Francis C. Yeh

Glacial vicariance in the Pacific Northwest: evidence from a lodgepole pine mitochondrial DNA minisatellite for multiple genetically distinct and widely separated refugia

The Canadian side of the Pacific Northwest was almost entirely covered by ice during the last glacial maximum, which has induced vicariance and genetic population structure for several plant and animal taxa. Lodgepole pine (Pinus contorta Dougl. ex. Loud.) has a wide latitudinal and longitudinal distribution in the Pacific Northwest. Our main objective was to identify relictual signatures of glacial vicariance in the population structure of the species and search for evidence of distinct glacial refugia in the Pacific Northwest. A maternally inherited mitochondrial DNA minisatellite‐like marker was used to decipher haplotype diversity in 91 populations of lodgepole pine located across the natural range. Overall population differentiation was sizeable (GST = 0.365 and RST = 0.568). Four relatively homogeneous groups of populations, possibly representative of as many genetically distinct glacial populations, were identified for the two main subspecies, ssp. latifolia and ssp. contorta. For ssp. contorta, one glacial lineage is suggested to have been located at high latitudes and possibly off the coast of mainland British Columbia (BC), while the other is considered to have been located south of the ice sheet along the Pacific coast. For ssp. latifolia, two genetically distinct glacial populations probably occurred south of the ice sheet: in the area bounded by the Cascades and Rocky Mountains ranges, and on the eastern side of the Rockies. A possible fifth refugium located in the Yukon may have also been present for ssp. latifolia. Zones of contact between these ancestral lineages were also apparent in interior and northern BC. These results indicate the role of the Queen Charlotte Islands and the Alexander Archipelago as a refugial zone for some Pacific Northwest species and the vicariant role played by the Cascades and the American Rocky Mountains during glaciation.

Functional characterization of drought-responsive aquaporins in Populus balsamifera and Populus simonii×balsamifera clones with different drought resistance strategies

We have characterized poplar aquaporins (AQPs) to investigate their possible functions in differential drought responses of Populus balsamifera and Populus simonii×balsamifera leaves. Plants were exposed to mild and severe levels of drought stress and to drought stress recovery treatment, and their responses were compared with well-watered controls. Compared with P. balsamifera, P. simonii×balsamifera used drought avoidance as the main drought resistance strategy, and rapidly reduced stomatal conductance in response to stress. This strategy is correlated with growth rate reductions. Eleven AQPs were transcriptionally profiled in leaves from these experiments and five were functionally characterized for water channel activity. PIP1;3 and PIP2;5 were among the most highly expressed leaf AQPs that were responsive to drought. Expression of PIP1;3 and five other AQPs increased in response to drought in the leaves of P. simonii×balsamifera but not in P. balsamifera, suggesting a possible role of these AQPs in water redistribution in the leaf tissues. PIP2;5 was upregulated in P. balsamifera, but not in P. simonii×balsamifera, suggesting that this AQP supports the transpiration-driven water flow. Functional characterization of five drought-responsive plasma membrane intrinsic proteins (PIPs) demonstrated that three PIP2 AQPs (PIP2;2, PIP2;5, PIP2;7) functioned as water transporters in Xenopus laevis oocytes, while the two PIP1 AQPs (PIP1;2 and PIP1;3) did not, consistent with the notion that they may be functional only as heterotetramers.

Nucleotide divergence between populations of trembling aspen (Populus tremuloides) estimated with RAPDs

In the present study, a total of 142 trees sampled from five populations of trembling aspen (Populus tremuloides Michx.) in Alberta was analyzed by the polymerase chain reaction (PCR) with five random oligonucleotide primers. Null-allele frequencies of 28 putative RAPD loci were estimated using the given departure from Hardy-Weinberg equilibrium (FIS) previously estimated with isozyme markers for the same population. Nucleotide divergence between populations was then estimated in a fashion similar to restriction-fragment data, but considering the dominance of the RAPDs. The average of nucleotide divergence between populations was in the order of 0.0005 and nucleotide divergence were found to be highly correlated with geographic distance. The results suggest that isolation by distance may be an important factor in the genetic differentiation of trembling aspen.

Isozyme variation of Thuja plicata (cupressaceae) in British Columbia

The level and distribution of genetic variability within and among western red cedar populations (Thuja plicata D. Dort) were assessed using enzyme electrophoresis. Nineteen loci representing 15 enzymes were examined in 2300 megagametophytic tissues from 230 trees in eight populations. The mean number of alleles per locus was 1.17±1:0.03, the mean percentage of polymorphic loci was 16+−0.06, and the mean heterozygosity was 0.04±0.02. Most of the genetic variability was not unique and different allelic fixation was not observed. The mean value of FIS was low (0.057), closely approaching expectations at Hardy-Weinberg equilibrium. The major component of FIT was FIS; the relatively low FST suggested little heterogeneity among populations. Maximum likelihood estimate of number of migrants exchanged per generation among populations was 15.37+−3.05. This estimate, among geographic populations separated by many kilometres, suggests that gene flow amongneighbouring populations of western red cedar was quite extensive. A single bottleneck some 10 000 years ago could explain sufficiently its low level of genetic variability in British Columbia.

Segregation of allozymes in megagametophytes of viable seed from a natural population of jack pine, Pinus banksiana Lamb.

SummarySegregation ratios of allozymes in haploid female gametophytes obtained from viable seed were studied in a natural population of jack pine, Pinus banksiana. Stability of these ratios was assessed for three levels of the sexually reproductive crown as well as for four years of natural fertilization. Analyses of observed segregation ratios of four of five polymorphic isozyme loci showed good correspondence to the overall 1∶1 ratios expected for simple Mendelian inheritance. Allozymes of glucose-6-phosphate dehydrogenase did not segregate in the expected 1∶1 ratio. In addition, there were significant deviations from the expected segregation ratio for all the loci at some sampling positions on individual trees. Heterogeneity of segregation among trees, strata and years could be the result of pollen pool heterogeneity, segregation distortion and/or recessive lethal and semi-lethal gene combinations resulting in early embryo abortion. These types of segregation deviations in viable seed can affect the estimation of allele frequencies from bulked samples of a small number of individuals, the inference of heterozygosity/homozygosity of parental trees, and estimates of selfing rates.

Multilocus structure in Pinus contorta Dougl.

We studied isozyme variation at 21 loci in 66 populations from three subspecies of Pinus contorta Dougl.; 35 in spp. latifolia, 20 in spp contorta and 11 in spp. murrayana. The objectives were to assess gametic disequilibria and multilocus structure. There was considerable differentiation of allele frequencies at 19 polymorphic loci across the 66 populations and within the subspecies. Allele frequencies at many loci correlated with geographic variables. Genetic variability varied considerably among populations within subspecies but the subspecies means were similar. The mean number of polymorphic loci and the mean heterozygosity over 19 polymorphic loci were, respectively, 13 and 0.194 in latifolia, 12 and 0.196 in murrayana, and 12 and 0.180 in contorta. The mean heterozygosity correlated with longitude and altitude across the 66 populations and with latitude in latifolia. Gametic disequilibria were evident in 40 populations; 29 in latifolia, eight in murrayana and three in contorta. Gametic disequilibria correlated with latitude across the 66 populations and with longitude in latifolia. The single-locus FST averaged 0.0339 in latifolia, 0.0567 in murrayana, and 0.0764 in contorta. The multilocus FSTM was 0.1227 in latifolia, 0.2926 in murrayana, and 0.3328 in contorta. Multilocus Wahlund and founder effects, migration patterns, and natural selection, probably played significant roles in generating and maintaining the multilocus genetic structure in P. contorta in general and the subspecies latifolia in particular.

Estimation of mating system parameters in plant populations using the EM algorithm

SummaryAn EM algorithm procedure is presented for the maximum-likelihood estimation of mating system parameters of mixed mating system models for both angiosperms and gymnosperms. One advantage of the procedure is the ability to accommodate any number of alleles in the mature population and pollen pool. Estimates of the outcrossing rate (

Genetic parameters for seasonal height and height growth curves of white spruce seedlings and their implications to early selection

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