Over the last half-century, Anolis sagrei sagrei, a Cuban native, has become a global citizen. Likely as a stowaway in agricultural trade shipments, it has traveled to near-Cuba places like Florida, Jamaica, and Grand Cayman. It has gone as far Hawaii, Guam, and Taiwan. It is a stout lizard, males about 60mm long, brown in body color with a deep red dewlap bordered by a yellow margin. Jason Kolbe’s research documented the origin and spread of invasive populations of this subspecies around the globe.
Another subspecies of A. sagrei, A. sagrei luteosignifer, is endemic to Cayman Brac, the easternmost of the three Cayman Islands islands. On Brac, A. s. luteosignifer has evolved a mustard-yellow dewlap, in stark contrast to the red dewlap of A. s. sagrei.
On his last trip to Brac, Losos lab post-doc Thom Sanger noticed several unusual A. sagrei luteosignifer individuals with orange dewlaps. Because A. s. luteosignifer normally has yellow dewlaps, Thom hypothesized that there may be a previously unnoticed invasion of A. s. sagrei on Cayman Brac.
Alexis Harrison and I recently visited Cayman Brac to investigate whether A. s. sagrei individuals are on Cayman Brac, and if so, are they hybridizing with the native yellow-dewlapped subspecies?
From the 9th to the 14th of January, joined by Jonathan and Melissa Losos, we visited 19 sites across tiny Brac and captured 10-12 males per population to photograph and take spectrometric readings of their dewlaps. We’ve provided a few representative dewlap photos below. The dewlaps vary from dirty yellow to orange, and we found this variation in most populations on the island.
Out of approximately 200 lizards examined, we only found one lizard that looked unambiguously like A. s. sagrei, pictured below. It has a dewlap with the deep red center and bright yellow margin that is the trademark of this invader. Genetic data will help us test whether this is indeed an A. s. sagrei individual.
The presence of this A. s. sagrei individual suggests that there are others and that it is probable that individuals of this subspecies have been arriving to Cayman Brac regularly. Cayman Brac is supplied weekly by barge shipments from Grand Cayman, where A. s. sagrei has successfully established itself (probably from Cuba by way of Florida). A worker at the port told us that he’s seen all sorts of critters (e.g. snakes, spiders, iguanas, and more) skittering away from shipping containers that are unloaded from the barge onto Brac. Given the tendency for A. s. sagrei to be found in construction materials and potted plants, it is likely that it is among those critters being brought to Cayman Brac by the barge.
Are the orange dewlaps we found in Brac’s A. s. luteosignifer populations part of the natural color variation of that subspecies, or is the orange dewlap the result of hybridization with A. s. sagrei? If the two subspecies aren’t reproductively isolated, they could be hybridizing to produce the orange-dewlapped lizards.
We will use genetic tools to address whether A. s. sagrei genes are introgressing into the gene pool of the Cayman Brac subspecies. We collected tail tips from every lizard we caught on Cayman Brac during this trip, and we have access to A. s. luteosignifer tissues collected approximately 20 years ago by J. Losos. Moreover, Alexis and I are currently collecting tail tips from A. s. sagrei on Grand Cayman. We will use these tissue collections to test for a cryptic invasion of A. s. sagrei on Cayman Brac.