No vertebrate shows greater diversity than the humble fish, with over 30,000 species estimated globally. However, this diversity has never been at greater risk. Climate change, overfishing, and environmental alterations by humans are among the top reasons that around a third of fish species are threatened with extinction. Intervention to preserve these species is often delayed until long after the problem arises, when the species has already experienced a large population decline. Recent work from the lab of Christopher Martin in the Department of Integrative Biology at UC Berkeley highlights the importance of species preservation before population decline occurs.

The Devils Hole pupfish is a critically endangered species (just 263 in the wild, as of September 2022), found only in the water-filled cavern in Nevada it takes its name from. Martin’s group investigated this unique species to evaluate the effects of isolation and population decline on inbreeding and genetic mutation load. Sequencing a preserved specimen from 1980 showed that the species was already highly inbred before recent population bottlenecks, suggesting a long history of population decline and recovery. While this study didn’t directly evaluate the effect of species fitness, the types of inbred mutations observed by Martin’s group are widely considered harmful.

Over time, inbreeding within small populations can lead to a decline in fertility and subsequent extinction. Martin’s work highlights a unique species whose history of population decline and recovery has resulted in significant inbreeding while staying above the threshold for extinction. With the population of the Devils Hole pupfish on the rise, there may soon be more opportunities to study this unique species on the edge of extinction.