Tendencias contrastantes en el dimorfismo sexual de tamaño de dos especies de tucuras del género Dichroplus (Acrididae, Melanoplinae)

MARTÍ DARDO A, BIDAU, CLAUDIO J.

San Miguel de Tucumán

Congreso; VI Congreso Argentino de Entomología; 2005

Sexual size dimorphism (SSD) is normally the result of sexual selection (SS) although it may also be produced by natural selection (NS). In males, SS would favour increasing body mass if it gives and advantage in contests over mates. A larger size in females could be favoured by NS because egg production is related to body size (BS). In the Acrididae, SSD is female-biased. SSD was analysed in 16 and 19 argentine populations of the grasshoppers Dichroplus vittatus and D. pratensis, using principal components analysis and multiple regression. Both species showed latitudinal and elevational of BS inversely to Bergmann’s rule. SSD occurred in both species throughout their geographic ranges, also involving differences in body proportions that could be explained by differential allometry a shorter nymphal developmental time in males (protandry). The former could explain the inversion of Rensch’s rule observed in D. pratensis: SSD decreases as general BS increases at low latitudes and elevations. In contrast, D. vittatus obeyed Rensch’s rule: the degree od SSD increased significantly as general BS became larger. A plausible explanation is that SS could be favouring a differential increase in female size related to a preference of males for more fecund females. Considering their philogenetic proximity, the contrasting trends in SSD possible obey to differential selective pressures on characteristics of the life history and genetic system of both species.