Today@Sam Article

Professor Helps Sequence DNA From Extinct Giant Gecko

June 21, 2023
SHSU Media Contact: Mikah Boyd

Sam Houston State University associate professor Juan Diego Daza in the Department of Biological Sciences collaborated with fellow herpetology researchers nationwide to place an extinct, giant gecko in its proper place on the evolutionary timeline. Their collaborative research allowed them to not only contribute to the study of the evolution of geckos but also added to current discussions of gigantism in isolated island environments. 

DNA from a 200-year-old museum specimen helped researchers resolve the evolutionary relationships of an extinct, giant gecko. Extracting and sequencing DNA from the gecko allowed researchers to reconstruct its evolutionary relationships with living gecko species. The results, published in the journal "Scientific Reports," place the specimen in the gecko evolutionary tree and provide insights as to where the giant creature might have lived.

Delcourt's Giant Gecko, Gigarcanum delcourti, was formally described by scientists Aaron Bauer and Anthony Russell in 1986. The description is based on a single individual discovered in the collection of the Muséum d'Histoire Naturelle de Marseille in France. The specimen was unique for many reasons, the most obvious being its enormous size. The body, without the tail, was 14.5 inches (370 mm) long – approximately 50% longer than the next largest known gecko species, Rhacodactylus leachianus. 

"I cannot overemphasize how huge this gecko is. Most geckos are small, just a few inches long, Gigarcanum delcourti is the size of a small house cat," said Tony Gamble, from Marquette University, and co-author of the study.

Gigarcanum delcourti is presumed extinct as no living specimens have ever been found in the wild. This gecko is a close relative of the crested gecko, which is commonly used as a pet.

It is unknown where the giant gecko lived in the wild. The lone Gigarcanum delcourti specimen was most likely acquired by the museum between 1833 and 1869 but records from this time are incomplete, leaving the timing and exact source unknown. The giant gecko was outwardly similar to geckos from New Zealand and roughly matched the description of the kawekaweau, a giant lizard in Maori folklore. Gigarcanum delcourti DNA, however, shows that it is closely related to geckos from New Caledonia, a French island territory northeast of Australia and north of New Zealand.

“Gigarcanum delcourti was the first of more than 200 geckos I have described during my career, and it remains the most intriguing. It is rewarding to be able to revisit it and decipher its ancestry nearly 40 years after I first set eyes on the specimen in Marseille,” said Aaron Bauer, the Lemole endowed chair in Integrative Biology at Villanova University and co-author of the study.

The largest living gecko species, Rhacodactylus leachianus, is from New Caledonia, allowing researchers to make sense of these results in light of what they know about the evolution of large body size in geckos. But G. delcourti, which is here allocated to a new genus, represents an independent attainment of large size among the New Caledonian gecko lineage.

“Placing this species in its evolutionary context allows us to more accurately measure patterns of change over time in geckos,” said Matthew Heinicke from the University of Michigan-Dearborn and lead author of the study. “It turns out that this giant species belongs to an entire group of geckos that rapidly diverged in body size after they began diversifying in New Caledonia some 25 million years ago, perhaps because these rapid changes were adaptive in an isolated island environment that only a few other reptiles successfully colonized.”

To extract DNA, the researchers drilled the leg bone of the giant gecko, which is roughly smaller than a chicken thigh bone, and extracted dry bone marrow tissue, a rich tissue in blood vessels packed with platelets, which have mitochondria and blood cells.

“I am used to working with geckos in the other limit of the size spectrum, the miniaturized species like many geckolets living in the Caribbean and South America, so just looking at this giant animal makes you wonder about many physical constraints that they might have faced,” Daza said.

The study involved researchers from the University of Michigan–Dearborn; Louisiana State University Shreveport; Florida Museum of Natural History, University of Florida; Villanova University; Rutgers University–Camden; Sam Houston State University; The Bell Museum of Natural History, University of Minnesota; Milwaukee Public Museum; and Marquette University.

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