Dolphin Phylogeny

1
Dolphin Phylogeny
Introduction Our research question was to learn
how river dolphins are related to ocean dolphins
and other cetaceans. Our hypothesis was that
biogeography would show a higher correlation to
common ancestry than would habitat. A secondary
question was to use two different gene trees for
the same species to see if similar phylogenies
would be generated by each.
April Maskiewicz, Dawne Page Kerry Fulcher
Methods In order to test our hypothesis, we
chose to compare cetacean species with particular
biogeographic ranges. Due to the limited amount
of sequence available from river dolphins, we
could only use sequences from mitochondrial DNA.
We chose nucleic acid sequence from the 16S rRNA
gene and amino acid sequence from cytochrome b
for the species listed in Table 1.. We chose
hippo and horse sequences as potential outgroups.
Sequences were collected and edited for common
length on the Biology Workbench 3.2 via internal
(Workbench) or external (NCBI) database searches.
Alignments were made and unrooted sequence
similarity trees generated using Clustal W and
DrawTree respectively. Finally, an evolutionary
distance matrix was generated for the Cytochrome
B data using PROTDIST (Fig. 3)
Common Dolphin
Amazon RD
Indus RD
Results Two very different trees were generated.
The rRNA gene tree (Fig. 1) showed 3 clusters
horse, Amazon river dolphin with all of the
whales, and Asian river dolphins with the ocean
dolphins and hippo. These data imply separate
origins for the Amazon vs. Asian river dolphins.
However, the cytochrome b tree (Fig. 2) did not
imply such a simple conclusion. The Beluga and
Humpback whales were closely related to the ocean
dolphins (93-94). The Humpback whale was also
more closely related to the Indian river dolphins
(92) than to the Amazon Yangtze river dolphins
(88). In contrast, the Humpback whale was more
closely related to the Amazon river dolphin in
the 16S rRNA phylogeny. Conclusion Our
tentative conclusion is that the river dolphins
in India, the Amazon, and the Yangtze have
separate origins, but these origins are unclear
from the data, which illustrate the inherent
difficulties of constructing phylogenies from
several gene trees.