Altitudinal Variation in, and Morphological Divergence between, Three Related Species of Grasshopper, Praxibulus sp., Kosciuscola cognatus and K. usitatus (Orthoptera:Acrididae)

Abstract

Morphological variation between and within the closely related species Praxibuius sp.. Kosciuscola cognatus and K. usiratus has been examined along three independent altitudinal transects, by a multivariate statistical approach. The analyses, which were restricted to males. show that there is complete morphological separation between the three species. Moreover. there are species-specific patterns of character correlation which are consistent and relatively invariant within species, and do not exhibit altitudinal variation. The results suggest that there exist both distinct invariant species-specific character patterns and variable character patterns showing intraspecific variation. It is concluded that speciation in these grasshoppers could have involved genetic changes quite distinct from those involved in local intraspecific adaptation. Two further results are: first. evidence has been obtained for character displacement between Kosciuscola cognaius and Praxibulus sp. in an area of extensive sympatry: second. populations of K. cognatus along one transect, with a karyotype intermediate between typical K. cognatus and X usiiatus, show a parallel change in morphology towards that characteristic of K. usiiatus.