Spontaneous recombination in males ofDrosophila bipectinata was tested in five wild type laboratory stocks of different geographic origins by using sepia eye and black body colour double recessive mutant stock. The results indicate thatDrosophila bipectinata exhibits spontaneous male recombination. Further, recombination occurs at low rate and there is interstrain variation with respect to the rate of male crossing-over. This is the first report of spontaneous recombination in males ofDrosophila bipectinata.

Drosophila ananassae, a cosmopolitan and domestic species, belongs to theananassae subgroup of themelanogaster species group. Female remating was observed in ten mass culture stocks of this species, which were initiated from flies collected from different geographic localities. The frequency of female remating ranges from 24% to 56% in different strains. Strains show significant variation in remating latency (days). Significant variation has also been found in all the stocks for duration of copulation between first and second matings. The duration of copulation is shorter in second mating as compared to first mating inD. ananassae.

Using half-sib analysis, we analysed the consequences of extreme rearing temperatures on genetic and phenotypic variations in the morphological and life-history traits of Drosophila ananassae. Paternal half-sib covariance contains a relatively small proportion of the epistatic variance and lacks the dominance variance and variance due to maternal effect, which provides more reliable estimates of additive genetic variance. Experiments were performed on a mass culture population of D. ananassae collected from Kanniyakumari (India). Two extremely stressful temperatures (18°C and 32°C) and one standard temperature (25°C) were used to examine the effect of stressful and non-stressful environments on the morphological and life-history traits in males and females. Mean values of various morphological traits differed significantly among different temperature regimens in both males and females. Rearing at 18°C and 32°C resulted in decreased thorax length, wing-to-thorax (w/t) ratio, sternopleural bristle number, ovariole number, sex comb-tooth number and testis length. Phenotypic variances increased under stressful temperatures in comparison with non-stressful temperatures. Heritability and evolvability based on among-sires (males), among-dams (females), and the sum of the two components (sire + dam) showed higher values at both the stressful temperatures than at the non-stressful temperature. These differences reflect changes in additive genetic variance. Viability was greater at the high than the low extreme temperature. As viability is an indicator of stress, we can assume that stress was greater at 18°C than at 32°C in D. ananassae. The genetic variations for all the quantitative and life-history traits were higher at low temperature. Variation in sexual traits was more pronounced as compared with other morphometric traits, which shows that sexual traits are more prone to thermal stress. Our results agree with the hypothesis that genetic variation is increased in stressful environments.

Variation in the subtle differences between the right and left sides of bilateral characters or fluctuating asymmetry (FA) has been considered as an indicator of an organism’s ability to cope with genetic and environmental stresses during development. However, due to inconsistency in the results of empirical studies, the relationship between FA and stress has been the subject of intense debate. In this study, we investigated whether stress caused by artificial bidirectional selection for body size has any effect on the levels of FA of different morphological traits in Drosophila ananassae. The realised heritability (h²) was higher in low-line females and high-line males, which suggests an asymmetrical response to selection for body size. Further, the levels of FA were compared across 10 generations of selection in different selection lines in both sexes for sternopleural bristle number, wing length, wing-to-thorax ratio, sex combtooth number and ovariole number. The levels of FA differed significantly among generations and selection lines but did not change markedly with directional selection. However, the levels of FA were higher in the G10 generation (at the end of selection) than G0 (at the start of selection) but lower than the G5 generation in different selection lines, suggesting that the levels of FA are not affected by the inbreeding generated during the course of selection. Also, the levels of FA in the hybrids of high and low lines were significantly lower than the parental selection lines, suggesting that FA is influenced by hybridisation. These results are discussed in the framework of the literature available on FA and its relationship with stress.