Evol Ecol Res 19: 15-28 (2018)     Full PDF if your library subscribes.

Rugged fitness landscapes and by-product adaptation
in experimental populations of Drosophila melanogaster

Devin Arbuthnott¹, Brian S. Mautz² and Howard D. Rundle³

¹Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, Canada,  ²Department of Animal Ecology, Uppsala University, Uppsala, Sweden and  ³Department of Biology, University of Ottawa, Ottawa, Ontario, Canada

Correspondence: D. Arbuthnott, Department of Zoology and Biodiversity Research Centre, University of British Columbia, 4200–6270 University Boulevard, Vancouver, BC V6T 1Z4, Canada. email: darbuthnott@gmail.com

ABSTRACT

Background: While the concept of the fitness landscape is central to evolutionary theory, empirical characterizations of fitness landscapes have remained difficult. Recently, a number of laboratory experiments using microbes have suggested that fitness landscapes are often rugged, though there is some variation across environments and species. However, there have been very few characterizations of fitness landscapes in sexual organisms, making it unclear whether the conclusions from studies of microbes are applicable to other groups.

Questions: Are fitness landscapes smooth or rugged in simplified laboratory environments for sexual organisms? How does landscape topography influence patterns of adaptation?

Methods: We conducted a series of experiments using replicate populations of Drosophila melanogaster adapted to either cadmium- or ethanol-enriched food to characterize the fitness and phenotypes of these populations in a simplified laboratory environment (ethanol-enriched media).

Results: We found that replicate populations adapted to different laboratory environments have diverged phenotypically in physiology, mating behaviour, and offspring production in alternate environments. However, both ethanol- and cadmium-adapted populations show high fitness in the ethanol-enriched environment relative to their founding population, and cadmium-adapted males actually outcompete ethanol-adapted males for mates in an ethanol environment.

Conclusions: Our data indicate that the simplified ethanol-enriched medium represents a rugged fitness landscape, and that alternately adapted populations occupy different fitness peaks on this landscape. Because cadmium-adapted populations were never exposed to ethanol previously, it appears that these populations adapted to ethanol as a by-product of adaptation to their cadmium-enriched environment. Therefore, even in simplified laboratory environments, we find evidence for rugged fitness landscapes, and the overlap of fitness peaks on the phenotypic landscape allowed for by-product adaptation.

Keywords: adaptation, ecological divergence, ethanol, mate competition.

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