Evolution of the cercal sensory system in a tropical cricket clade (Orthoptera: Grylloidea: Eneopterinae): a phylogenetic approach LAURE DESUTTER-GRANDCOLAS 1 *, ELODIE BLANCHET 2,3 , TONY ROBILLARD 1 , CHRISTELLE MAGAL 2 , FABRICE VANNIER 2 and OLIVIER DANGLES 2,4.5 1 Muséum national d’Histoire naturelle, Département Systématique et Evolution, UMR7205 CNRS, 57 rue Cuvier, CP 50, 75231 Paris, Cedex 05, France 2 Institut de Recherche sur la Biologie de l’Insecte, UMR CNRS 6035, Faculté des Sciences et Techniques, Avenue Monge – Parc Grandmont, 37200 Tours, France 3 CIRAD Acridologie, F-34398 Montpellier, France 4 IRD, UR 072, Laboratoire Evolution, Génomes et Spéciation, UPR 9034, CNRS, 91198 Gif-sur-Yvette, Cedex, France 5 Université Paris-Sud 11, 91405 Orsay, Cedex, France Received 27 May 2009; accepted for publication 25 September 2009 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 air- sensitive 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. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99, 614–631. ADDITIONAL KEYWORDS: escape behaviour – evolution – filiform hair – predation pressure – setae arrays. INTRODUCTION Both structural and functional properties of periph- eral sensory organs can affect the way in which per- ceptual systems evolve in response to selection pressures by mates or predators (Barth & Schmid, 2001). During the last 10 years, research on the diversity and evolution of sensory organs has focused on comparisons of morphologies among species irre- spective of the phylogenetic history of animals (Chittka & Briscoe, 2001; Dangles et al., 2009). Several studies have investigated the phylogenetic position of sensory organs among clades (mainly above the family level) and provided estimates of the time of appearance of particular features inherent to each lineage (e.g. vision and olfaction in mammals: Barton, Purvis & Harvey, 1995; hearing in verte- brates: Fay & Popper, 2000; fish electroreception: Alves-Gomes, 2001; ultrasonic hearing in mantids: *Corresponding author. E-mail: desutter@mnhn.fr Biological Journal of the Linnean Society, 2010, 99, 614–631. With 3 figures © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99, 614–631 614