Biology subjects

Oke, K.

Publications and source records attributed to Oke, K..

3 recordsLinked to original sources

bioRxiv2026

Variable jackpot individuals provide most alleles for repeated, rapid adaptation to freshwater by anadromous Threespine Stickleback

Experimental introductions of anadromous stickleback into freshwater habitats lacking this species allow analysis of the process of adaptation to freshwater forward-in-time. We examined the population genomic dynamics during early stages of adaptation in three replicate lakes that were experimentally founded, each using [~]3000 anadromous ancestors. We replicated earlier results that rare individuals carrying large haploblocks of freshwater-adaptive alleles (jackpot carriers) provide most of the allelic variation for adaptation of anadromous Threespine Stickleback to freshwater within only a few generations in each lake. There were population bottlenecks two to three generations after founding in each lake, after which jackpot carriers dramatically increased in frequency and came to dominate the populations. Individuals lacking large adaptive haploblocks experienced low fitness in their new freshwater environments, consistent with our previous report based on a single lake population. Despite similarities of the demographic responses to selection, the alleles that were most common among jackpot carriers were different in each population, suggesting that each lake population likely adapted to conditions in freshwater environments through different genes. These results provide direct evidence for the genomic mechanisms underlying the rapid adaptation of anadromous sticklebacks to freshwater environments, a process that can occur within just a few generations.

evolutionary biology↗

bioRxiv2025

Hybridization but minimal introgression: ecologically-based divergent selection maintains a steep hybrid zone in parapatric stickleback fish

Steep hybrid zones provide key insights into the mechanisms of speciation by reflecting incomplete reproductive isolation between diverging populations. However, the specific reproductive barriers preventing the fusion of such populations generally remain unclear, particularly the role of ecologically-based divergent selection. To address the latter, we here investigate a steep hybrid zone between lake and stream ecotypes of threespine stickleback fish inhabiting contiguous habitats within a single watershed. Given the spatial proximity of these habitats and the systems postglacial age, historical allopatry is unlikely to have contributed to the evolution of reproductive isolation. Using individual whole-genome sequencing from clinal sampling sites, we find that hybridization occurs within a narrow zone - just a few hundred meters long - at the transition between lake and stream habitat. Individuals in this contact zone exhibit strongly bimodal genome-wide ancestry, with a rapid shift toward the stream ecotypes genomic background, consistent with strong selection against lake-derived alleles in the stream habitat. Individual-based simulations tailored to this system demonstrate that divergent ecological selection alone can maintain the observed sharp cline, and illustrate the sustained antagonism between gene flow and selection near the habitat transition. Our findings underscore the power of ecological divergence to generate and maintain reproductive isolation, even in the absence of historical separation, and motivate further empirical work on the ecological underpinnings of steep hybrid zones.

evolutionary biology↗

bioRxiv2025

Changes in body size with age do not follow the temperature-size rule

The temperature size-rule is often described as a reduction in ectothermic body size with warming. This coincides with the expectation that faster growth under warming would lead to larger sizes early in life but smaller sizes later in life. Here, we use > 99,000 observations of weight-at-age of four commercially-important fishes over 25 years to ask whether changes in size and growth can be explained by temperature. We also examine whether oxygen, a key part of a proposed mechanism behind the temperature size-rule, explains patterns of weight-at-age better than temperature. Changes in weight-at-age over time were more related to temperature than oxygen but the effect of temperature on weight was small and did not vary by age, counter to the temperature size-rule. Importantly, these results were sensitive to how the relationship between weight-at-age and temperature was modeled. While the functional form (linear or polynomial) mattered little, how space was included in the model led to different conclusions regarding how temperature affects size and growth. Assuming that spatial and spatiotemporal random effects - those that account for the higher degree of similarity between observations collected closer in space and time - are shared across ages led to different results compared to allowing these effects to vary by age. Models with shared effects suggested weight for younger ages had positive relationships with temperature and negative relationships for older ages. However, these models provided spurious support for the temperature size-rule as they had less statistical support than models that allowed spatial effects to vary by age. Overall, our work highlights that relationships among size, growth, temperature, and oxygen may not be as straightforward as theory suggests and illustrates that modeling decisions can have a large effect on tests of ecological theory, and more broadly, our ability to understand biological responses to climate change.

ecology↗