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2Jardín Botánico, Instituto de Biología, Universidad Nacional Autónoma de México, Apartado Postal 70-614, México, D.F., 04510, México; and 3Departamento de Ecología Evolutiva, Instituto de Ecología, Universidad Nacional Autónoma de México, Apartado Postal 70-275, México, D.F., 04510, México
Received for publication July 14, 1997. Accepted for publication December 1, 1998.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: Agave • Agavaceae • allozymes • conservation genetics • perennial • population genetics
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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; Rzedowski, 1993
; García-Mendoza, 1995
; Hernández and Bárcenas, 1995,
1996
). Because of their arid environments, slow growth rates, relatively low reproductive rates, and the value that many have as ornamentals, they are also very susceptible to human-caused disturbances and, consequently, the rate of loss of these species in Mexico is very high (Bye, 1993
). Loss of biodiversity occurs not only through the loss of these species, but also through the loss of genetic diversity within these species. Knowledge of the genetic structure of plants is central to designing effective in situ and ex situ conservation strategies (Hamrick et al., 1991
; Heywood and Watson, 1995
; Maxted and Hawkes, 1997
; Meffe and Carroll, 1997
), but we know relatively little about the population genetics of long-lived desert perennials.
In the deserts of North America, the Agavaceae is a dominant family with very high species diversity and endemicity, and many endangered species. For example, 75% (198 species) of all Agave species are found in Mexico, 74% of which are endemic (García-Mendoza, 1995
). Virtually nothing, however, is known about their genetic structure. The only reported study of the population genetic structure of an Agave focused on testing the optimal outcrossing hypothesis and provided no information on broadscale patterns of genetic variation (Trame, Coddington, and Paige, 1995
). We do not have data that indicate whether their often-isolated populations are genetically depauperate due to the effects of drift or whether they experience inbreeding. Information on the levels of genetic differentiation among populations would allow us to more effectively set genetic priorities for conservation, with more distinct populations receiving a higher priority than saving many genetically similar populations (Ceska, Affolter, and Hamrick, 1997
).
Agave victoriae-reginae T. Moore is an endemic species of subgenus Littaea found only on limestone outcrops, usually on vertical walls, in very localized populations in the northern Mexican states of Coahuila, Durango, and Nuevo León (Gentry, 1982
; Fig. 1). The species is diploid (2n = 60; Bhattacharyya, 1968
) with low levels of clonality (Gentry, 1982
). It is one of the most popular ornamental Agave species, and large plants command high prices in many countries (Martínez-Palacios, 1991
). Hence, the rate of illegal and uncontrolled collection for commercial trade has been very high, leading it to be one of the few Agave listed as endangered by the Mexican government (Anonymous, 1994
) and CITES (CITES, 1995
).
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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We collected a green leaf from each of 
40 adult individuals in each of ten populations, representing the full range of A. victoriae-reginae (Fig. 1; Table 1). We tried to sample the entire area of each population, choosing the larger nonreproductive (as the plants are monocarpic) healthy individuals so as to minimize impacts on survival and reproduction (Martínez-Palacios, 1998
). A 2 x 2 cm piece of the base of each leaf was stored in liquid nitrogen and transported to Mexico City, where the samples were then stored at -80°C.
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). Leaves were macerated with an electric drill, using 10–15 drops of an extraction buffer composed of a 3:1 mixture of the Veg II buffer of Pitel and Cheliak (1984)
and the buffer of Yeh and O'Malley (1980)
. The extract was adsorbed on 12 x 1.5 mm chromatographic paper wicks and stored at -80°C until electrophoresis.
Allozymes were separated by electrophoresis at 60 mA for 6–7 h on 12% starch gels (450 mL). We used the LiOH buffer 8 of Soltis et al. (1983)
, with gel buffers of two different pHs. We analyzed diaphorase (E.C. [Enzyme Commission number] 1.6.4.3, DIA, two loci), esterase (E.C. 3.1.1.1, EST, two loci), leucine aminopeptidase (E.C. 3.4.11.1, LAP, one locus), and phosphoglucose isomerase (E.C. 5.3.1.9, PGI, two loci) at pH 7.6 and glutamate oxaloacetate transaminase (E.C. 2.6.1.1, GOT, one locus), malic enzyme (E.C. 1.1.1.40, ME, one locus), and acid phosphatase (E.C. 3.1.3.2, ACP, one locus) at pH 8.0. We selected these enzyme systems because they stained with sufficient intensity and resolution to be scored with confidence. Enzyme stain recipes were those of Soltis et al. (1983)
.
The fastest migrating loci and alleles were designated 1, followed by 2, 3, etc. Allele frequency data are available from the corresponding author. For each population, we estimated the proportion of polymorphic loci (P), expected heterozygosity (He), the mean (A) and effective (Ae; Hedrick, 1983
) numbers of alleles per locus, and the average fixation index (F). We used 
2 tests to test for deviations from genotypic frequencies expected under Hardy-Weinberg equilibrium (Snedecor and Cochran, 1967
) and for heterogeneity of allelic frequencies among populations (Workman and Niswander, 1970
). When the expected number of individuals in a class was less than 1, we bulked the least common alleles until all classes had an expected number of at least 1. When bulking of alleles did not meet this goal, we did not perform the test because it was considered unreliable (Snedecor and Cochran, 1967
). We used Bonferroni's method to achieve an experiment-wide 
of 0.05 (Weir, 1990
).
Wright's (1965)
F statistics were estimated by the method of Weir and Cockerham (1984)
, using a modified version of Weir's (1990)
program (Alvarez-Buylla et al., 1996
). Phenetic clustering of the populations was performed using Nei's (1978)
unbiased genetic distances and the neighbor-joining (Saitou and Nei, 1987
) and UPGMA (Sneath and Sokal, 1973
) algorithms as implemented in PHYLIP (Felsenstein, 1993
).
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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' = 0.0009 to maintain an experiment-wide of 0.05; Tables 1, 2).
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' = 0.005 to maintain an experiment-wide of 0.05), and the mean FST estimate was relatively high (0.236) and significantly different from zero (Table 2), indicating a moderately high level of differentiation among populations. This differentiation among populations (0.236) was partitioned into 0.14 among populations within the three regions and 0.10 among the regions. Genetic distance was relatively high between all pairs of populations (mean D = 0.182). Both the neighbor-joining and UPGMA phenograms gave the same topology, showing striking differences among groups of populations, with at least three clusters of clearly differentiated populations (Fig. 2). These clusters represented the western populations (6, 7; D = 0.025), the central populations (4, 5, 8, 9, 10; average D = 0.091), and the eastern populations (1, 2, 3; average D = 0.097). The average genetic distance between the eastern and western populations was 0.189, between the central and eastern populations was 0.211, and between the central and western populations was 0.250.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). In the few remaining easily accessible populations (mainly growing on hills), commercial collection has decreased drastically in recent years because of stricter enforcement of collecting regulations and because the plants are now so rare as to make collection economically impractical. Their infructescences, however, are almost always removed by collectors to propagate the plants from seeds for commercial trade. Given the low frequency of clonal recruitment in the species, this practice is potentially dangerous because each plant flowers only once after many years of life (e.g., Agave horrida, another member of the subgenus Littaea, takes 30–70 yr to attain reproductive size; L. E. Eguiarte., personal observation) and complete removal of infructescences eliminates recruitment.
A. victoriae-reginae displays high levels of genetic diversity within populations and high levels of differentiation among populations. Compared to other plants with a similar breeding system, seed dispersal mechanism, life form, geographic range, and taxonomic status (monocotyledon), A. victoriae-reginae has somewhat higher than average levels of variation within populations and differentiation among populations (Hamrick and Godt, 1989,
1996a, b
). The high levels of genetic variation are consistent with the relatively large population sizes (Martínez-Palacios, 1998
) and suggest that the populations have not experienced a recent bottleneck. The relatively high level of interpopulation differentiation (mean FST = 0.236) is particularly notable, since most other studied long-lived perennial plants have very low levels of allozyme differentiation among populations (Hamrick et al., 1992
). Hamrick and Godt (1996a, b)
have pointed out, however, that life history traits alone explain a relatively low amount of the variation in genetic structure that we see among species. The fixation indices indicate that there is relatively little inbreeding in the populations, possibly due in part to the efficiency of the pollinators, presumably bees, hummingbirds, bats, and moths (Gentry, 1982
).
The few other studies of population genetic structure of long-lived desert perennials have yielded varying results. In the Cactaceae, the other major family of the North American deserts, the tetraploid Echinocereus engelmannii var. munzii of southern California, displays high levels of genetic variation within populations, but low differentiation among populations (Neel, Clegg, and Ellstrand, 1996
). The columnar cactus Lophocereus schottii of southern Arizona displays moderate levels of genetic variation (average H = 0.126), with substantial differentiation among the subpopulations (GST = 0.130) and an excess of heterozygous individuals (FIS = -0.187) (Parker and Hamrick, 1992
). In contrast, Washingtonia filifera (Arecaceae), a long-lived desert monocotyledon of southern California, displays very low levels of genetic variation (H = 0.008) and very little differentiation among populations (GST = 0.023; McClenaghan and Beauchamp, 1986
). Keys and Smith (1994)
found little differentiation (FST = 0.07) among three populations of the pioneer dicotyledon tree Prosopis velutina (Fabaceae) in southeastern Arizona. Agave victoriae-reginae displays considerably higher levels of genetic diversity within populations and differentiation among populations than any of these species.
The relatively high levels of differentiation observed among populations of A. victoriae-reginae could have arisen by high levels of genetic drift, mutations occurring over a very long period since the populations were separated, and/or local selection on the allozyme loci or linked loci. The relatively high levels of variation observed in all populations and their relatively large total estimated population sizes suggest that drift has not played a strong role recently, although it could have led to differentiation in the past, followed by a recovery of variation. Our data do not permit us to make inferences about selection on the allozyme loci nor linked loci, but the outcrossing breeding system makes genetic linkage less of a factor and there are relatively few well-documented examples of selection on allozyme loci (Mitton, 1994
). An absence of gene flow can help maintain differentiation among populations. One can estimate Nm, an indirect measure of gene flow, as [(1/FST) - 1]/[4(n/n - 1)2], where n is the number of populations (Crow and Aoki, 1984
). In an island model, the estimate of Nm (0.655) we obtained from FST (0.236) corresponds to a situation in which drift would override the effects of gene flow (Slatkin, 1994
). This suggests that the animal pollinators of A. victoriae-reginae are not very effective in generating gene flow among the isolated populations. The 95% confidence interval of Nm (0.376–1.471) does, however, include values that would represent significant, although not high, levels of gene flow.
The proportion of the total genetic diversity in the species contained in n populations can be estimated as 1 - (1/FST)n (Ceska, Affolter, and Hamrick, 1997
). Given the mean FST estimate of 0.236, the proportions of total genetic diversity in the species contained in one, two, three, and four populations are 0.764, 0.944, 0.987, and 0.997, respectively. Given the variation in FST estimates among loci, these may be underestimates of the proportion of diversity conserved. This method assumes equal diversity in all populations and in the case of A. victoriae-reginae, some populations have higher levels of diversity than others. Information on relative levels of diversity in the different populations should be used in the design of a conservation strategy. For example, the combination of populations 6 and 9 contains all of the alleles found in our study. One should also consider favoring populations with more intermediate allele frequencies to reduce the probability of loss of alleles. Population size should also be considered, with preference being given to the larger populations.
The high level of differentiation among populations of A. victoriae-reginae represents a real conservation challenge. While we can theoretically conserve almost 95% of the total allozyme diversity in the species with just two populations, we must also consider that collection pressures could still eliminate populations (Martínez-Palacios, 1998
). Thus, we would want more than just two populations. In addition, we must consider the fact that allozymes often underestimate the levels of interpopulation differentiation for adaptive traits critical to the survival and reproduction of plants, particularly in outcrossing species such as A. victoriae-reginae (Furnier et al., 1991
; Hamrick et al., 1991
). Ex situ conservation could be very difficult, due to the need to maintain many large independent breeding populations to adequately represent the high amounts of diversity present in each of the very different natural populations. The long reproductive cycle could also be a complicating factor.
The levels of differentiation among populations of A. victoriae-reginae are comparable to those observed among different subspecies or even species in many plant genera (Crawford, 1983
). Thus, the three distinct groups of populations shown by the phenogram may actually represent distinct species or subspecies and this potential taxonomic structure, representing 10% of the total variation and 42% of the interpopulation differentiation that we observed, should be taken into account in the design of a conservation strategy. The genetic distances between populations indicate significant differentiation among populations even within these groups. Although we do not have detailed information on the pollinators of this species, the geographic distances between the populations and the relatively low estimate of Nm suggest that gene flow between them is infrequent and that each population may represent an evolutionarily independent unit meriting conservation efforts. If levels of genetic differentiation as high as those found in A. victoriae-reginae are common in desert plants, it would help explain the high species diversity of desert plant families, such as the Agavaceae and Cactaceae, and would suggest that conservation of the genetic diversity of desert plant species will be a very difficult endeavor.
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FOOTNOTES |
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4 Author for correspondence (e-mail: fruns@servidor.unam.mx, Phone: 52 5 622-9006, FAX: 52 5 616-1976 or 52 5 622-8995 fax).
5 Current address: TEAMS Program, College of Education, Arizona State University, P.O. Box 870911, Tempe, AZ 85287-0911.
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LITERATURE CITED |
|---|
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Anonymous. 1994 Norma Oficial Mexicana NOM-059-ECOL-1994, que determina las especies y subespecies de flora y fauna silvestre terrestres y acuáticas en peligro de extinción, amenazadas, raras y sujetas a protección especial y que establece especificaciones para su protección. SEDESOL, Diario Oficial de la Federación 488: 2–59.
Bhattacharyya, G. N. 1968 Chromosomes in different species of Agave. Journal of Cytology and Genetics 3: 1–6.
Bye, R. 1993 The role of humans in the diversification of plant in Mexico. In T. P. Ramamoorthy, R. Bye, A. Lot, and J. Fa [eds.], Biological diversity of Mexico: origins and distribution, 707–731. Oxford University Press, New York, NY.
Ceska, J. F., J. M. Affolter, and J. L. Hamrick. 1997 Developing a sampling strategy for Baptisia arachnifera based on allozyme diversity. Conservation Biology 11: 1133–1139.[CrossRef][ISI]
CITES. 1995 Appendices I, II, and III to the convention on international trade in endangered species of wild fauna and flora. United States Fish and Wildlife Service, Washington, DC.
Crawford, D. J. 1983 Phylogenetic and systematic inferences from electrophoretic studies. In S. D. Tanksley and T. J. Orton [eds.], Isozymes in plant genetics and breeding, part A, 237–287. Elsevier, Amsterdam.
Crow, J. F., and K. Aoki. 1984 Group selection for a polygenic behavioral trait: estimating the degree of population subdivision. Proceedings of the National Academy of Sciences, USA 81: 6073–6077.
Felsenstein, J. 1993 PHYLIP (Phylogeny Inference Package) version 3.5c. Distributed by the author. Department of Genetics, University of Washington, Seattle, WA.
Furnier G. R., M. Stine, C. A. Mohn, and M. A. Clyde. 1991 Geographic patterns of variation in allozymes and height growth in white spruce. Canadian Journal of Forest Research 21: 707–712.[CrossRef]
García-Mendoza, A. 1995 Riqueza y endemismo de la familia Agavaceae en México. In E. Linares, P. Dávila, F. Chiang, R. Bye, and T. Elias [eds.], Conservación de plantas en peligro de extinción: diferentes enfoques, 51–75. Universidad Nacional Autónoma de México, México.
Gentry, H. S. 1982 Agaves of continental North America. University of Arizona Press, New York, NY.
Hamrick, J. L., and M. J. W. Godt. 1989 Allozyme diversity in plant species. In A. H. D. Brown, M. T. Clegg, A. L. Kahler, and B. S. Weir [eds.], Plant population genetics, breeding, and genetic resources, 43–63. Sinauer, Sunderland, MA.
———, and ———. 1996a Effects of life history traits on genetic diversity in plant species. Philosophical Transactions of the Royal Society of London B 351: 1291–1298.
———, and ———. 1996b Conservation genetics of endemic plant species. In J. C. Avise and J. L. Hamrick [eds.], Conservation genetics: case histories from nature, 281–304. Chapman and Hall, New York, NY.
———, ———, D. A. Murawski, and M. D. Loveless. 1991 Correlations between species traits and allozyme diversity: implications for conservation biology. In D. A. Falk and K. E. Holsinger [eds.], Genetics and conservation of rare plants, 75–86. Oxford University Press, New York, NY.
———, ———, and S. L. Sherman-Broyles. 1992 Factors influencing levels of genetic diversity in woody plant species. New Forests 6: 95–124.[CrossRef]
Hedrick, P. W. 1983 Genetics of populations. Science Books International, Boston, MA.
Hernández, H. M., and R. T. Bárcenas. 1995 Endangered cacti in the Chihuahuan Desert: I. Distribution patterns. Conservation Biology 9: 1176–1190.[CrossRef][ISI]
———, and ———. 1996 Endangered cacti in the Chihuahuan Desert: II. Biogeography and conservation. Conservation Biology 10: 1200–1209.[CrossRef][ISI]
Heywood, V. H., and R. T. Watson. (eds.). 1995 Global biodiversity assessment. Cambridge University Press, New York, NY.
Keys, R. N., and S. E. Smith. 1994 Mating system parameters and population genetic structure in pioneer populations of Prosopis velutina (Leguminosae). American Journal of Botany 81: 1013–1020.[CrossRef][ISI]
Martínez-Palacios, A. 1991 Propagación masiva in vitro y recuperación de poblaciones de orquídeas en peligro de extinción. Tesis de Maestría, Facultad de Ciencias, Universidad Nacional Autónoma de México, México.
———. 1998 Evaluación genética y demográfica de Agave victoriae-reginae T. Moore y aplicación del cultivo de tejidos para su conservación. Tesis de Doctorado en Ciencias (Biología), Facultad de Ciencias, Universidad Nacional Autónoma de México, México.
Maxted, N., and J. G. Hawkes. 1997 Selection of target taxa. In N. Maxted, B. V. Ford-Lloyd, and J. G. Hawkes [eds.], Plant genetic conservation: the in situ approach, 43–68. Chapman and Hall, London.
McClenaghan, L. R., and A. C. Beauchamp. 1986 Low genic differentiation among isolated populations of the California fan palm (Washingtonia filifera). Evolution 40: 315–322.[CrossRef][ISI]
Meffe, G. K., and C. R. Carroll. 1997 Principles of conservation biology, 2d ed. Sinauer, Sunderland, MA.
Mitton, J. B. 1994 Molecular approaches to population biology. Annual Review of Ecology and Systematics 25: 45–69.
Neel, M. C., J. Clegg, and N. C. Ellstrand. 1996 Isozyme variation in Echinocereus engelmannii var. munzii (Cactaceae). Conservation Biology 10: 622–631.[CrossRef][ISI]
Nei, M. 1978 Estimation of average heterozygosity and genetic distance from a small number of individuals. Genetics 89: 583–590.
Parker, K. C., and J. L. Hamrick. 1992 Genetic diversity and clonal structure in a columnar cactus, Lophocereus schottii. American Journal of Botany 79: 86–96.
Pitel, J. A., and W. H. Cheliak. 1984 Effect of extraction buffers on characterization of isoenzymes from vegetative tissues of five's conifers species: a user's manual. Information Report PI-X-34, Petawawa National Forestry Institute, Canadian Forestry Service, Chalk River, Ontario, Canada.
Rzedowski, J. 1993 Diversity and origins of the phanerogamic flora of Mexico. In T. P. Ramamoorthy, R. Bye, A. Lot, and J. Fa [eds.], Biological diversity of Mexico: origins and distribution, 129–144. Oxford University Press, New York, NY.
Saitou, N., and M. Nei. 1987 The neighbor-joining method: a new method for reconstructing phylogenetic trees. Molecular Biology and Evolution 4: 406–425.[Abstract]
Slatkin, M. 1994 Gene flow and population structure. In L. A. Real [ed.], Ecological genetics, 4–17. Princeton University Press, Princeton, NJ.
Sneath, P. H. A., and R. R. Sokal. 1973 Numerical taxonomy. W. H. Freeman, San Francisco, CA.
Snedecor, G. W., and W. G. Cochran. 1967 Statistical methods, 6th ed. The Iowa State University Press, Ames, IA.
Soltis, D. E., C. H. Haufler, D. C. Darrow, and G. J. Gastrony. 1983 Starch gel electrophoresis of ferns: a compilation of grinding buffers, and staining schedules. American Fern Journal 73: 9–27.[CrossRef][ISI]
Trame, A. M., A. J. Coddington, and K. N. Paige. 1995 Field and genetic studies testing optimal outcrossing in Agave schottii, a long-lived clonal plant. Oecologia 104: 93–100.[CrossRef][ISI]
Weir, B. S. 1990 Genetic data analysis. Sinauer, Sunderland, MA.
———, and C. C. Cockerham. 1984 Estimating F-statistics for the analysis of population structure. Evolution 38: 1358–1370.[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: 24–49.[ISI][Medline]
Wright, S. 1965 The interpretation of population structure by F-statistics with special regard to systems of mating. Evolution 19: 395–420.[CrossRef][ISI]
Yeh, F. C., and D. M. O'Malley. 1980 Enzyme variation in natural populations of Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, from British Columbia. I. Genetic variation patterns in coastal populations. Silvae Genetica 29: 83–92.
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