GENE DIFFERENTIATION IN PACIFIC SALMON (ONCORHYNCHUS SP) - FACTS AND MODELS WITH REFERENCE TO PINK SALMON (ONCORHYNCHUS-GORBUSCHA)

Analyzing population genetic data usually involves examining relations hips among populations followed by analysis of the distribution of gen etic variability. Genetic relationships are often depicted with multid imensional scaling or trees constructed from genetic distances; geneti c variation within and among populations is partitioned using gene div ersity measures such as F-ST or G(ST). Genetic distances or gene diver sity are often used to estimate influences of gene drift, migration, a nd/or selection on observed gene differentiation. We used allozyme dat a for pink salmon populations to examine the. theoretical models avail able for estimating magnitudes of these factors in Pacific salmon popu lations. The models included (1) mutation and gene drift; (2) mutation and migration; (3) migration and gene drift; and (4) gene drift, migr ation, and selection. These models suggest that gene drift and migrati on are probably important at the lowest levels of population hierarchy , but even very small forces such as weak heterogeneous selection and low migration levels may be important at higher levels. The accuracy o f some estimates should be questioned because for many situations appr opriate models are either not yet available or are not sufficiently re fined. Also, the dynamic genetic structure of salmon populations makes it unlikely that the steady state assumed for many theoretical models has obtained.