Hypervariable genetic markers and population differentiation in the minke whale Balaenoptera acutorostrata.

The minke whale is a small balaenopterid whale with a worldwide distribution. The major populations of the North Atlantic, North Pacific and Southern Hemisphere oceans are separated from each other by geographical and/or physiological boundaries. Much less is known about the population structure within each ocean. The International Whaling Commission (IWC) currently recognises a number of populations in the North Atlantic and North Pacific. Historically, six Management Areas have been employed in the Southern Hemisphere, based on observed feeding concentrations of humpback whales (Megaptera novaeanglia), but the validity of this division for minke whales is questionable. Continuing whaling interests urgently require knowledge of population structure for successful management. The aim of the present study was to investigate the structure of minke whale populations, with emphasis on die Antarctic Whaling Areas IV and V, using recently developed variable number of tandem repeats (VNTR) DNA markers. To this purpose, minke whale samples from the North Atlantic, the North Pacific and these two Antarctic Whaling Areas were analysed. First of all, the potential of multilocus DNA fingerprinting (Jeffreys et al, 1985) to identify these populations was evaluated. Using polycore probe 33.15, it was shown that the North Atlantic population revealed a very distinct hybridisation pattern, in which the band sharing was high compared to that of the other populations. This difference in the band sharing coefficient disappeared completely, however, when poly core probe 33.6 was used. The marked difference between the probes in the extent to which they reflect population differences, illustrates that population inferences, based on molecular data, can only be drawn by taking the molecular evolution of the markers into account. Under the conditions used, the technique was unable to detect any distinction between the adjacent Antarctic Areas IV and V. The biggest disadvantage of multilocus fingerprinting is that alleles cannot be allocated to individual loci. To overcome this problem, a charomid library was constructed which was enriched for repeated sequences. From 24 minisatellite clones, initially isolated and characterised, six clones were selected for further population screening. These six loci covered a wide range of variability levels, with heterozygosities from 0 - 0.99. Statistical analysis showed that minke whales from the three major oceans were well diverged, but no significant differences were observed between the two Antarctic Whaling Areas. One locus contained a mutation which appeared to be diagnostic for the Antarctic minke whales. Tests for heterogeneity within populations on samples from each major ocean did not reveal significant substructuring. Pilot whale Globicephala malaena derived microsatellite flanking primers were used to amplify four polymorphic microsatellite loci in minke whales. These markers confirmed the genetic divergence between populations from the two hemispheres, but the distinction between the two northern populations was less clear cut than that resulting from the minisatellite data. Allele frequencies and heterozygosities in the two Antarctic Areas were not significantly different. The microsatellite data did not give any indication for heterogeneity within the pooled Antarctic sample. The data suggest the occurrence of back mutations at these microsatellite loci. The usefulness of minisatellites and microsatellites for population genetic studies is evaluated in relation to what is known about their molecular evolution. The final Chapter discusses the underlying rationale for the IWC's Revised Management Procedure and provides suggestions on how the present study could be extended to obtain some of the essential information required for its successful implementation.