Parkash R, Sharma V, Kalra B. Climatic adaptations of body melanisation in Drosophila melanogaster from Western Himalayas. Fly

Department of Biochemistry and Genetics, Maharshi Dayanand University, Rohtak, India.
Fly (Impact Factor: 3.33). 06/2008; 2(3):111-7. DOI: 10.4161/fly.6351
Source: PubMed


We investigated population divergence in body melanisation in wild samples of Drosophila melanogaster across an elevational gradient (512-2202 m) in the Western Himalayas. Wild populations are characterized by higher phenotypic variability as compared with laboratory populations. Significant differences in elevational slope values for three posterior abdominal segments (fifth, sixth and seventh) in wild versus laboratory populations suggest plastic effects. However, elevational slope values do not differ for the three anterior abdominal segments (second, third and fourth). Thus, elevational changes in melanisation include genetic as well as plastic effects. Fitness consequences of within population variability were analyzed on the basis of assorted darker and lighter flies from two highlands as well as from two lowland localities. There is lack of correlation of melanisation with body size as well as ovariole number in assorted darker and lighter flies. For each population, darker flies showed higher desiccation resistance, lower rate of water loss, longer copulation duration and greater fecundity as compared with lighter flies. Phenotypic variations in body melanisation can be interpreted in relation with seasonal changes in temperature as well as humidity (Tcv and RHcv) of the sites of origin of populations. Thus, elevational changes in body melanisation may represent genetic response to selection pressures imposed by colder and drier climatic conditions in the Western Himalayas.

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Available from: Bhawna Kalra, Oct 09, 2015
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    • "This is facilitated by tools available in model organisms, including D. melanogaster, which allow the expression of specific genes to be modified, and effects of polymorphisms to be assessed in controlled backgrounds. A combination of approaches has allowed the adaptive significance of particular genetic changes to be identified: for instance, expression of the ebony gene affects body pigmentation (Pool and Aquadro, 2007; Telonis- Scott et al., 2011), which in turn may influence fitness under different climatic conditions (Parkash et al., 2008) and shows clinal patterns (Telonis-Scott et al., 2011); a set of polymorphisms in the regulatory region influences expression of this gene (Takahashi and Takano-Shimizu, 2011). The genus Drosophila itself and related genera contain an enormous range of species adapted to different climatic regions. "
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    • "Individuals of several species have been shown to be darker when reared at lower temperatures (for example, butterflies and hoverflies: Marriott & Holloway, 1998). While geographic variation in melanism and body size has been studied separately, they have rarely been considered together, even though many authors invoke a thermal explanation for the observed patterns (but see Guppy, 1986; Parkash et al., 2008, 2010). To determine whether intraspecific body size clines in ectotherms reflect local adaptations to thermal conditions (Mayr, 1956; Endler, 1977; Gardner et al., 2009), we need to consider not only body size, but colour as well, because together they influence the thermal conditions experienced by an organism. "
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    ABSTRACT: Aim We explore geographic variation in body size within the wingless grasshopper, Phaulacridium vittatum, along a latitudinal gradient, and ask whether melanism can help explain the existence of clinal variation. We test the hypotheses that both male and female grasshoppers will be larger and lighter in colour at lower latitudes, and that reflectance and size will be positively correlated, as predicted by biophysical theory. We then test the hypothesis that variability in size and reflectance is thermally driven, by assessing correlations with temperature and other climatic variables. Location Sixty-one populations were sampled along the east coast of Australia between latitudes 27.63° S and 43.10° S, at elevations ranging from 10 to 2000 m a.s.l. Methods Average reflectance was used as a measure of melanism and femur length as an index of body size for 198 adult grasshoppers. Climate variables were generated by BIOCLIM for each collection locality. Hierarchical partitioning was used to identify those variables with the most independent influence on grasshopper size and reflectance. Results Overall, there was no simple relationship between size and latitude in P. vittatum. Female body size decreased significantly with latitude, while male body size was largest at intermediate latitudes. Rainfall was the most important climatic variable associated with body size of both males and females. Female body size was also associated with radiation seasonality and male body size with reflectance. The reflectance of females was not correlated with latitude or body size, while male reflectance was significantly higher at intermediate latitudes and positively correlated with body size. Analyses of climate variables showed no significant association with male reflectance, while female reflectance was significantly related to the mean temperature of the driest quarter. Main conclusions Geographic variation in the body size of the wingless grasshopper is best explained in terms of rainfall and radiation seasonality, rather than temperature. However, melanism is also a significant influence on body size in male grasshoppers, suggesting that thermal fitness does play a role in determining adaptive responses to local conditions in this sex.
    Journal of Biogeography 08/2012; 39(8). DOI:10.1111/j.1365-2699.2012.02710.x · 4.59 Impact Factor
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    • "For instance, melanism tends to be higher in ectotherms from cool environments (Clusella Trullas et al. 2007), assisting species in achieving higher body temperatures for activity. Insects with a high level of melanism might also benefit from a decrease in the rate of water loss, leading to an increase in desiccation resistance (Parkash et al. 2008). Under hot conditions melanism is likely to be a disadvantage for species because dark individuals tend to warm up relatively more quickly and then become heat stressed. "
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    ABSTRACT: Many insects are climate specialists – restricted to a narrow range of latitudes, humidity conditions and/or altitudes. Yet there are also numerous climate generalists, whose distribution might span from the tropics to temperate areas. Comparisons of related insect species normally indicate that the resistance of species to climatic extremes and reproductive output under different climatic conditions match expectations based on their distributions. Yet these patterns do not ultimately explain why climate specialists and generalists have evolved over time. Three evolutionary hypotheses that are invoked to explain climate specialisation are (1) constraints arising from antagonistic pleiotropy (costs); (2) DNA decay due to mutational processes; and (3) the difficulty of adapting due to the requirement of multidimensional changes or because of gene flow. Here I outline these hypotheses, and consider predictions and supporting evidence from several sources including polymorphism studies, quantitative genetic studies, species comparisons and genomic comparisons. All three explanations are likely to contribute to climate specialisation and the DNA decay/multidimensional adaptation hypotheses deserve more consideration.
    Australian Journal of Entomology 04/2010; 49(2):93 - 103. DOI:10.1111/j.1440-6055.2010.00744.x · 1.01 Impact Factor
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