Molecular Evolution (Mitochondrial and Nuclear Microsatellites Markers) in the Andean Bear (Tremarctos ornatus; Ursidae, Carnivora): How Many ESUs Are There?

We sequenced mitochondrial genes ND5, 12s rRNA, and COI in 302 Andean or spectacled bears (Ursidae) from Venezuela, Colombia, Ecuador, Peru, and Bolivia. Of this total, 294 of the bears were from the wild whereas the remaining eight were from zoos in Mexico, Argentina, France, and Switzerland. A subset of 127 individuals, representing the above five South American countries, was genotyped at seven nuclear microsatellites (GID, G10B, G10C, G10L, G10M, G10P, and G10X). Our results support the following: (1) There are two evolutionary significant units (ESUs), following the definition of Moritz (1994). The first (Northern Andean Clade, NAC) comprises all the bears from Venezuela, Colombia, Ecuador, and northcentral Peru, whereas the second (Southern Andean Clade, SAC) comprises the bears from southern Peru and the northern and central Bolivian Andes. The temporal split between the ESUs was estimated to have occurred around 500,000 years ago (YA). Additionally, in Bolivia, a few of the sampled Andean bears in the Santa Cruz Department were more related to NAC than to SAC; (2) The eight captive bears belonged to the NAC, and thus, individuals from the SAC could be underrepresented in international zoos; 3) Different historical demographic analyses showed signatures of significant population expansions for the species as a whole and in each one of the ESUs found. These population expansions began between 690,000 and 450,000 YA. Nevertheless, one procedure detected a population decrease in the last few hundred to few thousand years for the species as a whole and in each one of the ESUs.