Genetic signatures of historical bottlenecks in sympatric lake trout (Salvelinus namaycush) morphotypes in Lake Superior

Abstract

Humans have played a significant role in reducing levels of genetic diversity and differentiation of many teleost fishes, leading to homogenization across biological entities. We compare patterns of historical and contemporary genetic structure for three sympatric Great Lake’s lake trout (Salvelinus namaycush) morphs (lean, siscowet, and humper) that differ in patterns of habitat occupancy, susceptibility to overfishing and predation by invasive sea lamprey (Petromyzon marinus). Differential susceptibilities to overfishing and predation were expected to result in different impacts to levels of genetic diversity loss for each morphotype. Genetic data was collected for samples at three points in time: 1948 (pre-collapse), 1959 (collapse) and 1990s (current), corresponding to periods of intensive fishing, mortality due to lamprey and recovery, respectively. The lean morph preferentially targeted by the fishery and recognized as highly preyed upon by sea lamprey was more highly impacted genetically than other morphs, as evidenced by greater loss of genetic diversity first during the period of overfishing, then during the period of high sea lamprey abundance once the fishery collapsed. The siscowet morph also experienced genetic bottlenecks during the period of overfishing (pre-collapse period). Results indicate significant levels of genetic differentiation among morphs historically prior to declines in abundance and also among contemporary populations, suggesting that periods of population decline and resurgence in abundance and distribution did not result in loss of genetic distinctiveness among morphs.