MOLECULAR ECOLOGY AND SYSTEMATICS OF SOTALIA DOLPHINS - Biology, Evolution and Conservation of River Dolphins Within South America and Asia - page 271

comprised of S. bredanensis , a larger dolphin found around the globe in tropical and
subtropical waters (Jefferson et al., 1993).
Molecular markers have also been used to investigate delphinid evolution. LeDuc et al.
(1999) reassessed the phylogenetic relationships within Delphinidae using full cytochrome b
sequences (about 1.2 kilobases) of 33 species. Among several interesting findings, their
analysis placed Sousa outside Stenoninae, which comprised Steno and Sotalia . Stenoninae,
however, had low bootstrap support. According to their results, Sousa belongs to Subfamily
Delphininae.
The most recent analyses used a less complete taxon sampling (17 species) but a larger
number of sequences (5.2 kilobases, including two mitochondrial and ten nuclear markers;
Caballero et al., 2008). Differently from the work by LeDuc et al (1999), Caballero et al.
showed Sousa and Sotalia as sister taxa within Delphininae, separated from Steno . The
combined phylogeny grouped Sousa with the Delphininae species in the analyses, and both
Sotalia species as a monophyletic clade branching from this grouping. Steno is placed with
Globicephalinae, Orcaella and Grampus .
The phylogenetic position of Sotalia will probably remain unsettled until the taxonomy of
Steno and Sousa is resolved. None of the above mentioned studies included S. teuszii , which
is the Sousa species geographically closer to Sotalia , or Sousa dolphins from Australia, which
may belong to a third species according to mitochondrial control region sequences (Frère et
al., 2008). The existence of other species of Steno is also still an open issue, since very little is
known about those dolphins (Jefferson, 2002).
Conservation Aspects
The uncertainty about the taxonomic situation of Sotalia dolphins hindered the evaluation
of their conservation status, and combined with the lack of information on their biology and
ecology, determined their classification as ―data deficient‖ by the International Union for the
Conservation of Nature (IUCN; 2008) and the Brazilian Institute of Environment and
Renewable Natural Resources (IBAMA, 2001). The clarification of the specific status of both
Sotalia species was an important first step toward the proper assessment of their conservation
status.
One of the consequences of the recognition that the two ecotypes of Sotalia constitute
different species is that Sotalia fluviatilis becomes the only exclusively freshwater delphinid
in the world (Cunha et al., 2005). To date, there are only three other living species of
cetaceans known to exist exclusively in freshwater, two of them belonging to the Platanistidae
( Platanista gangetica and P. minor ) family, and the other to the Iniidae family ( Inia
geoffrensis , which probably includes a fourth species, Inia boliviensis , Banguera-Hinestroza
et al. 2002). The baiji ( Lipotes vexillifer , Family Lipotidae) was another river dolphin,
endemic to the Yangtze River, but is now believed extinct in the wild (Turvey et al., 2007).
At least four other dolphin species can be found both at sea and in rivers: three are
delphinids ( Sousa chinensis , S. teuszii and Orcaella brevirostris ), and the other is a phocoenid
( Neophocaena phocaenoides ). However, there is no agreement about the degree of
differentiation between their marine and riverine populations, except for Orcaella
brevirostris . Beasley et al. (2005) demonstrated, using molecular analyses, that there are two
Orcaella species ( O. brevirostris and O. heinsohni ), and that Orcaella brevirostris has both