Abstract
We conducted a laboratory based selection experiment with two allopatric populations of Drosophila ananassae collected from two isolated geographic regions of India, namely Mysuru and Port Blair. The populations were infected enterically with the bacteria Pseudomonas aeruginosa for 55 generations followed by rearing for the next 10 generations under relaxed selection. We tested development of immune-competence of the selected flies through the generations and inquired if elicitation of immune responses were needed to pay cost by trading-off with life history and morphological traits and observed progressive increase in immune response in the selected flies, which also exhibited gradual increase in survival, reproductive life span, post-reproductive life span, developmental time, fecundity rate, fat content in contrast to body length and water content that exhibited longitudinal decrease. Under relaxed selection regime the traits showed reversion of the trend but not to the basal level. Responses exhibited by the selected flies from Port Blair and Mysuru differed, with the former group exhibiting more reduction in body length, more reduction in water content, greater antioxidant enzyme activity, longer post-infection period, greater survival than the later group. On the other side, Mysuru flies showed greater fat deposition, faster developmental time and longer oviposition time than Port Blair flies. Interestingly, Port Blair flies exhibited an increase in post-ovipository period, in contrast to Mysuru flies that showed a decrease for the same. We inferred that two allopatric populations of D. ananassae from the Indian sub-continent show different trade-off between evolving immune response and life history traits. Further, the outcome of our study leads us to a point of realization how allopatric populations of a given species respond differently under given selection pressure and gradually diverge from each other in nature to develop a species barrier.
Published Version
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