Genetic Diversity, Population Divergence and Effective Number of Breeders in Introduced Rainbow Trout Oncorhynchus mykiss in Two Patagonian Lakes with Different Effects of Trout Farming

Recent studies have shown that propagule pressure from trout farming escapees may drive significant changes in genetic diversity and population divergence among self-sustained introduced populations, and thus possibly influencing dispersal, connectivity and the effective number of breeders (Nb). Here we evaluate differences in genetic diversity, population divergence and Nb among two contrasting lakes that rainbow trout (RT, Oncorhynchus mykiss) inhabit in northern Patagonia: a) Lake Llanquihue, Chile’s largest producer of RT smolts; and b) Lake Todos Los Santos (TLS), where farming is forbidden by law. Over two years we genotyped 1,390 trout from inlet streams within each lake using a panel of 94 single nucleotide polymorphisms. We found higher expected heterozygosities within Lake Llanquihue than Lake TLS; genetic divergence between inlets was similar within each lake, but genetic divergence was large between lakes, possibly suggesting two different sources of introduction. We also detected small numbers of effective breeders (Nb: 16–131) within both lakes, pointing to recently founded populations, but no significant differences in Nb between lakes. Collectively, our findings imply that propagule pressure from aquaculture may increase genetic diversity, but may not differentially influence population divergence and Nb between systems affected and unaffected by trout farming.