Toad on brink of extinction, scientists race to study amphibian for bioactive compounds
Back in Tanzania, the wild Kihansi Spray Toad population had its own ups and downs. In late June 2003, with the implementation of an improved sprinkler system in the Kihansi Gorge, the wild toad population had climbed back to near 20,000 individuals. Then in July the population was hit by the devastating introduction of chytid fungus, the same pathogen that has been decimating amphibian populations around the world. The population collapsed to a mere 40 toads in early July 2003. Recent reports back from the gorge all but suggest the toad is extinct outside of captivity. The outlook for potential wild survivors is not good: once the chytid fungus arrives in an area, it never leaves. The only way to treat the fungus, which kills amphibians by invading layers of their skin, is with medicinal baths for individual toads -- there is no way to bathe an entire ecosystem.
No one knows the origin of chytid fungus in Tanzania -- the fungus had never previously been documented in Tanzania before the dam's construction. There were three exotic frog species accidentally introduced during construction, as well as trout, rumored to have been introduced in the Kihansi River upstream from the dam. Both are possible candidates for bringing the fungus. More likely however, the pathogen stowed away on an inadequately sterilized boot of a visiting biologist who had come from an infected area. The project employed biologists from both Australia and South Africa, countries with serious outbreaks of the fungus.
Attempts to revive the species through controlled releases of water through the dam have probably done more harm than good. The sudden increase in water flow during the summer of 2003 may well have swept away remaining toads and washed down trace amounts of deldrine, a pesticide used in agricultural areas above the dam, that may have contaminated the toad habitat.
Mating Kihansi Spray Toads.
In captivity, Kihansi Spray Toads usually mate in groups when the artificial misters are turned on. The misters recreate conditions once found in their natural habitat.
The difficulty in breeding and raising Kihansi Spray Toads
According to Sam Lee, one of the leading herpetologists on the Kihansi Spray Toad project, young toads are difficult to feed given their incredibly small size. In general, the diminutive stature of these amphibians makes identification and regulation of individuals rather difficult. Scientists are actually unable to tell the toads apart at all, save for individuals with deformities. This renders tracking individual progress and husbandry virtually impossible. Lee has estimated clutch sizes to range from 8 to 28 toadlets, averaging out to 12 or 13 individuals. Attributing young to any one individual and thus determining whether a female has multiple clutches in a year is difficult for the reasons discussed above. Only intensifying the problem, the Kihansi Spray Toads proved to breed best in large groups, so as the population dropped, so did the
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