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.

Overall, the analysis of nearly 3,000 species showed more diversity of body types among the pelagic fishes, those that swim in open water, than among the benthic species spending their life on the ocean floor. Pelagic fish body types span from the round anglerfish to skinny eels, while benthic fishes generally share a common elongated, tapered shape. 

“We found that evolution pushes and pulls fish body shape in different directions depending on whether they’re benthic or pelagic,” said lead study author Elizabeth Santos, assistant professor of evolution, ecology and organismal biology at The Ohio State University. 

“We talk about the deep sea as if it is sort of all one thing, when really it is not – it is actually quite diverse,” she said. “There are very different types of environments in the deep sea that have their own different effects on evolution.” 

The study was published recently in the journal Evolution.

Santos and colleagues analyzed shape characteristics among ray-finned fishes living 200 or more meters below the surface, the portion of the world’s oceans constituting almost 90% of their volume. 

Using previously published datasets of fish body shape measurements, evolutionary relationships and habitats, the researchers included 2,882 deep-sea species in this study. 

They found that increasing ocean depth promoted diversification in body shape, and that evolution occurred more rapidly at deeper depths than in shallower waters. 

The faster rate of evolution – essentially, a lot of change in a relatively short period of time – was most common in bottom-dwellers, suggesting their similar body shapes resulted from more closely related species adapting in place. In contrast, the higher diversity of body shapes in open-water fishes hinted at the possibility that colonization by invading species has resulted in a community of more distantly related species. 

“Colonization of the deep pelagic seems to be a more typical route for achieving diversity than the benthic,” Santos said. “In the water column, you see more lineages that are very distantly related from each other that probably colonized that habitat at all different times. And that’s why you get a lot of diversity. 

“Whereas in the benthic environments, that’s true to some extent but not to the same level. You get fewer lineages that have been in that habitat a little longer – and that’s potentially why you see less variety in body shape.” 

The findings also shed light on how living in the dark affects the evolution of marine life. Only trace amounts of sunlight can reach the 200-meter depth, but it’s not enough to enable photosynthesis – making the deep sea a dividing line that has an impact on how fishes spend their time hunting for food, one driver of evolutionary change. 

For example, Santos said, compare with a well known shallow-water pelagic fish like the tuna, a very active species. 

“In the deep water column, you don’t see a lot of big, powerful swimmers because it’s a very different kind of environment. It’s dark,” she said. “And so you tend to see fishes that sit in the water and wait for food to find them. Being pelagic in the deep sea seems to be fine for many different types of body shapes, from the blobby all the away to the skinny.” 

The lack of sunlight and photosynthesis in the deep sea also affects the ocean floor environment. 

“In shallow water, oftentimes you’ll be in an environment like a coral reef or a kelp forest, which has organisms undergoing photosynthesis. There are a lot of things to interact with, and that creates a diversity of body shapes because fish are designed to interact with different things,” Santos said. 

“The deeper bottom tends to be more plain and boring and muddy, so the fishes that live there don’t tend to be shaped in different ways.” 

Overall, the study’s rare look at life in Earth’s largest habitat shows that the different body types of deep-sea fishes are products of multiple evolutionary pathways defined largely by location. 

“The one place that humans have not dominated on this planet is the deep sea – and there is still so much to learn about the mystery of what all is there,” Santos said. “This paper moves us forward with a recognition that evolution can work really differently depending on where exactly in the deep sea the fishes are.” 

Co-authors of the paper include Sarah Friedman of the NOAA Alaska Fisheries Science Center and Christopher Martinez of the University of California, Irvine.