A hotspot of groundwater amphipod diversity on a crossroad of evolutionary radiations

Abstract

Aim: Groundwater harbours an exceptional fauna and provides invaluable ecosystem services, yet is among the least explored and consequently least protected ecosystems. Successful protection of its biodiversity depends on complete species inventories, knowledge of species spatial distribution, and quantification of biodiversity patterns, as well as disentanglement of the processes that shaped biodiversity patterns. We studied the hyper-speciose amphipod genus Niphargus as a model system within a global subterranean biodiversity hotspot. We linked the biodiversity patterns with possible underlying processes and discuss the needs to include information on different origins of biodiversity into conservation approaches.Location: Europe, Western Balkans. Methods:We analysed biodiversity patterns of Niphargus using two biodiversity metrics, species richness and phylogenetic diversity, on a grid-based approach. To account for high cryptic diversity, we replaced nominal species with taxonomic units identified in unilocus delimitations (MOTUs). We built a time-calibrated multilocus phylogeny of 512 Niphargus MOTUs from within and outside the study area, and calculated Faith's phylogenetic diversity, standardized effect sizes of phylogenetic diversity, and residual of phylogenetic diversity regressed onto species richness.Results: Within the study area, we recognized 245 MOTUs, belonging to different Niphargus clades. Species richness is highest in a north-western hotspot, although some species-rich cells were detected also in the south-east. High phylogenetic diversity coincides with high species richness in the north-west, while in the south-east it is lower than expected. Main conclusions:We have shown that species richness does not predictably correlate with phylogenetic diversity. This difference suggests that different processes have led to the formation of species-rich areas in the Western Balkans: through a combination of dispersal and speciation in the north-west, and local radiation in the south-east, respectively. This calls for caution in conservation strategies relying solely on number of species and may change the view on conservation priorities within this region.

Climate, immigration and speciation shape terrestrial and aquatic biodiversity in the European Alps

“…In this way, fragmentation of the terrestrial habitat and consequently of populations during the Pleistocene might have accelerated allopatric speciation (Pleistocene species pump) in terrestrial organisms, explaining part of the endemic diversity in this realm. A similar phenomenon likely drove Pleistocene speciation in amphipods, as recently proposed [ 94 ]. Therefore, differential impacts of Quaternary climate fluctuations and the resulting glaciations on different biomes and taxa go a long way in helping to explain extant patterns of diversity and endemism in the region.…”

“…Unlike fish, endemic amphipods, the second fully aquatic taxon in our data, emerged during or above all before the Pleistocene. Amphipod radiations in Europe are known for being rather ancient, predating the Pleistocene [ 28 , 92 , 93 ], while the youngest radiations probably are from the Pleistocene [ 94 ]. This corresponds to the paucity of postglacial speciation noticed here for this group across the Alps.…”

“…This corresponds to the paucity of postglacial speciation noticed here for this group across the Alps. The presence of many relatively old endemic amphipods in this region could be because, surviving in smaller water bodies than those required by fish, they may have persisted under ice cover, in glacier forefields [ 95 ], or in subterranean refugia, such as caves or groundwaters [ 26 , 28 , 94 ], habitats that were not completely erased by the Pleistocene glaciations.…”

New progress in exploring the mechanisms underlying extraordinarily high biodiversity in global hotspots and their implications for conservation

“…Borko et al (2022) analysed biodiversity patterns of Niphargus using two biodiversity metrics, species richness and phylogenetic diversity, on a grid‐based approach in Western Balkans. They found that species richness does not predictably correlate with phylogenetic diversity.…”

Determinants of range sizes pinpoint vulnerability of groundwater species to climate change: A case study on subterranean amphipods from the Dinarides

“…The potential determinants of the range sizes of aquatic subterranean species were explored using the subterranean amphipod genus Niphargus, a mega-diversified genus of the Western Palaearctic, with more than 500 described and undescribed species (Borko et al, 2022). Niphargus species differ in their ranges; some are narrowly distributed or even single-site, and some have exceptionally large ranges extending over 1000 km (Copilas ¸-Ciocianu et al, 2017;Bregovi c, Fišer & Zagmajster, 2019).…”