The ancient B ritons: groundwater fauna survived extreme climate change over tens of millions of years across NW E urope

Abstract

Global climate changes during the C enozoic (65.5–0 Ma) caused major biological range shifts and extinctions. In northern E urope, for example, a pattern of few endemics and the dominance of wide‐ranging species is thought to have been determined by the P leistocene (2.59–0.01 Ma) glaciations. This study, in contrast, reveals an ancient subsurface fauna endemic to B ritain and I reland. Using a B ayesian phylogenetic approach, we found that two species of stygobitic invertebrates (genus N iphargus ) have not only survived the entire P leistocene in refugia but have persisted for at least 19.5 million years. Other N iphargus species form distinct cryptic taxa that diverged from their nearest continental relative between 5.6 and 1.0 Ma. The study also reveals an unusual biogeographical pattern in the N iphargus genus. It originated in north‐west E urope approximately 87 Ma and underwent a gradual range expansion. Phylogenetic diversity and species age are highest in north‐west E urope, suggesting resilience to extreme climate change and strongly contrasting the patterns seen in surface fauna. However, species diversity is highest in south‐east E urope, indicating that once the genus spread to these areas (approximately 25 Ma), geomorphological and climatic conditions enabled much higher diversification. Our study highlights that groundwater ecosystems provide an important contribution to biodiversity and offers insight into the interactions between biological and climatic processes.

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