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Departamento de Ecología Evolutiva Instituto de Ecología, Universidad Autónoma de México, Apartado Postal 70-275, México D. F., 04510 México
Received for publication January 19, 1998. Accepted for publication September 16, 1998.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: conservation • gene flow • genetic structure • Pinaceae • Pinus rzedowskii.
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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; Yeh and Layton, 1979
; Yeh and El-Kassaby, 1980
; Yeh and O'Malley, 1980
; Weber and Stettler, 1981
; Guries and Ledig, 1982
; Hiebert and Hamrick, 1983
; Ledig and Conkle, 1983
; Furnier and Adams, 1986
; Li and Adams, 1989
; Merkle and Adams, 1987
; Ledig, 1998
), and relatively little genetic differentiation among populations ( <15%; Ledig, 1998
). However, most studies have focused upon wide-ranging species and less attention has been paid to species with fragmented and restricted distributions and small population sizes (Szmidt, 1982
; Ledig and Conkle, 1983
; Mejnartowicz and Bergmann, 1985
; Niebling and Conkle, 1990
). The common explanation for the low genetic differentiation found in conifer species is based on the reproductive systems particular to this group: in most conifers, seed and pollen are wind dispersed and this allows a more efficient gene flow among distant populations. However, this pattern can be modified by other factors, such as environmental fluctuations, historical events, and microspatial habitat selection (Hamrick and Godt, 1990
).
Here, we present a study on the levels of genetic variation in and patterns of genetic differentiation among populations of Pinus rzedowskii (Madrigal et Caballero), an endangered species from Michoacán, México. Our goal was to provide baseline information for this conservationally important and morphologically intriguing species (Madrigal and Deloya, 1969
; Delgado, 1997
). Pinus rzedowskii is represented by small populations, its distribution is extremely restricted and fragmented, and it is listed as an endangered species (Mexican government order, NOM-PA-CRN-001/93). Pinus rzedowskii exhibits traits representative of both subgenera Strobus and Pinus: dorsal umbo, winged seeds, and wood anatomy typical of hard pines; number and position of resin canals, resin secondary compound composition and wood composition typical of soft pines (Madrigal and Deloya, 1969
; Perry, 1991
). Finally, the small population sizes of this species and extremely restricted and fragmented geographic distributions offer an excellent opportunity to determine whether the quantity and distribution of genetic variation are related to population size and degree of isolation. We expected P. rzedowskii populations to show low levels of genetic variation and low population structuring. The results are surprising, however, in that P. rzedowskii is not genetically impoverished and shows a marked genetic structure. Furthermore, historical demography results strongly suggest that population densities of this endangered pine have been increasing steadily.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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; Farjon and Styles, 1997
). These are SOL3, CHI6, and PIN8 (Table 1). There are a total of 12 populations in an approximate area of 1.6 million ha. Of these, four have very low densities (SOL3, TEJ10, DUR11, and TAB12; Table 1) and of these only SOL3 was included in this study. Mean annual rainfall is 1500 mm, mainly between July and October. Average annual minimum and maximum temperatures are -5° and 30°C, respectively. Pinus rzedowskii populations have only been found on cambisol soils (
160 ha). These soils are poorly developed, with a subsoil layer that is more like a rock layer and an accumulation of materials such as clay, iron, and manganese. The topography is very rugged, with slopes from 85° to 90°. Vegetation types are wide ranging, with pine-oak, oak, subdeciduous, and deciduous tropical forest. However, most of the area is covered with pine-oak forest.
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). It is also one of only two soft pine species that have been described for the state of Michoacán, the other being P. ayacahuite var. veitchii. Pinus rzedowskii trees range in height from 15 to 50 m, with irregular treetops, diameters of up to 120 cm and a dark bark, 3-6 cm thick (Delgado, 1997
).
Sample collection
Primary growth branches with developing buds were collected and kept in polyethylene sealed bags in ice. In the laboratory, a replicate from each individual was stored in a cold room at 4°C and another one was kept in an ultrafreezer at -70°C. Three hundred and ten individuals (6-200 yr old) were sampled (Table 2). Samples were obtained from nine populations (excluding DUR11, TEJ10, and TAB12; Table 1) clearly restricted to patches of limey soil. Due to the terrain's rugged topography, a single sampling strategy was unwarranted. Three kinds of sampling schemes were followed, according to local conditions: in most populations an altitudinal transect was made from the upper part of a slope towards the lower part of the distribution area. Population ALB5 (Table 1) was sampled at five points in the population's margins and one in the middle, as this population was more readily accesible. In sparser populations, such as CHI6 and SOL3, all individuals were sampled.
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) and one part Yeh and O'Malley's buffer (1980
). The extract was absorbed into chromatography paper wicks, which were put in Eppendorf tubes and stored in an ultrafreezer at -70°C for later use. Gels were prepared with 12% w/v hydrolyzed starch. Three buffer systems (Miles et al., 1977
; Mitton et al., 1977
; Conkle et al., 1982
) and 12 enzymes with good resolution were used. A total of 14 loci were analyzed. Staining recipes were from Hakim-Elahi (1981)
for APX-1, APX-2, and CPX-2, Conkle et al. (1982)
for MNR-1 and GDH-2, Soltis et al. (1983)
for EST-2 and F-EST-2, Werth, Karlin, and Guttman (1982)
for LAP-1, and Selander et al. (1986)
for IDH-2. Loci and alleles were designated based upon relative protein mobility. Loci marked with number 1 are those farthest from the cathode.
Data analyses
All estimates were made based on nine polymorphic loci and five monomorphic ones. We obtained allele and genotypic frequencies, genetic identities, and distances following Nei (1975)
and fixation indices for each locus and population following Wright (1965)
.
Wright's F statistics as well as 99% confidence intervals of their mean values were obtained by bootstrapping over loci for the multilocus estimates and jackknifing over populations for the single-locus estimates (Weir and Cockerham, 1984
; Alvarez-Buylla et al., 1996a
). To find out whether FIS and FIT values for each locus were significantly different from 0, the statistic 
2 = F (2N) (K-1) was obtained with K(K-1)/2 degrees of freedom and where N is the sample size (number of individuals) and K the number of alleles (Li and Horvitz, 1953
). To determine the significance of FST values per locus, the statistic 2 = (2N) FST(K-1), with (K-1)(s-1) degrees of freedom was used, where s is the number of subpopulations (Workman and Niswander, 1970
). Gene flow (Nm) estimation was made indirectly using the formula proposed by Crow and Aoki (1984)
. Mean Nm value was used to obtain indirect estimates of effective population size per neighborhood (Nb; Slatkin and Barton, 1989
). Isolation by distance was analyzed with the method proposed by Slatkin (1993)
based on an island population structure model. The statistic M = (1 / FST - 1/4) was used in which population pairs with restricted dispersal and in genetic equilibrium would show lower M ratios and where FST are estimates for each pair of populations (Slatkin, 1993
; Alvarez-Buylla and Garay, 1994
). The Mantel statistic with 1000 permutations was used to test for significance of the isolation by distance pattern (Rohlf, 1993
). To describe the genetic relationships among populations, dendograms (UPGMA [unweighted pair group method with arithmetic mean]; Sneath and Sokal, 1973
; neighbor-joining; Swofford and Olsen, 1990
) were obtained using the matrix of genetic distances. The reconstructed tree was used to describe the demographic status of the species as proposed by Moritz (1996)
for conservation studies. This method is easily applied if phylogenetic relations among populations can be established. It is based on the idea that expanding populations are expected to show a star-like phylogeny that would result in a parabolic relation between the genetic distance, as an estimate of time of divergence, and the logarithm of the number of lineages following the UPGMA analysis. On the contrary, stable populations would show a strongly structured phylogeny and would result in an exponential relationship.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Two alleles were found for loci Apx-1, Cpx-1, Lap-1, Idh-2, and Gdh-2, four alleles for loci Apx-2, Est-2, and Sdh-2, and five alleles for locus Got-1. Allele frequencies were significantly different among populations using a multiple comparisons G test (Sokal and Rohlf, 1981
; data not shown). Twenty-eight out of 59 fixation indices were significantly different (P < 0.05; data not shown) from those expected under Hardy-Weinberg equilibrium. Twenty-four of these indices were positive. This indicates an excess of homozygotes for several loci in several populations.
All three of Wright's F statistics for polymorphic loci were positive and significantly (P < 0.01; Table 3) different from zero for all loci except FIS and FIT for locus Est-1.
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17% of the genetic variation is explained by differences among populations. All FST values were significantly different from zero. Therefore, many of the values obtained for FIT are due to differences among populations. FIT values ranged from 0.083 to 0.902, with a mean of 0.405 and a confidence interval between 0.256 and 0.816 (P < 0.05). Gene flow (Nm) estimates ranged from 0.14 to 3.48 (average = 1.5), which suggests that there is relatively little genetic exchange among P. rzedowskii populations. Effective neighborhood size (Nb; Slatkin and Barton, 1989
) was also low (0.88 to 21.88, with a mean of 9.0), suggesting that few individuals are contributing allelic variants and that gene flow may be insufficient to prevent differentiation among populations (Table 3).
Genetic relatedness among populations and isolation by distance
Estimators of genetic identity were heterogeneous (Table 4). The largest genetic identity was 0.986, between populations AGU9 and PIN8, and the smallest was 0.870, between populations ALB5 and SOL3. No specific pattern was found to match the distances separating the populations. This was confirmed using both Slatkin's (1993)
method in which no significant relationship was found between a logarithmic estimate of gene flow and geographic distance among populations (data not shown) and the Mantel test on data from Table 4 (
= 0.11, P = 0.460). This suggests that the populations' structure appears not to be due to differences in gene flow produced by an isolation by distance model.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). We expected that P. rzedowskii with small and fragmented populations would have low levels of genetic variation. However, it shows genetic variation levels similar to those found for other pine species with large and continuous populations (Hamrick, Mitton, and Linhart, 1981
; Niebling and Conkle, 1990
). For instance, mean allele number per locus (1.8) is comparable to values found in P. maximinoi (1.7; Mathenson, Bell, and Barnes, 1989
), P. attenuata and P. muricata (1.7 for both; Millar et al., 1988
). Unlike P. rzedowskii, these species are wide-ranging and have large population sizes. Expected heterozygosity in P. rzedowskii (0.219) was higher than the estimate reported for P. muricata (0.120; Millar et al., 1988
), a wide-ranging species with fragmented populations. The percentage of polymorphic loci is higher in P. rzedowskii (46.8) than in P. torreyana (3.4; Ledig and Conkle, 1983
), a species with restricted distribution and only two small populations (2000 and 7000 individuals). Another interesting species is P. washoensis, an endangered pine from California (expected heterozygosity = 0.148; Niebling and Conkle, 1990
), which like P. rzedowskii has higher variability than that found in species of wider distribution. Observed heterozygosity in P. rzedowskii (0.162; Table 2) was significantly lower than expected heterozygosity (0.210). In contrast, in most studied pine species inbreeding is rare (Ledig, 1998
). Pinus rzedowskii shows both fixation indices and FIS statistics that deviate from Hardy-Weinberg equilibrium, revealing a moderate inbreeding level.
Pinus rzedowskii has significant levels of genetic differentiation among populations, with 17.5% of the total variation due to differences among populations. The mean FST value for P. rzedowskii is higher than that found in most studied conifers, most of which are wide-ranging species (Table 5). However, the FST values found for P. rzedowskii are within the range of values reported for species with discontinuous distributions and large populations. For instance, P. cembra has an FST value of 0.32 (Szmidt, 1982
), P. nigra has a value of 0.135 (Nicolié and Tucié, 1983
), and P. torreyana has a value of 1.0 with different alleles fixed in each one of its two populations (Ledig and Conkle, 1983
). Bermejo (1993)
and Mathenson, Bell, and Barnes (1989)
also found relatively high FST values in P. engelmanii, P. oocarpa, and P. caribea (0.13, 0.1, and 0.13, respectively). This could be related to the species' distributions on rugged mountain ranges (Perry, 1991
) where topography could act as a natural barrier to gene flow.
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Higher FST values can result from reduced population sizes and gene flow (Wright, 1965
; Slatkin, 1993
). The mean gene flow per generation (1.5) estimated for P. rzedowskii is lower than that reported for other species of conifers (Table 5). This indicates that there is little genetic exchange among populations, although there may be enough to prevent complete isolation among them. Gene flow as estimated by Nm and neighborhood size (Nb) are directly related. For P. rzedowskii, Nb estimates are 9.0 individuals per population but these estimations were made indirectly and are therefore preliminary. Data on cone production (less than a cone per reproductive tree per year) and seedling recruitment (less than one per tree per year; Delgado, 1997
) support the idea that only a few individuals reproduce, yielding low effective population size.
Genetic relations and isolation by distance
The isolation by distance analysis does not show any significant pattern, suggesting that the distribution of genetic variation may not be explained by the geographic distances separating the populations (data not shown). The analysis of genetic relationships among populations shows this clearly. The six populations with the highest population sizes (VPI1, FRE4, ALB5, CHI6, PIN8, and AGU9; average, 1069 individuals; Table 1) and the highest levels of genetic variation (average polymorphism = 51% and average expected heterozygosity = 0.24; Table 2) formed one group. The rest of the populations form a second group and include the ones with the smallest population sizes (average = 90 individuals) and the least genetic variation (average polymorphism = 38% and average expected heterozygosity = 0.18). The two populations found at the north end of the distribution (CHI6 and SOL3) belong to different groups. The grouping by population size suggests that genetic drift may be the main evolutionary force acting on the distribution of genetic variation in this species.
In addition to soil characteristics of the sites where P. rzedowskii populations are established (limey soils) and the species' life history (slow growing, long lived), its reproductive behavior seems to play a role in explaining its patterns of genetic variation. Probably, gene flow rates are more likely to be affected by microgeographic features (such as the limey soil and the rugged topography) that isolate populations to different extents. Also, P. rzedowskii shows reproductive asynchrony. During four consecutive years (1992-1995) only modest cone production has been observed (a maximum of 15 cones per tree) and only a few individuals have reproduced at all (21 out of 300). There is no evidence of a large annual seed production during the last 6 yr (Delgado, 1997
). Reproductive asynchrony has probably increased genetic differentiation because genetic exchange is occurring only among a few reproductive individuals within populations. This enhances local inbreeding. The observed heterozygote deficit suggests significant inbreeding levels, which, together with reduced population sizes and microgeographic isolation, might underlie the observed genetic structure.
Two historical scenarios may account for our results. The first one involves the populations' distribution as being the result of dispersal from a central population. Differentiation levels would therefore be a function of gene flow levels, number of founders, and the time since the founder event. The second scenario involves a single ancestral panmictic population that became fragmented into several patches because of geological events during the Pleistocene (Millar, 1998
). Here, genetic differentiation would depend on gene flow levels, population sizes, and the degree of geographical isolation. It is difficult to discern which scenario actually took place.
Conservation implications
The information available warrants two management and conservation strategies. The first one would consist of an in situ conservation plan that would define core areas completely free from perturbation, at least for the genetically most diverse populations (namely VPI1, FRE4, ALB5, CHI6, PIN8, and AGU9). This would guarantee the maintenance of most of the species' genetic variation, including uncommon and unique alleles. The latter is the case of alleles found in CHI6 (the only one having Got-1, allele 5), PVA2, and AGU9. Nevertheless, high FST values suggest that all populations are important for conservation because they are differentiated. Conservation plans for tree species should also consider demographic traits of populations such as population size and recruitment rate (Alvarez-Buylla et al., 1996b
). In that respect, we present a simple analysis (Fig. 3) to get an insight about P. rzedowskii historical demography (Moritz, 1996
). It is based on the idea that expanding populations are expected to show a star-like phylogeny that would result in a parabolic relation between the genetic distance, as an estimate of time of divergence, and the logarithm of the number of populations following the UPGMA analysis. On the contrary, stable populations would show a strongly structured phylogeny and would result in an exponential relationship. Our results show that since the curve is parabolic, P. rzedowskii populations have increased historically. These results also agree with our genetic data and highlight the importance of maintaining demographically viable populations since recent man produced habitat fragmentation has not yet affected this endangered species. This has probably been due to its longevity (200 yr) that would produce a time lag before the effects of habitat transformation change both the demography and the genetic structure. Low recruitment has been observed by us in all populations and thus it appears as the most critical aspect for an in situ conservation strategy. Enforcement of methods to guarantee the survival of seedlings seems the most appropriate way to assure the viability of these populations.
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). However, it is critical to recover in the short term as many seeds as possible to obtain a good representation of the species' genetic diversity. Tree nurseries should also be established together with field plots. Reintroduction tests should be carried out with seedlings produced ex situ. The genetic and demographic analyses of this study strongly suggest that despite the small size and population fragmentation of the populations, P. rzedowskii is not at risk of extinction under undisturbed conditions. An encouraging fact is that proposals for the establishment of areas free of anthropogenic perturbation have been made by the local people to government forestry officials. The information gathered in this study may guide, in part, various plans for the in situ and ex situ conservation of this conservationally important and morphologically intriguing pine species.
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FOOTNOTES |
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LITERATURE CITED |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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———, A. Chaos, D. Piñero, and A. A. Garay. 1996a Demographic genetic of a pioneer tropical tree species: patch dynamics, seed dispersal, and seed banks. Evolution 50: 1155–1166.[CrossRef][ISI]
———, R. García-Barrios, C. Lara-Moreno, and M. Martínez-Ramos. 1996b Demographic and genetic models in conservation biology- applications and perspectives for tropical rain forest trees. Annual Review of Ecology and Systematics 27: 387–421.
Bermejo, V. B. 1993 Genetic diversity and the mating system in Pinus engelmannii Carr. Ph.D. disseration. University of Wisconsin, Madison, WI.
Betancourt, L. J., W. S. Schuster, J. B. Mitton, and R. S. Anderson. 1991 Fossil and genetic history of a pinyon pine (Pinus edulis) isolate. Ecology 72: 1685–1696.[CrossRef][ISI]
Brown, A. H. D., and G. F. Moran. 1981 Isozymes and the genetic resources of forest trees. In M. T. Conkle [ed.], Isozymes in North American forest trees and forest insects, Technical Report Number 48, 1–10. Pacific Southwestern Forest Range Experimental Station Berkeley, CA.
Cheliak, W. M., and J. A. Pitel. 1984 Electrophoretic identification of clones in trembling aspen. Canadian Journal of Forest Research 14: 740–743.[CrossRef]
Conkle M. T., P. D. Hodgskiss., L. B. Nunnally, and S. C. Hunmter. 1982 Starch gel electrophoresis of conifer seeds: a laboratory manual. United States Forest Service. General Technical Report PSW-64.
Critchfield, W. B., and E. L. Little. 1966 Geographic distribution of the Pinus of the world. Miscellaneous Publication, United States Department of Agriculture, Washington, DC.
Crow, J. F., and K. Aoki. 1984 Group selection for a polygenetic behavioral trait: estimating the degree of population subdivition. Proceedings of the National Academy of Sciences, USA 81: 6073–77.
Delgado, V. P. 1997 Estructura genética y demográfica de una especie del género Pinus (Pinus rzedowskii) endémica de Michoacán, México. Master's thesis. Universidad Nacional Autónoma de México. México D.F.
Farjon, A., and B. T. Styles. 1997 Pinus. Flora Neotropica Monograph 70. New York Botanical Garden, New York, NY.
Furnier, G. R., and W. T. Adams. 1986 Geographic patterns of allozyme variation in Jeffrey pine. American Journal of Botany 73: 1009–1015.[CrossRef][ISI]
Guries, R. P., and F. T. Ledig. 1982 Genetic diversity and estructure in pitch pine (Pinus rigida Mill). Evolution 36: 387–402.[CrossRef][ISI]
Hakim-Elahi, A. 1981 Temporal changes in the population structure of the slender wild oat (Avena barbata) as measured by allozyme polymorphism. Ph.D. dissertation. University of California, Davis, CA.
Hamrick, J. L., and M. J. Godt. 1990 Allozyme diversity in plant species. In A. H. D. Brown, M. T. Clegg, A. L. Kalher, and B. S. Weir [eds.], Plant population genetics, breeding and genetic resources 43-63. Sinauer, Sunderland, MA.
———, J. B. Mitton, and Y. B. Linhart. 1981 Levels of genetic variation in trees: influence of life history characteristics. In M.T. Conkle [ed.], Isozymes in North American forest trees and forest insects, Technical Report Number 48, 35–41. Pacific Southwestern Forest Range Experimental Station, Berkeley, CA.
Hiebert, R. D., and J. L. Hamrick. 1983 Patterns and levels of genetic variation in Great Basin bristle cone pine (Pinus longaeva). Evolution 37: 302–310.[CrossRef][ISI]
Ledig, F. T. 1998 Genetic variation in Pinus. In D. M. Richardson [ed.], Ecology and biogeography of Pinus, 251–280. Cambridge University Press, Cambridge.
———, and M. T. Conkle. 1983 Gene diversity and genetic structure in a narrow endemic Torrey pine (Pinus torreyana Parry et Carr.). Evolution 37: 70–85.
Li, C. C., and D. G. Horvitz. 1953 Some methods of estimating the inbreeding coefficient. American Journal of Human Genetics 5: 107–117.[ISI][Medline]
Li, P., and W. T. Adams. 1989 Range-wide patterns of allozyme variation in Douglas-fir (Pseudotsuga menziesii). Canadian Journal of Forest Research 19: 149–161.
Madrigal, S. X., and M. C. Deloya. 1969 Una nueva especie mexicana de Pinus. Boletín Técnico del Instituto Nacional de Investigaciones Forestales Number 26. México D.F.
Mathenson, A. C., J. C. Bell, and R. D. Barnes. 1989 Breeding systems and genetic structure in some central american pine populations. Silvae Genetica 38: 107–113.[ISI]
Mejnartowicz, L., and F. Bergmann. 1985 Genetic differentiation among Scots pine populations from the lowlands and the mountains in Poland. In H.R. Gregorius [ed.], Population genetics in forestry. Lecture Notes in Biomathematics 60: 253–266.
Merkle, S. A., and W. T. Adams. 1987 Patterns of allozyme variation within and among Douglas-fir breeding zones in Southwest Oregon. Canadian Journal of Forest Research 17: 402–407.
Miles, M. A., P. J. Toye., S. C. Oswald, and D. G. Godfrey. 1977 The identification by isoenzyme patterns of distinct strain groups of Trypanosoma cruzi circulating independently in a rural area of Brazil. Transactions of the Royal Society of Tropical Medicine and Hygiene 71: 217–225.[CrossRef][ISI][Medline]
Millar, C. I. 1998 Early evolution of pines. In D. M. Richardson [ed.], Ecology and biogeography of Pinus, 69–91. Cambridge University Press, Cambridge.
———, S. H. Strauss., M. T. Conkle., and R. D. Westfall. 1988 Allozyme differentiation and biosystematics of the Californian closed-cone pines (Pinus subsect. Oocarpae). Systematic Botany 13: 351– 370.[CrossRef][ISI]
Mitton, J. B. 1983 Conifers. In D. Tanksley and T. J. Orton [eds.], Isozymes in plant genetics and breeding, 443–472. Elsevier, Amsterdam.
———, Y. B. Linhart, J. L. Hamrick, and J. S. Beckman. 1977 Observations on the genetic structure and mating system of Pondersa Pine in the Colorado front Range. Theoretical and Applied Genetics 51: 5–13.
Moritz, C. 1996 Uses of molecular phylogenies for conservation. In P. H. Harvey, A. J. Leigh Brown, and J. Maynard Smith [eds.], New uses for new phylogenies, 203–216. Oxford University Press. Oxford.
Nei, M. 1975 Molecular population genetics and evolution. Elsevier, New York, NY.
Niebling, A. U., and M. T. Conkle. 1990 Diversity of washoe pine and comparisons with allozymes of ponderosa pine races. Canadian Journal of Forest Research 20: 298–308.
Nicolié, D., and N. Tucié. 1983 Isoenzyme variation within and among population of european Black pine (Pinus nigra Arnold). Silvae Genetica 32: 80–89.[ISI]
O'Malley D. M., F. W. Allendorf, and G. M. Blake. 1979 Inheritance of isozyme variation and heterozygosity in Pinus ponderosa. Biochemical Genetics 17: 233–250.
Perry, J. P. 1991 The pines of Mexico and Central America. Timber Press, Portland, OR.
Rohlf, F. J. 1993 NTSYS. Numerical taxonomy and multivariate analysis system, version 1.8. Exeter Software, New York, NY.
Schuster, W. S., L. D. Alles, and J. B. Mitton. 1989 Gene flow in limber pine: evidence from pollination phenology and genetic differentiation along an elevational transect. American Journal of Botany 76: 1395–1403.[CrossRef][ISI]
Selander, R. K., D. A. Caugant, H. Ochman, J. M. Musser, M. N. Gilmour, and T. S. Whittam. 1986 Method of multilocus enzyme electrophoresis for bacterial populations genetics and systematics. Applied and Environmental Microbiology 5: 873–884.
Slatkin, M. 1993 Isolation by distance in equilibrium and non-equilibrium populations. Evolution 47: 264–279.[CrossRef][ISI]
———, and N. H. Barton. 1989 A comparison of three indirect methods for estimating average levels of gene flow. Evolution 43: 1349–1368.[CrossRef][ISI]
Sneath, P. A., and R. R. Sokal. 1973 Numerical taxonomy. W. H. Freeman, San Francisco. CA.
Sokal, R. R., and F. J. Rohlf. 1981 Biometry. Freeman. New York. NY.
Soltis, D. E., C. H. Haufler, D. C. Darrow, and G. J. Gastony. 1983 Starch gel electrophoresis of ferns: a compilation of grinding buffers, gel and electrode buffers, and staining schedules. American Fern Journal 73: 9–27.[CrossRef][ISI]
Swofford, D. L., and G. J. Olsen. 1990 Phylogenetic reconstruction. In D. M. Hillis and C. Moritz [eds.], Molecular systematics, 411–501. Sinauer, Sunderland, MA.
Szmidt, A. E. 1982 Genetic variation in isolated populations of stone pine (Pinus cembra). Silvae Fennica 16: 196–200.
Weber, J. C., and R. F. Stettler. 1981 Isozyme variation among ten populations of Populus trichocarpa Torr. et Gray in the Pacific Northwest. Silvae Genetica 30: 82–87.[ISI]
Weir, B. S., and C. C. Cockerham. 1984 Estimating F-statistics for the analysis of population structure. Evolution 38: 1358–1370.[CrossRef][ISI]
Werth, C. A., A. A. Karlin, and S. I. Guttman. 1982 Enzyme extraction from phenolic-containing plant using caffeine. Isozyme Bulletin 15: 139.
Wright, S. 1965 The interpretation of population structure by F-statistics with special regard to systems of mating. Evolution 19: 395–420.[CrossRef][ISI]
Workman, P. L., and J. D. Niswander. 1970 Population studies on southwestern Indian tribes II. Local genetic differentiation in the Papago. American Journal of Human Genetics 22: 24–29.[ISI][Medline]
Yeh, F. C., and Y. A. El-Kassaby. 1980 Enzyme variation in natural populations of sitka spruce (Picea sitchensis) I. Genetic variation patterns among trees from 10 provenances. Canadian Journal of Forest Research 10: 415–422.
———, and R. W. Layton. 1979 The organization of genetic variability in central and marginal populations of lodgepole pine Pinus contorta spp. latifoliata. Canadian Journal of Genetics and Cytology 21: 487–503.[ISI]
———, and D. O'Malley. 1980 Enzyme variation in natural populations of Douglas fir. Pseudotsuga menziesii (Mirb). Franco, from British Columbia. 1. Genetic variation patterns in coastal populations. Silvae Genetica 29: 83–92.
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J. GONZALEZ-ASTORGA and G. CASTILLO-CAMPOS Genetic Variability of the Narrow Endemic Tree Antirhea aromatica Castillo-Campos & Lorence, (Rubiaceae, Guettardeae) in a Tropical Forest of Mexico Ann. Bot., May 1, 2004; 93(5): 521 - 528. [Abstract] [Full Text] [PDF]
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 F. T. Ledig, M. A. Capo-Arteaga, P. D. Hodgskiss, H. Sbay, C. Flores-Lopez, M. Thompson Conkle, and B. Bermejo-Velazquez Genetic diversity and the mating system of a rare Mexican pinon, Pinus pinceana, and a comparison with Pinus maximartinezii (Pinaceae) Am. J. Botany, November 1, 2001; 88(11): 1977 - 1987. [Abstract] [Full Text] [PDF]
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E. Aguirre-Planter, G. R. Furnier, and L. E. Eguiarte Low levels of genetic variation within and high levels of genetic differentiation among populations of species of Abies from southern Mexico and Guatemala Am. J. Botany, March 1, 2000; 87(3): 362 - 371. [Abstract] [Full Text]
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