Seema Ramniwas

Publications (13) View all

• Article: Direct and correlated responses to laboratory selection for body melanisation in D. melanogaster: support for melanism- desiccation resistance hypothesis.

  Seema Ramniwas, Babita Kajla, Kapil Dev, Ravi Parkash
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  ABSTRACT: For Drosophila melanogaster, cuticular melanisation is a quantitative trait, varying from no melanin to complete dark. Variation in melanisation has been linked with stress resistance, especially desiccation, in D. melanogaster and other species. As melanism has a genetic component, we selected melanic and non- melanic phenotypes of D. melanogaster, in order to confirm the association of desiccation resistance and rate of water loss with cuticular melanisation previously reported for this species. A bidirectional selection experiment for dark (D1- D4) and light (L1- L4) body color in D. melanogaster was conducted for 60 generations. In 60 generations of selection for pigmentation, an increase of 1.6 fold in selected dark strain and decrease of 14 folds in selected light strain was observed as compared to control populations. Desiccation hour increased significantly in the dark selected morphs as compared with control. The observed increase in desiccation resistance appeared as a consequence of decrease in cuticular permeability. Our results show that water balance related traits were significantly correlated with abdominal melanisation and were simultaneously selected bidirectionally along with melanisation.
  Journal of Experimental Biology 12/2012; · 3.00 Impact Factor
• Article: Divergent strategy for adaptation to drought stress in two sibling species of montium species subgroup: Drosophila kikkawai and Drosophila leontia.

  Seema Ramniwas, Babita Kajla
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  ABSTRACT: Drosophila leontia (warm adapted) has been considered as a sister species of Drosophila kikkawai (sub-cosmopolitan) with a very similar morphology. We found divergent strategies for coping with desiccation stress in these two species of montium subgroup. Interestingly, in contrast to clinal variation for body melanization in D. kikkawai, cuticular lipid mass showed a positive cline in D. leontia across a latitudinal transect. On the basis of isofemale line analysis, within population trait variability in cuticular lipid mass per fly is positively correlated with desiccation resistance and negatively correlated with cuticular water loss in D. leontia. A comparative analysis of water budget of these two species showed that higher abdominal melanization, reduced rate of water loss and greater dehydration tolerance confer higher desiccation resistance in D. kikkawai while the reduced rate of water loss is the only possible mechanism to enhance desiccation tolerance in D. leontia. The use of organic solvents has supported water proofing role of cuticular lipids in D. leontia but not in D. kikkawai. Thus, we may suggest that body melanization and cuticular lipids may represent alternative strategies for coping with dehydration stress in melanic versus non-melanic drosophilids. In both these species, carbohydrates were utilized under desiccation stress but a higher level of stored carbohydrates was evident in D. kikkawai. Further, we found increase desiccation resistance in D. kikkawai through acclimation while D. leontia lacks such a response. Thus, species specific divergence in water balance related traits in these species are consistent with their adaptations to wet and dry habitats.
  Journal of insect physiology 09/2012; · 2.24 Impact Factor
• Article: Divergence of desiccation-related traits in two Drosophila species of the takahashii subgroup from the western Himalayas.

  Ravi Parkash, Seema Ramniwas, Babita Kajla, Dau Dayal Aggarwal
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  ABSTRACT: Drosophila nepalensis is more abundant under colder and drier montane habitats in the western Himalayas compared with Drosophila takahashii, but the mechanistic basis of such a climatic adaptation is largely unknown. We tested the hypothesis that divergence in the physiological basis of desiccation-related traits is consistent with species-specific adaptations to climatic conditions. Drosophila nepalensis showed approximately twofold higher desiccation resistance, hemolymph content as well as carbohydrate content than D. takahashii despite a modest difference in rate of water loss (0.3% h(-1)). Water loss before succumbing to death (dehydration tolerance) was much higher in D. nepalensis (82.32%) than in D. takahashii (∼50%). A greater loss of hemolymph water under desiccation stress until death is associated with higher desiccation resistance in D. nepalensis. In both species, carbohydrates were utilized under desiccation stress, but a higher level of stored carbohydrates was evident in D. nepalensis. Further, we found increased desiccation resistance in D. nepalensis through acclimation whereas D. takahashii lacked such a response. Thus, species-specific divergence in water-balance-related traits in these species is consistent with their adaptations to wet and dry habitats.
  Journal of Experimental Biology 07/2012; 215(Pt 13):2181-91. · 3.00 Impact Factor
• Article: Adaptive changes in the plasticity of body melanisation of generalist, cold and warm adapted Drosophila species.

  Ravi Parkash, Seema Ramniwas, Chanderkala lambhod, Babita kajla
  Acta Entomologica sinica. 08/2011;
• Article: Fitness consequences of body melanization in Drosophila immigrans from montane habitats

  Shama SINGH, Seema RAMNIWAS, Ravi PARKASH
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  ABSTRACT: We investigated eight populations of Drosophila immigrans from low to high montane localities (600–2202 m) for altitudinal variations in abdominal melanization and fitness-related traits (desiccation resistance, copulation duration, and fecundity). On the basis of common garden experiments, persistence between-population differences at 21°C suggests that observed variations in fitness-related traits have a genetic basis. Parent–offspring regression analyses showed higher heritability (h2= 0.77) for melanization patterns on all the abdominal tergites. All the traits showed significantly higher repeatability across generations. Under colder and drier environments in dispersed montane localities, abdominal melanization and desiccation resistance significantly increased (1.5–1.9 fold) along altitude. Thus, there are correlated effects of abdominal melanization on desiccation resistance. Genetic correlations, based on family means, were significantly high between abdominal melanization and other fitness traits. Furthermore, darker flies along increasing altitude resulted in a 35–40% increase in copulation duration as well as fecundity. There are significantly positive correlations of abdominal melanization with copulation duration as well as fecundity on the basis of within- as well as between-population variations. Such observations are in agreement with the thermal budget hypothesis. Present data suggest that changes in body melanization impact fitness-related traits in montane populations of Drosophila immigrans.
  Entomological Research 05/2009; 39(3):182 - 191.