Monday, September 12, 2011

The Cost of Extinction

Last year we wrote about The Sixth Extinction?, the name given to the dramatically increased rate of extinction in recent years.  Considering the cost of preserving threatened species, we have to ask "What is the cost in losing a species?" I read about a memorable example in a 1982 Gastroenterology journal.

Gastric-brooding frog- Wikimedia
The first Gastric-brooding frog was found in 1973, the last specimen was found in 1981 and the last laboratory specimen died in 1983.  Except for a lucky timing, the gastric-brooding frog might have escaped detection.

The Southern gastric-brooding frog (Rheobatrachus silus) was an unimpressive looking amphibian which was found in wet forested areas in a small area of southeastern Queensland, Australia.  They were 2-3 inches long and were rare when first described.  Their ability to raise their young in their stomach brought them to medical attention.

The female would eat the eggs it laid, hold them in her stomach as the tadpoles emerged and developed, carrying them for 6 weeks before regurgitating the young frogs.  Studies showed that the stomach was normal prior to ingesting the eggs and after "delivery."  During the time she carried the developing eggs and tadpoles acid production and gastric motility ceased.  The female frog didn't eat during that six weeks and remained active as the stomach got progressively larger until it comprised most of her body volume.

At the time, the mechanism for the acid inhibition was unknown.  Due to laboratory studies done on specimens in the few years before they became extinct, we know now.  The jelly around each egg contains prostaglandin E2 (PGE2), a substance which was able to turn off gastric secretion and motility.  The tadpoles in turn also produced PGE2 in the mucus secreted from their gills, keeping their gastric womb dormant until they are vomited up as frogs.

Consider how many other species hold secrets of medical value, secrets that may follow them into extinction.

See Wikipedia for more details.

4-11-2013  Interesting that R. silus is now being cloned, with embryos living for several days.  Stay tuned for de-extinction.

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