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the Orinoco's lineages are temporally more recent than the Bolivian divergence from the
Amazon population (which was demonstrated by Ruiz-García, 2010, using mtDNA) and/or
the physical-chemical water characteristics and the number and types of pathogens of the
Orinoco basin waters are less divergent from the Amazon ones than those present in the
Bolivian waters.
Bear in mind that most of the alleles are represented by animals of the three basins, and
that the differences are in allele frequencies among these populations. The results suggest that
the most frequent genotypes could provide the dolphins some selective advantage to specific
physicochemical and microbiological conditions, as a result of the diverse selective pathogen
pressures in the different water characteristics (white, black and mixed waters) and
physicochemical conditions of the rivers. It could be interesting in the future to compare the
microbiological and physicochemical characteristics of these basins and their main tributaries
with the current results. However, the data are in the meantime insufficient for this kind of
comparison.
Comparing the levels of
MHC
genetic diversity of this work with other cetacean species,
we see that the genetic variability and allelic diversity of the Amazon River dolphin are very
high, similar to that found in the Yangtze river dolphin (Yang et al., 2005) and the finless
porpoise population in the Yangtze River (Xu et al., 2007) and clearly higher than what is
found in many marine species (Slade, 1992; Murray et al., 1995; Nigenda-Morales et al.,
2008). This could be due to the low environmental pathogenic pressure in marine systems, as
has been proposed before (Trowsdale et al., 1989; Slade, 1992) and the higher pathogenic
pressure in freshwater systems which are similar to terrestrial ones. However, several studies
have shown many diseases and epizootic episodes in marine mammal populations (Acevedo-
Whitehouse et al., 2006, 2003; Raga et al., 1997; van Bressem et al., 1998, 1999), and
therefore an explanation of why freshwater dolphins present such high levels of variability at
this gene is not yet clear.
A
CKNOWLEDGMENTS
Economic resources to carry out this study were obtained from the Administrative
Department of Science, Technology and Innovation (Colciencias) (1203-09-11239;
Geographical population structure and genetic diversity of two river dolphin species,
Inia
boliviensis
and
Inia geoffrensis
, using molecular markers) and Fondo para la Acción
Ambiental (120108-E0102141; Structure and Genetic Conservation of river dolphins,
Inia
and
Sotalia
, in the Amazon and Orinoco basins). Additional thanks go to Dr. F. Trujillo (
Omacha Foundation), H. Gálvez (Peru), M. Escovar and Dr. J. Vargas (Bolivia), Dr. D.
Alvarez, A. Rodríguez, and P. Escobar-Armel (Colombia), A. Castellanos (Ecuador) and
Isaias and his sons (Requena, Peru). Many thanks go to the Bolivian, Peruvian, Ecuadorian
Ministry of Environment for their role in facilitating the obtainment of the CITES and
collection permits. Thanks also go to the Pontificia Universidad Javeriana (Colombia) and to
the Universidad de Baja California Sur (México) for respective economic assistance.
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