Adaptation to larval crowding in Drosophila ananassae and Drosophila nasuta

37 The standard view of adaptation to larval crowding in fruitflies, built on results from 25 38 years of multiple experimental evolution studies on D. melanogaster, is that enhanced 39 competitive ability evolves primarily through increased larval feeding and foraging rate, at 40 the cost of efficiency of food conversion to biomass, and increased larval tolerance to 41 nitrogenous wastes. These results, moreover, were at odds from the predictions of classical 42 K-selection theory, notably the expectation that selection at high density should result in 43 the increase of efficiency of conversion of food to biomass, and were better interpreted 44 through the lens of α-selection. We show here that populations of D. ananassae and D. n. 45 nasuta subjected to extreme larval crowding evolve greater competitive ability and pre46 adult survivorship at high density primarily through a combination of reduced larval 47 duration, faster attainment of minimum critical size for pupation, greater time efficiency 48 of food conversion to biomass, increased pupation height with a relatively small role of 49 increased urea/ammonia tolerance, if at all. This is a very different suite of traits than that 50 seen to evolve under similar selection in D. melanogaster and seems to be closer to the 51 expectations from the canonical theory of K-selection. We discuss possible reasons for 52 these differences in results across the three species. Overall, the results reinforce the view 53 that our understanding of the evolution of competitive ability in fruitflies needs to be more 54 nuanced than before, with an appreciation that there may be multiple evolutionary routes 55 through which higher competitive ability can be attained. 56 peer-reviewed) is the author/funder. All rights reserved. No reuse allowed without permission. The copyright holder for this preprint (which was not . http://dx.doi.org/10.1101/011684 doi: bioRxiv preprint first posted online Nov. 20, 2014;