Phenotypic divergence despite high levels of gene flow in Galápagos lava lizards (Microlophus albemarlensis).

The extent of evolutionary divergence of phenotypes between habitats is predominantly the result of the balance of differential natural selection and gene flow. Lava lizards (Microlophus albemarlensis) on the small island of Plaza Sur in the Galápagos archipelago inhabit contrasting habitats: dense vegetation on the western end of the island thins rapidly in a transitional area, before becoming absent on the eastern half. Associated with these habitats are phenotypic differences in traits linked to predator avoidance (increased wariness, sprint speed, and endurance in lizards from the sparsely vegetated habitat). This population provides an opportunity to test the hypothesis that reduced gene flow is necessary for phenotypic differentiation. There was no evidence of any differences among habitats in allele frequencies at six out of seven microsatellite loci examined, nor was there any indication of congruence between patterns of genetic variability and the change in vegetation regime. We infer that gene flow between the habitats on Plaza Sur must be sufficiently high to overcome genetic drift within habitats but that it does not preclude phenotypic differentiation.

A survey of the coccidian parasites of reptiles from islands of the Galápagos Archipelago: 1990-1994.

From 1990 through 1994, fecal samples were collected and examined for coccidian parasites from 26 giant land tortoises Geochelone nigra, from 715 lava lizards Tropidurus spp., from 139 land iguanas Conolophus subcristatus, and from 128 marine iguanas Amblyrhynchus cristatus, all of which inhabit various islands in the Galápagos Archipelago. None of the samples from A. cristatus or from C. subcristatus was infected with coccidia. Only 1 of 26 (4%) G. nigra was infected with a single Eimeria species that we describe here as new. A total of 262 of 715 (37%) individuals representing 3 species of Tropidurus discharged oocysts of 1-3 different coccidian species; these included 2 previously described species Eimeria tropidura and Isospora insularius, and an eimerian that we describe here as new. Additionally, 104 fecal samples from Tropidurus spp. were from 51 animals recaptured in either 2 or 3 yr; 21 had no infections in any year, 15 were infected at least once, 14 were infected in 2 yr, and only 1 was infected during 3 yr. No animal was recaptured and sampled during each of the 4 yr of this study. Of the 262 infected individuals, 30 (12%) had multiple coccidial infections at the time of collection (eimerian and isosporan, or 2 eimerians). Where determination of the sexes was possible in the lava lizards, there was no difference in prevalence rates between males (39%) and females (41%). Sporulated oocysts of the new eimerian from Tropidurus are ellipsoidal, 27.1 x 15.6 (25-31 x 14-18) microns, with a polar body, but without a micropyle or oocyst residuum; they contain ellipsoidal sporocysts, 11.8 x 6.7 (10-14 x 6-8) microns, without Stieda, sub-, or parastieda bodies, but with a sporocyst residuum. Sporulated oocysts of the new eimerian from G. nigra are ellipsoidal to ovoidal, 21.6 x 18.1 (18-25 x 16-20) microns, with a large polar body, but without a micropyle or oocyst residuum; they contain ellipsoidal sporocysts 10.7 x 7.0 (8-12 x 5-8) microns, with Stieda body but no sub- or parastieda bodies. Also present is a sporocyst residuum of medium to large granules randomly distributed among the sporocysts.