REPRODUCTIVE ISOLATION BETWEEN 2 SPECIES OF FLOUR BEETLES, TRIBOLIUM-CASTANEUM AND T-FREEMANI - VARIATION WITHIN AND AMONG GEOGRAPHICAL POPULATIONS OF T-CASTANEUM

Tribolium castaneum and T. freemani produce sterile hybrid progeny in reciprocal crosses. The reciprocal crosses differ significantly in the mean numbers of progeny, progeny sex ratios, hybrid male body size an d male antennal and leg morphologies. These results suggest an effect of either the X chromosome or the cytoplasm on characteristics of F-1 hybrids. In contrast, large X chromosome effects on morphological trai ts are not usually oberved in interspecific crosses among drosophilid flies. We also report large, significant differences in progeny number s, body mass and degree of female bias in sex ratio between different geographic strains of T castaneum when mated in reciprocal crosses wit h T. freemani, Sex ratio bias also varies significantly among matings- within geographic strains of T. castaneum. When T. castaneum males are mated with T. freemani females, but not in the reciprocal cross, the F-1 sex ratio is female biased, uncorrelated with family size and rang es from 57.14 per cent to 72.23 per cent female, depending on the geog raphic strain of the T. castaneum male.