Microlophus albemarlensis

About: Microlophus albemarlensis is a research topic. Over the lifetime, 8 publications have been published within this topic receiving 267 citations.

Historical fragmentation of islands and genetic drift in populations of Galápagos lava lizards (Microlophus albemarlensis complex).

Abstract: The formation of islands following a rise in sea level at the end of Pleistocene is expected to disrupt the equilibrium between genetic drift and gene flow in species with limited ability to disperse. Here, we test the hypothesis that genetic drift in isolation has caused the differentiation of Galapagos lava lizards (Microlophus albemarlensis complex) found on 12 islets that are likely to have been connected to a larger island, Isla Santa Cruz, during the late Pleistocene. Using 11 microsatellite loci, screened on 524 individuals from 17 localities distributed among and within 15 islands, we found marked differences in allelic richness and heterozygosity. Genetic differentiation was strong (global F(ST) = 0.44), with pairwise differences found among populations on islets being larger than differences among three localities sampled within Isla Santa Cruz. As expected under a scenario of drift in isolation, there was a positive correlation of genetic diversity with island size, no relationship between genetic and geographical distance and a strong negative correlation between heterozygosity and measures of genetic differentiation. We conclude that seawater is a significant barrier to gene flow in lava lizards on this timescale. Our results suggest that the shallow diversification of the M. albemarlensis complex is not due to recent gene flow and that genetic drift may have played a substantial role in observed patterns of phenotypic variation among islands.

Estimating Lizard Home Range: The Rose Model Revisited

Abstract: In 1982, B. Rose pointed out that home-range area could easily be underestimated unless sufficient numbers of sightings were obtained for each individual, and recommended a population-specific test to determine the minimum sample size at which home-range area can be accurately measured. This recommendation has been generally ignored. We explore how sample size affects interpretation of space use data in male lava lizards, Microlophus albemarlensis, and male eastern collared lizards Crotaphytus collaris. Using the criteria established by Rose, the minimum sample sizes for collared lizards and lava lizards were 45 and 84 sightings, respectively. These are much larger samples than we anticipated and reinforce the need for empirical determination of minimum sample size. Our data suggest that lizard movement rate is a better predictor of minimum sample size than home-range area. Collared lizard home ranges were over 10 times larger than lava lizard home ranges, yet the higher movement rates of collare...

Intrapopulation variation in endurance of Galápagos lava lizards (Microlophus albemarlensis): evidence for an interaction between natural and sexual selection

Abstract: Variation in the risk of predation may profoundly affect the evolution of anti-predator behaviours. Theory predicts that selection would favour enhanced locomotor capacity in highrisk environments, such as open habitats. An earlier study demonstrated significant intrapopulation and intersexual variation in wariness and sprint speed among the lava lizards (Microlophus albemarlensis) that was concordant with presumed risk of predation on Isla Plaza Sur in the Galápagos Archipelago. In particular, males and females from sparsely vegetated areas had greater approach and flight distances than those of more highly vegetated areas; males were also faster than females. We now compare endurance capacities of males and females from the same population on Isla Plaza Sur. We predicted the higher presumed risk of predation in the sparsely vegetated region would favour enhanced performance capacities. In addition, we predicted that sexual selection for territory defence would favour males that had the ability to flee long distances. Lizards from the sparsely vegetated area did have higher endurance than those from the vegetated area. Males had higher endurance times than females, but this difference was an outcome of body size, which was inconsistent with the sexual selection hypothesis. The significant differences in endurance between locations combined with the absence of dimorphism in performance suggest that the intrapopulation differences are an outcome of natural selection for predator escape.

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

Abstract: 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 Galapagos 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.