Geographic Genetic Differentiation of a Malaria Parasite, Plasmodium mexicanum, and Its Lizard Host, Sceloporus occidentalis

Abstract

Gene flow, and resulting degree of genetic differentiation among populations, will shape geographic genetic patterns and possibly local adaptation of parasites and their hosts. Some studies of Plasmodium falciparum in humans show substantial differentiation of the parasite in locations separated by only a few kilometers, a paradoxical finding for a parasite in a large, mobile host. We examined genetic differentiation of the malaria parasite Plasmodium mexicanum, and its lizard host, Sceloporus occidentalis, at 8 sites in northern California, with the use of variable microsatellite markers for both species. These lizards are small and highly territorial, so we expected local genetic differentiation of both parasite and lizard. Populations of P. mexicanum were found to be differentiated by analysis of 5 markers (F(st) values >0.05-0.10) over distances as short as 230-400 m, and greatly differentiated (F(st) values >0.25) for sites separated by approximately 10 km. In contrast, the lizard host had no, or very low, levels of differentiation for 3 markers, even for sites >40 km distant. Thus, gene flow for the lizard was great, but despite the mobility of the vertebrate host, the parasite was locally genetically distinct. This discrepancy could result if infected lizards move little, but their noninfected relatives were more mobile. Previous studies on the virulence of P. mexicanum for fence lizards support this hypothesis. However, changing prevalence of the parasite, without changes in density of the lizard, could also result in this pattern.

TESTING SEX RATIO THEORY WITH THE MALARIA PARASITEPLASMODIUM MEXICANUMIN NATURAL AND EXPERIMENTAL INFECTIONS

“…Naturally infected and not infected fence lizards were collected at the University of California Hopland Research and Extension Center and two private ranches near the town of Hopland in Mendocino County, California (Schall ; Fricke et al. ). Lizards were captured using a noose on a fishing pole, and a few drops of blood were taken by toe clip to produce a blood smear for staining (Giemsa) and microscopic examination.…”

Leukocyte Profiles for Western Fence Lizards,Sceloporus occidentalis, Naturally Infected by the Malaria ParasitePlasmodium mexicanum

“…Lizards were collected from various field sites around the HREC field station (details in Fricke et al, 2010) via a nylon noose at the end of a fishing pole and transferred to the on-site laboratory. Lizards were measured (snout-to-vent length, SVL, in millimeters) and their tail status was recorded (intact, broken, or regenerated).…”

Lack of Sequence Variation of the Mitochondrial CytochromebGene From a Malaria Parasite, Plasmodium mexicanum

“…We have surveyed numerous sites in northern California and have found the parasite in only small, geographically isolated patches of habitat. Microsatellite markers reveal that gene flow among these patches is low; sites only a few kilometers apart reveal substantial genetic differentiation for the parasite (Fricke et al, 2010).…”

“…The HREC has been the site of a long-term study on the parasite since 1978 (Schall, 1996). These sites are 6.4 to 10.9 km apart and were chosen because microsatellite markers reveal they are geographically distinct, with low rates of gene flow (Fricke et al, 2010). The last site, the University of California Sierra Foothills Research and Extension Center (SFREC), was more distant (156 km from HREC), near the town of Browns Valley (Yuba County).…”

“…First, microsatellite markers reveal substantial diversity, with 50-80% of infections multi-clonal, depending on prevailing prevalence levels among sites (Vardo and Schall, 2007). Second, microsatellite markers reveal that the parasite is geographically distinct among sites even a few kilometers apart (Fricke et al, 2010). Last, studies that establish experimental infection with differing specific microsatellite alleles and diversity of alleles (interpreted as distinct clones and thus variation in clonal diversity) show different life history characteristics, including rate of replication, final parasite density, and virulence (VardoZalik andSchall, 2008, 2009).…”