Early investigations suggested that genetic variability might be associated with longevity, and that tree species were the most heterozygous of organisms. However, these ideas may be modified as species representing a wider range of population structure are investigated. Torrey pine, a California endemic, occurs in only two populations, one on the coast at San Diego and one 280 km northwest on Santa Rosa Island. Populations number only ca. 7,000 and 2,000 individuals, respectively. Each population is composed of identical homozygous genotypes at 59 isozyme loci. The island population is fixed for alternate alleles to those in the coastal population at two of the 59 loci. These results agree with other lines of evidence that suggest Torrey pine is characterized by minor differences between relatively uniform populations. Drift is the most likely explanation for lack of variability in Torrey pine. It probably experienced one or more reductions in population size, most recently during the Xerothermic period 8,500 to 3,000 B.P. The founder effect may have operated during colonization of Santa Rosa Island ca. 18,000 B.P. Apparently, the Northern Channel Islands to which Santa Rosa belongs were not connected to the adjacent mainland in recent geologic history, and colonization would require transport across at least a 6- to 7-km channel. Red pine and western redcedar, conifers with greater ranges than Torrey pine, are only slightly more variable. Thus, despite the presence of mechanisms to maintain high levels of outbreeding, it appears the conifer breeding system can survive inbreeding with its consequence of genetic depauperization.
