and degree to which populations are expected to respond to natural selection is thought to depend significantly on demographic and genetic characteristics of populations and the traits under selection (Lynch & Walsh, 1998). For instance, small populations are less likely to carry potentially adaptive alleles and are more likely to be subject to strong genetic drift depleting genetic variation and reducing the effect of selection than large populations, and thus are probably subject to reduced adaptive potential (Lanfear et al., 2014;Stern & Orgogozo, 2009;Willi et al., 2006). Constraints on local adaptation may also be imposed by the genetic architecture of the traits under selection (Arnold, 1992;Kemppainen et al., 2021), or strong gene

The rapid invasion of the pelagic zone in Lake Constance by three-spined sticklebacks (Gasterosteus aculeatus) since 2012 and their subsequent drastic population growth has had stark ecosystem-wide effects, such as food-web shifts and declines in native biodiversity, including commercially important fish species. Yet, the origin of this invasive pelagic ecotype remains unclear. This study aims to determine if the pelagic ecotype arose in situ from the existing littoral population or following external colonisation, identify potential phenotypic differences between individuals from different habitats, and assess genomic signals of selection. Integrating RAD-sequencing of Lake Constance individuals and whole-genome sequence data for European outgroup populations, this study shows that the pelagic Lake Constance population likely arose recently within the lake from the littoral population, with only weak genome-wide differentiation between individuals from different habitats. This is further supported by minimal differences in meristic and morphometric traits, with shape differences only found between pelagic/inflow sticklebacks and littoral sticklebacks. Using genome scans, we identified multiple outlier loci between littoral and pelagic ecotypes across the genome, potentially suggesting early signs of sympatric speciation despite high connectivity. Furthermore, increased differentiation between pelagic and littoral sticklebacks for body shape-associated loci and the overlap of outlier loci with quantitative trait loci for ecologically relevant traits points toward a driving role of selection in this pelagic invasion. This study provides an important example of rapid ecological diversification from standing genetic variation and a rare case of littoral-pelagic ecotype divergence under high gene flow in a large oligotrophic lake. Ultimately, the results of this study will have major implications for the management of the invasive pelagic ecotype, and the entire stickleback population as a whole.

The current effects of global warming on marine ecosystems are predicted to increase, with species responding by changing their spatial distributions. Marine ectotherms such as fish experience elevated distribution shifts, as temperature plays a key role in physiological functions and delineating population ranges through thermal constraints. Distributional response predictions necessary for population management have been complicated by high heterogeneity in magnitude and direction of movements, which may be explained by both biological as well as methodological study differences. To date, however, there has been no comprehensive synthesis of the interacting ecological factors influencing fish distributions in response to climate change and the confounding methodological factors that can affect their estimation. In this study we analyzed published studies meeting criteria of reporting range shift responses to global warming in 115 taxa spanning all major oceanic regions, totaling 595 three‐dimensional population responses (latitudinal, longitudinal, and depth), with temperature identified as a significant driver. We found that latitudinal shifts were the fastest in non‐exploited, tropical populations, and inversely correlated with depth shifts which, in turn, dominated at the trailing edges of population ranges. While poleward responses increased with rate of temperature change and latitude, niche was a key factor in predicting both depth (18% of variation) and latitudinal responses (13%), with methodological predictors explaining between 10% and 28% of the observed variance in marine fish responses to temperature change. Finally, we found strong geographical publication bias and limited taxonomical scope, highlighting the need for more representative and standardized research in order to address heterogeneity in distribution responses and improve predictions in face of changing climate.

The current effects of global warming on marine ecosystems are predicted to increase, with species responding by changing their spatial distributions. Marine ectotherms such as fish experience elevated distribution shifts, as temperature plays a key role in physiological functions and delineating population ranges through thermal constraints. Distributional response predictions necessary for population management have been complicated by high heterogeneity in magnitude and direction of movements, which may be explained by both biological as well as methodological study differences. To date, however, there has been no comprehensive synthesis of the interacting ecological factors influencing fish distributions in response to climate change and the confounding methodological factors that can affect their estimation. In this study we analyzed published studies meeting criteria of reporting range shift responses to global warming in 115 taxa spanning all major oceanic regions, totaling 569 three-dimensional population responses (latitudinal, longitudinal and depth), with temperature identified as a significant driver. Overall, studies on marine fish distributional responses have generally been of limited spatial and temporal scope, with comparisons among studies being complicated by large variation in methodology. We identified varying degrees of heterogeneity in latitudinal range shifts (km year-1) across ecological and methodological predictors, with multivariate regression analysis revealing response rate differences due to niche affinity, depth changes, as well as methodological biases due to different approaches in estimating and reporting latitudinal range shifts. Finally, we found strong geographical publication bias and limited taxonomical scope, highlighting the need for more representative and standardized research in order to address heterogeneity in distribution responses and improve predictions in face of changing climate.