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by Pilleri et al. (1982). Furthermore, although the molecular dating estimates
obtained by Cassens et al. (2000) indicated that all the river dolphin lineages
diverged well before the radiation of delphinids (11-13 millions of years ago), the
current
Inia
is a recent species (such as it was ―prophetical‖ affirmed by Simpson,
1945) and not a relict species of otherwise successful Oligocene-Miocene groups,
like it was sustained by Cassens et al. (2000). Also, the construction of geological or
climatologic scenarios by the integration of palaeontological data with Tertiary
palaeooceanography events were not useful in understanding the evolution of the
river dolphins (Hamilton et al. 2001) because the actual evolution of
Inia
genera
occurred more recently than assumed by other authors. Following this argumentation
line, the affirmation of Martin & da Silva (2004) (―It is, nonetheless, important to
recall that the entire geomorphology of the Amazon is geologically recent. Várzea
Lake systems are a product of the Pleistocene and Holocene, Ayres 1993, and,
consequently, appeared late in the evolutionary development of Iniid dolphins,
Hamilton et al., 2001. The genus
Inia
has clearly adapted very successfully to habitat
changes on a geological timescales‖), is incorrect. The current
Inia
genus evolved in
parallel to these Pleistocene and Holocene geological changes because it is not older
than these geological changes, and probably, is a product of them.
2.
For the Zhivotovsky et al.'s test as well as for the Garza & Williamson' test, there
was clear evidence of a strong bottleneck affecting the Bolivian population. The
microsatellite heterozygosity level (not shown here), the mtDNA sequence gene
diversities ( and ) or the gene diversity for RAPD (Polymorphism rate and
expected heterozygosity in the Peruvian populations were 85.3 % and 0.211 and for
the Bolivian population were 38.9 % and 0.119, respectively; Ruiz-García et al.
2007) revealed that the Bolivian population is more genetically depauperate than the
other pink river dolphin populations. Therefore,
Inia boliviensis
could not be the
original form of
Inia
.
3.
The mitochondrial haplotypes showed that the Amazon form was original population
of the current
Inia
's forms. Thus, the origin of
Inia
was in the own Amazon River
and not in the Bolivian sub-Andean freshwater lake system such as it was previously
claimed. It is possible that the upper Amazon was the origin of the current
Inia
genera, because the samples analyzed in the Putumayo and Caquetá rivers (Amazon
River tributary) showed a considerably lower gene diversity, at least, for mtDNA.
Nevertheless, more Amazonian pink river dolphin populations should be analyzed to
determine the exact geographic origin of the primary population within the Amazon.
4.
The Bolivian population was derived from the Amazon population in a possible
peripatric or allopatric speciation process around 160,000 years ago (mt DNA) and
not five millions of year ago as established by Grabert (1984a, b, c) or two million of
years ago as sustained by Pilleri & Gihr (1980) because they established this age for
the historical origin of the rapids between Guayaramerin and Porto Velho. Previously
Ruiz-García et al. (2008) analyzed nine nuclear and Y chromosome introns and
determined a divergence of 543,000 years ago for the separation of
Inia geoffrensis
and
Inia boliviensis
. As the microsatellite analysis showed, this is a population which
crossed throughout a strong bottleneck and the mtDNA analysis presented a possible
diversification of haplotypes in this population very recently (around 4,000 years
ago). It means that the genetic drift was extremely important in the origin of this
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