In what should be our final belated post about talks at the Evolution meetings in Ottawa last month, I’d like to share some results from Bryan Falk from Susan Perkins’s Lab American Museum of Natural History. Bryan has been investigating the diversity of anole malaria parasites (Plasmodium). Like many other species of vertebrates, anoles have their own strains of malaria (not the same as the ones that effect us humans), and these lizard malaria have been the focus of numerous fascinating research projects over the years (see Schall 1996 for a review).
Bryan’s work investigated phylogenetic relationships among West Indian strains of lizard malaria using sequence data from mitochondrial DNA plus six nuclear loci. He found that Plasmodium samples on most islands form monophyletic groups, although some clades are found in both Florida and Cuba, suggesting travel between these two regions. Bryan also reported very low overall genetic diversity, the presence of most genetic variation among (rather than within) populations, and no evidence for purifying selection. Bryan’s previous work used tree-based delimitation to diagnose previously unrecognized or ambiguous taxa of Plasmodium on Hispaniola, and his new work uses a similar approach across a broader geographic scale. In the new study, species tree analyses tend to recover island-specific clades and identify 11 potentially unrecognized species within Plasmodium floridense (see Perkins 2000 for more on species delimitation in Plasmodium). Bryan’s time calibration work suggests that intra-island divergences are very young and his demographic analyses suggests that recent divergence and serial bottlenecks may be responsible for low diversity with in populations but high divergence among populations. It seems like more exciting new results with anole malaria on are on the horizon from Bryan and his collaborators.
- JMIH 2014: Early Records of Fossil Anolis from the Oligocene and Miocene of Florida, USA - August 13, 2014
- JMIH 2014: Relative Contribution of Genetic and Ecological Factors to Morphological Differentiation in Island Populations of Anolis sagrei - August 7, 2014
- JMIH 2014: The Ultrastructure of Spermatid Development within the Anole, Anolis sagrei - August 5, 2014
Armando Pou
Is it possible that prior declines in Anolis carolinensis populations was due to the spread of a parasitic disease such as this traveling in Anolis sagrei?
Rich Glor
Interesting suggestion. I’m not sure that anyone has looked into this. There is ample evidence that the ecological impact of A. sagrei has caused problems for A. carolinensis but I’m not sure if we have the data to determine if this ecological impact has been accompanied by problems due to introduced pathogens.
BryanFalk
It’s possible, but I’d be surprised if it were brought by sagrei. It seems that for most anole parasites, there’s little difference in prevalence and abundance between hosts, suggesting that virulence in different anole species is pretty much the same for most parasites.
But, it’s a little different with the scelops. We think that these malaria parasites evolved in anoles (where they seem to have little effect on the lizards’ health), and the parasites dispersed to Florida with them. There, these parasites could also infect Sceloporus undulatus, and in this case the infections are often fatal.
This is just one of many examples where a host switch results in an increase in virulence, and that increase is proportional to the evolutionary distance between the hosts. Same thing happens when pathogens switch to humans from other species, like the Hanta or West Nile viruses that have been in the news this summer.
So in answer to your question: if demographic changes in carolinensis occurred as a result of disease, those populations probably acquired the pathogen from something other than an anole. But… who knows!
ALSO – thanks for posting this, Rich!
Armando Pou
Rich, Bryan, thanks for the responses, this is a fascinating topic.