Wall lizards in Ohio reproduced their way out of a genetic bottleneck

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Wall lizards in Ohio reproduced their way out of a genetic bottleneck

Study suggests ecology mostly explains Cincinnati invasion success

Non-native wall lizards living in Cincinnati, Ohio, have thrived against the odds thanks to an ability to expand their population more quickly than any inbreeding-amplified harmful genes could weaken their chances for survival, new research suggests.

An estimated 10 of these European common wall lizards arrived in southwest Ohio in the 1950s, brought home by a boy who smuggled them in his luggage after a vacation in northern Italy. Now, hundreds of thousands - and maybe even millions - of them scamper through urban parks and neighborhoods across Cincinnati. They're called "Lazarus lizards" in a nod to the boy's family, founders of the Lazarus retail chain.

Researchers sequenced genomes from four different populations of the lizards, looking for genetic clues to explain how this tiny army could complete such a successful invasion. And though the analysis showed evidence of some loss of genetic variation and a dip in population size, the findings led the team to propose that rapid population growth was a major key to their survival, along with the likelihood that living conditions in Ohio resembled what they were used to back home.

"They just grew so fast. If you think you have a bottleneck, but it doesn't last very long, then you don't have a bottleneck," said senior study author H. Lisle Gibbs, professor emeritus of evolution, ecology and organismal biology at The Ohio State University. "The hypothesis that we argue is they just grew their way out of their potential genetic problem.

"In some ways, we're disproving the importance of genetic factors to the system, because it doesn't really explain a lot about the tremendous success of these lizards in Cincinnati," he said.

The study was published recently in the journal Molecular Ecology.

Genomes from four sets of samples were sequenced and analyzed for the study: a group collected in 2009 from the source location in northern Italy; samples from two Cincinnati populations collected in 2007 and 2022; and samples from a population that existed briefly in 2021 in Columbus, Ohio, which served as a surrogate for the original lizards introduced to Cincinnati in 1951 - in that it was a recent introduction likely founded by just a few individuals.

Results showed that the lizards experienced reduced genetic variation after their arrival in Cincinnati, but the loss didn't seem to have an effect on population health.

Based on what was seen in the Columbus population - lots of inbreeding, evidence of homozygosity that would increase the risk for harmful gene variants that could lower survival, and a big drop in numbers followed by rapid growth - the researchers concluded a similar scenario played out in Cincinnati decades ago.

"But all of the inbreeding with one another didn't seem to matter. They were able to get over that hump and grow like crazy," Gibbs said.

Eric Gangloff, associate professor of biological sciences at Ohio Wesleyan University and a co-author of the study, has been studying European common wall lizard ecology since 2017 in France and Ohio. The lizards are a great example of a species that can do well in nature despite the damaging effects human activity can have on biodiversity, he said.

"By and large, it seems like they were plopped into an environment that was very conducive to their spread and not that different from what they experienced in Europe originally," Gangloff said. "Milan and Cincinnati are very different. But from a lizard's point of view, they have a very similar climate and very similar structural habitat. And in their case in Cincinnati, they just didn't have any other competitors. And they were able to take off."

There were a few genomic differences between the Italian source lizards and the Cincinnati populations that hinted at adaptation to the new environment, including genes related to neural function - suggesting behavioral flexibility - and a pathway involving learning and memory that, in humans, helps lessen the effects of lead toxicity.

This second finding is of interest because European common wall lizards have astronomically high levels of lead in their blood, but show no signs of suffering from lead poisoning. Gangloff's lab is exploring this unusual characteristic.

"It is an interesting part of the story that of all the regions of the genome, we happened to find one that suggests they're responding to levels of lead in the environment," he said.

For these lizards, urban living may be a requirement rather than an environment they settle for.

"There are so many of them that you'd think they would just spill into the countryside, but they don't. So something is constraining them to urban areas," Gibbs said. "The world is full of invasive species, and we still don't really understand why one group does really well and another doesn't. This gives us a hint about that.

"But it's also a story about urban adaptation. We recognize that urban environments exert a lot of selective influences on species, and this is another example of that."

This work was funded by the U.S. National Science Foundation and Ohio State, and was performed using resources provided by the Ohio Supercomputer Center.

The collaboration between the Gibbs and Gangloff labs created valuable opportunities for others at both institutions. First author Emily Bode led this research while studying as an undergraduate at Ohio Wesleyan and a master's student at Ohio State. Co-author Andrew Mason, an Ohio State postdoctoral scholar, received experience in undergraduate supervision at a small liberal arts college as a mentor to Bode on the project, a partnership that continued between Bode and both Mason and postdoctoral scholar Peri Bolton, a study co-author, when she came to Ohio State for her graduate work. Ken Petren of the University of Cincinnati was also a co-author of the paper.

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