Molecular population genetic analysis of the spectacled bear (Tremarctos ornatus) in the northern Andean area.

Eighty-two Andean bear samples obtained in three South American Andean countries were analyzed using five hypervariable microsatellite markers. Neither the overall sample nor the samples coming from each of the countries analyzed were in Hardy-Weinberg equilibrium. This is attributable to the Wahlund effect caused by a fragmentation of the bear populations. The genetic variability levels found were in general low for this kind of molecular markers (H = 0.38 for the global population). The situation of the Ecuadorian bear population seems to be endangered (H = 0.24). This is the lowest level recorded for any bear population. The genetic heterogeneity among the three populations was large and highly significant (F(ST) = 0.39; R(ST) = 0.32-0.49). Likewise, the gene flow estimates were remarkably low among these populations (Nm = 0.2-0.3). This means that the populations are strongly isolated. Different methods were applied to determine the effective numbers in these populations. A significant spatial structure of the genotypes was analyzed with different procedures. In all cases, an isolation-by-distance structure was detected. This could be a consequence of the original South America colonization. There was no evidence for a recent genetic bottleneck. This could mean that the low heterozygosity and the population fragmentation could be explained by ancient events related to the bear colonization, with the arrival of humans beings in the Americas, and/or with the glacial maximum, 16.000-30.000 years ago.