Monday, 1 February 2016

Diabolically Fishy Problem For Creationists

Devil's Hole pupfish, Cyprinodon diabolis.
Image credit: Olin Feuerbacher / US Fish and Wildlife Service / CC BY 2.0
Diabolical survival in Death Valley: recent pupfish colonization, gene flow and genetic assimilation in the smallest species range on earth | PRSB.

Something diabolical indeed for creationism!

Now we have an example of rapid genetic diversification leading to a new species in just a few hundred years, and this could well have happened several times with repeated cycles of repopulation, evolution and extinction.

The Devil's Hole pupfish, Cyprinodon diabolis, has been described as one of the rarest fish on Earth and exists only in a small, aquifer-fed geothermal pool in a Mojave Desert cavern to the east of Death Valley, Nevada, USA. It is no more than 25mm long (1 inch) and is the smallest of the desert pupfish (Cyprinodon) genus. The temperature in the geothermal pool (33oC) would be fatal to many fish. The species is entirely dependent on a shallow limestone shelf of only 2 metres (6.6 ft) by 4 metres (13 ft) for spawning as well as for much of their diatom diet.

Devil’s Hole is one of the most ridiculous fish habitats I’ve seen. The water temperature would kill most fish within hours.

Christopher H. Martin, Department of Biology,
University of North Carolina, Chapel Hill, NC, USA
Lead author. (Quoted in New Scientist)
Pupfish have been isolated in springs and aquifers in the area since the former lake dried up at the end of the last Ice Age. The area is known to have last been flooded 13,000 years ago, so this was thought to have been the most recent date when genetic intermixing could have occurred and when the present population became isolated. However, this piece of research, using known mutation rates from related species of Cyprinodon in the Yucatan Peninsula, Mexico, based on known isolation times since Yucatan was last flooded, may show a much more recent last genetic isolation as recently as between 150 and 830 years ago. There appears to have been genetic mixing with related population as recently as a few hundred years ago. This means the Devil's Hole pupfish has diversified from related species in the area in just a few hundred years:

One of the most endangered vertebrates, the Devils Hole pupfish Cyprinodon diabolis, survives in a nearly impossible environment: a narrow subterranean fissure in the hottest desert on earth, Death Valley. This species became a conservation icon after a landmark 1976 US Supreme Court case affirming federal groundwater rights to its unique habitat. However, one outstanding question about this species remains unresolved: how long has diabolis persisted in this hellish environment? We used next-generation sequencing of over 13 000 loci to infer the demographic history of pupfishes in Death Valley. Instead of relicts isolated 2–3 Myr ago throughout repeated flooding of the entire region by inland seas as currently believed, we present evidence for frequent gene flow among Death Valley pupfish species and divergence after the most recent flooding 13 kyr ago. We estimate that Devils Hole was colonized by pupfish between 105 and 830 years ago, followed by genetic assimilation of pelvic fin loss and recent gene flow into neighbouring spring systems. Our results provide a new perspective on an iconic endangered species using the latest population genomic methods and support an emerging consensus that timescales for speciation are overestimated in many groups of rapidly evolving species.

© 2016 The Author(s)

This suggests that there is a small occasional movement of pupfish from nearby springs into the isolated Devil's Hole cavern, as few as a single fish every hundred years or so. Possible agents could be eggs stuck to wading bird's legs or even humans catching fish and releasing them in a new location. On that point, when I was a child, I used to try to introduce fish like pike into a local pond, until the owner said something was eating the ducklings.

This is a very interesting paper, and it deals with a fascinating study system. The short timeframe of evolution is really remarkable.

Simon Ho, computational evolutionary biologist,
University of Sydney, Australia (Quoted in Nature.)
In 2013, the population of C. diabolis was reduced to just 35 individuals, though there has been some recovery since. This small population as well as the highly specialised and vulnerable habitat would normally be expected to lead to eventual extinction due to inbreeding and habitat destruction, but this study suggests a cycle of extinction and repopulation, followed by diversification from the founder population is a distinct possibility. The present species could be the result of the last such repopulation just a couple of hundred years ago.

For creationists, who like to pretend that mutations are always deleterious, despite all the evidence to the contrary, this study takes some explaining. Depending on which contradictory belief creationists are pushing, either evolution never happens at all, or it is sufficiently fast to account for all the present species from just a handful of survivors on a boat from 4000 years ago. The problem is, even diversifying to this extent in just a few hundred years, is too slow to account for the several entirely new species every year for the warp-speed, post flood diversification they need but which has never been observed. It also shows that mutation is not deleterious, that in a small isolated population, evolution occurs and can be rapid.

It must be such a struggle being a creationist when none of the evidence ever supports you and instead always contradicts your beliefs. And you have to suffer all this just to try to impress an imaginary friend in the hope it won't hurt you because someone frightened you with stories when you were an impressionable child. No doubt they'll need to invoke the fall-back parody of evolution - that the TOE is a theory about how new orders evolve - with, "Well, they're still fish!",

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