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1. Microcoleus (Cyanobacteria) form watershed‐wide populations without strong gradients in population structure

   https://doi.org/10.1111/mec.16208  

   Bouma‐Gregson, Keith ; Crits‐Christoph, Alexander ; Olm, Mathew R. ; Power, Mary E. ; Banfield, Jillian F. ( October 2021 , Molecular Ecology)

   The relative importance of separation by distance and by environment to population genetic diversity can be conveniently tested in river networks, where these two drivers are often independently distributed over space. To evaluate the importance of dispersal and environmental conditions in shaping microbial population structures, we performed genome‐resolved metagenomic analyses of benthicMicrocoleus‐dominated cyanobacterial mats collected in the Eel and Russian River networks (California, USA). The 64 Microcoleusgenomes were clustered into three species that shared >96.5% average nucleotide identity (ANI). Most mats were dominated by one strain, but minor alleles within mats were often shared, even over large spatial distances (>300 km). Within the most commonMicrocoleusspecies, the ANI between the dominant strains within mats decreased with increasing spatial separation. However, over shorter spatial distances (tens of kilometres), mats from different subwatersheds had lower ANI than mats from the same subwatershed, suggesting that at shorter spatial distances environmental differences between subwatersheds in factors like canopy cover, conductivity, and mean annual temperature decreases ANI. Since mats in smaller creeks had similar levels of nucleotide diversity (π) as mats in larger downstream subwatersheds, within‐mat genetic diversity does not appear to depend on the downstream accumulation of upstream‐derived strains. The four‐gamete test and sequence length bias suggest recombination occurs between almost all strains within each species, even between populations separated by large distances or living in different habitats. Overall, our results show that, despite some isolation by distance and environmental conditions, sufficient gene‐flow occurs among cyanobacterial strains to prevent either driver from producing distinctive population structures across the watershed.

    

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2. Fine‐scale habitat heterogeneity and vole runways influence seed dispersal in Plagiobothrys nothofulvus

   https://doi.org/10.1002/ajb2.1433  

   Grasty, Monica R. ; Thompson, Pamela G. ; Hendrickson, Elizabeth C. ; Pheil, Avery E. ; Cruzan, Mitchell B. ( February 2020 , American Journal of Botany)

   Seed dispersal allows plants to colonize new sites and contributes to gene flow among populations. Despite its fundamental importance to ecological and evolutionary processes, our understanding of seed dispersal is limited due to the difficulty of directly observing dispersal events. This is particularly true for the majority of plant species that are considered to have gravity as their primary dispersal mechanism. The potential for long‐distance movement of gravity‐dispersed seeds by secondary dispersal vectors is rarely evaluated.

   We employ whole‐genome assays of maternally inherited cpDNAinPlagiobothrys nothofulvusto resolve patterns of genetic variation due to effective (realized) seed dispersal within a 16 hectare prairie that is characterized by a mosaic of habitat types. We evaluate the effects of microgeographic landscape features extracted from micro‐UAVaerial surveys on patterns of seed dispersal using landscape genetics methods.

   We found evidence of high resistance to seed‐mediated gene flow (effective dispersal) within patches ofPlagiobothrys nothofulvus, and strong genetic structure over distances of less than 20 m. Geographic distance was a poor predictor of dispersal distance, while landscape features had stronger influences on patterns of dispersal (distance and direction of seed movement). Patterns of dispersal were best predicted by the combined distribution of flower patches, habitat type, and the network of vole runways, with the latter explaining the largest proportion of variation in the model.

   Our results suggest that primary dispersal occurs mostly within microhabitats and infrequent secondary dispersal may occur over longer distances due to the activity of small mammals and other vertebrates.

    

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3. Population structure of Guyanagaster necrorhizus supports termite dispersal for this enigmatic fungus

   https://doi.org/10.1111/mec.14710  

   Koch, Rachel A. ; Aime, M. Catherine ( May 2018 , Molecular Ecology)

   Understanding how species accomplish dispersal of their propagules can shed light on how they are adapted for their ecosystem.Guyanagaster necrorhizusis a sequestrate fungus, meaning its dispersal propagules, or spores, are entirely enclosed within a fruiting body, termed a sporocarp. This fungus is most closely related toArmillariaand its allies. WhileArmillariaspecies form mushrooms and have forcibly discharged spores,G. necrorhizusspores have lost this ability, and by necessity, must be passively dispersed. However,G. necrorhizusdoes not possess characteristics of other sequestrate fungi with known dispersal mechanisms. Repeated observations of termites feeding onG. necrorhizussporocarps, and spores subsequently adhering to their exoskeletons, led to the hypothesis that termites disperseG. necrorhizusspores. To test this hypothesis, we used microsatellite markers and population genetics analyses to understand patterns of clonality and population structure ofG. necrorhizus. WhileArmillariaindividuals can spread vegetatively over large areas, high genotypic diversity inG. necrorhizuspopulations suggests spores are the primary mode of dispersal. Spatial genetic structure analyses show thatG. necrorhizussporocarps within 238 m of each other are more closely related than would be expected by chance and conservative estimates from population assignment tests suggest gene flow no longer occurs between sporocarps separated by 2 km. These distances are consistent with previous studies analysing foraging distances of the termites found associated withG. necrorhizussporocarps. Termites have rarely been recorded to specifically target fungal sporocarps, making this a potentially novel fungal–insect interaction.

    

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4. Genomic variation in the American pika: signatures of geographic isolation and implications for conservation

   https://doi.org/10.1186/s12862-020-01739-9  

   Klingler, Kelly B. ; Jahner, Joshua P. ; Parchman, Thomas L. ; Ray, Chris ; Peacock, Mary M. ( January 2021 , BMC Ecology and Evolution)

   Distributional responses by alpine taxa to repeated, glacial-interglacial cycles throughout the last two million years have significantly influenced the spatial genetic structure of populations. These effects have been exacerbated for the American pika (Ochotona princeps), a small alpine lagomorph constrained by thermal sensitivity and a limited dispersal capacity. As a species of conservation concern, long-term lack of gene flow has important consequences for landscape genetic structure and levels of diversity within populations. Here, we use reduced representation sequencing (ddRADseq) to provide a genome-wide perspective on patterns of genetic variation across pika populations representing distinct subspecies. To investigate how landscape and environmental features shape genetic variation, we collected genetic samples from distinct geographic regions as well as across finer spatial scales in two geographically proximate mountain ranges of eastern Nevada.

   Our genome-wide analyses corroborate range-wide, mitochondrial subspecific designations and reveal pronounced fine-scale population structure between the Ruby Mountains and East Humboldt Range of eastern Nevada. Populations in Nevada were characterized by low genetic diversity (π = 0.0006–0.0009; θ_W = 0.0005–0.0007) relative to populations in California (π = 0.0014–0.0019; θ_W = 0.0011–0.0017) and the Rocky Mountains (π = 0.0025–0.0027; θ_W = 0.0021–0.0024), indicating substantial genetic drift in these isolated populations. Tajima’sDwas positive for all sites (D = 0.240–0.811), consistent with recent contraction in population sizes range-wide.

   Substantial influences of geography, elevation and climate variables on genetic differentiation were also detected and may interact with the regional effects of anthropogenic climate change to force the loss of unique genetic lineages through continued population extirpations in the Great Basin and Sierra Nevada.

    

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5. Drift happens: Molecular genetic diversity and differentiation among populations of jewelweed ( Impatiens capensis Meerb.) reflect fragmentation of floodplain forests

   https://doi.org/10.1111/mec.15072  

   Toczydlowski, Rachel H. ; Waller, Donald M. ( May 2019 , Molecular Ecology)

   Landscape features often shape patterns of gene flow and genetic differentiation in plant species. Populations that are small and isolated enough also become subject to genetic drift. We examined patterns of gene flow and differentiation among 12 floodplain populations of the selfing annual jewelweed (Impatiens capensisMeerb.) nested within four river systems and two major watersheds in Wisconsin, USA. Floodplain forests and marshes provide a model system for assessing the effects of habitat fragmentation within agricultural/urban landscapes and for testing whether rivers act to genetically connect dispersed populations. We generated a panel of 12,856 single nucleotide polymorphisms and assessed genetic diversity, differentiation, gene flow, and drift. Clustering methods revealed strong population genetic structure with limited admixture and highly differentiated populations (mean multilocusF_ST = 0.32,F_ST’ = 0.33). No signals of isolation by geographic distance or environment emerged, but alleles may flow along rivers given that genetic differentiation increased with river distance. Differentiation also increased in populations with fewer private alleles (R² = 0.51) and higher local inbreeding (R² = 0.22). Populations varied greatly in levels of local inbreeding (F_IS = 0.2–0.9) andF_ISincreased in more isolated populations. These results suggest that genetic drift dominates other forces in structuring theseImpatienspopulations. In rapidly changing environments, species must migrate or genetically adapt. Habitat fragmentation limits both processes, potentially compromising the ability of species to persist in fragmented landscapes.

    

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