The cricket fauna of Chiapanecan caves (Mexico): systematics, phylogeny and the evolution of troglobitic life (Orthoptera, Grylloidea, Phalangopsidae, Luzarinae)

The present study deals with the cavernicolous Grylloidea of Chiapas. It details the composition of this fauna, which belongs exclusively to the Phalangopsid group Amphiacustae, and considers its troglobitic evolution in the methodological framework of Comparative Biology. This method consists in analysing the evolution of biological features in reference to phylogeny, using character state optimization. The material studied comes mostly from Italian biospeological expeditions, but also from the authors work in Mexico, from North American biospeological expeditions achieved in Central America and the West Indies, and from the collections of the Academy of Natural Sciences of Philadelphia, the Museum National d’Histoire naturelle de Paris and the University of Michigan Museum of Zoology. I first present a systematic and phylogenetic analysis of Amphiacustae. Six new genera are defined and the genus Amphiacusta Saussure, 1874 is clearly delimited; twenty-three of the twenty-six species considered in the paper are new and described. A key for genera and species groups is given. Phylogenetic relationships among genera are established using cladistics (implicit enumeration of Hennig 86 program). The evolution of troglobitic Amphiacustae is then analyzed. Available data on the biology of Amphiacust genera are presented and compared with what is known on other Phalangopsidae. Three biological attributes are moreover defined (troglobitic versus non troglobitic; cavernicolous versus non cavernicolous; leaf litter foraging versus leaf litter not foraging). The mapping of the attributes upon our cladogram has shown that Amphiacustae evolved twice toward cave life and that their ancestral habitat could be characterized by cavernicolous habits and leaf litter foraging. The results are discussed in reference to theories on troglobitic taxa evolution, and to the exaptation concept of Gould & Vrba (1982). This leads to three main conclusions: 1) Amphiacust adaptation to caves could be the result of a tentative to exploit karstic resources in Central America; 2) An epigean dispersion by cave living species can be hypothesized; 3) For Grylloidea, having cavernicolous habits at ground level appears to be exaptative to troglobitic life.