Fitness differences and persistent founder effects determine the clonal composition during population build-up in Daphnia

• Published in: Oikos Vol. 124; no. 5; pp. 620 - 628
• Main Authors: Thielsch, Anne, Glass, Nicole, Streit, Bruno, Meester, Luc De, Ortells, Raquel, Schwenk, Klaus
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.05.2015; Nordic Society Oikos
• Subjects: Cloning; Evolution; Insects; Population genetics
• ISSN: 0030-1299; 1600-0706
• DOI: 10.1111/oik.01575

During the initial stages of population build-up in new habitats, the time at which immigrants arrive may influence their contribution to the population and thus determine population genetic structure. While the numerical advantage associated with founder effects may promote dominance of the offspring of early colonizers, fitness differences associated with ecological differences among genotypes may potentially overwhelm these founder effects. We conducted an outdoor mesocosm experiment to test whether the sequence of arrival determines the relative contribution of genetic lineages (clones) to populations of the water flea Daphnia. A set of D. galeata clones was inoculated pairwise in different time sequences and clonal abundances were monitored over time. In general, we found that, after six weeks (four generations), clones with an initial time advantage of five or fifteen days (1/3 of a generation or one generation) had higher relative abundances than in the treatments with simultaneous inoculations. These differences were in some cases maintained over a longer period (nine months). However, in cases where abundances of genetic lineages varied strongly when inoculated simultaneously, reflecting strong differences in fitness among clones in our experimental containers, initial numerical advantages could be overwhelmed and the competitively strongest clone became dominant after nine months independently of inoculation sequence. Our results highlight the importance of two different processes that determine the fate of clonal lineages and ultimately determine population genetic structure. First, the sequence of arrival is crucial, with an advantage of five days being already sufficient to dominate the population in specific cases. Second, if fitness differences among clones are sufficiently strong, then they may overrule founder effects.