INTROGRESSIVE HYBRIDIZATION AND PHYLOGENETIC-RELATIONSHIPS BETWEEN NORWAY, PICEA-ABIES (L) KARST, AND SIBERIAN, PICEA-OBOVATA LEDEB, SPRUCESPECIES STUDIED BY ISOZYME LOCI
Kv. Krutovskii et F. Bergmann, INTROGRESSIVE HYBRIDIZATION AND PHYLOGENETIC-RELATIONSHIPS BETWEEN NORWAY, PICEA-ABIES (L) KARST, AND SIBERIAN, PICEA-OBOVATA LEDEB, SPRUCESPECIES STUDIED BY ISOZYME LOCI, Heredity, 74, 1995, pp. 464-480
We analysed patterns of genetic variation at 26 isozyme loci across th
e area of two main forest-forming spruce species in Eurasia, Norway sp
ruce (Picea abies (L.) Karst.) and Siberian spruce (P. obovata Ledeb.)
. Ten seed samples from distant parts of the P. abies-P. obovata area
and from a supposedly wide zone of introgressive hybridization between
them were investigated. A very high level of allozyme variation was f
ound in populations of both species. As parameters of gene diversity,
the mean number of alleles per locus, percentage of polymorphic loci (
95 per cent criterion) and expected heterozygosity averaged 2.8, 61.5
and 0.252 for P. abies and 2.4, 61.5 and 0.213 for P, obovata, respect
ively. Norway and Siberian spruces turned out to be extremely similar
genetically. We did not find any fixed allele differences between them
, i.e. there were no diagnostic loci and only a few alleles could be c
haracteristic of some populations. Cluster and multivariate analyses h
ave shown that these two species should be considered as two closely r
elated subspecies or two geographical races of one spruce species unde
rgoing considerable gene exchange. Our genetic data agree with morphol
ogical data and confirm the existence of a wide zone of introgressive
hybridization between Norway and Siberian spruces - perhaps the widest
known among plants. The samples which, according to morphological and
geographical data, were taken from presumably 'hybrid' populations sh
owed 'intermediate' genetic characteristics. Clinal variation was sugg
ested for some alleles, and the 'rare allele phenomenon', i.e. higher
frequencies of rare and unique alleles, was observed in the 'hybrid' s
pruce populations.