Studies on Karyotype of some species of Dacus in Thailand

Abstract

Four species of Dacus (D. corectus, D. dorsalis, D. tau and D. cucurbitae) were studied cytologically using Giemsa staining, Hoechst-33258 staining and C-banding techniques. These four species show uniform mitotic karyotype (2n=12) consisting of 5 pairs of autosomes and one pair of sex chromosome (XX/XY). The Y chromosome is small a submetacentric in all four species. The X chromosome of D. correctus is a small metacentric compared with the medium metacentric X chromosome of the other three species. All four species have metacentric chromosome 2 and submetacentric chromosome 5. Chromosome 3 is submetacentric in D. dorsalis compared with the metacentric shape of the other three species. Chromosome 4 is submetacentric in D. cucurbitae compared with the metacentric configuration of the others. Chromosome 6 is a submetacentric shape in D. correctus and D. dorsalis, but it is a metacentric configuration in D. tau and D. cucurbitae. D. correctus shows negative H-band in the X chromosome while that of D. dorsalis, D. tau and D. cucurbitae exhibits positive H-band of approximately 38.74%, 94.01% and 87.35% respectively. Conversely, the Y chromosome of D. correctus shows positive H-band of 38.50% while it is negative in D. dorsalis, D. tau and D. cucurbitae. The autosomes of D. correctus shows 31.99-43.00% of pericentric positive area while those of D. dorsalis, D. tau and D. cucurbitae show only 0.03-16.50% of pericentric H-band. Total H-band positive areas of D. correctus, D. dorsalis, D. tau and D. cucurbitae are 35.32%, 8.32%, 11.62% and 13.87% in male and 33.40%, 9.95%, 16.71% and 16.87% in female respectively. D. correctus shows the C-band positive area of approximately 4.58% in the X, 89.72% in Y and 30.28-41.00% in each autosome. Total C-band areas of male is 35.68% and of female is 34.17%. In D. dorsalis, the C-band positive areas in chromosomes X and chromosome Y is 53.04%, 38.51% respectively. D. tau shows 94.85% positive C-band area in the X and 7459% in the Y. D. cucurbitae shows 88.63% positive C-band area in the X and 79.87% in the Y. Total C-banded positive areas of D. dorsalis, D. tau and D. cucurbitae are 15.11%, 19.91% and 18.67% in male and 17.38%, 23.31% and 21.17% in female respectively. The four species can be separated by a combination of staining techniques. Based on cytological evidence, D. correctrs is quite different from D. dorsalis although they are morphologically belonging to the same subgenus. D. tau and D. cucurbitae apparently closer relationship than the other two species. Thus, cytological evidence seems to be in accordance with the Drews classification and Grewal and Kapoors suggestion that D. cucurbitae and D. tau belongs to the same subgenus, Zeugodacus.