Geology topics

David W. Weisrock

Publications and source records attributed to David W. Weisrock.

5 recordsLinked to original sources

USGS2019

Microbial assemblages reflect environmental heterogeneity in alpine streams

Alpine streams are dynamic habitats harboring substantial biodiversity across small spatial extents. The diversity of alpine stream biota is largely reflective of environmental heterogeneity stemming from varying hydrological sources. Globally, alpine stream diversity is under threat as meltwater sources recede and stream conditions become increasingly homogeneous. Much attention has been devoted to macroinvertebrate diversity in alpine headwaters, yet to fully understand the breadth of climate change threats, a more thorough accounting of microbial diversity is needed. We characterized microbial diversity (specifically Bacteria and Archaea) of 13 streams in two disjunct Rocky Mountain subranges through 16S rRNA gene sequencing. Our study encompassed the spectrum of alpine stream sources (glaciers, snowfields, subterranean ice, and groundwater) and three microhabitats (ice, biofilms, and streamwater). We observed no difference in regional (γ) diversity between subranges but substantial differences in diversity among (β) stream types and microhabitats. Within‐stream (α) diversity was highest in groundwater‐fed springs, lowest in glacier‐fed streams, and positively correlated with water temperature for both streamwater and biofilm assemblages. We identified an underappreciated alpine stream type—the icy seep—that are fed by subterranean ice, exhibit cold temperatures (summer mean <2°C), moderate bed stability, and relatively high conductivity. Icy seeps will likely be important for combatting biodiversity losses as they contain similar microbial assemblages to streams fed by surface ice yet may be buffered against climate change by insulating debris cover. Our results show that the patterns of microbial diversity support an ominous trend for alpine stream biodiversity; as meltwater sources decline, stream communities will become more diverse locally, but regional diversity will be lost. Icy seeps, however, represent a source of optimism for the future of biodiversity in these imperiled ecosystems.

Montana↗

USGS2019

Early genetic outcomes of American black bear reintroductions in the Central Appalachians, USA

Habitat loss and overexploitation extirpated American black bears (Ursus americanus) from most of the Central Appalachians, USA, by the early twentieth century. To attempt to restore bears to the southwestern portion of this region, 2 reintroductions that used small founder groups (n = 27 and 55 bears), but different release methods (hard versus soft), were conducted during the 1990s. We collected hair samples from black bears in the reintroduced Big South Fork (BSF) and Kentucky–Virginia populations (KVP), their respective Great Smoky Mountains (GSM) and Shenandoah National Park (SNP) source populations, and a neighboring population in southern West Virginia (SWV) to investigate the early genetic outcomes of bear reintroduction. Despite having undergone genetic bottlenecks, genetic diversity remained similar between reintroduced populations and their sources ~15 years after the founder events (ranges: AR = 4.86–5.61; HO = 0.67–0.75; HE = 0.65–0.71). Effective population sizes of the reintroduced KVP and BSF (NE = 31 and 36, respectively) were substantially smaller than their respective SNP and GSM sources (NE = 119 and 156, respectively), supporting founder effects. Genetic structure analysis indicated that the hard released (i.e., no acclimation period) KVP founder group likely declined considerably, whereas the soft released BSF founder group remained mostly intact, suggesting superior effectiveness of soft releases. Asymmetrical gene flow via immigration from the SWV has resulted in the KVP recovering from the initial founder group reduction. Sustained isolation, small NE, and small population size of the BSF may warrant continued genetic monitoring to determine if gene flow from neighboring populations is established or NE declines. For future bear reintroductions, we suggest managers consider sourcing founders from populations with high genetic diversity and soft-releasing bears to locales that are, if possible, within the dispersal capability of extant populations to mitigate the potential consequences of founder effects and isolation.

Central Appalachians↗

USGS2018

Congruent population genetic structure but differing depths of divergence for three alpine stoneflies with similar ecology and geographic distributions

Comparative population genetic studies provide a powerful means for assessing the degree to which evolutionary histories may be congruent among taxa while also highlighting the potential for cryptic diversity within existing species. In the Rocky Mountains, three confamilial stoneflies ( Zapada glacier , Lednia tumana , and Lednia tetonica ; Plecoptera, Nemouridae) occupy cold alpine streams that are primarily fed by melting ice. Lednia tumana and L. tetonica are sister species diagnosed from systematic morphological differences, and they are endemic to areas surrounding Glacier National Park and Grand Teton National Park, respectively, in the U.S. Rocky Mountains. Zapada glacier is also present in alpine streams from Glacier National Park to the Teton Range, sometimes co‐occurring with either Lednia species. We used mitochondrial sequence data to clarify species boundaries, compare population genetic patterns, and test demographic models in a coalescent framework for the three stoneflies. We addressed four questions: (1) Is there genetic support for the morphology‐based species boundaries in Lednia ? (2) Is there genetic support for cryptic, or as‐yet undescribed, diversity within Z. glacier ? (3) Do similar geographic distributions and ecological requirements yield spatial congruence of genetic structure between high‐elevation Lednia and Z. glacier populations? (4) Is there evidence for contemporary gene flow among isolated populations in either group? Our results supported the existing taxonomy with Z. glacier and the two Lednia species differing in their depths of divergence among study regions (e.g. maximum sequence divergence within Z. glacier = 1.2% versus 5% between L. tumana and L. tetonica ). However, spatial population genetic patterns were broadly congruent, indicating stonefly populations isolated on mountaintop islands. Coalescent modelling supported the possibility of rare, extremely limited contemporary gene flow among Z. glacier populations, with no support for gene flow between L. tumana and L. tetonica . The focal stoneflies and associated assemblages occupy the highest elevation, coldest permanent alpine streams in the study region. This lotic habitat type faces an uncertain future under a diminishing alpine cryosphere. Given spatial congruence of genetic structure demonstrating unique biodiversity associated with individual alpine islands, we encourage conservation management strategies be developed and applied at corresponding spatial scales.

Montana, Wyoming↗

USGS2017

Demographic modelling reveals a history of divergence with gene flow for a glacially tied stonefly in a changing post-Pleistocene landscape

Aim Climate warming is causing extensive loss of glaciers in mountainous regions, yet our understanding of how glacial recession influences evolutionary processes and genetic diversity is limited. Linking genetic structure with the influences shaping it can improve understanding of how species respond to environmental change. Here, we used genome-scale data and demographic modelling to resolve the evolutionary history of Lednia tumana , a rare, aquatic insect endemic to alpine streams. We also employed a range of widely used data filtering approaches to quantify how they influenced population structure results. Location Alpine streams in the Rocky Mountains of Glacier National Park, Montana, USA. Taxon Lednia tumana , a stonefly (Order Plecoptera) in the family Nemouridae. Methods We generated single nucleotide polymorphism data through restriction-site associated DNA sequencing to assess contemporary patterns of genetic structure for 11 L. tumana populations. Using identified clusters, we assessed demographic history through model selection and parameter estimation in a coalescent framework. During population structure analyses, we filtered our data to assess the influence of singletons, missing data and total number of markers on results. Results Contemporary patterns of population structure indicate that L. tumana exhibits a pattern of isolation-by-distance among populations within three genetic clusters that align with geography. Mean pairwise genetic differentiation ( F ST ) among populations was 0.033. Coalescent-based demographic modelling supported divergence with gene flow among genetic clusters since the end of the Pleistocene (~13-17 kya), likely reflecting the south-to-north recession of ice sheets that accumulated during the Wisconsin glaciation. Main conclusions We identified a link between glacial retreat, evolutionary history and patterns of genetic diversity for a range-restricted stonefly imperiled by climate change. This finding included a history of divergence with gene flow, an unexpected conclusion for a mountaintop species. Beyond L. tumana , this study demonstrates the complexity of assessing genetic structure for weakly differentiated species, shows the degree to which rare alleles and missing data may influence results, and highlights the usefulness of genome-scale data to extend population genetic inquiry in non-model species.

Montana↗

USGS2017

Climate change and alpine stream biology: progress, challenges, and opportunities for the future

In alpine regions worldwide, climate change is dramatically altering ecosystems and affecting biodiversity in many ways. For streams, receding alpine glaciers and snowfields, paired with altered precipitation regimes, are driving shifts in hydrology, species distributions, basal resources, and threatening the very existence of some habitats and biota. Alpine streams harbour substantial species and genetic diversity due to significant habitat insularity and environmental heterogeneity. Climate change is expected to affect alpine stream biodiversity across many levels of biological resolution from micro- to macroscopic organisms and genes to communities. Herein, we describe the current state of alpine stream biology from an organism-focused perspective. We begin by reviewing seven standard and emerging approaches that combine to form the current state of the discipline. We follow with a call for increased synthesis across existing approaches to improve understanding of how these imperiled ecosystems are responding to rapid environmental change. We then take a forward-looking viewpoint on how alpine stream biologists can make better use of existing data sets through temporal comparisons, integrate remote sensing and geographic information system (GIS) technologies, and apply genomic tools to refine knowledge of underlying evolutionary processes. We conclude with comments about the future of biodiversity conservation in alpine streams to confront the daunting challenge of mitigating the effects of rapid environmental change in these sentinel ecosystems.

Biological Reviews↗