The role of the use of different cactus hosts in the maintenance of the inversion polymorphism in Drosophila buzzatii.

FERNANDEZ IRIARTE, P, E HASSON

EVOLUTION

WILEY-BLACKWELL PUBLISHING, INC

Año: 2000 vol. 54 p. 1295 - 1302

0014-3820

Inversion polymorphisms often have been associated with fitness variation. Cactophilic Drosophila buzzatii has been used widely for the study of the maintenance of chromosomal variation. The purpose of this paper is to address the relative importance of variable selection regimes associated with the use of three different host cacti and antagonistic pleiotropy in the maintenance of chromosomal variation. Using homokaryotypic stocks derived from several lines homozygous for four second-chromosome arrangements, we show that inversions significantly affect first-instar larva to adult viability (VT), developmental time (DT) and adult thorax length (TL). We also show that the effects of inversions on DT and VT are dependent on the cactus rearing media. The effects of polymorphic gene arrangements on life-history traits suggest the existence of trade-offs between early and late fitness components. The dosage of arrangement 2st, the ancestral gene order, was negatively correlated with DT and TL, whereas flies carryingthe derived arrangements 2j and 2jq7 had longer DTs and larger TLs. Arrangements 2st and 2jq7 increased viability, at least in one of the cactus media tested. Our results suggest that environmental heterogeneity, as represented by the use of different cactus hosts and the trade-off between DT and TL, may be involved in the maintenance of the polymorphism. In addition, our data suggest that the chromosomal phylogeny may be decoupled from the evolution of the genes affecting life-history traits linked to the inversion system.