Populations occurring along low latitude ranges are expected to retain high and unique genetic diversity because they persisted throughout the last glacial period and until our times. However, recent climate change is producing range shifts at the edge of distributions, where changes on the limiting niche of species is leading to the extinction of many populations of distinct species. Such processes may erode the genetic diversity of populations, a process that prevails over past historical effects and with potential consequences on reducing future adaptive capacity.

Using a kelp species (Saccorhiza polyschides) as a model, we tested if a decline in population abundance towards the range edge may be reflected on decreasing diversity and increasing population isolation and differentiation. We also evaluated the signatures of recent bottleneck events to determine whether the recently recorded range shifts had a negative influence on effective population size.

We report a decrease in population density and an increase in spatial fragmentation and local extinctions towards the range edge. As predicted, higher differentiation and signs of bottlenecks were found at the edge region. However, a decrease in genetic diversity associated with this pattern was not verified. Surprisingly, genetic diversity increased towards the edge despite bottlenecks and much lower densities</>, suggesting that extinctions and recolonizations have not strongly reduced diversity or that diversity might have been even higher there in the past, a process we branded as shifting genetic baselines.