Evaluating an icon of population persistence: the Devil's Hole pupfish

Abstract

The Devil's Hole pupfish Cyprinodon diabolis has iconic status among conservation biologists because it is one of the World's most vulnerable species. Furthermore, C. diabolis is the most widely cited example of a persistent, small, isolated vertebrate population; a chronic exception to the rule that small populations do not persist long in isolation. It is widely asserted that this species has persisted in small numbers (less than 400 adults) for 10 000–20 000 years, but this assertion has never been evaluated. Here, we analyse the time series of count data for this species, and we estimate time to coalescence from microsatellite data to evaluate this hypothesis. We conclude that mean time to extinction is approximately 360–2900 years (median 410–1800), with less than a 2.1% probability of persisting 10 000 years. Median times to coalescence varied from 217 to 2530 years, but all five approximations had wide credible intervals. Our analyses suggest that Devil's Hole pupfish colonized this pool well after the Pleistocene Lakes receded, probably within the last few hundred to few thousand years; this could have occurred through human intervention.

Phylogenetics support an ancient common origin of two scientific icons: Devils Hole and Devils Hole pupfish

“…). For these reasons, DHP has been called ‘the rarest fish on earth’ and ‘an icon of population persistence’ (Bittel ; Crew ; Reed & Stockwell ).…”

Diabolical survival in Death Valley: recent pupfish colonization, gene flow and genetic assimilation in the smallest species range on earth

“…Rather than using an approximate simulation of the likelihood (e.g. [38]), dadi directly calculates the likelihood of the joint-site frequency spectrum under various demographic scenarios using a diffusion approximation [63].…”

“…However, additional uncertainty in microsatellite mutation rates (10 23 - 10 26 ) was not accounted for by use of a point estimate from mammals (10 23 ), nor was the known failure of a molecular clock for microsatellite mutation rates [39]. Thus, despite substantial attention, diabolis age estimates still range from 90 to 20 000 years [38,40]. Furthermore, additional outstanding questions about the survival of this species within its habitat remain: was Devils Hole colonized only once?…”

“…The census population size of Cyprinodon diabolis within Devils Hole has varied from only 35-548 individuals since semi-annual monitoring began in 1972 [23], reaching its record low in 2013 and second lowest point (38) in [2006][2007]. In addition to limited spawning habitat (a single 2.6 Â 6.1 m shelf [22]: figure 1d), the population is limited by the productivity of Devils Hole, which receives no direct sunlight for two months each year and produces 200 times less algal biomass than neighbouring springs [24].…”

“…A recent study estimated the age of diabolis from the coalescence of 12 microsatellite loci using approximate Bayesian computation without assumptions about overland dispersal and placed the age between 90 and 14 400 years (95% credible intervals in table 1: [38]). However, additional uncertainty in microsatellite mutation rates (10 23 - 10 26 ) was not accounted for by use of a point estimate from mammals (10 23 ), nor was the known failure of a molecular clock for microsatellite mutation rates [39].…”