Mouth morphology of the diving beetle Hyphydrus japonicus (Dytiscidae: Hydroporinae) is specialized for predation on seed shrimps

Abstract

Two-shelled organisms, such as bivalves and seed shrimps, protect themselves from external stresses by firmly closing both shells. We found that the diving beetle Hyphydrus japonicus Sharp, 1873 (Dytiscidae: Hydroporinae) larvae frequently prey on seed shrimps. Other predatory aquatic insects have difficulty in capturing seed shrimps owing to the general form of their mandibles. Larvae of H. japonicus bear a projection on the head (the nasale), which is used in conjunction with vertical movements of the mandibles to fixate the valves of their prey and gain access to the soft body within them. This capture method does not destroy shells and is extremely efficient. The present study provides the first report on the use of a unique morphological trait for attacking prey animals without destroying their shells.

The enduring value of reciprocal illumination in the era of insect phylogenomics: a response to Cai et al. (2020)

“…Alternatively, it is entirely possible that the cerebrum of Hyphydrus (De Marzo, 1979: fig. 47) and other hydroporines, is not in a different position relative to that of other dytiscid larvae, but appears posteriad due to elongation of the anterior portion of the cephalic capsule into the nasale, another structure adapted for specialized feeding habits (Matta, 1983; Friis et al ., 2003; Hayashi & Ohba, 2018). Furthermore, this could also be a result of shortening the posterior region of the cephalic capsule due to a developmental trade‐off for lengthening of the nasale, given an increase in certain structures is known to result in compensatory decreases in other anatomical features (Nijhout & Wheeler, 1996; Moczek & Nijhout, 2004), including those located near the exaggerated trait (Emlen, 2001).…”

Species' traits and taxonomic distance can predict the hatching phenology of ostracod (Crustacea) resting eggs from tropical floodplain lakes

“…The bivalve carapace of ostracods protects against predation, although it can still occur without destroying the valves. Hayashi and Ohba (2018) showed that laterally flattened ostracod species and those without spines seem to be preferred by larvae of predatory diving beetles (see Hayashi & Ohba, 2018-video in Supporting Information Material). The presence of pointed or rounded external structures (helmets, spines) is common in ostracods and important for the identification of species .…”

Specialized Predation Drives Aberrant Morphological Integration and Diversity in the Earliest Ants

“…Vertical mandible movement is present in aquatic larvae of some Hydrophus beetles [57,58]. The larvae are predators of shelled shrimp and use their specialized head projection in conjunction with mandibles to grasp prey [59]. Despite staggering anatomical diversity of insects, larval dytiscid beetles and hell ants together appear to represent the only two known instances of mandible-on-head contact used in prey capture [59], both appearing with vertically articulating mouthparts.…”