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

Abstract

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.

Long-distance dispersal, ice sheet dynamics and mountaintop isolation underlie the genetic structure of glacier ice worms

“…However, until more is known about the specific interactions of ice worms with various bird species, and by proxy, their potential to act as LDD vectors, relating bird migrations to ice worm distributions and demography will remain difficult. Beyond ice worms, ice sheets have been implicated as a key driver of speciation in boreal birds [47] and phylogeographic structure of many taxa, from nematodes to grey wolves [13,26,48,49], and our results clearly support these broader implications for biodiversity accumulation and maintenance in North America.…”

Rock glaciers and related cold rocky landforms: Overlooked climate refugia for mountain biodiversity

“…More frequent snow drought is also expected to disproportionally reduce in‐stream habitat types associated with higher levels of biodiversity (e.g., riffles, Herbst et al, 2018). The heterogeneity of hydrological sources in alpine headwaters has promoted high beta (among‐site) diversity in alpine streams from genetic diversity to invertebrates (Fell et al, 2018; Finn et al, 2013; Hotaling, Giersch, et al, 2019; Wilhelm et al, 2013). Until recently, CRLs were vastly underappreciated as an additional common source type, a crucial oversight given their hydrology (Figure 4) and greater resistance to climate change versus alpine glaciers and snowfields.…”

Microbial assemblages reflect environmental heterogeneity in alpine streams

“…Streams above the tree line in the alpine zone exhibit substantial environmental heterogeneity over small spatial scales, due in large part to variable hydrological sources (Brown, Hannah, & Milner, 2007;Füreder, 2007;Hotaling, Finn, Giersch, Weisrock, & Jacobsen, 2017;Ward, 1994). With such extensive habitat diversity, it is no surprise that alpine streams also support high among-stream (β) diversity across multiple taxonomic scales and classifications, including macroinvertebrate species diversity (Brown et al, 2007;Finn, Bonada, Murria, & Hughes, 2011;Giersch, Hotaling, Kovach, Jones, & Muhlfeld, 2016;Jacobsen, Milner, Brown, & Dangles, 2012), macroinvertebrate genetic diversity (Finn, Khamis, & Milner, 2013;Finn, Zamora-Muñoz, Múrria, Sáinz-Bariáin, & Alba-Tercedor, 2014;Hotaling et al, 2019;Jordan et al, 2016;Leys, Keller, Räsänen, Gattolliat, & Robinson, 2016), and microbial diversity (Fegel, Baron, Fountain, Johnson, & Hall, 2016;Freimann, Bürgmann, Findlay, & Robinson, 2013a;Wilhelm, Singer, Fasching, Battin, & Besemer, 2013). The biodiversity of alpine streams is under threat, however, as rising ambient temperatures drive the ongoing decline of mountain glaciers and perennial snowfields worldwide, and with them, the loss of hydrological variation on local and regional scales (Hotaling, Finn, et al, 2017).…”