Biology subjects

Greenway, R.

Publications and source records attributed to Greenway, R..

5 recordsLinked to original sources

bioRxiv2026

Glaciers retreat, stickleback advance: variation in demographic histories of freshwater stickleback populations

When colonizing new habitats, the evolution of populations can be affected by their demographic history and structure, including their effective population sizes and the time and nature of their divergence from an ancestral population. The deglaciation of Southern Greenland following the last glacial maximum offers the opportunity to comparatively study colonization events of fish populations among lakes of varying size and altitude, the latter of which partially reflects their geological age and isolation. This study investigates the demographic history of threespine stickleback (Gasterosteus aculeatus) from 17 freshwater lake populations in comparison to a marine population sampled across four fjord sites in Southern Greenland using whole-genome data. Our findings suggest that divergence of freshwater from ocean populations was concurrent with ice sheet retreat and lake formation, which occurred ~4-13 thousand years ago. In all 17 freshwater populations, demographic modeling revealed a population decline upon lake colonization and prolonged periods of gene flow between freshwater and marine populations. We also found that bigger lakes had larger effective population sizes. These findings emphasize the interplay between local landscape and demographic history in shaping the population genetic structure of Southern Greenland stickleback populations. Our results underscore the relevance of such small scale variation in demographic history across the landscape for understanding postglacial colonization into freshwater ecosystems.

evolutionary biology↗

bioRxiv2025

Differential phoretic host use among sympatric Caenorhabditis nematodes and an association with invasive nitidulid beetles in southwestern Germany

Little is known about the natural history of many Caenorhabditis nematodes, despite their relationship to the model species C. elegans. While these nematodes rely on invertebrate vectors to disperse to new habitats (phoresy), vector use for most species has not been characterized. We surveyed the invertebrate community of a habitat containing three sympatric Caenorhabditis in southwestern Germany, determining differential and specific vector use for each of these co-occurring species. We documented a specific association between C. apta n. sp. and two species of invasive nitidulid beetles, and a particularly strong association of the nematode with the beetle Stelidota geminata, where we recovered more nematodes per individual beetle and a higher proportion of beetles carrying nematodes compared to the co-occurring Epuraea ocularis. Our results provide evidence for group dispersal using beetles in C. apta, supporting previous observations of collective dispersal behavior in this species, and establish a starting point for further dissecting the evolutionary and mechanistic causes and consequences of interactions between Caenorhabditis nematodes and their vector species in ecologically relevant conditions.

ecology↗

bioRxiv2023

Gene expression signatures of salinity transitions in Limia perugiae (Poeciliidae), with comparisons to other teleosts

Salinity gradients act as strong environmental barriers that limit the distribution of aquatic organisms. Changes in gene expression associated with transitions between freshwater and saltwater environments can provide insight into organismal responses to variation in salinity. We used RNA-sequencing (RNA-seq) to investigate genome-wide variation in gene expression between a hypersaline population and a freshwater population of the livebearing fish species Limia perugiae (Poeciliidae). Our analyses of gill gene expression revealed potential molecular mechanisms underlying salinity tolerance in this species, including the enrichment of genes involved in ion transport, maintenance of chemical homeostasis, and cell signaling in the hypersaline population. We also found differences in gene expression patterns associated with cell cycle and protein folding processes between the hypersaline and freshwater L. perugiae. Bidirectional freshwater-saltwater transitions have occurred repeatedly during the diversification of fishes, allowing for broad-scale examination of repeatable patterns in evolution. We compared transcriptomic variation in L. perugiae with other teleosts that have made freshwater-saltwater transitions to test for convergence in gene expression. Among the four distantly related population pairs from high- and low-salinity environments that we included in our analysis, we found only ten shared differentially expressed genes, indicating little evidence for convergence. However, we found that differentially expressed genes shared among three or more lineages were functionally enriched for ion transport and immune functioning. Overall, our results--in conjunction with other recent studies-- suggest that different genes are involved in salinity transitions across disparate lineages of teleost fishes.

physiology↗

bioRxiv2021

Ecology drives the degree of convergence in the gene expression of extremophile fishes

Convergent evolution, where independent lineages evolve similar traits when adapting to similar habitats, is a common phenomenon and testament to the repeatability of evolutionary processes. Still, non-convergence is also common, and a major question is whether apparently idiosyncratic, lineage-specific evolutionary changes are reflective of chance events inherent to evolutionary processes, or whether they are also influenced by deterministic genetic or ecological factors. To address this question, we quantified the degree of convergence in genome-wide patterns of gene expression across lineages of livebearing fishes (family Poeciliidae) that span 40 million years of evolution and have colonized extreme environments in the form of toxic, hydrogen-sulfide-rich springs. We specifically asked whether the degree of convergence across lineage pairs was related to their phylogenetic relatedness or the ecological similarity of the habitats they inhabit. Using phylogenetic comparative analyses, we showed that the degree of convergence was highly variable across lineage pairs residing in sulfide springs. While closely related lineages did not exhibit higher degrees of convergence than distantly related ones, we uncovered a strong relationship between degree of convergence and ecological similarity. Our results indicate that variation in the degree of convergence is not merely noise associated with evolutionary contingency. Rather, cryptic environmental variation that is frequently ignored when we employ reductionist approaches can significantly contribute to adaptive evolution. This study highlights the importance of multivariate approaches that capture the complexities of both selective regimes and organismal design when assessing the roles of determinism and contingency in evolution. Significance StatementWhen different species adapt to similar environmental conditions, we frequently observe a mix between shared (convergent) and lineage-specific (nonconvergent) evolutionary changes. Shared changes provide evidence for the repeatability and predictability of evolution. However, it remains unclear whether lineage-specific changes are caused by random forces that limit the predictability of evolution, or whether they reflect deterministic processes shaped by unidentified genetic and environmental factors. By analyzing patterns of gene expression across fishes in extreme environments, we show that the degree of convergence between lineages is related to ecology, indicating that lineage-specific evolutionary changes are not just noise caused by random processes. Thus, acknowledging the complexity of nature in empirical research is critical if we want to predict evolution.

evolutionary biology↗

bioRxiv2020

Convergent evolution of conserved mitochondrial pathways underlies repeated adaptation to extreme environments

Extreme environments test the limits of life; yet, some organisms thrive in harsh conditions. Extremophile lineages inspire questions about how organisms can tolerate physiochemical stressors and whether the repeated colonization of extreme environments is facilitated by predictable and repeatable evolutionary innovations. We identified the mechanistic basis underlying convergent evolution of tolerance to hydrogen sulfide (H2S)--a toxicant that impairs mitochondrial function--across evolutionarily independent lineages of a fish (Poecilia mexicana, Poeciliidae) from H2S-rich springs. Using comparative biochemical and physiological analyses, we found that mitochondrial function is maintained in the presence of H2S in sulfide spring P. mexicana, but not ancestral lineages from nonsulfidic habitats, due to convergent adaptations in the primary toxicity target and a major detoxification enzyme. Genome-wide local ancestry analyses indicated that convergent evolution of increased H2S tolerance in different populations is likely caused by a combination of selection on standing genetic variation and de novo mutations. At a macroevolutionary scale, H2S tolerance in 10 independent lineages of sulfide spring fishes across multiple genera of Poeciliidae is correlated with the convergent modification and expression changes of genes associated with H2S toxicity and detoxification. Our results demonstrate that the modification of highly conserved physiological pathways associated with essential mitochondrial processes mediates tolerance to physiochemical stress. In addition, the same pathways, genes, and--in some instances--codons are implicated in H2S adaptation in lineages that span 40 million years of evolution. Significance StatementSome organisms can tolerate environments lethal for most others, but we often do not know what adaptations allow them to persist and whether the same mechanisms underly adaptation in different lineages exposed to the same stressors. Investigating fish inhabiting springs rich in toxic hydrogen sulfide (H2S), we show that tolerance is mediated by the modification of pathways that are inhibited by H2S and those that can detoxify it. Sulfide spring fishes across multiple genera have evolved similar modifications of toxicity targets and detoxification pathways, despite abundant lineage-specific variation. Our study highlights how constraints associated with the physiological consequences of a stressor limit the number of adaptive solutions and lead to repeatable evolutionary outcomes across organizational and evolutionary scales.

evolutionary biology↗