Abstract. We conducted a comparative population genetic analysis of levels of genetic variation and its geographical structuring in three closely related species of grasshopper that co-occur in the Mediterranean Basin: Calliptamus italicus, C. barbarus and C. wattenwylianus. In the western part of their distributions 5 populations of C. italicus, 13 of C. barbarus and 10 of C. wattenwylianus were sampled. Bootstrap re-sampling of populations and microsatellite loci within each species indicated a lower level of genetic diversity and higher level of genetic differentiation in C. barbarus, which is less of an outbreak pest species than either of the other Calliptamus species studied. This may be due to lower effective sizes of non-outbreak populations and/or lower gene flow among them.
445C. wattenwylianus (Pantel, 1896) are syntopic across the western part of Mediterranean Basin. C. italicus and C. barbarus have the widest distributions, from the Mediterranean Basin to southern Siberia, whereas C. wattenwylianus is recorded only along the Mediterranean coasts of France, Spain, Morocco and Algeria. Morphological discrimination between the juvenile stages and adult females of these three closely related species is ambiguous, whereas adult males can be identified based on the shape of their wings and pallium (Jago, 1963;Harz, 1975). However, the three species can be easily differentiated genetically, with sequence divergences in Cytochrome Oxidase I mtDNA estimated to be over 3% (Blanchet et al., 2010b). These three species of grasshopper damage crops (COPR, 1982) and share some general ecological features, such as, a one-year generation time, a seasonal diapause, feed on grass (Poacea) (Chopard, 1951) and a moderate dispersal ability (Reinhardt et al., 2005). Given that these three species co-occur and are closely related, ecological and evolutionary factors that affect one species are likely to affect the others, therefore a comparison of these species might provide insights into the relative importance of the factors that shape genetic structuring (McCoy et al., 2005;Brouat et al., 2007).Although the three species of Calliptamus studied are closely related, ecologically similar, and syntopic, previous studies report fine-scale differences between them in terms of ecological features and neutral genetic variation (see Fig. 1). Firstly, Blanchet et al. (2012) showed that at a scale of 70 km 2 between sites in Southern France, gene flow was restricted only in C. wattenwylianus, a species thought to be relatively sedentary compared to other congeneric species (Chara, 1987). Indeed, Jago (1963) showed that C. italicus and C. barbarus have a higher wing/body length ratio, which is a reliable proxy of dispersal ability, than C. wattenwylianus. Secondly, the same fine-scale microsatellite study highlighted lower levels of genetic diversity in C. barbarus than in C. italicus and C. wattenwylianus. This result suggests that long-term effective sizes of populations of C. barbarus might be lower than those of the other s...