Species-specific sex chromosome behaviour and banding patterns in three Largid species (Heteroptera)

Abstract

Cytologically, Largidae is a very interesting family as it possesses low diploid number and large chromosome size. So far, only ten of its species belonging to two subfamilies Larginae (6) and Physopeltinae (4) have been analysed karyologically. In the present study male specimens of Physopelta gutta, P. quadriguttata and Neophysopelta schlanbuschi having the same chromosomal formula i.e., 2n=17=12A+2m+X1X2Y, were cytologically examined. The behaviour of the sex chromosomes during prophase-I has been found to be specific to each species. In P. gutta, all the three sex chromosomes remain separate throughout the diffuse stage and prophase-I. In P. quadriguttata, X1 and Y remain closely associated while X2 remains separate at the diffuse stage and prophase-I. In N. schlanbuschi, X1, X2 and Y form a single chromatin body at the diffuse stage that remains so throughout prophase-I. In P. gutta and P. quadriguttata, dispersed C-bands are observed in autosomal bivalents excepting one bivalent in P. gutta which shows two heavy terminal C-bands, while in N. schlanbuschi, all the bivalents are found to be C-negative. Sex chromosomes X1, X2 and Y exhibit heterogeneous C-banding pattern whereas m-chromosomes are found to be C-negative in all the three species. Most of the C-heterochromatin in autosomal bivalents is found to be DAPI/CMA3 bright in P. quadriguttata but in P. gutta, base specificity of C-bands is not resolved. Sex chromosomes X1 and Y are found to be DAPI/CMA3 bright in all the three species while X2 exhibits diverse response to fluorochromes. Differences in banding pattern can serve as useful cytological markers.