Whiptails in the Flood Zone

By Bruce G. Marcot, Ecology Picture of the Week:

Pictured here -- in a somewhat artistic compilation of photos -- is the western whiptail lizard.  Notice the background: a typical flash flood in the American Southwest desert of the Colorado Plateau in southern Utah.

You would expect that such floods would be catastrophic to these ground- and burrow-dwelling lizards, but some whiptail species hold a special trick in reserve.  In some locations, at some times, after catastrophe strikes, this lizard is capable of parthenogenesis, or the live birth of female offspring from female adults, without the need for fertilization by males!  In parthenogenesis, the unfertilized egg develops into a new lizard -- essentially a clone of the adult -- without contribution of male sperm.  

This capability means that whiptails are able to quickly repopulate an area wiped out by a flood.  The downside may be a simplification of the gene pool, but that might be a disadvantage only if the population was small and isolated for a relatively long period of time.  Whiptails likely are good dispersers and local populations probably readily reconnect and interbreed, so simplification of the gene pool might not be a common problem.   

Parthenogenesis is known from many invertebrates, including rotifers, snails, fruit flies, cladocerans, and others.  However, it is quite uncommon in vertebrates.  It is known in some geckos and has only very recently been discovered in the Komodo dragon.  

In fact, only or mostly females are known from some species of whiptails, such as Chihuahua whiptail (Cnemidophorus exsanguis) and checkered whiptail (C. tesselatus).  

All this has conservation importance, because it is vital to know when a wildlife population is genetically isolated or otherwise threatened, and what key habitats may be needed for its recovery.  It also could have importance for human health, by studying ways to "breed" stem cells more ethically.

  --Bruce G. Marcot

Image and text © Bruce G. Marcot, Ph.D. Research Wildlife Ecologist,
who produces the Ecology Picture of the Week website.