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1. The geno-geo-climate nexus: contributions of geographic and ecological factors in shaping the genomic divergence of two closely related threatened rainforest species of Fontainea Heckel (Euphorbiaceae)

   https://doi.org/10.1007/s10980-024-01828-w  

   Brunton, Aaron J. ; Farleigh, Keaka ; Ogbourne, Steven M. ; Rossetto, Maurizio ; Schoeman, David S. ; Conroy, Gabriel C. ( January 2024 , Landscape Ecology)

   Processes that shape genomic and ecological divergence can reveal important evolutionary dynamics to inform the conservation of threatened species.Fontaineais a genus of rainforest shrubs and small trees including critically endangered and threatened species restricted to narrow, but complex geographic and ecological regions. Several species ofFontaineaare subject to spatially explicit conditions and experience limited intra-specific gene flow, likely generating genetic differentiation and local adaptation.

   Here, we explored the genetic and ecological mechanisms underlying patterns of diversification in two, closely related threatenedFontaineaspecies. Our aim was to compare spatial patterns of genetic variation between the vulnerableFontainea australis(Southern Fontainea) and critically endangeredF. oraria(Coastal Fontainea), endemic to the heterogeneous subtropical region of central, eastern Australia, where large-scale clearing has severely reduced rainforest habitat to a fraction (< 1%) of its pre-European settlement extent.

   We used a set of 10,000 reduced-representation markers to infer genetic relationships and the drivers of spatial genetic variation across the two species. In addition, we employed a combination of univariate and multivariate genome-environment association analysis using a set of topo-climatic variables to explore potential patterns of local adaptation as a factor impacting genomic divergence.

   Our study revealed that Coastal Fontainea have a close genetic relationship with Southern Fontainea. We showed that isolation by distance has played a key role in their genetic variation, indicating that vicariance can explain the spatial genetic distribution of the two species. Genotype-environment analyses showed a strong association with temperature and topographic features, suggesting adaptation to localised thermal environments. We used a multivariate redundancy analysis to identify a range of putatively adapted loci associated with local environmental conditions.

   Divergent selection at the local-habitat scale as a result of dispersal limitations and environmental heterogeneity (including physical barriers) are likely contributors to adaptive divergence between the twoFontaineaspecies. Our findings have presented evidence to indicate that Southern and Coastal Fontainea were comprised of distinct genetic groups and ecotypes, that together may form a single species continuum, with further phenotype research suggested to confirm the current species boundaries. Proactive conservation actions, including assisted migration to enhance the resilience of populations lacking stress-tolerant single nucleotide polymorphisms (SNPs) may be required to secure the long-term future of both taxa. This is especially vital for the critically endangered Coastal Fontainea given projections of habitat decline for the species under future climate scenarios.

    

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2. Impacts of female body size on cannibalism and juvenile abundance in a dominant arctic spider

   https://doi.org/10.1111/1365-2656.13230  

   Koltz, Amanda M. ; Wright, Justin P. ; O'Gorman, ed., Eoin ( May 2020 , Journal of Animal Ecology)

   Body size influences an individual's physiology and the nature of its intra‐ and interspecific interactions. Changes in this key functional trait can therefore have important implications for populations as well. For example, among invertebrates, there is typically a positive correlation between female body size and reproductive output. Increasing body size can consequently trigger changes in population density, population structure (e.g. adult to juvenile ratio) and the strength of intraspecific competition.

   Body size changes have been documented in several species in the Arctic, a region that is warming rapidly. In particular, wolf spiders, one of the most abundant arctic invertebrate predators, are becoming larger and therefore more fecund. Whether these changes are affecting their populations and role within food webs is currently unclear.

   We investigated the population structure and feeding ecology of the dominant wolf spider speciesPardosa lapponicaat two tundra sites where adult spiders naturally differ in mean body size. Additionally, we performed a mesocosm experiment to investigate how variation in wolf spider density, which is likely to change as a function of body size, influences feeding ecology and its sensitivity to warming.

   We found that juvenile abundance is negatively associated with female size and that wolf spiders occupied higher trophic positions where adult females were larger. Because female body size is positively related to fecundity inP. lapponica, the unexpected finding of fewer juveniles with larger females suggests an increase in density‐dependent cannibalism as a result of increased intraspecific competition for resources. Higher rates of density‐dependent cannibalism are further supported by the results from our mesocosm experiment, in which individuals occupied higher trophic positions in plots with higher wolf spider densities. We observed no changes in wolf spider feeding ecology in association with short‐term experimental warming.

   Our results suggest that body size variation in wolf spiders is associated with variation in intraspecific competition, feeding ecology and population structure. Given the widespread distribution of wolf spiders in arctic ecosystems, body size shifts in these predators as a result of climate change could have implications for lower trophic levels and for ecosystem functioning.

    

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3. Genotype–environment associations across spatial scales reveal the importance of putative adaptive genetic variation in divergence

   https://doi.org/10.1111/eva.13444  

   Alvarado, Allison H. ; Bossu, Christen M. ; Harrigan, Ryan J. ; Bay, Rachael A. ; Nelson, Allison R. P. ; Smith, Thomas B. ; Ruegg, Kristen C. ( August 2022 , Evolutionary Applications)

   Identifying areas of high evolutionary potential is a judicious strategy for developing conservation priorities in the face of environmental change. For wide‐ranging species occupying heterogeneous environments, the evolutionary forces that shape distinct populations can vary spatially. Here, we investigate patterns of genomic variation and genotype–environment associations in the hermit thrush (Catharus guttatus), a North American songbird, at broad (across the breeding range) and narrow spatial scales (at a hybrid zone). We begin by building a genoscape or map of genetic variation across the breeding range and find five distinct genetic clusters within the species, with the greatest variation occurring in the western portion of the range. Genotype–environment association analyses indicate higher allelic turnover in the west than in the east, with measures of temperature surfacing as key predictors of putative adaptive genomic variation rangewide. Since broad patterns detected across a species' range represent the aggregate of many locally adapted populations, we investigate whether our broadscale analysis is consistent with a finer scale analysis. We find that top rangewide temperature‐associated loci vary in their clinal patterns (e.g., steep clines vs. fixed allele frequencies) across a hybrid zone in British Columbia, suggesting that the environmental predictors and the associated candidate loci identified in the rangewide analysis are of variable importance in this particular region. However, two candidate loci exhibit strong concordance with the temperature gradient in British Columbia, suggesting a potential role for temperature‐related barriers to gene flow and/or temperature‐driven ecological selection in maintaining putative local adaptation. This study demonstrates how patterns identified at the broad (macrogeographic) scale can be validated by investigating genotype–environment correlations at the local (microgeographic) scale. Furthermore, our results highlight the importance of considering the spatial distribution of putative adaptive variation when assessing population‐level sensitivity to climate change and other stressors.

    

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4. Diversity, divergence and density: How habitat and hybrid zone dynamics maintain a genomic cline in an intertidal barnacle

   https://doi.org/10.1111/jbi.14142  

   Wares, John P. ; Strand, Allan E. ; Sotka, Erik E. ( June 2021 , Journal of Biogeography)

   As within‐species genomic data have been shown useful in interpreting broader biogeographic trends, we analysed the mode of population genomic isolation involved in a well‐studied intertidal genomic cline to better understand the mechanisms maintaining it. These results were interpreted in the context of spatial variation in habitat use and availability as well as likely fitness consequences for hybridization between the two lineages.

   Pacific coast of North America.

   Arthropods (Class Maxillopoda, Order Sessilia, Family Balanidae;Balanus glandula).

   Genotype‐by‐sequencing approaches were used to generate single‐nucleotide polymorphism markers across sites sampled between southern Alaska and Southern California. Inference using standard population genomic methods, including analysis of population structure, inbreeding and linkage disequilibrium, was used to identify the steepest transitions across the largest number of loci examined. These data were put in the context of observed population density and habitat availability.

   We show that the majority of markers analysed show strong clinal transitions in a very narrow portion of the California coast. Patterns of linkage disequilibrium among markers, along with prior evidence of variation in reproductive potential by latitude and by mitochondrial lineage, suggest some reproductive isolation among the northern and southern lineages ofB. glandulathat are concordant with the drop in population density and habitat availability in central California.

   A significant clinal transition in genomic diversity is stronger and more localized than previously recognized and exhibits statistical patterns suggesting that the lineages are reproductively and phenotypically distinct in ways that may be ecologically important. As this species has been used to infer process in coastal biogeography, further study of concordant patterns will be important for advancing our understanding of this region.

    

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5. The influence of history, geography and environment on patterns of diversification in the western terrestrial garter snake

   https://doi.org/10.1111/jbi.14146  

   Hallas, Joshua M. ; Parchman, Thomas L. ; Feldman, Chris R. ( June 2021 , Journal of Biogeography)

   A central aim of biogeography is to understand how biodiversity is generated and maintained across landscapes. Here, we establish phylogenetic and population genetic patterns in a widespread reptile to quantify the influence of historical biogeography and current environmental variation on patterns of genetic diversity.

   Western North America.

   Western terrestrial garter snake,Thamnophis elegans.

   We used double‐digest RADseq to estimate phylogenetic relationships and characterize population genetic structure across the three widespread subspecies ofT. elegans:T. e. vagrans(wandering garter snake),T. e. elegans(mountain garter snake) andT. e. terrestris(coast garter snake). We assessed patterns of dispersal and vicariance across biogeographic regions using ancestral area reconstruction (AAR) and deviations from isolation‐by‐distance across the landscape using estimated effective migration surfaces (EEMS). We identified environmental variables potentially shaping local adaptation in regional lineages using genetic‐environment association (GEA) analyses.

   We recovered three well‐differentiated genetic groups that correspond to the three subspecies. AAR analyses inferred the eastern Cascade Range as the ancestral area, with dispersal to both the east and west across western North America. Populations ofT. e. elegansdisplayed a latitudinal gradient in genetic variation across the Sierra Nevada and northern California, while populations ofT. e. terrestrisshow discrete genetic breaks consistent with well‐known biogeographic barriers. Lastly, GEA analyses identified allele frequency shifts at loci associated with a common set of environmental variables in bothT. e. elegansandT. e. terrestris.

   T. elegansis composed of distinct evolutionary lineages, each with its own geographic range and history of diversification.T. e. elegansandT. e. terrestrisshow unique patterns of diversification as populations dispersed from east to west and while adapting to the new environments they colonized. Historical events, landscape features and environmental variation have all contributed to patterns of differentiation inT. elegans.

    

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