Thermal refugia and the survival of species in changing environments: new evidence from a nationally extinct freshwater fish.

Variation in global climate during the Quaternary has helped shape current species distributions. The stenohaline fish fauna of the British Isles is generally thought to have colonised eastern England via a landbridge following the last glacial maximum. This theory is investigated using the nationally extinct burbot, Lota lota , as a model species. Samples were collected from 15 museum specimens of known English provenance and analysed for differences in the mitochondrial DNA control region. The DNA analysis produced eight sequences of 270 base pairs, with one sample reaching 420 base pairs in length. Genetic analysis suggests the extinct English population of the burbot was a distinct lineage, differing from those previously described from across the species’ global distribution. Despite this, network analysis suggests that the English lineage is closely related to populations in western Europe, supporting colonisation via a postglacial landbridge. The rate of genetic divergence suggests that the timing of L. lota's colonisation of English rivers was prior to the last glacial maximum. Lota lota appears to have survived the last glacial maximum in refugia within the British Isles. This study adds to the evidence for a British freshwater refugia and furthers our understanding of the colonisation history of British freshwater fishes. These results also provide valuable information for conservation strategies for L. lota indicating the western European clade as most genetically appropriate for potential future reintroductions to English rivers.