Home » LSUS faculty co-authors research that reclassifies world’s largest known gecko

LSUS faculty co-authors research that reclassifies world’s largest known gecko

by Minden Press-Herald

The world’s largest known gecko will have a new name thanks to research conducted by a group of herpetologists, which included LSUS faculty member Dr. Stuart Nielsen. 

Nielsen co-authored a study in which DNA was extracted from a 200-year-old museum specimen, the only existing example of Hoplodactylus delcourti, which is approximately 50 percent longer than the next largest known gecko species – Rhacodactylus leachianius (about 14.5 inches long). 

Dr. Stuart Nielsen, LSUS Assistant Professor of Biological Sciences, co-authored a study in which DNA was extracted from a 200-year-old museum specimen gecko, the largest known gecko species in human history. Genetic analysis led to the renaming of this species to Gigarcanum delcourti. 

This gecko, which was collected in the mid-1800s by the Museum d’Historie Naturelle de Marseille in France, had similar physical characteristics to New Zealand geckos and roughly matched the description of the kawekaweau, a giant lizard in Maori folklore. Incomplete records prevented researchers from knowing exactly where and when this likely extinct species was collected. 

But DNA analysis suggests that H. delcourti is more closely related to “diplodactylid” geckos from New Caledonia, a French island territory north of New Zealand and east of Australia and home to the other giant gecko, R. leachianus

Nielsen’s group renamed the giant gecko with the genus name Gigarcanum, which consists of two Latin words that mean “giant secret or mystery.” The gecko’s new name in scientific communities isGigarcanum delcourti

“Lizards in the genus Hoplodactylus are restricted to New Zealand, and the closest lineages to H. delcourti are from New Caledonia,” said Nielsen, who was involved in the genetic data analysis and the generation of phylogenetic trees (hypotheses of relationships based on genetic data). “Although we can’t 100 percent say this gecko is not from New Zealand, all of the evidence we have at the moment suggests it is probably not the kawekaweau of Maori folklore and probably lived in New Caledonia. 

“This meant we needed to give it a new genus name reflecting this novel finding.” 

The research is published in the journal Scientific Reports. 

Dr. Aaron Bauer, who has described more than 200 geckos and first described H. delcourti nearly 40 years ago, said it’s rewarding to solve the mystery surrounding its origin. 

Marquette University biologist Tony Gamble, one of the authors of this study,holds a Rhacodactylusleachianus, the largest living species of gecko. Photo credit: Aaron H. Griffing.

“Placing this species in its evolutionary context allows us to more accurately measure patterns of change over time in geckos,” said Bauer, the Lemole Endowed Chair in Integrative Biology at Villanova University and co-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. 

“With more than 2,200 species, geckos provide an excellent study system for asking evolutionary questions of all types. G. delcourti challenges our ideas about how big a gecko can be and helps fuel the long-standing interest in the phenomenon of island gigantism.” 

One particular facet for broader evolution is that the sharing of physical traits doesn’t necessarily correlate to the closest relationship upon DNA comparison. 

Gigarcanum delcourti shared similar toepad structures among other physical traits with geckos in thegenus Hoplodactylus from New Zealand, but it’s genetic connection to diplodactlylid geckos of New Caledonia is telling. 

Diplodactlylids feature a wide range of body sizes and toepad structures, features that repeatedly changed throughout its evolution, presumably because of environmental pressures. 

“This is a mystery that could be only be solved with modern advances in DNA extraction and sequencing,” Nielsen said. “The result has completely rewritten the history of the island rule with respect to gigantism within this lizard family. 

“Before, both New Zealand and New Caledonia seemed to have been evolutionary hotbeds for size disparity (both gigantism and dwarfism). That now seems to be mostly restricted to New Caledonia in terms of these extremes in size. Hopefully this research spurs others to try and answer why New Caledonia is different in this way.” 

Nielsen, the Hubert & Pat Hervey Endowed Professor for the LSUS Museum of Life Sciences, joined Villanova’s Bauer and researchers from the University of Michigan-Dearborn, University of Florida, Rutgers University, Sam Houston State University, University of Minnesota, Marquette University, The Bell Museum of Natural History and the Milwaukee Public Museum. 

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