Education:Stories from the Field

Anegada iguanas: buddies or siblings?

When six confiscated Anegada iguanas were given to the San Diego Zoo by authorities, it was a mixed blessing. On one hand, these six individuals were the only representatives of the critically endangered species outside of the British Virgin Islands. And if keepers at the Zoo could get them to breed, the iguanas would become the founders of a captive population, serving to safeguard against the loss of the few hundred individuals left on the Caribbean island of Anegada. But first the Zoo had to know if and how these iguanas were related.

To get to the bottom of this mystery, scientists knew they would have to compare the genes of the six iguanas to those of the wild population. For determining relatedness, scientists look at parts of the genome called microsatellites. Microsatellites are strings of DNA that repeat a sequence of nucleotides (the building block of DNA). For example, one microsatellite could be AGAGAGAGAGAGAG, which could be written as AG7 (AG repeated 7 times). Like most animals, including humans, iguanas have two microsatellites at each locus, or point, where a microsatellite occurs: one microsatellite from each parent.

Determining relatedness takes more than just knowing where the microsatellites are. There has to be some kind of uniqueness within those microsatellites. For example, if all the iguanas had the microsatellite AG7 at one locus, it might mean that they are all siblings or it might not. Only by looking at many loci (the plural of locus) can scientists determine how closely related animals are. In the case of the Anegada iguanas, scientists from the San Diego Zoo Institute for Conservation Research compared the genes of the six individuals to genes of the wild population and, using some complex statistics, found that the six iguanas were actually three pairs of siblings: one brother- sister pair, one pair of sisters, and one pair of brothers.

Funding for this project was provided by a grant from the Institute of Museum and Library Services.


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