Variations in body melanisation, ovariole number and fecundity in highland and lowland populations of Drosophila melanogaster from the Indian subcontinent

Abstract

We investigated geographical variations in three fitness‐related traits (body melanisation, ovariole number and fecundity) in laboratory‐reared offspring of 10 populations of Drosophila melanogaster. The populations were collected from adjacent lowland and highland localities (∼80–100 km apart) in the tropical as well as subtropical regions (11.15–31.06 °N) covering a linear distance about 3 000 kilometers from south to north on the Indian subcontinent. Persistence of within‐as well as between‐population differences at 21 °C suggest that observed variations in fitness‐related traits have a genetic basis. Populations from higher altitudes showed consistently higher trait values (1.4‐fold increase) as compared with their corresponding lowland populations. By contrast, latitudinal variations were about two‐fold higher across the entire continent. Along latitude as well as altitude, population means showed higher correlation values (r > 0.98) between all the three fitness traits. However, on the basis of within‐population analysis (assorted darker and lighter flies), changes in body melanisation were significantly correlated with fecundity but not with ovariole number. Thus, analysis of within‐population trait variability should be preferred as compared with data on population means for adaptive significance of fitness‐related traits. In the present study, the role of climatic selection is evident from regression analysis with changes in annual average temperature of the sites of origin of populations along latitude as well as altitude.

Intraspecific variation in wing and pupal melanization in copper butterflies (Lepidoptera: Lycaenidae)

“…An increasing wing or body melanization with increasing altitude or latitude was found earlier in a number of insects (Munjal et al, 1997;Pool & Aquadro, 2007;Rajpurohit et al, 2008). In the present study, we show a parallel pattern for pupal melanization in two related butterfly species, L. hippothoe and L. tityrus.…”

“…Patterns were similar across species, although the difference between lowand high-altitude populations was more pronounced in L. hippothoe. The recurrent pattern of darker phenotypes being associated with cooler environments is strongly indicative of directional thermal selection on pigmentation (Pool & Aquadro, 2007;Rajpurohit et al, 2008). However, most studies investigating variation in pupal melanization were placed within the context of selection for inconspicuousness because pupae are potentially easy targets for visually oriented predators (Wiklund & Sillentullberg, 1985;Ferreira, Garcia & de Araujo, 2006;Jones et al, 2007).…”

The costs of being dark: the genetic basis of melanism and its association with fitness‐related traits in the sand cricket

“…More convincing evidence comes from common garden experiments that compare variation among and within populations, the former demonstrating genetic variance for the traits and the latter a trade‐off at the level of the phenotype. Positive phenotypic correlations between melanization and fecundity have been demonstrated in Drosophila melanogaster (Rajpurohit et al ., ) and D. immigrans (Singh et al ., ). These results are clearly at variance with the trade‐off hypothesis.…”

Convergent evolution of a reproductive trait through distinct developmental mechanisms in Drosophila

“…However, average ovariole number in both Ds (15.2) and Ind (24.8) are below the ancestral range, indicating that ovariole number was independently reduced in both of these lineages. To address the possibility that Ind represents a segregating variant of the North American D. melanogaster range, we note that ovariole numbers in Indian populations (Rajpurohit et al, 2008) are, on average, smaller than those in North American populations (Capy et al, 1993). We also counted ovariole number in five additional D. melanogaster strains from North America, and found that their average ovariole numbers were always higher than those for Ind (Table 1).…”