Morphometric Variation in Chromosomally Polymorphic Grasshoppers (Orthoptera: Acrididae) from South America: Bergmann and Converse Bergmann Patterns

Abstract

Leptysma argentina Bruner, Trimerotropis pallidennis (Burmeister), and Cornops aquaticum Bruner are South-American grasshoppers (Orthoptera: Acrididae) whose chromosome polymorphisms were intensively studied. Leptysma argentina lives in central-east Argentina and in Uruguay and was polymorphic for a centric fusion whose presence is significantly correlated with a larger body size; this parameter was shown to be associated with sexual selection and longevity selection; this species exhibited a marked latitudinal Bergmann pattern. In contrast, Trimerotropis pallidipennis followed a converse altitudinal Bergmann cline; males from higher altitudes were significantly smaller. This species supported an extended polymorphism for several inversions, which are correlated intrapopulationally with larger body size. Finally, C. aquaticum showed an evident example of Bergmann's rule for tegmen length; this species was polymorphic for 3 centric fusions, whose frequency increased southward, as in L. argentina. One of the fusions was associated with increased body size. We noticed that in all cases the rearrangement that was related to body size increased in the direction in which this variable was adaptive, thus suggesting a possible involvement of chromosome polymorphism in body size selection.