Cayman’s island-hopping lizards offer evolutionary insight

The Grand Cayman blue anole stands out for its distinctive colour, seen most prominantly in males. Excluding the tail, this blue anole measures 2.5 inches. - Photo: Inbar Maayan

Most visitors to Cayman Brac will likely not have noticed one of the island’s now established transplants: the Maynard’s anole.

This non-native lizard spends much of its time just out of eyesight, perched in the tree branches where its bright green colour blends with the foliage. The elusive anole, originally from Little Cayman, has captured the interest of researchers, intrigued by the insight the species can offer about evolution in island ecosystems.

And the Maynard’s anole is not the only island-hopping lizard on the minds of Cayman Islands researchers these days. While far from the invasive status of the prolific green iguana, the brown anole is also creating questions about the potential impact on Grand Cayman’s native blue anole.

Through separate studies – one carried out by Caymanian researcher Vaughn Bodden and another by National Geographic Society grantee Inbar Maayan – biologists are getting a better idea of how invasive species adapt and populate new territories.

Maynard’s anole in Cayman Brac

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While the Maynard’s anoles in Cayman Brac are not far from their native home, Little Cayman, the lizard sheds light on how invasive species colonise new habitat.

Fortunately for Cayman Brac, the Maynard’s anole does not appear to pose a threat to the native Cayman Brac anole and has not shown potential for hybridisation.

“Based on similar invasions on other Caribbean islands, we expect the potential for a negative impact to be low. The native anole in Cayman Brac is found low on tree trunks and on the forest floor, while the introduced anole is predominantly found on upper tree trunks and in the canopy so direct interaction between the two species should be limited,” said Bodden, who studied the species while completing his bachelor’s in conservation biology at the University of Plymouth. He is now completing his master’s in biodiveristy and conservation at the University of Glasgow.

“Any impacts on the native anole are more likely to be indirect, such as a shift in habitat use to further avoid interacting with the introduced anole,” he added.

Researcher Inbar Mayaan captures lizards in Grand Cayman. – Photo: Jane Hakkonsson

The Maynard’s anole, first spotted in the Brac in 1987, does show signs of adaptation, however, when compared to its counterpart in Little Cayman.

Through fieldwork capturing and analysing the anoles in both Sister Islands, Bodden’s team, assisted by University of Plymouth lecturer Robert Puschendorf, found some interesting differences in their morphology and ecology. While the team hypothesised that the introduced anole might have developed longer hind legs – a trait that can aid dispersal and movement – their findings did not support this. In fact, they found much the opposite. The anole had instead developed longer forelimbs.

“Potential explanations for the rapid divergence could be that the founding individuals of the introduced population had a unique phenotype and these characteristics became exaggerated over time through the process of genetic drift, or that some habitat use characteristics that we did not measure on Cayman Brac are driving the morphological adaptation,” Bodden said.

Another interesting discovery about the introduced anole population was the presence of a parasite not previously recorded in the Sister Islands.

The source of this parasite remains unclear.

“The ectoparasites we found infecting A. maynardi [Maynard’s anole] have not been recorded in the Sister Islands, so this study provides the first evidence of its presence there. It is unclear whether the parasite species is native to both islands, invasive to both islands, or co-introduced from Little Cayman to Cayman Brac with its host,” Bodden said.

The Maynard’s anole is native to Little Cayman but introduced to Cayman Brac. – Photo: Vaughn Bodden

“We found that the introduced population [in Cayman Brac] had a reduced ectoparasite prevalence compared to the native population [in Little Cayman].”

The further researchers ventured from long-settled habitats, the lower the prevalence they found of the parasite.

This is something that may have benefited the introduced population and encouraged colonisation.

While the origin of the anole’s introduction to Cayman Brac is unclear, its presence there sends a reminder about the importance of safeguarding borders.

Due to the islands’ prevailing easterly trade winds, Bodden suspects the lizard had human rather than natural assistance in its introduction, possibly as a stowaway in a flight or boat.

“This is a unique situation where we have a species endemic to one of the Cayman Islands being introduced to another one of our islands. Fortunately, this introduction is not a major threat to the ecosystem in Cayman Brac, but it highlights the need for more vigilant bio-security control at our ports,” Bodden said.

“Unchecked cargo transportation provides a route for other invasive species, such as the green iguana, to be transported into or between the three islands.”

A female blue anole perches in Grand Cayman. – Photo: Inbar Maayan

Brown anole in Grand Cayman

Theories about how the brown anole, found endemically in Cuba and the Bahamas, arrived in Grand Cayman reinforce the call for careful biosecurity measures at ports. While researchers do not know exactly how the anole arrived here in the 1980s, its prevalence in the western end of Grand Cayman hints that it may have arrived through shipping.

Although Maayan, currently a Ph.D. candidate at Harvard University, did not find brown anoles in the numbers she had expected, she warned of complacency when it comes to invasive species.

“I was expecting them to be more of a problem than I saw, but it speaks to the importance of monitoring introduced and invasive populations,” she said.

Maayan said the brown anole should not be considered invasive in the same sense as the green iguana. But she cautioned that at a time, even the green iguana’s population numbers were much lower than they are now.

Much of the findings of her Grand Cayman research is not ready to share with the public, but she shared a few takeaways from her time on island.

Maayan described Cayman’s native blue anole as an incredibly charismatic and stunningly beautiful animal.

“They are a good ambassador for the Cayman Islands,” she said.

Maayan was interested in whether the presence of the brown anole had led to changes in the native anole’s habitat or physical characteristics. Physical changes in leg and head size, for example, could communicate competition between the species for habitat and resources.

An invasive male brown anole in Grand Cayman – Photo: Inbar Maayan

“The reason why these [island] species introductions are particularly useful is they mimic what we would see in evolutionary time,” she said.

“It gives a glimpse in a natural setting of when species come into contact and compete.”

With the help of local researchers, including Vaughn Bodden, Morgan Ebanks and Jane Haakonsson, she scouted out sites where just the Grand Cayman anole lived and sites where both species lived, for comparison.

Finding the brown anole was not as easy as she expected, however. While the lizard is found abundantly in Belize, where it is also an invasive species, this was not what Maayan observed in Grand Cayman.

Researchers sampled two sites heavily, taking data from more than 200 lizards. The team took data on habitat use of both species, and took measurements of the blue anole’s physical characteristics.

Maayan’s next step will be performing DNA analysis on the lizards to determine the level of migration and morphology.

Fortunately for the Grand Cayman anole, Maayan’s initial findings show little impact on how the lizard interacts with its native habitat.

While the brown anoles seemed to prefer perching in lower, sunnier areas, the Grand Cayman anole stuck to shadier natural areas. It would appear the lizards have adapted to separate habitats.

The full findings of Maayan’s research are expected to be released this summer, after the study has been reviewed and published by the National Geographic Society.

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