Adaptability of lake charr (Salvelinus namaycush) in a changing world: newly recolonized landscapes reveal the significance of traits shaped during the Pleistocene

Abstract

Lake charr (Salvelinus namaycush), one of the most widely distributed freshwater species in northern North America (currently in about 5200 lakes), evolved as a distinct species more than 3 M years ago in the Pliocene era. It then further diversified and adapted to the extremely harsh conditions throughout the repeated glacial cycles of the Pleistocene. Our study examines how its ancient traits, such as thermal tolerance, longevity, iteroparity, mobility and omnivory, allowed lake charr to colonize recently created lakes at the southern extent of its range when the land rose through isostatic rebound to isolate individual small lakes. A second challenge to the adaptability of these charr populations occurred with the depopulation of many of these same lakes in our study area through severe acid deposition from the massive Sudbury metal smelters that began operation in the 1920s. The regional air pollution disturbances lasted for nearly 60 years before government-imposed pollution controls and the resulting improving water quality allowed lake charr to be re-established or to begin to naturally recolonize many of these lakes. This case history of recovery helps us better understand the inherent adaptability of lake charr to challenging conditions while also considering the likely adverse effects of new disturbances such as climate change and the arrival of warm-water invasive species. It reinforces the need to protect critical habitat features, such as cold, well-oxygenated refuge areas.