Geographic patterns of chromosomal variation in populations of the grasshopper (Trimerotropis pallidipennis) from southern Argentina

Abstract

Geographic variation has been studied on seven south Argentina populations of Trimerotropis pallidipennis polymorphic with respect to centromere position. Univariate and multivariate statistical analysis were used to assess interpopulation relationships by considering the inversion frequency, the chiasma frequency, and the population distance from the Andes, which is considered to be the hypothetical pathway of migration of this typically North American species to southern latitudes. A cluster analysis indicated strong chromosomal differentiation between the almost monomorphic populations in the Andes' "precordillera" and the highly polymorphic populations in more eastern locations. It also showed that chromosomal similarity between populations could be predicted by geographic proximity. No attempt has been made to relate such a pattern of chromosome variation to ecological data. The lack of any clear relationship with phytogeographic regions or climatic characteristics suggests that microenvironmental factors related to aridity may be important in this case. The presence of inversions within a population has a notable effect on chiasma frequency and position. Chiasmata are suppressed within the inverted region of both inversion heterozygotes and homozygotes. The allelic sequences in the inverted region are thus preserved from recombination and exchanges are limited to terminal regions.Key words: geographic variation, chromosome polymorphism, chiasma frequency, B chromosome, pseudomultiple associations.