MOLECULAR ECOLOGY AND SYSTEMATICS OF SOTALIA DOLPHINS - Biology, Evolution and Conservation of River Dolphins Within South America and Asia - page 267

morphological approaches maximizes the likelihood of understanding true evolutionary
relationships (Hillis, 1987; Knowlton, 2000; Avise, 2004).
Cunha et al . (2005) clarified the taxonomic status of Sotalia dolphins using sequences of
the mitochondrial control region and the cytochrome b of 56 samples (12 riverine and 44
marine). This was the first study to include samples of the Amazon Estuary in analyses of
differentiation between Sotalia ecotypes. Three phylogenetic approaches were used, and all of
them recovered the same topology, displaying marine and freshwater Sotalia as reciprocally
monophyletic groups (Figure 4). This result was corroborated by a Nested Clade Analysis
(NCA; Templeton, 1998) of the same data. Notwithstanding some of its limitations in
analyses of recently diverged lineages, NCA is a powerful tool that quantitatively and
qualitatively investigates population structure and evolutionary history, including speciation
(Templeton, 1998, 2001; Sites and Marshall, 2003). The NCA of Sotalia samples indicated a
relatively old allopatric fragmentation event, which separated marine and riverine populations
(Figure 5). Fragmentation events are evidence of speciation, especially if they: (a) are in
higher level (older) clades; (b) reflect the separation of two clusters by several mutational
steps and (c) coincide with independent evidence from other type of data (Templeton, 2001).
The fragmentation observed between the two Sotalia ecotypes meets all three conditions.
Interestingly, dolphins from Pará, at the mouth of the Amazon River, were genetically much
closer to dolphins from Santa Catarina (4,700 km southwards, along the coast) than to the
geographically closer (2,000 km) riverine dolphins (Cunha et al., 2005).

B (PA)
A (PA)
C (S/SE )

66/51/ -

F (RN)
I (PA/RN)
J (PA)
L (PA)
K (PA)
N (PA)

91/62/81

O (PA)
M (PA)

AM1

AM2

93/57/91

AM3

73/76/70

AM4
AM5

70/ - / -

Steno bredanensis

0,005

Figure 4. Neighbor-Joining (NJ) phylogenetic tree (p distances) of Sotalia spp. control region
haplotypes. Maximum-Likelihood (ML) and Maximum Parsimony (MP) retrieved the same topology.
Bootstrap values (NJ/ML/P) higher than 50% are shown. Hypothetical synapomorphies of control
region and cytochrome b haplotypes from marine and riverine species are indicated by vertical bars.
Thicker bar corresponds to 10 synapomorphies. Adapted from Cunha et al. (2005).