A critically endangered Puerto Rican toad was for the first time born via in vitro fertilization as U.S. scientists attempt to save it from extinction. 

Olaf – named in honor of the frozen semen he came from – is the first of more than 300 Puerto Rican crested toads that hatched after the first attempt failed. 

The scientists traveled to the southwest town of Guayanilla last year to collect semen from six male Puerto Rican crested toads that were later released back into the wild. The scientists were careful to select bigger toads that had what are called "nuptial pads" on their thumbs, which indicate sexual maturity and help them grab on to females. 

The team, which included scientists with the U.S. Fish and Wildlife Service and Puerto Rico's Department of Natural Resources, among others, preserved the semen in liquid nitrogen as they transported it to the Fort Worth Zoo, where a couple of female toads injected with hormones awaited. 

To prepare the toads for successful reproduction, scientists expose them to cooler temperatures for about three months and sometimes will even re-create rain. 

Of the more than 300 toads that were born via in vitro, 100 were sent to other zoos with captive breeding programs and the remaining 200 will be sent to Puerto Rico in December via FedEx to be released into the wild. 

The Puerto Rican crested toad was thought extinct until the 1960s and was then rediscovered in the early 1980s. Most of the population lives in the southern half of the U.S. territory, with no northern toads spotted since 1992. But concerns are growing about their ability to survive climate change. In the southwest coastal town of Guánica, where the population remains most stable, rising sea levels are threatening their habitat. The toads live near the beach, and scientists fear that in upcoming years, saltwater will seep into the ponds they use for breeding. 

The toad's wild population in Puerto Rico is estimated anywhere from 300 to 3,000. 

(Cover photo via VCG. Edited by Li Yujun.)

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