Going underwater: Multiple origins and functional morphology of piercing-sucking feeding and tracheal system adaptations in water scavenger beetle larvae (Coleoptera: Hydrophiloidea)

Abstract

Larvae of water scavenger beetles (Coleoptera: Hydrophiloidea) are adapted to a wide variety of aquatic habitats, butlittle is known about functional and evolutionary aspects of these adaptations. We review the functional morphologyand evolution of feeding strategies of larvae of the families Hydrophilidae and Epimetopidae based on a detailedscanning electron microscope (SEM) analysis, analysis of video records of feeding behaviour and observations ofliving larvae. There are two main types of feeding mechanisms: chewing and piercing-sucking. The character mappingusing the latest phylogenetic hypothesis for Hydrophiloidea infers the chewing system as the ancestral condition. Thepiercing-sucking mechanism evolved at least four times independently: once in Epimetopidae (Epimetopus) and threetimes in Hydrophilidae (Berosini: Berosus + Hemiosus; Laccobiini: Laccobius group; Hydrobiusini: Hybogralius). Thepiercing-sucking apparatus allows underwater extra-oral digestion and decreases the dependence of larvae on an aerialenvironment. A detailed study of the tracheal morphology of the piercing-sucking lineages reveals four independentorigins of the apneustic respiratory system, all of them nested within lineages with piercing-sucking mouthparts. Weconclude that piercing-sucking mouthparts represent a key innovation, which allows for the subsequent adaptation ofthe tracheal system, influences the diversification dynamics of the lineages and allows the shift to new adaptive zones.