Indicators of population viability in red spruce, Picea rubens. II. Genetic diversity, population structure, and mating behavior

Red spruce (Picea rubens Sarg.) has become increasingly rare across large p ortions of its range in eastern North America as a result of a general and widespread decline over the past century. Genetic diversity, population gen etic structure, outcrossing rates in the filled seeds, and actual inbreedin g levels were characterized in five small, isolated, remnant red spruce pop ulations from the disjunct northwestern limits of its range in Ontario and five populations from the larger, more extensive Maritime populations of No va Scotia and New Brunswick to determine genetic and reproductive status, t o provide some benchmarks for monitoring genetic changes resulting from iso lation and restricted population sizes, and to assist the development of re storation and conservation strategies. Thirty-seven allozyme loci coding fo r 15 enzymes were used for genetic diversity assessments, and six of the mo st polymorphic loci were used for mating system determination. On average, 29.1% (95% criterion) of the loci were polymorphic, the number of alleles p er locus was 1.60, and the observed and expected heterozygosities were 0.09 7 and 0.100, respectively. The Ontario populations were comparable to or sl ightly less genetically variable than those from the Maritimes. Only 4.7% o f the detected genetic variation was among stands; the remainder was among individuals within stands. The Maritime populations were genetically less d ifferentiated from each other than those in Ontario. With the exception of three Maritime populations clustering tightly in one group, there was no cl ear separation of Ontario red spruce populations from Maritime red spruce p opulations based on genetic distance as well as canonical discriminant anal yses. The average multilocus (t(m)) and single-locus (t(s)) population outc rossing rates were 0.595 and 0.558, respectively, indicating a comparativel y high tolerance for inbreeding up to the filled seed stage of development in red spruce. The Ontario populations, on average, showed higher outcrossi ng rates (t(m) = 0.654, t(s) = 0.641) than the Maritime populations (t(m) = 0.535, t(s) = 0.475). Individual family outcrossing rates were similar to their respective population outcrossing rates and no significant difference s were observed among families within populations for the multilocus estima tes. When such high levels of inbreeding in filled seeds were combined with the proportions of empty (post-pollination-aborted) seeds, it appears that actual inbreeding levels may vary from 48 to 86%. The highest inbreeding l evels occurred in the smallest, most isolated Ontario populations and in th ose populations most likely to have been affected by poorer pollination con ditions. Allozyme variation indicates that in the short term, extant remnan ts of Ontario red spruce have maintained their genetic diversity and integr ity. For artificial restoration of red spruce in Ontario, local seed source s could be used without undue concern over losses of genetic diversity. How ever, over the longer term, genetic drift and inbreeding may be expected to result in further losses of genetic diversity and (or) reproductive fitnes s if population sizes, numbers, and distribution continue to decline.