Tuesday, September 15, 2015

The Devils Hole Pupfish

"Living wild species are like a library of books still unread. Our heedless destruction of them is akin to burning the library without ever having read the books." -John Dingell

Devils Hole Pupfish. Photo by U.S. Fish and Wildlife Service

The Devils Hole Pupfish is but one member of an extraordinary group of fishes. Fishes which may at first glance seem unremarkable. Looks can often be deceiving, and this fish has had profound impacts on the history of the United States, and its story is puzzling to many biologists. Many years ago this fish had its day in front of the United States Supreme Court when groundwater pumping threatened its only natural habitat. Ultimately the Court sided on the side of conservationists, stating that the Federal Government owned the water rights associated with Devils Hole in order to preserve the resources therein. 

The evolutionary history of this fish and its ecology are far from unremarkable. The story of this fish merges biology, politics, anthropology, and conservation. Remember that the desert region of the Southwest is in terms of earth's history very new. A few thousand years ago huge lakes covered much of the region. Nevada, now the driest state in the United States was covered by parts of two gigantic lakes: Lake Bonneville and Lake Lahontan. The climate was generally much wetter and cooler in the Southwestern United States. Death Valley was covered by Lake Manly and Tecopa Lake. Many fish lived in these large lakes. 

The entire area started to warm and dry due to climatic factors. The lakes mentioned above started to disappear, leaving behind only remnants of their former selves. Fish in these lakes became caught in small thermal springs as deserts formed and started on new evolutionary tracts shaped by the living and non-living forces present in their unique habitats. Eventually these fish became distinct from their relatives in other springs. This is the story of most desert pupfish, this group of fish constitute some of the most endangered animals on the planet. Many species in this group have already been forced into extinction. Presumably the Devils Hole Pupfish were then trapped in their cavernous warm spring as Lake Manly receded in Death Valley?

Devils Hole, Nevada. 

Except that there is much evidence that current drainages and springs with other pupfish were at a time interconnected. There is NO EVIDENCE that Devils Hole was ever connected to another water source within the last 100,000 years. This presents a problem for many biologists who suggest that the fish separated from its ancestors well less than 100,000 years ago and some even guess that this separation might have been as recent as 360 years ago. This fish somehow colonized a secluded spring relatively recently with significant separation from other water sources and ZERO geologic evidence that it was ever connected to another water source during this time frame.

How then did this fish get into Devils Hole? Given that no evidence suggests that there was ever a way for this fish to cross a kilometer of dry land and make it into Devils Hole many biologists refuse to discount the hypothesis that humans, perhaps native peoples of the area, moved fish from another nearby spring into Devils Hole. The harsh environment of Devils Hole then provided the pressures which made this fish different from its relatives.

Recently biologists have begun to question whether the environment provided the pressure for these changes in the form of natural selection or whether the conditions at Devils Hole alter the development of this fish in a meaningful way (fish here have large heads, small bodies, and tend to lack pelvic fins). When environmental forces alter the expression of genetic material in the overlying organism we call it "phenotypic plasticity". Phenotypic plasticity could be an important reason why these fish look so different from their close relatives.

How did fish get into Devils Hole? How did they become so different from their close relatives? What role did the environment play and over what time period?

Better examination of the biology of this fish may help scientists better understand exactly what constitutes a 'species' and the role that environmental stresses play in organismal development and the evolution of populations. 

The Devils Hole Pupfish has the most restricted range of any vertebrate, and the entire population of this species is often less than 100 individuals. Luckily we began to "read the books in this library", but we almost didn't get the chance. The continued efforts of conservationists and ultimately the decision of the Supreme Court ensure that we are able to continue reading these books which may hold the answers to big questions regarding ecology and evolution.

References and further reading:

Reed, J. Michael, and Craig A. Stockwell. "Evaluating an icon of population persistence: the Devil's Hole pupfish." Proceedings of the Royal Society of London B: Biological Sciences 281.1794 (2014): 20141648.

Riggs, Alan C., and James E. Deacon. "Connectivity in desert aquatic ecosystems: The Devils Hole story." Conference proceedings. Spring-fed wetlands: important scientific and cultural resources of the intermountain region. Vol. 11. 2002.

Deacon, James E., Frances R. Taylor, and John W. Pedretti. "Egg viability and ecology of Devils Hole pupfish: insights from captive propagation." The Southwestern Naturalist (1995): 216-223.

Phillips, Kathryn. "WHAT MAKES DEVILS HOLE PUPFISH SPECIAL?."Journal of Experimental Biology 209.18 (2006).

Lema, Sean C. "The Phenotypic Plasticity of Death Valley's Pupfish Desert fish are revealing how the environment alters development to modify body shape and behavior." American Scientist 96.1 (2008): 28-36.