Variations in morphological and life-history traits under extreme temperatures in <Emphasis Type="Italic">Drosophila ananassae</Emphasis> |
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Authors: | Seema Sisodia B N Singh |
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Institution: | (1) Genetics Laboratory, Department of Zoology, Banaras Hindu University, Varanasi, 221 005, India |
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Abstract: | 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. |
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Keywords: | Drosophila ananassae genetic variation morphometric and life-history traits stressful temperatures |
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