Award: OCE-2023297

For centuries, people have sought to understand why species are distributed in the way that they are – what makes one species common in the south while another is more common in the north? One emergent observation is that species ranges are often limited by environmental variables such as temperature. In recent decades, with shifting environments, species are being redistributed across the globe. These sometimes rapid changes in species range boundaries offer a unique opportunity to disentangle the ecological and evolutionary mechanisms limiting species ranges and therefore understand the drivers of range shifts. In marine species, range shifts tend to happen more quickly than on land because species disperse more readily and there are fewer physical barriers to movement. While many studies of species range shifts have focused on long-term (decadal scale) shifts in species ranges, extreme events such as marine heatwaves can also cause shifts in range boundaries in the short-term. For example, the marine heatwaves of 2014-2016 on the California coast led to northward range expansion of many previously southern species. This project focused on one such species, the owl limpet (Lottia gigantea). Owl limpets were previously rare in Northern California, but during the marine heatwaves there was increased recruitment in the northernmost part of the range. We have been able to use this range expansion to observe eco-evolutionary processes in real time, leveraging a combination of population monitoring, ecological experiments, and genomic analyses to understand mechanisms of range expansion.

One model of range expansion is that a subset of individuals enter a new region, establishing a population outside the previous range. In this case, we expect lower genetic diversity and potentially efficient selection for traits that are advantageous in the new region. Using genomic sequencing of owl limpets across the entire range, we found high amounts of dispersal from the core of the range, with no loss of genetic diversity at the northernmost range edge. This supports our monitoring observations of ongoing recruitment at the northern range limit, suggesting that the range expansion was not fueled by a one-time arrival of a few individuals but is ongoing. We also examined the potential for selection in the northern zone of range expansion. In the field, we found that limpets at the northern range limit grew fastest. However, this result was not replicated in a laboratory common garden, suggesting that the growth differences were plastic rather than under selection. However, genomic data did suggest that there were some signals of selection in the genome, paving the way for further studies of traits that selectively differ across the range. Overall, our project lends mechanistic insight into eco-evolutionary dynamics of range expansions, demonstrating that rapid range expansions can maintain genetic variation and result in selection, potentially fueling future expansions.

Last Modified: 01/26/2026
Modified by: Rachael A Bay