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Sequence variation at the major histocompatibility complex DRB loci in beluga (Delphinapterus leucas) and narwhal (Monodon monoceros) 总被引:2,自引:2,他引:0
The variation at loci with similarity to DRB class II major histocompatibility complex loci was assessed in 313 beluga collected from 13 sampling locations across North
America, and 11 narwhal collected in the Canadian high Arctic. Variation was assessed by amplification of exon 2, which codes
for the peptide binding region, via the polymerase chain reaction, followed by either cloning and DNA sequencing or single-stranded
conformation polymorphism analysis. Two DRB loci were identified in beluga: DRB1, a polymorphic locus, and, DRB2, a monomorphic locus. Eight alleles representing five distinct lineages (based on sequence similarity) were found at the
beluga DRB1 locus. Although the relative number of alleles is low when compared with terrestrial mammals, the amino acid variation found
among the lineages is moderate. At the DRB1 locus, the average number of nonsynonymous substitutions per site is greater than the average number of synonymous substitutions
per site (0.0806 : 0.0207, respectively;P<0.01). Most of the 31 amino acid substitutions do not conserve the physiochemical properties of the residue, and 21 of these
are located at positions implicated as forming pockets responsible for the selective binding of foreign peptide side chains.
Only DRB1 variation was examined in 11 narwhal, revealing a low amount of variation. These data are consistent with an important role
for the DRB1 locus in the cellular immune response of beluga. In addition, the ratio of nonsynonymous to synonymous substitutions is similar
to that among primate alleles, arguing against a reduction in the balancing selection pressure in the marine environment.
Two hypotheses may explain the modest amount of Mhc variation when compared with terrestrial mammals: small population sizes at speciation or a reduced neutral substitution
rate in cetaceans.
Received: 15 July 1997 / Revised: 24 March 1998 相似文献
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Rune Dietz Mads Peter Heide-Jørgensen Pierre Richard Jack Orr Kristin Laidre Hans Christian Schmidt 《Polar Biology》2008,31(11):1295-1306
Twenty-one narwhals tagged in 2003 and 2004 in Admiralty Inlet showed a different summer distributional pattern than previous
narwhal-tracking studies from Somerset Island, Eclipse Sound and Melville Bay. The migration of the narwhals tracked from
Admiralty Inlet moved out through Lancaster Sound 15 days earlier (P < 0.0001) than the narwhals summering around Eclipse Sound, whereas the Admiralty Inlet narwhals reached the mouths of Eclipse
Sound 18 days later (P < 0.0001) than the Eclipse Sound summering population. The winter range of the Admiralty Inlet narwhals overlapped with the
winter range of narwhals from Melville Bay and Eclipse Sound in central southern Baffin Bay and Northern Davis Strait, but
not with the winter range of narwhals from Somerset Island that wintered further north. Distribution size of range, and population
size did not appear to be related. An example of considerable year to year variation between area of summer and winter distribution
in the 2 years was believed to be related to the sample size and number of pods of whales tagged, rather than to differences
in sex or age classes. 相似文献
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Preliminary observations on the morphology of the inner ear of the fetal narwhal (Monodon monoceros)
The inner ear of the narwhal (Monodon monoceros) was investigated on the basis of a complete series of microslides of an early fetus. In this well‐preserved specimen, the cochlea is about twice as large as the vestibular apparatus. The latter exhibits a high degree of specialization. Whereas the utriculus and sacculus are of normal size in comparison with those of other mammals, the semicircular canals are miniaturized but not obliterated, as in the case of some adult toothed whales. In comparison with other mammals, there is relatively little perilymphatic space around the vestibular organ, but the inner radius of the lymphatic ducts comes close to that of the adult human. Although there are some hints that the sensitivity of the vestibular system may be high in this species, detailed analysis of the adult narwhal ear is needed to confirm this inference. 相似文献
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