"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

June 8, 2010

June 8 - Plasmodium floridense

In January, you read about Plasmodium minuoviride, a malaria parasite of lizards, and learned that over 100 malaria parasites use lizard hosts. Today’s parasite – Plasmodium floridense – is another of these lizard parasites. As you might have guessed from its species name, it was first described in Florida, but its distribution includes the southern United States, most of the Caribbean, as well as parts of Central America. It is known from roughly 30 lizard species (a high host number for this kind of parasite), with most of these belonging to the lizard genus Anolis.

Prevalence (the percentage of animals infected) of P. floridense varies greatly among these hosts, ranging 5 to 50%. The cause of this variation is unknown. Differences in host ecology might affect prevalence, because – for example – some lizard species occur in open areas and infected lizards might use heat from the sun to raise their body temperature (i.e., a “behavioral fever”). Likewise, a vector species may encounter some lizard species more frequently than others, based on differences in these lizards’ roosting preferences, thereby skewing the rates of infection. These and several other potential factors could be causing the variation in prevalence of P. floridense.

Anolis lizards make good subjects in which evaluate the factors affecting parasite prevalence. They have undergone a repeated pattern of adaptive evolution in the Greater Antilles, and based on their behavior, morphology, and ecology, these lizards can be categorized into one of several “ecomorph” types. The pattern on each island is very similar, as near to a replicated experimental design as an evolutionary biologist could hope. Preliminary research on Hispaniola has shown that P. floridense infections are found primarily in lizards of one ecomorph type, and ongoing work will determine if this pattern is consistent across other islands (Falk et al., unpublished).

Contributed by Bryan Falk.

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