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As climatic variation re‐shapes global biodiversity, understanding eco‐evolutionary feedbacks during species range shifts is of increasing importance. Theory on range expansions distinguishes between two different forms: “pulled” and “pushed” waves. Pulled waves occur when the source of the expansion comes from low‐density peripheral populations, while pushed waves occur when recruitment to the expanding edge is supplied by high‐density populations closer to the species' core. How extreme events shape pushed/pulled wave expansion events, as well as trailing‐edge declines/contractions, remains largely unexplored. We examined eco‐evolutionary responses of a marine invertebrate (the owl limpet,Lottia gigantea) that increased in abundance during the 2014–2016 marine heatwaves near the poleward edge of its geographic range in the northeastern Pacific. We used whole‐genome sequencing from 19 populations across >11 degrees of latitude to characterize genomic variation, gene flow, and demographic histories across the species' range. We estimated present‐day dispersal potential and past climatic stability to identify how contemporary and historical seascape features shape genomic characteristics. Consistent with expectations of a pushed wave, we found little genomic differentiation between core and leading‐edge populations, and higher genomic diversity at range edges. A large and well‐mixed population in the northern edge of the species' range is likely a result of ocean current anomalies increasing larval settlement and high‐dispersal potential across biogeographic boundaries. Trailing‐edge populations have higher differentiation from core populations, possibly driven by local selection and limited gene flow, as well as high genomic diversity likely as a result of climatic stability during the Last Glacial Maximum. Our findings suggest that extreme events can drive poleward range expansions that carry the adaptive potential of core populations, while also cautioning that trailing‐edge extirpations may threaten unique evolutionary variation. This work highlights the importance of understanding how both trailing and leading edges respond to global change and extreme events. 

Abstract The extent of parallel genomic responses to similar selective pressures depends on a complex array of environmental, demographic, and evolutionary forces. Laboratory experiments with replicated selective pressures yield mixed outcomes under controlled conditions and our understanding of genomic parallelism in the wild is limited to a few well‐established systems. Here, we examine genomic signals of selection in the eelgrassZostera marinaacross temperature gradients in adjacent embayments. Although we find many genomic regions with signals of selection within each bay there is very little overlap in signals of selection at the SNP level, despite most polymorphisms being shared across bays. We do find overlap at the gene level, potentially suggesting multiple mutational pathways to the same phenotype. Using polygenic models we find that some sets of candidate SNPs are able to predict temperature across both bays, suggesting that small but parallel shifts in allele frequencies may be missed by independent genome scans. Together, these results highlight the continuous rather than binary nature of parallel evolution in polygenic traits and the complexity of evolutionary predictability. 

ABSTRACT Coastal organisms live in a dynamic environment where a myriad of environmental stressors, including climate change, ocean acidification, and human harvesting, act on variable spatio‐temporal scales. Each of these stressors may impose unique selective forces on a population, shaping a species' adaptive potential and its ability to persist under future climatic conditions. Genomic investigations of adaptive responses to environmental and anthropogenic disturbances remain rare, especially in marine systems. Here, we use whole genome sequencing data from the owl limpet,Lottia gigantea, and outlier detection methods to pinpoint signals of selection (1) across long‐standing environmental gradients spanning the species' distribution, (2) at the poleward edge of the species' range where it experienced a recent expansion, and (3) between sites vulnerable to or protected from human size‐selective harvesting within California. Loci associated with environmental gradients across the entire range show the strongest differentiation at the southern end of the species' range, potentially driven by adaptation to sea surface temperature and pH. Additionalad‐hocoutlier analyses revealed a distinct set of loci potentially under selection in the expanded range, with different functional roles than the range‐wide outliers. Despite demographic models suggesting that protection from harvesting has a positive impact on the abundance of large individuals, we did not find strong signals of selection or changes in genetic diversity between sites differing in harvesting vulnerability. Our findings suggest that range‐wide environmental selective signals established over longer time scales are distinct from those imposed by climatic anomalies at finer spatio‐temporal scales. We found that climatic variation has a stronger selective imprint than human harvesting, and thus conservation interventions should consider prioritizing the maintenance of climate‐related adaptive potential. Understanding how climatic trends and anomalies interact with anthropogenic pressures will allow us to make more informed decisions to sustain the evolutionary capacity ofL. giganteaand other key coastal species. 

Theoretically, species' characteristics should allow estimation of dispersal potential and, in turn, explain levels of population genetic differentiation. However, a mismatch between traits and genetic patterns is often reported for marine species, and interpreted as evidence that life-history traits do not influence dispersal. Here, we couple ecological and genomic methods to test the hypothesis that species with attributes favouring greater dispersal potential—e.g., longer pelagic duration, higher fecundity and larger population size—have greater realized dispersal overall. We used a natural experiment created by a large-scale and multispecies mortality event which created a “clean slate” on which to study recruitment dynamics, thus simplifying a usually complex problem. We surveyed four species of differing dispersal potential to quantify the abundance and distribution of recruits and to genetically assign these recruits to probable parental sources. Species with higher dispersal potential recolonized a broader extent of the impacted range, did so more quickly and recovered more genetic diversity than species with lower dispersal potential. Moreover, populations of taxa with higher dispersal potential exhibited more immigration (71%–92% of recruits) than taxa with lower dispersal potential (17%–44% of recruits). By linking ecological with genomic perspectives, we demonstrate that a suite of interacting life-history and demographic attributes do influence species' realized dispersal and genetic neighbourhoods. To better understand species' resilience and recovery in this time of global change, integrative eco-evolutionary approaches are needed to more rigorously evaluate the effect of dispersal-linked attributes on realized dispersal and population genetic differentiation. 

Abstract Susan Lynn Williams (1951–2018) was an exceptional marine ecologist whose research focused broadly on the ecology of benthic nearshore environments dominated by seagrasses, seaweeds, and coral reefs. She took an empirical approach founded in techniques of physiological ecology. Susan was committed to applying her research results to ocean management through outreach to decision-makers and resource managers. Susan’s career included research throughout the USA in tropical, temperate, and polar regions, but she specialized in tropical marine ecology. Susan’s scholarship, leadership, and friendship touched many people, leading to this multi-authored paper. Susan’s scholarship was multi-faceted, and she excelled in scientific discovery, integration of scientific results, application of science for conservation, and teaching, especially as a mentor to undergraduate and graduate students and postdoctoral scholars. Susan served in a variety of leadership positions throughout her career. She embodied all facets of leadership; leading by example, listening to others, committing to the “long haul,” maintaining trust, and creating a platform for all to shine. Susan was an important role model for women in science. Susan was also a loyal friend, maintaining friendships for many decades. Susan loved cooking and entertaining with friends. This paper provides an overview of the accomplishments of Susan in the broad categories of scholarship, leadership, and friendship.