ALTITUDINAL ADAPTIVE CHANGES IN ASSORTED PHENOTYPIC GROUPS OF ABDOMINAL MELANIZATION EVIDENCE CORRELATED REPRODUCTIVE SUCCESS IN DROSOPHILA IMMIGRANSVEER BHAN
Climatic stresses impose strong natural selection that may cause rapid phenotypic changes in body melanization with correlated changes in reproductive traits. In the present studies, six altitudinal populations of D. immigrans were assorted into non-overlapping phenotypic groups of body melanization (i.e. less dark [<30%], intermediate [35-50 %] and darker [>55 %]) and were investigated for correlated changes in reproductive fitness related traits (copulation duration and fecundity). Populations with increasing melanization display longer copulation duration and increased egg production. A simultaneous analysis of fitness traits on assorted categories of body melanization provided parallel changes on the basis of significant phenotypic correlations both within and between populations. Simple regression analysis helped in comparing slope values for all the three phenotypic categories for melanization with copulation duration and fecundity. Local climatic conditions (i.e. annual temperature and relative humidity) vary significantly with altitude and exert differential selection pressures on phenotypic traits. Such observations are in agreement with the thermal budget hypothesis and result in maintenance of a high reproductive success under colder conditions. Present investigations suggest a role of body melanization in maintaining the reproductive success in altitudinal populations of D. immigrans.
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