Ruling out genetic erosion in Picea chihuahuana Martínez

Abstract

Genetic erosion has been variously defined as the loss of particular alleles, the reduction in richness of the total number of alleles, and the reduction in evenness of the frequencies of alleles in a given place within populations or across species. Picea chihuahuana Martinez is an endangered endemic species known to occur in at least 40 locations along the Sierra Madre Occidental, in the states of Durango and Chihuahua (Mexico), but covering a total area of no more than 300 ha. The total number of individuals has been estimated to be around 42,600, and the number of mature individuals may be <2500. The populations (including mature trees, saplings and seedlings) vary in size from 21 to 5546 individuals. It has been suggested that small populations may be more susceptible to loss of genetic variability via genetic erosion caused by genetic drift, endogamy depression and strong unidirectional selection. The predicted reduction and eventual disappearance of a suitable habitat for P. chihuahuana due to climatic change imposes an additional risk of extinction. The principal aim of this study was therefore to estimate genetic erosion in 14 populations of P. chihuahuana Martinez by comparing genetic diversity across diameter at breast height classes (as a proxy for age classes) by using AFLP markers and four indices of genetic diversity that are commonly applied in combination with dominant genetic markers. No evidence of genetic erosion was found in the 14 P. chihuahuana populations analyzed.