Climate structures genetic variation across a species' elevation range: a test of range limits hypotheses

Area of Science:

• Ecology
• Evolutionary Biology
• Conservation Genetics

Background:

• Understanding gene flow is crucial for predicting species range limits, especially with rapid environmental change.
• Patterns of gene flow relative to environmental gradients and range edges remain poorly understood.
• Conservation efforts require knowledge of how gene flow influences species distribution.

Purpose of the Study:

• To investigate gene flow patterns in Mimulus laciniatus across its elevation-based climate range in the California Sierra Nevada.
• To assess the influence of environmental gradients and proximity to range limits on genetic variation and gene flow.
• To test common center-edge hypotheses regarding species range formation.

Main Methods:

• Assessed genetic variation, gene flow, and population abundance across the entire elevation range of Mimulus laciniatus.
• Analyzed genetic differentiation and contemporary gene flow between central and peripheral populations.
• Investigated isolation by environment and isolation by distance across the species range.

Main Results:

• Contrary to expectations, population density increased towards both high and low elevation climate limits.
• Edge populations showed less genetic diversity than neighboring interior populations, though overall mean genetic diversity was equivalent.
• Gene flow was primarily driven by elevation (isolation by environment), not distance, with no directional contemporary gene flow signals detected.

Conclusions:

• Climate, specifically elevation-driven environmental gradients, is a key factor structuring Mimulus laciniatus populations across its range.
• Findings contradict common center-edge hypotheses related to decreasing habitat quality, population size, or gene flow swamping.
• This study is the first to empirically link environmental patterns of gene flow to range limit hypotheses, highlighting the need for similar studies across diverse taxa.