Variations in morphological and life-history traits under extreme temperatures in Drosophila ananassae.
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2009-06
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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 signifi cantly 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 refl ect 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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Sisodia Seema, Singh B N. Variations in morphological and life-history traits under extreme temperatures in Drosophila ananassae. Journal of Biosciences. 2009 Jun; 34(2): 263-274.