How are Amazon and Orinoco rivers related? Preliminary results on the comparative history, structure and dynamics of Giant otters, Pteronura brasiliensis, from Western Amazonia

This is a preliminary study on the possible genetic structure and phylogeography ofthe Giant otter (Pteronura brasiliensis) in the upper Amazon basin (Colombia, Peru,Bolivia and western Brazilian Amazon) and in the Orinoco basin (Colombia) by means ofsequences of the mtCyt-b gene. The animals from the upper Amazon and those from theOrinoco basin were not isolated and no significant heterogeneity was detected. Ourresults showed that the animals clustered in two main clades, one only integrated byupper Amazon individuals, with moderate haplotype diversity, and the second by otherupper Amazon animals as well as the Orinoco animals and one sampled in the BolivianAmazon with a higher haplotype diversity. No population expansion processes weredetected with different procedures and the Bayesian analyses determined that the twomain clades diverged around 37,000 years ago, while within each one of the clades, thedivergences times among haplotypes were around 10,000-20,000 years ago. These timesplits were correlated with climatic changes in the fourth glacial period of the Pleistoceneand during the Holocene.