MOLECULAR ECOLOGY AND SYSTEMATICS OF SOTALIA DOLPHINS - Biology, Evolution and Conservation of River Dolphins Within South America and Asia - page 275

The residency of local populations of S. guianensis could reflect the phylopatry of one of
the sexes. In most mammals, females are the phylopatric sex while males disperse (Dobson,
1982). This pattern has been observed in almost all small cetacean species studied so far (e.g.
Tursiops truncatus - Scott et al., 1990; Duffield Wells 1991; Delphinapterus leucas -
O'Corry-Crowe & Lowry, 1997; Phocoena phocoena - Rosel et al., 1999; Phocoenoides dalli
- Escorza-Treviño & Dizon, 2000; Cephalorhynchus hectori - Pichler and Baker, 2000;
Tursiops aduncus - Möller & Beheregaray, 2004). It is possible that S. guianensis shares the
same sex bias in dispersal, but until now that could not be evaluated due to the impossibility
of visually sexing the resident animals. The hypothesis of female phylopatry can be tested
with the comparison of maternally inherited mitochondrial DNA with bi-parentally
transmitted markers such as microsatellites, as well as through studies of social structure
coupling photo-identification and biopsy sampling.
The genetic analysis of biopsies from photo-identified dolphins will also provide a finer-
scale picture of the social structure of S. guianensis , by seeking correlations between kinship
and social affiliations, as has been done with other delphinids recently (e.g. Möller et al.,
2001, 2006; Krützen et al., 2004).
The above mentioned methods can also help to unveil the social structure of S. fluviatilis .
The only available information on the social organization of this species are from mark and
recapture data, suggesting that S. fluviatilis in the Central Amazon is not territorial, but shows
strong site fidelity (spending up to 9 years in the same area). Group structure seems to be
socially organized by fusion-fission strategies, and some animals have been sighted together
8.5 years after marking (da Silva & Martin, unpublished data).
Another interesting prospect is the investigation of the mating system of Sotalia dolphins.
Until now, the only hypothesis advanced was of polyandry of both Sotalia species, based on
their large testis sizes (an indication of sperm competition) (da Silva & Best, 1996; Rosas &
Monteiro-Filho, 2002). Mating system can be studied using microsatellites because they have
the ability to ascertain paternity. That is useful when different mother-calf pairs from the
same group are biopsied, and also when known siblings are sampled (for instance as calves
from the same female), since the genotype of the father can be reconstructed from the calf's
genotype if the mother's genotype is known. Hence, it is possible to check how many calves
from the same cohort are fathered by the same male, and if calves of the same female born in
different years are full siblings.
Conservation Implications
Studies on the population structure, phylogeography and social structure of Sotalia
species will certainly help in the evaluation of their conservation status, and contribute to the
design of effective measures for their conservation.
A proper evaluation of the impact of non-natural mortality on populations can only be
achieved when their geographical boundaries are known. Additionally, population
delimitation is fundamental for the design of effective conservation measures (O'Brien, 1994;
Avise, 1997). The goal of any conservation plan should be to preserve the target species both
in time and space. That means the entire range of the species should be maintained, which is
an obvious challenge because there is hardly any species charismatic enough to stop human
plans of growth and development in face of the low ecological responsibility of our species.