Gates Foundation Announces New Initiative to Eradicate Lizard Malaria

From Falk et al., 2011.

The Gates Foundation today announced a multi-billion dollar initiative to eradicate malaria from all lizardkind. Through a combination of heightened prophylactic use, development of genetically modified lacertilians, and enhanced mosquitivory, the Foundation hopes to eliminate this scourge, which afflicts millions of saurians throughout the world.

Well, maybe some day. But a recent paper on Anolis malaria set my mind a-wandering. Most people, likely the Gates Foundation included, are unaware that malaria is a disease not just of humans, but of many other species as well, including lizards. When I first learned that lizards got malaria, I thought it was just a curiosity, not of particular importance. However, I’ve come to realize that I was very wrong in a number of respects.

First, malaria in some cases can have substantial physiological effects on lizards (though this has yet to be demonstrated in anoles). Increasingly, ecologists and evolutionary biologists are realizing that disease may play an important role in population ecology and perhaps even evolutionary diversity. In this respect, understanding the effects of malaria may be important to understanding anole biodiversity.

Second, malaria may be an important factor structuring communities. In the only detailed population level study, on St. Maarten, A. pogus was only found to coexist with A. gingivinus where malaria was present. Where it was absent, A. pogus was not present. The implication was that malaria mediates coexistence of the two species, presumably by its detrimental effects on A. gingivinus. See below for more details.

Third, there is great variability among species, populations, locales, and through time in anole malaria prevalence. At present, we have no idea how to account for such variability.

Finally, fourth, multiple malarial parasite species (Plasmodium) infect anoles, and it is possible that by understanding the evolutionary history and biogeography of these parasites, we might learn something about anole evolution as well.

So, from an anole biologist’s perspective, malaria is a pretty interesting and still greatly unexplored topic (for those interested in the little more that I know about anole malaria, I’ve appended the relevant sections from Lizards in an Evolutionary Tree below).

But there’s another side of the coin. Some people study malaria in anoles not because they are interested primarily in the anoles (hard as that may be to believe), but because they are interested in the malaria species! Work in this area was initiated by Joseph Schaal, and now is primarily led by Susan Perkins at the American Museum of Natural History. The latest work from Perkins’ lab, headlined by Brian Falk, was published a few months back in the International Journal of Parasitology. In that paper, Falk et al. tackle a difficult question: just how many species of malaria parasites are there infecting anoles? The problem is that traditionally Plasmodium species are recognized based on morphological differences, but there aren’t all that many morphological characters, and work by Perkins and others have shown that there is a lot of cryptic, species-level diversity lurking within homogenous morphologies.

To address this problem, Falk and colleagues conducted an enormous blood sample collecting effort throughout Hispaniola, in which they sampled 677 lizards from 26 anole species at 52 sites. Fifty-five lizards were infected with Plasmodium, including several new host species records, but only 24 of these infections could be definitively assigned to previously morphologically diagnosed species. Examination of mitochondrial and nuclear DNA indicated that in addition to the two clearly established species, another two Plasmodium species, morphologically indistinguishable, occur in Hispaniolan anoles. The authors note, however, that it is possible that additional Plasmodium species occur on Hispaniola. Moreover, some of the Hispaniolan species putatively occur elsewhere in the Caribbean and Central America, so there is much work left to do to figure out the extent of anoliphilic Plasmodium, much less to elucidate their evolutionary history.

From Lizards in an Evolutionary Tree: Ecology and Adaptive Radiation of Anoles:

“Malaria parasites have been a particular focus of research, and several species are known to afflict anoles (Telford, 1974; Schall and Vogt, 1993; Staats and Schall, 1996; Perkins, 2001; Perkins et al., 2007). However, the individual and population level consequences of such parasitism are not well known. Plasmodium infection has detrimental effects on A. gingivinus (Schall, 1992), but little or no detectable effect on A. gundlachi (Schall and Pearson, 2000) or A. sabanus (Schall and Staats, 2002). No direct studies of the population effects of malaria have been conducted…”

“The best and almost only study of the community effects of parasitism on anoles concerns malaria and the two species of anoles on St. Martin (Schall, 1992), which is the only Lesser Antillean island on which a small and a medium-sized species coexist. The smaller species, A. pogus, has an unusually patchy and restricted range on the island as compared to its close relatives on other islands. Anolis gingivinus is more vulnerable to malaria than A. pogus, and A. pogus is only found in places in which malaria has been found, whereas A. gingivinus occurs throughout the island. Moreover, the abundance of A. pogus correlated positively with the prevalence of infection in A. gingivinus.

Schall’s (1992) conclusion based on these data is that in the absence of malaria, A. gingivinus excludes A. pogus, but that the malaria parasite’s presence alters the competitive balance enough to permit coexistence. This hypothesis may be tested quite soon, because recent surveys have failed to find the malaria parasite on St. Martin, suggesting that it may have disappeared (Perkins, 2001). If the parasite-mediated coexistence theory is correct, then A. pogus populations ought to be in decline.

What role, if any, malaria plays in structuring anole communities elsewhere is unclear. On other islands in the West Indies, malaria occurs in some anole species, but not others: in one of five species in Puerto Rico (Schall and Vogt, 1993) and in 12 of 22 populations of 12 species in the Lesser Antilles and Virgin Islands (Staats and Schaal, 1996).”

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Jonathan Losos

Professor of Biology and Director of the Living Earth Collaborative at Washington University in Saint Louis. I've spent my entire professional career studying anoles and have discovered that the more I learn about anoles, the more I realize I don't know.

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