The Himalayan uplift and evolution of aquatic biodiversity across Asia: Snowtrout (Cyprininae: Schizothorax) as a test case

primitive barbin clade was isolated by tectonism on the QTP [19], thus serving as the progeni- tor for contemporary Schizothorax. The subfamily Cyprininae was recently revised [20], based on a combination of molecular markers [i.e., cyt-b (N = 791); mitogenomes (N = 85); nuclear RAG-1 sequences (N = 97)], with Schizothorax being retained within the monophyletic tribe Schizothoracini, which evolved either pre- or post-Barbini, depending upon the molecular marker employed. Six major biogeographic groups of Snowtrout have been proposed [21]: A Central Asiatic clade, followed by five drainage-specific sister-clades: YLTR/ Brahmaputra; Indus; Irrawaddy; Mekong/Salween; and Yangtze. However, this perspective remains topographically incomplete as data for major Himalayan drainages were unavailable. We extended these results by focus- ing on two previously unrepresented regions: Bhutan (eastern Himalaya) and Nepal (central Himalaya). In tandem, they link the far eastern Himalaya with its western terminus, thus allowing for a more complete evaluation of tectonism, orogeny, and the potential diversifica- tion of aquatic biodiversity in the region. By filling these biogeographic gaps, Snowtrout can be more appropriately recognize as a biodiversity component extending from Central Asia, across the QTP into eastern, southern, and western Asia. This, in turn, provides a formal tem- plate of regional biodiversity from which potential impacts of Quaternary climate oscillations can be more appropriately interpreted [22]. Contemporary significance

The QTP (and surrounding mountains) are termed the “third pole” because the region con- tains the greatest amount of global snow and ice beyond the Arctic/Antarctic. It also represents the headwater source for 10 large Asian rivers (Fig 1A), which collectively provide ecosystem services for >1.5 billion people [23]. Glaciers in the eastern Himalaya, for example, represent an estimated 14.5% of the global total, a quarter of which has been lost since 1970 [24], due largely to a regional warming 2x greater than the global average [2]. These cumulative impacts are recorded as increasing precipitation, decreasing glacial surface area, diminishing snow cover, expanding glacial lakes, and a loss of permafrost [25]. These biophysical occurrences have substantially impacted the distribution of Schizothorax, provoking a migration into higher-elevation streams with a concomitant contraction of trail- ing-edge habitats [26]. This redistribution has also facilitated contact with invasive aquatic predators [27], and represents an essential element of ecological resilience for Schizothorax (e.g., its adaptive capacity). This shift further adds to the taxonomic uncertainties within the genus, as well as emphasizing the strong potential for unrecognized, cryptic diversity. A comprehensive understanding of endemic biodiversity is a necessary requirement for holistic, scalable approaches that mitigate the impacts of regional climate-change. These must be derived from standardized metrics that quantify interspecific variation across political

boundaries. Such an approach can provide templates for cooperative regional conservation [25] and help define the ecological resilience of native biota, against which climate impacts are defined and incorporated. Herein, our approach is to evaluate a biologically-complex genus of freshwater fish as a focal point for the development of such components. Materials and methods Ethics statement All methods were performed in accordance with relevant guidelines and regulations. Nepali samples were collected as one component of a Fulbright Award to DRE (see Acknowledg- ments), whereas Bhutanese collecting permits were in conjunction with the National Research and Development Centre for Riverine & Lake Fisheries (NRDCR&LF), Ministry of Agriculture PLOS ONE Himalayan uplift and aquatic evolution PLOS ONE | https://doi.org/10.1371/journal.pone.0289736 October 24, 2023 4 / 27