Taxonomy, larval morphology and cytogenetics of Lihelophorus, the Tibetan endemic subgenus of Helophorus (Coleoptera: Hydrophiloidea)

Abstract: The taxonomy, larval morphology and cytogenetics of Lihelophorus Zaitzev, 1908, a subgenus of Helophorus Fabricius, 1775 endemic to the Tibetan Plateau, are examined based on recently collected material and the inspection of type and historical specimens. Three species are recognized: Helophorus (Lihelophorus) lamicola Zaitzev, 1908 (type species), H. (L.) ser Zaitzev, 1908 and H. (L.) yangae sp. nov.; all of them are (re)described and their diagnostic characters are discussed and illustrated. First instar larvae of two species, H. lamicola and H. yangae, both obtained from egg cases laid by field-collected adults and confirmed as conspecific with them by means of cox1 DNA sequences, are described and compared in detail with the larva of H. (Helophorus) liguricus Angus, 1970. Larvae of both species differ from all other Helophorus larvae by strongly asymmetrical nasale and extremely long legs, larvae of H. lamicola are unique among Helophorus in the presence of abdominal tracheal gills. Mitotic karyotypes from mid-gut cells and meiotic karyotypes from testes are described for all three species, revealing the karyotype 2n = 20 +Xyp for all of them. All these data (larval morphology, DNA sequences and karyotypes) are in agreement with the presence of three species of Lihelophorus revealed by adult morphology, and also support the monophyly of the subgenus. Known data on biology and distribution of Lihelophorus are summarized, including the highest known altitudinal record for an aquatic beetle (5350 m a.s.l.). The unusual larval morphology of Lihelophorus is discussed in detail and hypothesized as adaptation for high altitude cold changeable environment. The systematic position of Lihelophorus and the composition of the Helophorus fauna of the Tibetan Plateau are briefly discussed.

Key words: Coleoptera, Helophoridae, new species, immature stages, egg case, biology, tracheal gills, high altitude, Tibetan Plateau, China, Palaearctic Region