HIGH LEVEL OF MHCPOLYMORPHISM IN THE BAIJI AND FINLESS PORPOISE, WITH SPECIAL REFERENCE TO POSSIBLE CONVERGENT ADAPTATION TO THE FRESHWATER YANGTZE RIVER - Biology, Evolution and Conservation of River Dolphins Within South America and Asia - page 413

sympatric in the middle and lower reaches of the Yangtze River and face similar selection
pressures such as pathogens. As a consequence, shaping the same motifs or alleles in both
species in order to adapt to the similar environmental pressures may be inferred. Furthermore,
identical alleles at the DQB and MHC-I loci were only shared by the baiji and finless
porpoise. Although we sequenced some individuals from eight species in three families (i.e.,
Pontoporiidae, Phocoenidae, and Delphinidae) at the MHC-I and DQB loci, no identical allele
was detected between the baiji and these species. Also, Hayashi et al. (2003) sequenced the
DQB gene of 16 cetacean species but did not find any allele shared by different species. The
other evidence to support convergent evolution between the baiji and finless porpoise came
from the sequence divergence between both species which was comparable to those between
each pair of relatively related cetacean species, as shown in Tables 3 and 4. Further studies,
however, are needed to clarify the convergent evolution between the baiji and finless porpoise
with more MHC loci or other molecular data.

A CKNOWLEDGMENTS

We thank Mr Anli Gao, Xinrong Xu, Hua Chen, and Qing Chang for collecting samples
for many years, and members of the Institute of Genetic Resources, Nanjing Normal
University, for their contributions to this paper. This study was supported by the National
Natural Science Foundation of China grant numbers 30830016, 30670294 and 30470253, the
Program for New Century Excellent Talents in Universities (NCET-07-0445), the Ministry of
Education of China, the Specialized Research Fund for the Doctoral Program of Higher
Education (SRFDP 20060319002), the Ministry of Education of China, and the Major Project
for Basic Researches of Jiangsu Province Universities (07KJA18016).

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