Life on the effective bubble: exocrine secretion delivery systems (ESDS) and the evolution and classification of beetles in the family Hydraenidae (Insecta: Coleoptera)

Abstract

Exocrine secretion delivery systems (ESDS) of aquatic beetles in the family Hydraenidae are described for the first time, and used to clarify phylogenetic relationships within the family. ESDS components include secretion-grooming behavior, surface cuticular specializations for secretion delivery, locations of exocrine pores, and locations and densities of ductules and end-apparatus of exocrine glands. ESDS structures are illustrated with scanning electron micrographs and drawings. The systems function, at least in part, to maintain the respiratory bubble by making the cuticular surfaces within the bubble, and especially at critical marginal areas of the bubble, clean of hydrophilic microbes and debris. Secretion-grooming is performed out of the water, often with the beetle "on edge," the legs on the "free" side acting together in patterns of secretion spreading and mutual rubbing. Spreading of secretions on the cuticular surface, movement of secretions between body areas, and cleaning of the cuticle by scraping and rubbing are achieved by specialized patches and rows of setae on the legs.A reclassification of the family is proposed, based in large part on putative synapomorphic characters and morphoclines of the ESDS and antennal pocket. The following suprageneric taxa are proposed and characterized: Orchymontinae, new subfamily; new tribes Madagastrini, Parhydraenini, and Ochtheosini; and new subtribes Meropathina, Neochthebiina, Protochthebiina, and Enicocerina. In the Ochthebiinae, the "subgenera" Calobius Wollaston, Cobalius Rey, Liochthebius J. Sahlberg, and Notochthebius Orchymont are reduced to synonymy with Ochthebius, whereas full generic status is proposed for Aulacochthebius Kuwert and Enicocerus Stephens. In the Hydraeninae, Hydraenopsis Janssens and Spanglerina Perkins are synonymized with Hydraena Kugelann, whereas Haenydra Rey and Hadrenya Rey are considered valid subgenera.The following new genera and new species are described: Haptaenida huggerti (Ecuador), Madagaster steineri (Madagascar), Ochtheosus fungicolus (Chile), Protochthebius satoi (Nepal), Protozantaena labrata (South Africa), Pneuminion velamen (South Africa), and Tympallopatrum longitudum (Australia). Davidraena bacata n. sp. is described from India. Keys to the subfamilies, tribes, and genera of Hydraeninae, and tribes, subtribes, and genera of Ochthebiinae are given. Annals of Carnegie MuseumVOL. 66 maintained, and uses these new character systems to clarify relationships and classification of the family. Hydraenid beetles live in a wide variety of aquatic habitats. Although most species live at the sandy-gravelly margins of streams and ponds (Perkins, 1981), some species live in stagnant water (Cuppen, 1993), a very small percentage of the species are semiaquatic or humicolous (Perkins and Balfour-Browne, 1994), and one species, described herein, is fungicolous.Three hydraenid genera, Ochthebius, Hydraena, and Limnebius, have specialized "exocrine secretion delivery systems" (ESDS), described below, that help maintain the respira...

Minute moss beetles in the Southern Hemisphere: Molecular phylogeny, historical biogeography and habitat shifts (Coleoptera: Hydraenidae)

“…Monotypic and lentic; known only from the type locality, a shallow lakeshore at 4100 m in the Ecuadorian Andes. Morphologically close to Parhydraenida, as discussed by Perkins (1997); placed here tentatively in the absence of molecular data.…”

“…this group of genera in our molecular analyses. Pneuminion retains the 11-segmented antennal configuration which we consider may be an ancestral feature of the 'Gondwana Seven species, five in Madagascar, one (P. labrata) from Namibia and one (P. birdi Bilton) recently described from South Africa (Bilton, 2022;Perkins, 1997Perkins, , 2009Perkins, , 2017. Collecting data suggest a mix of aquatic and humicolous habits.…”

“…Ten humicolous species, all endemic to South Africa (Bilton & Perkins, 2012;Perkins, 1997Perkins, , 2004a. Perkins (2009) noted, from a morphological perspective, the rather isolated position of Pneuminion amongst similar African genera, something which is reflected by its sister grou position wrt.…”

“…Orchymontiinae Perkins were proposed to accommodate three genera of lotic New Zealand hydraenids (Homalaena Ordish, Orchymontia Broun and Podaena Ordish), which Beutel et al (2003) considered basal within the family, based on an analysis of head morphology. Within Hydraeninae, Perkins (1997) proposed three new tribes: Hydraenidini (South America), Parhydraenini (sub-Saharan Africa and the Malagasy Region) and Madagastrini (Malagasy Region and India) (see Bilton, 2021;Perkins, 1980Perkins, , 1997Perkins, , 2009Perkins, , 2017. Perkins (2017) moved the Madagastrini from the Hydraeninae to the Prosthetopinae, on the basis of antennal segmentation.…”

“…Many of the higher taxa of Perkins (1997) are based largely on the structure of the antennal pocket, hypomeron and ventral vestiture. The evolution and character polarity of these features remain unclear, however and, given their critical role in gas exchange (Perkins, 1997), such character systems may be subject to convergence due to strong selection associated with habitat shifts (see Jäch & Díaz, 1998).…”