Linking heterozygosity, demography, and fitness of tropical populations of Liomys pictus

Abstract

The relationship between heterozygosity and spatial and temporal changes in population density, and between heterozygosity and body weight, were studied in four populations of the spiny pocket mouse, Liomys pictus, from tropical dry forests in Chamela, Jalisco, Mexico. Individuals of L. pictus experience profound fluctuations in populations mainly due to the strong environmental seasonality of their habitat. Nineteen presumptive gene loci were assayed with starch-gel electophoresis to estimate heterozygosity, and mean body weight was analyzed as a fitness-correlated character. Observed average heterozygosity values were high (H = 0.188-0.198), whereas average fixation values (F = 0.350-0.429) were positive, indicating a significant deficiency of heterozygotes. Changes in numbers of individuals and heterozygous loci per individual were associated with different phases of fluctuations in density of L. pictus. During the increase phase, persistence of individuals was higher and average heterozygosity values declined, probably due to inbreeding. During the decline of the population when food and water were scarce, heterozygosity increased, and adults, which overall showed less deficiency of heterozygotes, were significantly more abundant. Average number of heterozygous loci and body weight also showed a positive and significant correlation. These results agree with the hypothesis that changes in genetic variability may be a consequence of demographic changes, and that, consequently, traits associated with fitness could show correlations with heterozygosity.