Profound head modifications in Claviger testaceus (Pselaphinae, Staphylinidae, Coleoptera) facilitate integration into communities of ants

Abstract

Clavigeritae is a group of obligate myrmecophiles of the rove beetle subfamily Pselaphinae (Staphylinidae). Some are blind and wingless, and all are believed to depend on ant hosts through feeding by trophallaxis. Phylogenetic hypotheses suggest that their ancestors, as are most pselaphines today, were free-living predators. Morphological alterations required to transform such beetles into extreme myrmecophiles were poorly understood. By studying the cephalic morphology of Claviger testaceus, we demonstrate that profound changes in all mouthpart components took place during this process, with a highly unusual connection of the maxillae to the hypopharynx, and formation of a uniquely transformed labium with a vestigial prementum. The primary sensory function of the modified maxillary and labial palps is reduced, and the ventral mouthparts transformed into a licking/'sponging' device.

The specialized thoracic skeletomuscular system of the myrmecophile Claviger testaceus (Pselaphinae, Staphylinidae, Coleoptera)

“…Due to their greatly reduced mouthparts, C. testaceus and related species rely on feeding by host ant workers (Akre and Hill 1973;Hermann 1982). Profound myrmecophilous adaptations related to the mouthparts and other cephalic structures of Claviger were a subject of a separate study (Jałoszyński et al, 2020). Despite of lacking defensive glands, myrmecophilous pselaphine species can permanently live and reproduce in ant colonies (Parker 2016a).…”

“…Like other species of the genus (Parker 2016a), Claviger testaceus Preyssler, 1790 displays very advanced morphological specializations, among them the complete loss of eyes and optic neuropils (Jałoszyński et al 2020) and the reduced and non-functional flight apparatus. Behavioral patterns of C. testaceus have been described by Donisthorpe (1927) and Cammaerts (1977) and were summarized by Hermann (1982).…”

“…Bizarre morphological modifications in this clade have attracted attention of different researchers (e.g., Parker and Grimaldi 2014). However, most studies were focused on structural features of the head and abdomen, such as the distinctly reduced mouthparts and specialized armatures of abdominal and elytral trichomes (see Hermann 1982;Parker 2016a;Jałoszyński et al 2020), and also on appeasement glands (e.g., Cammaerts 1973Cammaerts , 1974. The trichomes on the abdominal tergites are a presumptive synapomorphy of the group and linked with the association with host ants, which have been recorded to lick on these hair-like structures of several species of Clavigeritae (Hermann 1982;Cammaerts 1992Cammaerts , 1995Cammaerts , 1996.…”

Diversification of myrmecophilous Clavigeritae beetles (Coleoptera: Staphylinidae: Pselaphinae) and their radiation in New Caledonia

“…These structures are positioned near the base of the abdomen and their secretions are highly attractive to host ants, likely promoting the beetle's acceptance inside the nest (Park, 1932, 1942; Akre & Hill, 1973; Cammaerts, 1992; Parker & Grimaldi, 2014). Anatomically, clavigerite beetles are amongst the most specialized myrmecophiles known: the mouthparts are strongly reduced and internalized to facilitate trophallaxis (Akre & Hill, 1973; Jałoszynski et al ., 2020), and the body as a whole is strengthened via extensive fusions of segments. The tergites are combined into a single ‘tergal plate’, and the antennae likewise show a reduction of segments, with all modern species possessing between three and six flagellomeres.…”

“…In addition to the trichomes, a diversity of smaller glandular structures decorate the integument and appendages (Cammaerts, 1974; Hill et al ., 1976). Some of the most anatomically extreme genera are additionally eyeless and wingless (Akre & Hill, 1973; Jałoszynski et al ., 2020).…”