| Summary: | Ecological opportunity is considered a crucial factor for adaptive radiation. Here, we combine genetic, morphological and ecological data to assess species and ecomorphological diversity of Artic charr in six lakes of a catchment in southernmost Greenland, harbouring only charr and stickleback. Because the diversity of habitats and resources increases with lake size, we predict a positive association between lake size and the extent of ecomorphological diversity. The largest lake of the catchment harbours the largest Arctic charr assemblage known today. It consists of six genetically differentiated species belonging to five ecomorphs (anadromous, littoral benthic, profundal dwarf, planktivorous, piscivorous), of which the latter comprises two ecomorphologically extremely similar species. Lakes of intermediate size contain two ecomorphologically and genetically distinct species. Small lakes harbour one genetically homogenous, yet sometimes ecomorphologically variable population. Supporting our prediction, lake size is positively correlated with the extent of ecomorphological specialization towards profundal, pelagic and piscivorous lifestyle. Furthermore, assemblage-wide morphospace increases sharply when more than one genetic cluster is present. Our data suggest that ecological opportunity and speciation jointly determine phenotypic expansion in this charr radiation. Individual genetic, morphological and ecological data of Greenlandic charr Individual data on charr diversity in Greelandic lakes. Net_trap_rod indicates the type of fishing: benthic nets are indicated with B, pelagic nets with P, stickleback traps with ST, scoop nets with SN, flyfishing with F, catching a fish with the hand with H. Depth_site indicates the depth of the lake at the site where the fish was caught, Catching_Depth the depth at which the fish was caught. Geno_max indicates the genetic assignment obtained in the hierarchical structure analysis for the full dataset. Cluster1-7 are individual genetic assignments to each of the 7 clusters ...
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