Phylogenetic, geographic and ecological distribution of a green-brown polymorphisms in European Orthopterans

The green-brown polymorphism among polyneopteran insects represents one of the most penetrant color polymorphisms in any group of organisms. Yet systematic overviews are lacking. I here present analyses of the phylogenetic, geographic and habitat distribution of the green-brown polymorphism across the complete European orthopteran fauna. Overall, 30% of European orthopterans are green-brown polymorphic. Polymorphic species are scattered across the entire phylogenetic tree, including roughly equal proportions of Ensifera and Caelifera. A few taxonomic groups, however, include only brown species. Polymorphic species occur more frequently in clades that contain monomorphic green species than in those without green species. The relative abundance of color morphs in polymorphic species is skewed towards green, and in particular rare/exceptional brown morphs are more common in predominantly green species than rare/exceptional green morphs in predominantly brown species. The patterns of abundances support the hypothesis that loss-of-function mutations play a role in creating polymorphic populations from green species. Polymorphic species are particularly common in moist to mesic grasslands, alpine and arboreal habitats. Dry, open, rocky and cave habitats as well as nocturnal lifestyles are dominated by monomorphic brown species. The proportion of polymorphic species increases from southern to northern latitudes. These marked habitat-dependencies also show that coloration is affected by natural selection and/or environmental filtering. Overall, the results illustrate that the occurrence of the polymorphism is phylogenetically, geographically and ecologically widespread and they suggest that polymorphism is thus potentially in mutation-selection balance across a large number of species.