Phylogeny, evolution and classification of the giant water scavenger beetles (Coleoptera: Hydrophilidae: Hydrophilini: Hydrophilina)

Evidence of morphological adaptation to life underwater: sternal keel affects swimming speed in giant water scavenger beetles (Coleoptera: Hydrophilidae: Hydrophilini)

Fundamentally, insects evolved on land and secondarily inhabited aquatic environments multiple times. To live underwater, aquatic insects have acquired enormously variable morphological, developmental, physiological, and ecological traits, such as gas exchange systems and swimming-related characteristics. Giant water scavenger beetles of the tribe Hydrophilini (Coleoptera: Hydrophilidae) are characterized by the presence of a sternal keel, which often extends posteriorly. Despite being a conspicuous morphological trait, its function remains unclear. Here, I verified two hypotheses: keel affects (1) submergence time following air replacement and (2) speed and oscillatory movement during forward swimming in Hydrophilus acuminatus Motschulsky, 1854. Submergence time was affected by body mass rather than keel removal; in other words, larger individuals replaced their gas gills more frequently. Keel removal reduced swimming speed by 12.5%. These observations support the second hypothesis, and are also consistent with previous speculations that the sternal keel is a key adaptation for swimming, but the results showed that the degree of oscillation was closely related to body mass but not to keel removal. Further studies are warranted to elucidate precise factors through which the presence of the keel increases swimming speed. Such studies would provide clues into understanding the associations among body size, swimming methods, and morphological traits.

Genetic and Morphologic Variation in a Potential Mosquito Biocontrol Agent, Hydrochara Affinis (Coleoptera: Hydrophilidae)

Hydrochara affinis (Coleoptera: Hydrophilidae), a water scavenger beetle, was recently identified as a natural and effective agent for biological mosquito control; it was reported to exhibit high rates of mosquito larvae predation. However, maintaining the quality (i.e., natural ecological attributes, such as genetic variation) of laboratory-reared populations is essential for ensuring the long-term success of biological control programs. Accordingly, here, we aimed to use mitochondrial Cytochrome c oxidase subunit I (COI) sequences to document the genetic diversity, population structure, and phylogenetic position of natural and lab-reared H. affinis populations in South Korea and use geometric morphometric analysis to investigate the populations’ morphological divergence. The natural H. affinis populations possessed high genetic diversity and numerous COI haplotypes, suggesting that these populations were healthy and could be directly applied to mosquito habitats without alterations to their natural genetic attributes. The lab-reared populations also possessed high genetic diversity and, thus, the potential for high adaptive capacity to new environments. Although no distinct population genetic structures were observed, quantitative variation was observed in the body shape of both the natural and lab-reared populations. The high levels of genetic and morphologic variation observed in the H. affinis populations examined here indicate the species’ favorable conservation status, genetic diversity, adaptive capacity, and, thus, “suitability” for field application as an effective mosquito control agent.

Asymmetric larval head and mandibles of Hydrophilus acuminatus (Insecta: Coleoptera, Hydrophilidae): Fine structure and embryonic development

The larvae of a water scavenger beetle, Hydrophilus acuminatus, have strongly asymmetric mandibles; the right one is long and slender, whereas the left one is short and stout. The fine structure and embryonic development of the head capsule and mandibles of this species were examined using light and scanning electron microscopy, and asymmetries in shape were detected in these structures applying an elliptic Fourier analysis. The larval mandibles are asymmetric in the following aspects: whole length, the number, structure and arrangement of retinacula (inner teeth), and size and shape of both the molar and incisor regions. The larval head is also asymmetric; the left half of the head capsule is larger than the right, and the left adductor muscle of the mandible is much thicker than the right. The origin and developmental process of asymmetric mandibles were traced in developing embryos whose developmental period is about 270 h and divided into 10 stages. Mandibular asymmetries are produced by the cumulative effects of six stepwise modifications that occur from about 36% of the total developmental time onward. The significance of these modifications was discussed with respect to the functional advantages of asymmetries and the phylogeny of members of the Hydrophilidae.

Phylogenetic study of the genus Sternolophus Solier (Coleoptera, Hydrophilidae) based on adult morphology

The phylogeny of the hydrophilid genus Sternolophus Solier, 1834 was examined in this study using 60 morphological adult characters, eight of them continuous and 52 discrete. The cladistic analysis resulted in a single most parsimonious tree with two major subclades corresponding, respectively, to species previously assigned to the subgenera Sternolophus s. str. Solier and Neosternolophus Zaitzev, although they are not re-instated. The species groups S. angolensis (Erichson, 1843) and S. solieri Castelnau, 1840 are recovered as monophyletic. The biogeography and diversification of the species of Sternolophus are briefly discussed.

Discovery of the water scavenger beetle genus Brownephilus Mouchamps in Turkey (Coleoptera, Hydrophilidae, Hydrophilini

The recently described Hydrochara major İncekara, Mart, Polat, & Karaca, 2009 from Turkey is transferred to the genus Brownephilus Mouchamps. New records and habitat information are given for the species, as well as diagnostic features for separating it from the only other described member of the genus, Brownephilus levantinus Balfour-Browne. The discovery of Brownephilus in Turkey marks the first time the lineage has been found since its original description more than seventy years ago.

Diversification of the greater hydrophilines clade of giant water scavenger beetles dated back to the Middle Eocene (Coleoptera:Hydrophilidae:Hydrophilina)

Fossil representatives of the hydrophilid genera Hydrochara Berthold, 1827, Hydrobiomorpha Blackburn, 1888 and Hydrophilus Geoffroy, 1762 were recorded at the lower Middle Eocene locality Grube Messel in Germany. Four morphospecies were recognised, including Hydrobiomorpha eopalpalis, sp. nov. showing sexually dimorphic maxillary palpomere 2 unknown in any recent or fossil species of the genus. These fossils are the oldest known records of the mentioned genera and indicate a minimum age of 47 million years for the divergence of the Hydrobiomorpha and Hydrophilus clades. Based on these data, we assume that the diversification of the ‘greater hydrophilines’ clade predated the lower Middle Eocene. The fossil record of the subtribe Hydrophilina is briefly reviewed, the reasons of the scarcity or absence of some genera in the fossil record are discussed, and the paleoenviromental significance of the presented fossils is discussed.