title: Ecosystem size matters: the dimensionality of intralacustrine diversification in Icelandic stickleback is predicted by lake size.
abstract: Cases of evolutionary diversification can be characterized along a continuum from weak to strong genetic and phenotypic differentiation. Several factors may facilitate or constrain the differentiation process. Comparative analyses of replicates of the same taxon at different stages of differentiation can be useful to identify these factors. We estimated the number of distinct phenotypic groups in three-spine stickleback populations from nine lakes in Iceland and in one marine population. Using the inferred number of phenotypic groups in each lake, genetic divergence from the marine population, and physical lake and landscape variables, we tested whether ecosystem size, approximated by lake size and depth, or isolation from the ancestral marine gene pool predicts the occurrence and the extent of phenotypic and genetic diversification within lakes. We find intralacustrine phenotypic diversification to be the rule rather than the exception, occurring in all but the youngest lake population and being manifest in ecologically important phenotypic traits. Neutral genetic data further indicate nonrandom mating in four of nine studied lakes, and restricted gene flow between sympatric phenotypic groups in two. Although neither the phenotypic variation nor the number of intralacustrine phenotypic groups was associated with any of our environmental variables, the number of phenotypic traits that were differentiated was significantly positively related to lake size, and evidence for restricted gene flow between sympatric phenotypic groups was only found in the largest lakes where trait specific phenotypic differentiation was highest.
authors.affiliation: Aquatic Ecology and Evolution Institute of Ecology and Evolution University of Bern Baltzerstrasse 6CH-3012 Bern Switzerland; Department of Fish Ecology and Evolution EAWAG Swiss Federal Institute of Aquatic Science and Technology Center for Ecology, Evolution and Biogeochemistry CH-6047 Kastanienbaum Switzerland; Department of Animal and Plant Sciences University of Sheffield Sheffield UK.
authors.forename: Kay
authors.initials: K
authors.lastname: Lucek
authors.affiliation: Department of Aquaculture and Fish Biology Hólar University College 550 Saudárkrókur Iceland.
authors.forename: Bjarni K
authors.initials: BK
authors.lastname: Kristjánsson
authors.affiliation: Department of Aquaculture and Fish Biology Hólar University College 550 Saudárkrókur Iceland.
authors.forename: Skúli
authors.initials: S
authors.lastname: Skúlason
authors.affiliation: Aquatic Ecology and Evolution Institute of Ecology and Evolution University of Bern Baltzerstrasse 6CH-3012 Bern Switzerland; Department of Fish Ecology and Evolution EAWAG Swiss Federal Institute of Aquatic Science and Technology Center for Ecology, Evolution and Biogeochemistry CH-6047 Kastanienbaum Switzerland.
authors.forename: Ole
authors.initials: O
authors.lastname: Seehausen
keywords: Ecological speciation; Gasterosteus aculeatus; multivariate evolution; speciation continuum