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Subterranean ecosystems harbor globally important yet highly threatened biodiversity. Unfortunately, subterranean biodiversity is often neglected in regional and global conservation initiatives, including conservation assessments. We reviewed the conservation status and threats to subterranean species based on the two most popular conservation assessment protocols in North America, NatureServe and International Union for Conservation of Nature (IUCN) Red List, as well as federal and state/provincial protection status of the 1,460 described cave-obligate species occurring in the United States and Canada. Only 9.3% of species have been assessed under IUCN Red List criteria compared to 77.9% of species assessed under NatureServe criteria; notably, 1,065 and 116 of species are assessed at an elevated risk of extinction by NatureServe and IUCN Red List, respectively. Just 41 species are listed or proposed to be listed under the U.S. Endangered Species Act and none of the 10 species that occur in Canada are federally listed. Vertebrates (fishes and salamanders), decapods (crayfishes and shrimps), and U.S. federally listed species are overrepresented on the list of species with IUCN Red List assessments compared to other taxonomic groups, particularly arachnids, millipedes, and insects. Most species assessed under IUCN Red List criteria as well as federally listed species occur in the Edwards Plateau and Balcones Escarpment karst region of Texas. Major threats frequently reported in conservation assessments include habitat degradation, pollution/contamination, recreational activities, climate change, and groundwater exploitation; however, information on threats was lacking for most species for nearly all major taxonomic groups, except decapods, fishes, and salamanders. The intrinsic vulnerability of subterranean biodiversity coupled with the many potential threats facing species and extensive biodiversity knowledge gaps makes assessing their conservation status and ultimately their protection a challenging endeavor. We highlight several limitations of implementing current conservation assessment approaches while offering recommendations to improve our ability to assess the conservation status of subterranean biodiversity to better inform sound local to global conservation policies and actions. 

We describe a new species of subterranean amphipod (Amphipoda: Crangonyctidae) in the genusStygobromusfrom a hypotelminorheic seepage spring at Shepherd Parkway, part of National Capital East Parks, Washington, D.C., USA, part of the National Park System, using both morphological and genetic approaches. The Anacostia Groundwater Amphipod,S. anacostensissp. nov.is a member of theS. tenuisspecies group but differs from related congeners based on body size, serrate blade-like edge of both palms of gnathopods 1 and 2, presence of rastellate setae on the posterodistal margin of the carpus of gnathopod 2, and aspects of the second antennae, mandibular palp, pereopods 5–7, uropods 1 and 2, and telson. Moreover,S. anacostensissp. nov.is genetically distinct fromS. tenuisin the Washington D.C. metropolitan area. The description ofS. anacostensissp. nov.increases the number of describedStygobromusspecies to eight in the Washington D.C. area and highlights the need for continued biodiversity studies, even in regions that have received considerable attention. 

Throughout the evolutionary tree, there are gains and losses of morphological features, physiological processes, and behavioral patterns. Losses are perhaps nowhere so prominent as for subterranean organisms, which typically show reductions or losses of eyes and pigment. These losses seem easy to explain without recourse to natural selection. Its most modern form is the accumulation of selectively neutral, structurally reducing mutations. Selectionist explanations include direct selection, often involving metabolic efficiency in resource poor subterranean environments, and pleiotropy, where genes affecting eyes and pigment have other effects, such as increasing extra-optic sensory structures. This dichotomy echoes the debate in evolutionary biology in general about the sufficiency of natural selection as an explanation of evolution, e.g., Kimura’s neutral mutation theory. Tests of the two hypotheses have largely been one-sided, with data supporting that one or the other processes is occurring. While these tests have utilized a variety of subterranean organisms, the Mexican cavefish,Astyanax mexicanus, which has eyed extant ancestral-like surface fish conspecifics, is easily bred in the lab, and whose whole genome has been sequenced, is the favored experimental organism. However, with few exceptions, tests for selection versus neutral mutations contain limitations or flaws. Notably, these tests are often one sided, testing for the presence of one or the other process. In fact, it is most likely that both processes occur and make a significant contribution to the two most studied traits in cave evolution: eye and pigment reduction. Furthermore, narrow focus on neutral mutation hypothesis versus selection to explain cave-evolved traits often fails, at least in the simplest forms of these hypotheses, to account for aspects that are likely essential for understanding cave evolution: migration or epigenetic effects. Further, epigenetic effects and phenotypic plasticity have been demonstrated to play an important role in cave evolution in recent studies. Phenotypic plasticity does not by itself result in genetic change of course, but plasticity can reveal cryptic genetic variation which then selection can act on. These processes may result in a radical change in our thinking about evolution of subterranean life, especially the speed with which it may occur. Thus, perhaps it is better to ask what role the interaction of genes and environment plays, in addition to natural selection and neutral mutation. 

Abstract Groundwater is a vital ecosystem of the global water cycle, hosting unique biodiversity and providing essential services to societies. Despite being the largest unfrozen freshwater resource, in a period of depletion by extraction and pollution, groundwater environments have been repeatedly overlooked in global biodiversity conservation agendas. Disregarding the importance of groundwater as an ecosystem ignores its critical role in preserving surface biomes. To foster timely global conservation of groundwater, we propose elevating the concept of keystone species into the realm of ecosystems, claiming groundwater as a keystone ecosystem that influences the integrity of many dependent ecosystems. Our global analysis shows that over half of land surface areas (52.6%) has a medium‐to‐high interaction with groundwater, reaching up to 74.9% when deserts and high mountains are excluded. We postulate that the intrinsic transboundary features of groundwater are critical for shifting perspectives towards more holistic approaches in aquatic ecology and beyond. Furthermore, we propose eight key themes to develop a science‐policy integrated groundwater conservation agenda. Given ecosystems above and below the ground intersect at many levels, considering groundwater as an essential component of planetary health is pivotal to reduce biodiversity loss and buffer against climate change.