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 408

Similar and Identical Alleles between the Baiji and Finless Porpoise

In combination with DQB data previously reported in the baiji and three MHC loci
(MHC-I, DQB and DRA ) data in the finless porpoise (Yang et al., 2005; Hayashi et al., 2006;
Xu et al., 2007), three MHC loci on exon 2 of the baiji and finless porpoise revealed a striking
and unexpected similarity. Especially, some alleles of the baiji were identical to those of the
finless porpoise of China waters at both nucleotide and amino acid levels. A baiji allele, i.e.,
Live-DRA*01 , is identical to an allele of the finless porpoise ( Neph-DRA*01 ). At the DQB
locus, two alleles of the baiji, i.e., Live-DQB*16 , 04 were, respectively, identical to the finless
porpoise alleles Neph-DQB*03 and 14 . Similarly, three baiji MHC-I alleles (i.e., Live-I*01 ,
02 , 04 ) were separately identical to alleles found in the finless porpoise, i.e., Neph-I*19 , 33 ,
and 14 . It was noted that the baiji and finless porpoise are highly divergent with each other,
with the baiji included in Lipotidae of the superfamily Lipotoidea (de Muizon, 1988; Yang et
al., 2002) and the finless porpoise in Phocoenidae of the superfamily Delphinoidea (Rice,
1998), respectively. Besides the above identical alleles, other alleles also showed high
similarity between both species. The average K2P distances between the baiji and finless
porpoise at the DQB and MHC-I loci were comparable to those between each pair of
relatively related cetacean species, such as the finless porpoise in the family Phocoenidae, and
some species of Delphinidae and Monodonitdae, which were included in the superfamily
Delphinidea (Tables 3 and 4). At the MHC-I locus, the mean K2P distance between two
closely related species, i.e., the finless porpoise and vaquita (0.1014 ± 0.0011) was
comparable to that between the baiji and finless porpoise (0.1321 ± 0.0021). And at the DQB
locus, the mean K2P distance between the baiji and finless porpoise was 0.0815 ± 0.0006,
which was not significantly different from the distances between either species of
Delphinidae (0.0972 ± 0.0003) or Monodontidae (0.0731 ± 0.0003) and the finless porpoise
(P > 0.05) (Table 3).

Table 3. Average Kimura 2-parameter nucleotide acid distances
(± standard error) among DQB alleles.

Baiji Finless porpoise Delphinidae Monodontidae

Baiji 0.0511±0.0012

Finless porpoise 0.0815±0.0006 0.0386±0.0006

Delphinidae a 0.1088±0.0001 0.0972±0.0003 0.0736±0.0008
Monodontidae b 0.0919±0.0003 0.0731±0.0003 0.0750±0.0141 0.0360±0.0003
a Including D. delphis (Dede-a: AB164220), L. obliquidens (Laob-a: AB164224), and G.
macrorhynchus (Glma-a: AB164226), b Including M. monoceros (Momo-DQB*0201: U16991), D.
leucas (Dele-DQB*0201: U16989; Dele-DQB*0101: U16986)
Table 4. Average Kimura 2-parameter nucleotide acid distances (± standard error)
among MHC-I alleles

Baiji Finless porpoise Vaquita

Baiji 0.1335±0.0047

Finless porpoise 0.1321±0.0021 0.0863±0.0015

Vaquita c

0.1470±0.0019 0.1014±0.0011 0.0322±0.0087

c Six alleles, i.e. Phsi*01 - Phsi*06 (AY170890-AY170895), were used