Evolution 2019: Can Archival DNA Illuminate A. roosevelti’s Evolutionary History?

Resolving how extinct species are related to extant ones is often a challenge, as we may not possess the right information, especially genetic data, needed to understand how these species evolved from others. Recently, scientists have increasingly employed archival DNA, or DNA taken from preserved specimens such as those in natural history collections, to understand the evolution of extinct species, including the quagga and thylacine among others.

Thylacines (Thylacinus cynocephalus) in the National Zoo, Washington D.C. (Smithsonian Institute).

Fortunately, to our best knowledge, only one species of anole is suspected to have become extinct in historical times, Anolis roosevelti, the presumed crown giant anole of the eastern Puerto Rico Bank, where it was found on Vieques, Culebra, St. John, and Tortola. Something of a holy grail for anolologists, many researchers have done their best Indiana Jones and taken a crack at finding living A. roosevelti, including some truly heroic fieldwork.

Puerto Rico and the Virgin Islands, with the known distribution of Anolis
roosevelti (stars). From west to east: Vieques, Culebra, St. John, and Tortola. From Mayer and Gamble 2019.

Despite these efforts, no live individuals have been found. Only six specimens of A. roosevelti are known to exist and thus are precious records of this presumably lost species. Previous work has used quantitative characters to attempt to resolve the placement of A. roosevelti in the anole phylogeny, but genetic data is the gold standard for describing evolutionary relationships. Could archival DNA from these specimens, preserved at museums across the world, resolve how A. roosevelti is related to extant species?

MCZ 36138, the holotype of Anolis roosevelti. Laszlo Meszoly, del. From Mayer and Gamble 2019.

Greg Mayer at University of Wisconsin-Parkside and Tony Gamble at Marquette University have embarked on their own quest to answer this question. First, Greg tracked down all six known specimens of A. roosevelti. He determined that they have all been preserved in ethanol, rather than formalin, indicating a reasonable chance of obtaining DNA from these individuals. Because the roosevelti specimens are so precious, Greg and Tony worked to generate a proof of concept for the use of archival DNA sequencing on them. They extracted DNA from specimens of the common crested anole (Anolis cristatellus) preserved using the same methods by the same collectors and at the same times and general locations.

One of the six extant specimens of A. roosevelti (ZMUK 37642, Vieques, A.H. Riise; photo by Mogens Andersen).

They were able to successfully extract and sequence at least partial mitogenomes from 5 of 8 historical samples, including some preserved as far back as 1861! The sequences from these archival specimens clustered with those collected contemporaneously from similar localities. These results indicate that the sequencing of archival DNA provides quality data and that similar procedures are likely to be effective in A. roosevelti specimens.

Greg and Tony’s next step is to obtain tissue from these important specimens, sequence their mitogenomes, and add to our knowledge of this presumably extinct species. Stay tuned for their findings!

For more info, check out the article in Anolis Newsletter VII:

Mayer, G. C. and T. Gamble. 2019. Using archival DNA to elucidate anole phylogeny. Anolis Newsletter VII, p. 158-168. Eds. Stroud, J.T., Geneva, A.J., Losos, J.B. Washington University, St. Louis MO.