Reinventing the leaf: multiple origins of leaf-like wings in katydids (Orthoptera : Tettigoniidae) Joseph Mugleston A,C , Michael Naegle A , Hojun Song B , Seth M. Bybee A , Spencer Ingley A , Anton Suvorov A and Michael F. Whiting A A Department of Biology and M.L. Bean Life Science Museum, Brigham Young University, 4102 Life Science Building, Provo, UT 84602, USA. B Department of Entomology, Texas A&M University, 2475 TAMU, College Station, TX 77843-2475, USA. C Corresponding author. Email: joseph.mugleston@gmail.com Abstract. Insects have developed incredible means to avoid detection by predators. At least five insect orders have species that resemble leaves. Katydids (Orthoptera : Tettigoniidae) are the most diverse and wide-ranging of the leaf-like insects. At least 14 of the 20 extant katydid subfamilies contain species with leaf-like wings. Although it is undisputed that many katydids resemble leaves, methods for delineating the leaf-like from non-leaf-like forms have varied by author and in many cases are not explicitly stated. We provide a simple ratio method that can be used to differentiate the leaf-like and non- leaf-like forms. Geometric morphometrics were used to validate the ratio method. Leaf-like wings have been independently derived in at least 15 katydid lineages. Relative rates of speciation were found to be greater in the non-leaf-like forms, suggesting that leaf-like wings within Tettigoniidae are not a driver of diversification. Likewise, throughout Tettigoniidae, selection seems to be favouring the transition away from leaf-like wings. However, within the large Phaneropterinae subclade, relative speciation and transition rates between the leaf-like and non-leaf-like forms do not differ significantly. Received 4 December 2015, accepted 5 March 2016, published online 31 August 2016 Introduction Selective pressures exerted by visual predators have resulted in an incredible array of animal defences including camouflage and mimicry (Johannesson and Ekendahl 2002; Ruxton et al. 2004; Svanbäck and Eklöv 2011). Species that are better able to conceal their identity from a predator through more elaborate forms of crypsis, or more convincing disguises, have a selective advantage over species whose crypsis is less convincing (Johannesson and Ekendahl 2002). How well an organism resembles its surroundings (crypsis), resembles an aposematic organism (mimicry), or resembles an uninteresting object (masquerade or mimesis) can all affect rates of predation (Johannesson and Ekendahl 2002; Ruxton et al. 2004; Skelhorn et al. 2010a; Skelhorn et al. 2010b; Svanbäck and Eklöv 2011). Studies on the evolution of camouflage from a phylogenetic standpoint are just beginning to elucidate the evolution of crypsis in animals (Vane-Wright and Boppre 1993; Crespi and Sandoval 2000; Hultgren and Stachowicz 2009; Marshall and Gluckman 2015; Rajabizadeh et al. 2015). Insects exhibit a wide range of camouflage including many species that closely resemble leaves (Nentwig 1985; Schmidt 1990; Svenson and Whiting 2009; Conner 2014; Fabricant and Herberstein 2014; Pinheiro and Freitas 2014). At least five insect orders contain species with leaf-like mimesis, including Lepidoptera (butterflies and moths), Neuroptera (lacewings), Mantodea (mantises), Phasmatodea (walking sticks and leaf insects) and Orthoptera (grasshoppers, katydids and crickets) (Fig. 1). In each of these orders, the specialised mimetic morphology, colouration or behaviour is thought to aid in avoiding detection by predators or prey (Robinson 1969; Edmunds 1974; Castner 1995; Castner and Nickle 1995b). Among insects, the most frequently encountered and most diverse range of leaf-like disguises is found in the orthopteran family Tettigoniidae (katydids and bush crickets). Katydids are a cosmopolitan family with more than 7000 described species (Eades et al. 2015). The similarity between katydid forewings and leaves has long been recognised and forms the basis for some of their taxonomic names (e.g. Pseudophyllinae: ‘false leaf’ and Phylloptera: ‘leaf-winged’). The leaf-like appearance of katydid wings is achieved by modifications to the forewing (tegmina) shape, wing positioning, colour, venation and in some species additional modifications to the legs enhance the overall leaf-like appearance (Fig. 2). The diversity of leaf-like disguises makes Tettigoniidae an ideal system to study the evolution of leaf-like wings and the influence of these modifications on katydid diversity. What remains unclear is what specific morphological Ó The authors 2016 www.publish.csiro.au/journals/is CSIRO PUBLISHING Invertebrate Systematics, 2016, 30, 335–352 http://dx.doi.org/10.1071/IS15055