Anole Annals

Fig. 1 from Muñoz et al. (2013) Anolis marmoratus subspecies on Basse Terre (left) and Grande Terre (right)

Unlike the extensive within-island speciation that anoles have undergone in the Greater Antilles, we have no evidence that the same has occurred in the Lesser Antilles. Rather, Lesser Antillean islands that contain two species are thought to be the result of dispersal events rather than in situ cladogenesis. Despite such low species diversity, however, phenotypic diversity on many of these islands certainly is not lacking. Some Lesser Antillean anoles exhibit spectacular geographic variation in head, body and dewlap colouration and pattern, as well as body size and scalation, that appears to be adaptive to different environments. So, while this variation has not led to complete speciation in any Lesser Antillean anole, is there some evidence that these phenotypically divergent populations are at some stage of the speciation process? Also, how does phenotypic divergence occur on these smaller islands when there seems to be little opportunity for geographical isolation?

AA contributor, Martha Muñoz and colleagues tackle these very questions in a recent paper in Molecular Ecology. Muñoz et al. focus on the stunning phenotypic diversity of the Anolis marmoratus complex on Guadeloupe, which has been categorised into 12 subspecies. On Grande Terre, in particular, two subspecies can be found: A. m. speciosus inhabits mesic habitats in the southwest and A. m. inornatus inhabits the xeric lowlands of the north and east. Males share a yellow-orange coloured dewlap but differ in head, body and eye ring colouration, while females and juveniles of the two subspecies are similarly drab in colour.

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Seaweed washed ashore on a Bahamian island. Photo by Dave Spiller.

Ecologists are increasingly recognizing the myriad connections not only among species within an ecosystem, but between species in different ecosystems. Case in point: seaweed often washes ashore, and it affects leaves on the plants found near the shoreline. How’s that, you might ask? Well, the seaweed decays and releases nutrients that act as fertilizer, increasing the growth of land plants. That’s good for the plants, but it also makes their leaves more tasty, and hence plant-eating insects are attracted and cause more damage to the leaves.

That seems straightforward enough, but then it gets more complicated. As the seaweed decays, it attracts lots of insects. And the insects, in turn, attract lizards. And, in fact, if you happen to be studying this process on small islands in the Bahamas, as Jonah Piovia-Scott and a team from UC-Davis were, then those lizards are our favorites, brown anoles. And if there are more brown anoles around, then they’ll eat more of the herbivorous insects that plague the land plants, and so the washed-up seaweed actually decrease the damage to land plant leaves, thanks to the helpful consumption of the anoles.

Except…maybe the lizards will be so delighted by the seaweed that they’ll spend all of their time there, eating the insects on the seaweed, and thus neglecting the insects on the landplants, so now the effect of seaweed on the land plants becomes negative again.

So which is it? That’s what Piovia-Scott et al. set out to discover, and they’ve just reported the results in a paper in Oecologia. And the diagram to the left explains it succinctly. Seaweed increases nitrogen in the leaves, which increases herbivory. Seaweed also increases lizard density, which decreases herbivory, though the negative effect isn’t as great as the positive effect of the nitrogen. Moreover, seaweed also causes lizards to shift their diet, which has a small (and statistically non-significant) positive effect on herbivory because the lizards aren’t eating as many of the land plant herbivores. Bottom line: seaweed increases leaf damage; lizards can’t prevent it, in part because their effects are schizophrenic: more lizards, but eating fewer herbivores.

Interestingly, these results are opposite of what the same team of authors found in a study we discussed two years ago. The difference was that in that study, a big pile of seaweed was laid out at one time and the results were followed over a short period, whereas this study followed natural seaweed deposition and compared sites differing in the amount of seaweed washed ashore, following their sites for a lengthier period of time.

One last point: how did the researchers document that the lizards were switching diet? Not from sitting around and watching the lizards, but by measuring the carbon isotope ratios in their tails. Marine vegetation tends to have higher ratios of Carbon-13 than terrestrial sources, and so insects feeding on plants from different areas will, in turn, have different ratios, which means that, in turn, one can look at the Carbon-13 ratios in lizard tissue and get a sense of from which ecosystem they’re deriving their carbon. And in this case, the more seaweed, the higher the ratio. Pretty nifty!

Anolis ginaelisae

Six large anoles of the Dactyloa clade occur in western Panama. In their explorations, Lotzkat and colleagues have collected all of them, and have just published a paper in Zootaxa reviewing these species. Their phylogenetic analyses based both on DNA and morphological characters confirm the existence of the six taxa, but also find geographically-oriented genetic differentiation in two species. In combination with morphological data, the authors split A. microtus into two species, the new one under the name A. ginaelisae.

The paper includes a nice review of all the species including spiffy color plates (see A. ibanezi below as an example) and natural history notes (short take: they’re all arboreal and almost all individuals have been caught at night). A key is also included.

Anolis ibanezi

One last note. The derivation of the new specific epithet gianaelisae is touching: “Sebastian Lotzkat dedicates this exceptionally beautiful new species to his even more enchanting fiancée Gina Elisa Moog, who has made more than a third of his life worthwhile by now, in deepest gratitude for that wonderful time and pleasant anticipation of a mutual future.”

Abstract: “Six species of giant alpha anoles of the genus Dactyloa are known to occur in western Panama: Dactyloa casildae, D. frenata, D. ibanezi, D. insignis, D. kunayalae, and D. microtus. Based on own material collected along the highlands in Bocas del Toro, Chiriquí, and Veraguas provinces and the Comarca Ngöbe-Buglé of western Panama, we review their variation in morphological characters and the 16S rRNA mitochondrial gene. Our results support all six nominal taxa, but reveal considerable genetic differentiation between populations of the two highland species, D. casildae and D. microtus, respectively, from different localities. Correlated morphological differences confirm the existence of a cryptic species among populations currently assigned to D. microtus, which we describe as Dactyloa ginaelisae sp. nov. We provide point distribution maps, morphology and color descriptions, photographs in life, conservation status assessments, and an identification key for all seven species.”