Evolution of the cercal sensory system in a tropical cricket clade (Orthoptera: Grylloidea: Eneopterinae): a phylogenetic approach
Résumé
The diversity of sensory systems in animals has poorly been explored on a phylogenetic basis at the species level. We addressed this issue using cricket cerci, comprising abdominal appendages covered with touch- and airsensitive hairs. Scanning electron microscopy measurements and spatial analyses of hair positioning were used to quantify the structural diversity of cercal structures. Eighteen Eneopterinae and two Gryllidae (outgroups) were studied from a phylogenetic perspective. Cerci were revealed to be complex, diverse, and variable between cricket species. Based on maximum likelihood estimations, the ancestral Eneopterinae cercus had a small size, and its hair equipment allowed the use of both air and touch mechanoreception. The evolution of Eneopterinae cerci was mainly unconstrained by the phylogeny; it was rather a punctuated process, involving apical transformations, and was mostly unrelated to environmental patterns. All studied species have enhanced their overall perceptive capacities compared to the ancestor. Most have longer cerci with more and/or longer hairs. Sensory abilities have improved either in the direction of touch or air movement detection, or both, without discarding the potential for any sensory capacity that was already present ancestrally. This pattern is consistent with the hypothesis of an evolutionary trade-off for sensory performances.