High and distinct range-edge genetic diversity despite local bottlenecks

Area of Science:

• Marine Biology
• Population Genetics
• Ecology

Background:

• The genetic consequences for populations at the edges of their distributional ranges remain debated.
• Rear-edge populations are often expected to retain unique genetic diversity, but environmental pressures may cause genetic erosion.
• Understanding these patterns is crucial for predicting adaptive capacity and species' responses to climate change.

Purpose of the Study:

• To empirically test if population declines at range edges correlate with reduced genetic diversity and increased isolation.
• To investigate the genetic differentiation and diversity of Saccorhiza polyschides along a latitudinal gradient towards its southern range edge.
• To assess the influence of recent distributional shifts and population declines on genetic diversity and effective population size.

Main Methods:

• Compared population genetic differentiation and diversity with abundance trends across a latitudinal gradient.
• Analyzed genetic data for Saccorhiza polyschides, a key kelp forest species in SW Europe.
• Evaluated genetic signatures of recent bottleneck events to assess the impact of distributional shifts.

Main Results:

• Observed decreasing population density, increasing spatial fragmentation, and local extinctions towards the southern range edge.
• Genetic data identified two distinct population groups with a central contact zone.
• Found higher genetic differentiation and evidence of bottlenecks in the southern edge region, but no decrease in overall genetic diversity.

Conclusions:

• Contrary to expectations, genetic diversity increased towards the southern range edge despite population declines and bottlenecks.
• This suggests that extinction and recolonization dynamics may not have severely reduced diversity, or past diversity was higher.
• The findings highlight a potential process of shifting genetic baselines at range peripheries.