Rapid trait evolution drives increased speed and variance in experimental range expansions

Christopher Weiss-Lehman,Brett A Melbourne,Ruth A Hufbauer

doi:10.1038/ncomms14303

Abstract

Range expansions are central to two ecological issues reshaping patterns of global biodiversity: biological invasions and climate change. Traditional theory considers range expansion as the outcome of the demographic processes of birth, death and dispersal, while ignoring the evolutionary implications of such processes. Recent research suggests evolution could also play a critical role in determining expansion speed but controlled experiments are lacking. Here we use flour beetles (Tribolium castaneum) to show experimentally that mean expansion speed and stochastic variation in speed are both increased by rapid evolution of traits at the expansion edge. We find that higher dispersal ability and lower intrinsic growth rates evolve at the expansion edge compared with spatially nonevolving controls. Furthermore, evolution of these traits is variable, leading to enhanced variance in speed among replicate population expansions. Our results demonstrate that evolutionary processes must be considered alongside demographic ones to better understand and predict range expansions.

Highlights

Range expansions are central to two ecological issues reshaping patterns of global biodiversity: biological invasions and climate change
A third way that spatial evolution can change the dynamics of range expansions is that allele frequencies can be influenced by the small population sizes and repeated founder events associated with the edge of the expanding population, resulting in the recently discovered phenomenon of gene surfing[8,9,10,11,12,13,14,15]
Our results demonstrate the importance of spatial evolutionary changes in determining the dynamics of range expansion over short timescales

Summary

Introduction

Range expansions are central to two ecological issues reshaping patterns of global biodiversity: biological invasions and climate change. We find that higher dispersal ability and lower intrinsic growth rates evolve at the expansion edge compared with spatially nonevolving controls. Evolution of these traits is variable, leading to enhanced variance in speed among replicate population expansions. Increased frequency of deleterious alleles in edge populations is predicted to reduce mean fitness[9,14] and decrease intrinsic growth rates at the edge, regardless of density. These three spatial evolutionary processes could act alone or together to change the speed of a range expansion over time. We evaluate the role played by spatial structure in driving evolution in experimental range expansions using laboratory microcosms of the red flour beetle, Tribolium castaneum

Methods

Results

Conclusion