Impact of Spatial Heterogeneity on Drosophila melanogaster Adaptation to Unfavourable Food Media: The Results of an Experimental Evolution Study

Abstract

The spatiotemporal variability of environmental conditions is assumed to have a strong impact on the course of microevolution processes, including the efficiency of adaptation to unfavourable conditions and the probability of ecological specialization or, conversely, generalization (the acquisition of multipurpose adaptations). The experimentаl research on these effects is still at the initial stage, and the temporal, rather than spatial, heterogeneity of the environment is analyzed in most studies. We performed an evolution experiment that involved the adaptation of Drosophila melanogaster lines to two unfavourable media: a high-salt (S) medium and a starch-based (St) medium of low nutritional value. Some of the experimental lines had access to one of the two unfavourable media only (homogeneous environment), whereas the others had access to both media and could choose between them (heterogeneous environment). The control lines were reared on a normal laboratory medium (N) that provided favourable conditions for the species. The degree of adaptation of lines obtained on the S, St, and N media was assessed after one and a half years of adaptation. The reproduction efficiency (the amount of adult progeny derived from a pair of parents within a specified time interval), adult lifespan, oviposition rate, and ageing-related changes in the former were assessed. Flies reared in a heterogeneous environment were superior to those reared in a homogeneous one with regard to most adaptation parameters on all three media. The results agree with the hypothesis concerning the promotion of generalization and more efficient adaptation to unfavourable conditions upon spatial heterogeneity of the environment. The obtained data do not support the hypothesis of antagonistic pleiotropy, which leads to “evolutionary trade-offs” and a lower competitiveness of generalists than that of specialists under stable conditions.