AMAZON RIVER DOLPHIN: HIGH PHYLOPATRY DUE TO RESTRICTED DISPERSION AT LARGE AND SHORT DISTANCES - Biology, Evolution and Conservation of River Dolphins Within South America and Asia - page 113

physical and chemical properties of the water divided in three main types: turbid white water
(depth of the Secchi disc: 0.10-0.50 m; pH 6.2-7.2), clear water (1.10-4.30 m; pH 4.5-7.8) and
black water (1.30-2.90 m; pH 3.8-4.9) (Sioli, 1984). Our results present a significant
differentiation in mtDNA variation between populations from different environments
separated by the Amazon River with turbid water. This is an indication of post-isolation
differentiation, which could be initially promoted by adaptive segregation of Inia populations
from diverse water environments. Besides, mtDNA divergence tends to accumulate by drift
much faster than autosomal loci because it presents a quarter of the effective population size
of diploid markers, such as microsatellites. Thus, it is not an expectation to also find
significant differentiation in autosomal markers, unless they are linked or directly involved
with putative genes associated to the adaptive response to different water environments.
In a previous long-term study of dolphins in the Mamirauá system, Martin & da Silva
(2004a) identified a high degree of fidelity, where 90% of the pink dolphin population sighted
in the system was considered to be resident of the area. These authors never recorded marked
dolphins at distances over 10 km from the area. However, they believe these animals use the
continuous ―várzea‖ system extensively, and can move tens to hundreds of kilometers, which
would grant them a high mixing potential. On the other hand, Martin and da Silva (2004b)
observed marked sexual segregation in which males would preferentially remain in the main
rivers' area, whereas females would tend to inhabit the more remote and protected portions of
the habitat. Even though Mamirauá is annually flooded with the turbid water of the Amazon
and Japurá rivers, Mamirauá and Tefé can be regarded as relatively isolated habitats,
separated by the Amazon River.
Taking into account the significant differentiation observed in Inia , with a unique spatial
distribution shaped by geography and ecological barriers, we suggest a specific conservation
management. To minimize anthropogenic impact, the reintroduction and translocation of the
animals in nature should consider the maintenance of the Inia phylopatry, managing local
populations as semi-independent evolutionary units. It will be a particularly important
consideration if translocations should be necessary in the future, involving individuals from
populations coming from farther regions and from different water environments. Finally, we
suggest further studies using several neutral markers and adaptation related genes in many
different Amazon habitats to investigate in detail the differentiation process among Inia
geoffrensis populations.
A CKNOWLEDGMENTS
This work received a research grant from CNPq (National Research Council of Brazil).
JAV and CH were supported by CAPES (Coordenação de Aperfeiçoamento do Pessoal de
Ensino Superior), FRS and RAFR by CNPq, and MM by MCT (Ministry of Science and
Technology) from Brazil. Thanks to the Cetacean Society International for their financial
support. All Brazilian samples were collected with the government permit IBAMA 130/2004.
This work was also performed according to the special authorization for access to genetic
resources in Brazil # 03/2004 issued by IBAMA/CGEN.