Against the central-marginal model: three cases in chromosomally polymorphic grasshoppers

COLOMBO, P.C.

EUROPEAN JOURNAL OF ENTOMOLOGY (CESKE BUDEJOVICE)

CZECH ACAD SCI

Lugar: Ceske Budejovice; Año: 2012 vol. 109 p. 317 - 324

1210-5759

The central-marginal model has a wide acceptance in chromosomally polymorphic species of Drosophila. In fact, geographically and ecologically central populations of Drosophila show higher levels of polymorphism for paracentric inversions, whereas marginal populations tend to be monomorphic. This fact has been diversely explained. Chromosomal polymorphisms in grasshoppers have also been attributed this geographical feature, as in the case of the South-American grasshopper Dichroplus pratensis. However, in three other cases (Leptysma argentina, Trimerotropis pallidipennis and Cornops aquaticum), it is clear that chromosomal polymorphisms (sometimes with a wide extension over the Argentine area) do not conform to this pattern, and show instead clear correlations with environmental variables, especially minimum temperature, showing low or null frequencies of the rearrangements at one extreme of the environmental gradient and with high or fixed frequencies at the other. Furthermore, it is suggested that this correlation with temperature might also be the case for D. pratensis. These facts and hints stress the dangers of over-generalization when it comes to chromosomal polymorphisms, and urges to consider every species as a special case when its genetic system is under study.