Macrogeographic patterns in B-chromosome and inversion polymorphisms of the grasshopper Trimerotropis pallidipennis

CONFALONIERI, V.A.

GENETICS SELECTION EVOLUTION

BIOMED CENTRAL LTD

Lugar: Londres; Año: 1995 vol. 27 p. 305 - 311

0999-193X

South American populations of Trimerotropis pallidipennis are polymorphic for pericentric inversions and B-chromosomes. Previous studies revealed the existence of altitudinal, latitudinal and longitudinal clines for 9 chromosomal sequences, whose repetition in independent groups of populations and over a wide area suggested the action of natural selection. The frequencies of B-chromosomes were analyzed in 25 samples from Argentina. In some of them, the B-chromosome interfers with the genetic control of chiasma formation, which is partly conditioned by inversions. Multiple regression analyses revealed that the frequency of B-carriers in each population is significantly associated with latitude (negatively) and longitude (positively), and that the frequency of inversions significantly decreases at higher altitudes and latitudes. The pattern of distribution observed for B-carriers is most probably related to the suitability of habitats. These results agree with the parasitic model, which claims that higher incidence of the B-chromosome in natural populations is associated with more favorable environments.