CHANGES IN THE DEMOGRAPHIC TRENDS OF PINK RIVER DOLPHINS (INIA) AT THE MICROGEOGRAPHICAL LEVEL IN PERUVIAN AND BOLIVIAN RIVERS AND WITHIN THE UPPER AMAZON:MICROSATELLITES AND MTDNA ANALYSES AND INSIGHTS INTO INIA’S ORIGIN - Biology, Evolution and Conservation of River Dolphins Within South America and Asia - page 179

that Inia is an efficient colonizer in small social propagules. Another very interesting result
from this analysis is that if the values are (and, in fact, all they are  > 1 (ln  > 0)) in
agreement with a population expansion proceeding from a bottleneck, then these values will
be present during several thousand generations (from 5,000 to 10,000 generations) before
these values show the signature of a population expansion ( < 1 (ln  < 0)). If, in the case of
Inia , a generation is about seven years, then the population expansion process after the initial
bottleneck is not older than 35,000 (5000 generations; more probable) or 70,000 (10,000
generations; less probable) years. This is one, of a series of results, which shows that the
expansion and colonization of the current Inia geoffrensis and Inia boliviensis in the Amazon
is a relatively recent process. The separation of both Inia ‗s forms could coincide with the
second maxim peak of the Riss-Illinois glaciation (around 150,000 years ago), while the
Amazon and Orinoco haplotype differentiation occurred during the last Würm-Wisconsin
glaciation, which elapsed from 120,000 to 10,000 years ago with a maximum peak 18,000
years ago. Therefore, the genetics divergence process within the Inia genus is not an old
process as a lot of researchers have previously claimed (Pilleri & Ghir, 1980; Pilleri et al.,
1982; Grabert 1984 a, b, c; Cassens et al., 2000; Hamilton et al., 2001; Banguera-Hinestroza
et al., 2002; Martin & da Silva, 2004).
The obtained results for S k and V in the diverse river dolphin populations are noteworthy
to be compared with the values for these statistics obtained in humans and with the theoretical
simulations obtained by Zhivotovsky et al. (2000). The values of S k and V over time weakly
depend on the rate of population increase and the final population size. Only extreme
differences in the growth rate could produce substantial differences between these statistics.
The three Peruvian river dolphin and the overall upper Amazon populations (this last
enclosing the Putumayo River's population) showed relatively similar S k and V values with a
moderate variance and little evidence of a strong population expansion. Therefore, similar
growth rate conditions affected these river dolphin populations. Nevertheless, the Bolivian
population presented extremely different S k and V estimates, which demonstrated that the
growth rate conditions for this population were extremely different than in the previous case
and represented a totally independent colonization process. The negative S k value and the
small V value demonstrated the existence of a strong bottleneck in this population. The
question is if this bottleneck occurred just before or during the population expansion. This last
event may greatly influence S k but only slightly affect V (Figure 6 from Zhivotovsky et al.,
2000). In the Bolivian case, both S k and V were extremely affected. Therefore, the striking
bottleneck was in the original population formation. This result is in disagreement with
Grabert (1984 a,b,c) who claimed that the original population gave origin to all other pink
river dolphin populations. An extreme bottlenecked population can not generate other
populations with more genetic diversity than itself. On the other hand, S k is not affected by
different mutation rates in the microsatellites studied (at least if this rate does not change over
time), whereas V is greatly affected. Therefore, as all the microsatellites studied were the
same in all the populations and all them were dinucleotide, different population S k values
could be not attributed to different mutation rates for the markers studied. Also, I have no
evidence that the mutation rate changed, at least when the population began to grow and if the
mutation rate had increased then both S k and V would be higher than the values found.
The river dolphin population of the Ucayali River showed the higher S k value, whereas
the Mara￱￳n River's dolphin population showed the highest V estimate. Such as I previously