsson and Angus, was reinstated by Ribera (2003) because DNA analysis showed it to be only distantly related to other Stictotarsus, and Angus (2010b) erected the genus Boreonectes for the Stictotarsus griseostriatus group of Nilsson and Angus
Summary
The Deronectes group of genera comprise small diving beetles (Dytiscidae) which belong to the subfamily Hydroporinae, tribe Hydroporini They typically inhabit stony or gravelly rivers or lakes, and often have a characteristic, quite flattened appearance. Nilsson and Angus (1992) sought to clarify the situation, and in particular to separate the mainly northern hemisphere Deronectes Sharp, 1882 group from various superficially similar southern hemisphere genera. They separated Deronectes itself as having a more or less uniformly coloured upper surface, parameres without an apical hook, and larvae without extra swimming-hairs on the legs. The genus Trichonectes Guignot, 1941, which was included in Stictotarsus by Nilsson and Angus, was reinstated by Ribera (2003) because DNA analysis showed it to be only distantly related to other Stictotarsus, and Angus (2010b) erected the genus Boreonectes for the Stictotarsus griseostriatus group of Nilsson and Angus
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