Abstract
Dioecy has evolved independently, many times, among unrelated taxa. It also appears to have evolved along two contrasting pathways: (1) from hermaphroditism via monoecy to dioecy and (2) from hermaphroditism via gynodioecy to dioecy. Most dioecious plants have close cosexual relatives with some means of promoting outcrossing (e.g., herkogamy, dichogamy, self-incompatibility, or monoecy). To the extent that these devices prevent inbreeding, the evolution of dioecy in these species cannot logically be attributed to selection for outcrossing. In these cases, the evolution of dioecy is, we believe, due to selection for sexual specialization. However, in other species, that lack outbreeding close relatives, dioecy may have evolved from gynodioecy (males and hermaphrodites) as an outbreeding device. Subsequent disruptive selection and selection for sexual specialization may have also shaped the evolution of dioecy from gynodioecy in these species, resulting in two genetically determined, constant sex morphs.
Both pathways for the evolution of dioecy require the operation of disruptive selection, though the gynodioecy route involves more restrictive disruptive selection and a genetic designation of gender. In contrast, the monoecy route is not dependent on the genetic designation of two sex morphs, but, rather, allows the possibility of sexual intermediates and sexual lability. Both pathways produce one morph in which maleness is suppressed and another in which the female function is negligible or nonexistent—the reproductive mode recognized as dioecy.
Evidence is presented here to support the thesis that instances of sexual lability, the presence of an array of sexual intermediates, sex-switching, and sexual niche segregation can be explained in terms of the pathway that was taken in the evolution of a particular dioecious species. In addition, the degree of sexual dimorphism seen in dioecious species is correlated with mode of pollination (insector wind-pollinated) and other ecological factors.
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Literature Cited
Agren, J. 1988. Sexual differences in biomass and nutrient allocation in the dioecious shrubRubus chamaemorus. Ecology69:962–973.
Allen, G. A. &J. A. Antos. 1988. Relative reproductive effort in males and females of the dioecious shrubOemleria cerasiformis. Oecologia76:111–118.
Anderson, G. J. 1989. Functional dioecy and andromonoecy inSolarium. Evolution43:204–219.
Antos, J. A. &G. A. Allen. 1990. A comparison of reproductive effort in the dioecious shrubOemleria cerasiformis using nitrogen, energy and biomass as currencies. Amer. Midl. Naturalist124:254–262.
Arnold, S. J. 1994a. Is there a unifying concept of sexual selection that applies to both plants and animals? Amer. Naturalist144(Suppl.):S1-S12.
— 1994b. Bateman’s principles and the measurement of sexual selection in plants and animals. Amer. Naturalist144(Suppl.):S126-S149.
Ashman, T. L. 1994. Reproductive allocation in hermaphrodite and female plants ofSidalcea oregana ssp.spicata (Malvaceae) using four currencies. Amer. J. Bot.81:433–438.
— &I. Baker. 1992. Variation in floral sex allocation with time of season and currency. Ecology73:1237–1243.
— &M. Stanton. 1991. Seasonal variation in pollination dynamics of sexually dimorphicSidalcea oregana ssp.spicata (Malvaceae). Ecology72:993–1003.
Baker, H. G. 1959. Reproductive methods as factors in speciation in flowering plants. Cold Spring Harbor Symp. Quant. Biol.24:177–191.
— &P. D. Hurd. 1968. Intrafloral ecology. Ann. Rev. Entomol.13:385–414.
Barrow, J. R. 1986. Effects of chromosome number on sex expression inAtriplex canescens. Bot. Gaz.148:379–385.
Bawa, K. S. 1980. Evolution of dioecy in flowering plants. Ann. Rev. Ecol. Syst.11:15–39.
—. 1982. Outcrossing and the incidence of dioecism in island floras. Amer. Naturalist119:866–871.
— &P. A. Opler. 1975. Dioecism in tropical forest trees. Evolution29:167–179.
Bell, C. R. 1976. Inflorescence shape and pollinator activity inDaucus carota L. (Apiaceae). ASB Bull23:42 (abstract).
Bertin, R. I. 1993a. Incidence of monoecy and dichogamy in relation to self-fertilization in angiosperms. Amer. J. Bot.80:557–560.
—. 1993b. Dichogamy in angiosperms. Bot. Rev. (Lancaster)59:112–152.
Bickel, A. M. &D. C. Freeman. 1993. Effects of pollen vector and plant geometry on floral sex ratio in monoecious plants. Amer. Midl. Naturalist130:239–247.
Bierzchudek, P. 1984. Determinants of gender in jack-in-the-pulpit: The influence of plant size and reproductive history. Oecologia65:14–18.
— &V. Eckhart. 1988. Spatial segregation of the sexes in dioecious plants. Amer. Naturalist132:34–43.
Boecklen, W. J. &T. M. Hoffman. 1993. Sex biased herbivory inEphedra trifurca: The importance of sex-by-environment interactions. Oecologia96:49–55.
Bond, W. &J. Midgley. 1988. Allometry and sexual differences in leaf size. Amer. Naturalist131:901–910.
Breese, E. L. 1959. Selection for differing degrees of out-breeding inNicotiana rustica. Ann. Bot.23:331–344.
Burd, M. &G. Head. 1992. Phenological aspects of male and female function in hermaphroditic plants. Amer. Naturalist140:305–324.
Charlesworth, B. &D. Charlesworth. 1978. A model for the evolution of dioecy and gynodioecy. Amer. Naturalist112:975–997.
Charlesworth, D. 1985. Distribution of dioecy and self-incompatibility in angiosperms. Pages 237–268in P. J. Greenwood, P. H. Harvey & M. Slatkin (eds.), Evolution: Essays in honour of John Maynard Smith. Cambridge University Press, Cambridge.
— 1993. Why are unisexual flowers associated with wind-pollination and unspecialized pollinators? Amer. Naturalist141:481–490.
— &B. Charlesworth. 1978. Population genetics of partial male-sterility and the evolution of monoecy and dioecy. Heredity41:137–153.
——. 1987. The effect of investment in attractive structures and allocation to male and female functions in plants. Evolution41:948–968.
Charnov, E. L. 1982. The theory of sex allocation. Monographs in population biology. Princeton University Press, Princeton.
Cipollini, M. L. &D. F. Whigham. 1994. Sexual dimorphism and cost of reproduction in the dioecious shrubLindera benzoin (Lauraceae) Amer. J. Bot.81:65–75.
Clarke, A. E. &E. Newbigin. 1993. Molecular aspects of self-incompatibility in flowering plants. Annual Rev. Genet.27:257–279.
Condon, M. A. &L. E. Gilbert. 1988. Sex expression ofGurania psiguria (Cucurbitaceae): Neotropical vines that change sex. Amer. J. Bot.75:875–884.
Cox, P. A. 1982. Vertebrate pollination and the maintenance of dioecism inFreycinetia. Amer. Naturalism120:65–80.
—. 1988. Monomorphic and dimorphic sexual strategies: A modular approach. Pages 80–97in J. Lovett Doust & L. Lovett Doust (eds.), Plant reproductive ecology: Patterns and strategies. Oxford University Press, Oxford.
Cronquist, A. 1981. An integrated system of classification of flowering plants. Columbia University Press, New York.
Cruden, R. W. 1988. Temporal dioecism: Systematic breadth, associated traits and temporal patterns. Bot. Gaz.149:1–15.
— &S. Hermann-Parker. 1977. Temporal dioecism: An alternative to dioecism? Evolution31:863–866.
— &D. L. Lyon. 1985. Patterns of biomass allocation to male and female functions in plants with different mating systems. Oecologia66:299–306.
Darwin, C. 1877. The different forms of flowers on plants of the same species. Murray, London.
Dawson, T. E. &L. C. Bliss. 1989. Patterns of water use and the tissue-water relations in the dioecious shrub,Salix artica: The physiological basis for habitat partitioning between the sexes. Oecologia79:332–343.
—. 1993. Gender-specific physiology, carbon isotope discrimination, and habitat distribution in box elder,Acer negundo. Ecology74:798–815.
De Jong, T. J. &P. G. L. Klinkhamer. 1994. Plant size and reproductive success through female and male function. J. Ecol.82:399–402.
Delph, L. F. 1990. Sex-differential resource allocation patterns in the subdioecious shrubHebe subalpina. Ecology71:1342–1351.
De Nettancourt, D. 1977. Incompatibility in angiosperms. Springer-Verlag, New York.
Dommee, B., L. Bompar &N. Denelle. 1990. Sexual tetramorphism inThymelaea hirsuta (Thymelaeaceae): Evidence of the pathway from heterodichogamy to dioecy at the interspecific level. Amer. J. Bot.77:1449–1462.
Dulberger, R. &A. Horowitz. 1984. Gender polymorphism in flowers ofSilene vulgaris (Moench) Garcke (Caryophyllaceae). J. Linn. Soc., Bot.89:101–117.
Eckart, V. M. 1992. Resource compensation and the evolution of gynodioecy inPhacelia linearis (Hydrophyllaceae). Evolution46:1313–1328.
El-Keblawy, A., J. Lovett Doust, L. Lovett Doust &K. H. Shaltout. 1995. Labile sex expression and dynamics of gender inThymelaea hirsuta. Ecoscience2:55–66.
———. 1996. Gender variation and the evolution of dioecy inThymelaea hirsuta (Thymelaeaceae). Canad. J. Bot.74:1596–1601.
Faegri, K. &L. van der Pijl. 1971. The principles of pollination ecology. Pergamon Press, New York.
Fisher, R. A. 1930. The genetical theory of natural selection. Oxford University Press, Oxford.
Flemming, T. H., S. Maurice, S. L. Buchmann &M. D. Tuttle. 1994. Reproductive biology and relative male and female fitness in a trioecious cactus,Pachycereus pringlei (Cactaceae). Amer. J. Bot.81:858–867.
Flores, S. &D. Schemske. 1984. Dioecy and monoecy in the flora of Puerto Rico and the Virgin Islands: Ecological correlates. Biotropica16:132–139.
Fox, J. F. 1985. Incidence of dioecy in relation to growth form, pollination and dispersal. Oecologia67:244–249.
—. 1991. Costs of reproduction in a willow: Experimental responses vs. natural variation. Ecology72:1013–1023.
—. 1993. Size and sex allocation in monoecious woody plants. Oecologia94:110–113.
— &G. C. Stevens. 1993. Costs of reproduction in a willow: Experimental responses vs. natural variation. Ecology72:1013–1023.
Frankel, R. &E. Galun. 1977. Pollination mechanisms, reproduction and plant breeding. Springer-Verlag, New York.
Freeman, D. C. &E. D. McArthur. 1982. A comparison of water stress between males & females of four species of desert shrubs. Forest Sci.28:304–308.
——. 1984. The relative influence of mortality, nonflowering and sex change. Bot. Gaz.145:385–394.
——. 1989.Atriplex canescens. Pages 75–86in A. Halvey (ed.), The handbook of flowering. Vol. 6. CRC Press, London.
— &J. J. Vitale. 1985. The influence of environment on the sex ratio of spinach. Bot. Gaz.146:137–142.
—,K. T. Harper &E. L. Charnov. 1980a. Sex change in plants: Old and new observations and new hypotheses. Oecologia47:222–232.
—— &W. K. Ostler. 1980b. Ecology of plant dioecy in the intermountain region of western North America. Oecologia44:410–417.
—,L. G. Klikoff &K. T. Harper. 1976. Differential resource utilization by the sexes of dioecious plants. Science193:597–599.
—,E. D. McArthur, S. C. Sanderson &A. R. Tiedemann. 1993. The influence of topography on male and female fitness components ofAtriplex canescens. Oecologia93:538–547.
Gehring, J. L. &R. K. Monson. 1994. Sexual difference in gas exchange and response to environmental stress in dioeciousSilene latifolia (Caryophyllaceae). Amer. J. Bot.81:166–174.
Ghiselin, M. T. 1969. The evolution of hermaphroditism among animals. Quart. Rev. Biol.44:189–208.
Givnish, T. J. 1980. Ecological constraints on the evolution of breeding systems in seed plants: Dioecy and dispersal in gymnosperms. Evolution34:959–972.
Grant, V. 1951. The fertilization of flowers. Sci. Amer.184:52–56.
—. 1995. Sexual selection in plants: Pros and cons. Proc. Natl. Acad. U.S.A.92:1247–1250.
Gregg, K.B. 1973. Studies on the control of sex expression in the generaCychnoches andCatesetum, subtribe Catasetinae, Orchidaceae. Ph.D. dissertation, University of Miami, Coral Gables.
—. 1975. The effect of light intensity on sex expression in species ofCychnoches andCatesetum (Orchidaceae). Selbyana1:101–113.
—. 1978. Ethylene physiology, sunlight intensity and sex in the orchid generaCychnoches (Orchidaceae). Selbyana2:212–223.
—. 1982. Sunlight-enhanced ethylene evolution by developing inflorescences ofCatasetum andCychnoches and its relation to female flower production. Bot. Gaz.143:466–475.
Heinrich, B. 1975. Energetics of pollination. Annual Rev. Ecol. Syst.6:139–170.
Hoffmann, M. T. 1992. Functional dioecy inEchinocereus coccineus (Cactaceae): Breeding system, sex ratios and geographical range of floral dimorphism. Amer. J. Bot.79:1382–1388.
Holtsford, T. P. &N. C. Ellstrand. 1992. Genetic and environmental variation in floral traits affecting outcrossing rate inClarkia tembloriensis. Evolution46:216–255.
Horowitz, A. 1978. Is the hermaphroditic flowering plant equisexual? Amer. J. Bot.65:485–486.
— &R. Dulberger. 1983. The genetic basis of gender inSilene vulgaris. Heredity51:371–376.
Irish, E. &T. Nelson. 1989. Sex determination in monoecious and dioecious plants. Pl. Cell1:737–744.
Kessili, R. &S. K. Jain. 1984. An ecological genetic study of gynodioecy inLimnanthes douglassi (Limnanthaceae). Amer. J. Bot.71:775–786.
Kohn, J. R. 1989. Sex ratio, seed production, biomass allocation and the cost of male function inCucurbita foetidissma HBK (Cucurbitaceae). Evolution43:1424–1434.
Lloyd, D. G. 1975. The maintenance of gynodioecy and androdioecy in angiosperms. Genetica45:325–339.
—. 1979. Evolution towards dioecy in heterostylous populations. Pl. Syst. Evol.131:71–80.
— &K. S. Bawa. 1984. Modification of gender of seed plants in varying conditions. Evol. Biol.17:255–338.
— &C. J. Webb. 1977. Secondary sex characters in plants. Bot. Rev. (Lancaster)43:177–215.
Lovett Doust, J. &P. B. Cavers. 1982. Sex and gender dynamics in jack-in-the-pulpit,Arisaema triphyllum (Araceae). Ecology63:797–808.
— &L. Lovett Doust. 1985. Sex ratios, clonal growth and herbivory inRumex acetosella. Pages 327–341in J. White (ed.), Studies on plant demography: A festschrift for John L. Harper. Academic Press, London.
——. 1988. Sociobiology of plants: An emerging synthesis. Pages 5–29in J. Lovett Doust & L. Lovett Doust (eds.), Plant reproductive ecology: Patterns and strategies. Oxford University Press, New York.
Lovett Doust, L. 1981. Population dynamics and local specialization in a clonal perennial (Ranunculus repens). 1. The dynamics of ramets in contrasting habitats. J. Ecol.69:743–755.
Mayer, S. S. &D. Charlesworth. 1991. Cryptic dioecy in flowering plants. Tree6:320–325.
McArthur, E. D. 1977. Environmental induced changes of sex expression inAtriplex canescens. Heredity38:97–103.
—. 1989. Breeding systems in shrubs. Pages 341–361in C. M. McKell (ed.), The biology and utilization of shrubs. Academic Press, San Diego.
— &D. C. Freeman. 1982. Sex expression inAtriplex canescens, genetics and environment. Bot. Gaz.143:476–482.
— &S. C. Sanderson. 1984. Distribution, systematics, and evolution of Chenopodiaceae: An overview. Pages 14–24in A. R. Tiedemann, E. D. McArthur, H. C. Stutz, R. Stevens & K. L. Johnson (compilers), Proceedings—Symposium on the biology ofAtriplex and related chenopods, 2–6 May 1983, Provo, Utah. Gen. Tech. Rep. INT-172. U.S.D.A. Forest Service, Intermountain Forest and Range Experiment Station, Ogden, Utah.
—,D. C. Freeman, L. Luckinbill, S. C. Sanderson &G. L. Noller. 1992. Are trioecy and sexual lability inAtriplex canescens genetically based: Evidence from clonal studies. Evolution46:1708–1721.
-,McArthur, E. D., A. P. Plummer, G. A. Van Epps, D. C. Freeman & K. R. Jorgensen. 1978. Producing fourwing saltbush seed in seed orchards. Pages 406–410in Proceedings of the First International Rangeland Congress.
Miglia, K. J. &D. C. Freeman. 1996. The effect of delayed pollination on stigma length, sex expression, and progeny sex ratio in spinach,Spinacia oleracea (Chenopodiaceae). Amer. J. Bot. 83:326–332.
Miller, J. &J. Lovett Doust. 1987. The effects of plant density and snail grazing on female and male spinach plants. New Phytol.107:613–621.
Moore, D. M. &H. Lewis. 1965. The evolution of self-pollination inClarkia xantiana. Evolution19:104–114.
Nakamura, R. R., M. L. Stanton &S. J. Mazer. 1989. Effects of mate size and mate number on male reproductive success in plants. Ecology70:71–76.
Niklas, K. J. 1985. The aerodynamics of wind pollination. Bot. Rev. (Lancaster)51: 328–386.
Peitgen, H., H. Jurgens &D. Saupe. 1992. Chaos and fractals, new frontiers of science. Springer-Verlag, New York.
Pendleton, R., E. D. McArthur, A. C. Blauer &D. C. Freeman. 1989. Heterodichogamy inGrayia brandegii. Amer. J. Bot.75:267–274.
Ramadan, A. A., A. El-Keblawy, K. H. Shaltout &J. Lovett Doust 1994. Sexual polymorphism, growth and reproductive effort in EgyptianThymelaea hirsuta (Thymelaeaceae). Amer. J. Bot.81:847–857.
Reinartz, J. A. &D. H. Les. 1994. Bottleneck-induced dissolution of self-incompatibility and breeding system consequences inAster furcatus. Amer. J. Bot.81:446–455.
Renner, S. S. &R. E. Ricklefs. 1995. Dioecy and its correlates in the flowering plants. Amer. J. Bot.82:596–606.
Rick, C. M., M. Holle &R. W. Thorp. 1978. Rates of cross pollination inLycopersicon pimpinellifolium. Impact of genetic variation in floral characters. Pl. Syst. Evol.129:31–44.
Ritland, C. &K. Ritland. 1989. Variation of sex allocation among eight taxa of theMimulus guttatus species complex (Scrophulariaceae). Amer. J. Bot.76:1731–1739.
Ross, M. D. 1970. Evolution of dioecy from gynodioecy. Evolution30:425–441.
—. 1982. Five evolutionary pathways to subdioecy. Amer. Naturalist119:297–318.
— &R. F. Shaw. 1971. Maintenance of male sterility in plant populations. Heredity26:1–8.
Schaffner, J. H. 1925. Experiments with various plants to produce change of sex in the individual. Bull. Torrey Bot. Club52:35–47.
Shaw, R. F. &J. D. Mohler. 1953. The selective advantage of the sex ratio. Amer. Naturalist87:337–342.
Shea, M. M., P. M. Dixon &R. R. Sharitz. 1993. Size differences, sex ratio, and spatial distribution of male and female water tupelo,Nyssa aquatica (Nyssaceae). Amer. J. Bot.80:26–30.
Shmida, A. & H. Leschner. In review. About humble females and dandy males: Why do old red crown anemones have a white ring?
Shoen, D. J. 1982. The breeding system ofGilia achilleifolia: Variation in floral characteristics and outcrossing rate. Evolution36:352–360.
Smith, B. N. 1982. General characteristics of terrestrial plants (agronomic and forests)—C3, C4 and Crassulacean acid metabolism plants. Pages 99–118in O. R. Zaborsky (ed.), CRC handbook of biosolar resources. Vol. 1. CRC Press, Boca Raton, Florida.
Solomon, B. P. 1985. Environmentally influenced changes in sex expression in an andromonoecious plant. Ecology66:1321–1223.
Snow, A. 1994. Postpollination selection and male fitness in plants. Amer. Naturalist144(Suppl.):S69-S83.
Stebbins, G. L. 1974. Flowering plants: Evolution above the species level. Harvard University Press, Cambridge.
Sutherland, S. &L. F. Delph. 1984. On the importance of male fitness in plants: Patterns of fruit-set. Ecology65:1093–1104.
Takhtajan, A. L. 1980. Outline of the classification of flowering plants (Magnoliophyta). Bot. Rev. (Lancaster)46:225–359.
Thomas, S. M. &B. G. Murray. 1981. Breeding systems and hybridization inPetrorhagia sect.Kohlrauschia (Caryophyllaceae). Pl. Syst. Evol.139:77–94.
Tiedemann, A. R., E. D. McArthur &D. C. Freeman. 1987. Variation in physiological metabolites and chlorophyll in sexual phenotypes of “Rincon” fourwing saltbush. J. Range Managern.40:151–155.
Vasek, F. C. 1977. Phenotypic variation and adaptation inClarkia sectionPhaeostoma. Syst. Bot.2:251–279.
Vitale, J. J. &D. C. Freeman. 1985. Secondary sex characteristics inSpinacia oleracea L.: Quantitative evidence for the existence of at least three sexual morphs. Amer. J. Bot.72:1061–1066.
——. 1986. Partial niche separation inSpinacia oleracea L.: An examination of reproductive allocation. Evolution40:426–430.
——,L. Merlotti &M. Delassandro. 1987. Resource allocation inSpinacia oleracea. Amer. J. Bot.74:1049–1054.
Wachocki, B. A. 1992. Maternal effects on sex ratio and sex expression in spinach. Ph.D. dissertation, Wayne State University, Detroit.
Warner, R. R., D. R. Robertson &E. G. Leigh. 1975. Sex change and sexual selection. Science190:633–638.
Watson, M. 1995. Sexual differences in plant developmental phenology affect plant-herbivore interactions. Tree10:180–182.
Welkie, G.W. &M. Caldwell. 1970. Leaf anatomy of species in some dicotyledon families as related to the C3 and C4 pathways of carbon fixation. Canad. J. Bot.48:2135–2146.
Weller, S. G. &R. Ornduff. 1977. Cryptic self-incompatibility inAmsinckia grandiflora. Evolution31:47–51.
Westergaard, M. 1958. The mechanisms of sex determination in dioecious flowering plants. Adv. Genet.9:217–281.
Willson, M. F. 1979. Sexual selection in plants. Amer. Naturalist113: 777–790.
—. 1983. Plant reproductive ecology. John Wiley, New York.
—. 1994. Sexual selection in plants: Perspective and overview. Amer. Naturalist144(Suppl.):S13-S39.
— &P. W. Price. 1977. The evolution of inflorescence size inAsclepias (Asclepiadaceae). Evolution31:495–511.
Wolfe, L. M. &A. Shmida. 1996. Regulation of gender and flowering behavior in a sexually dimorphic desert shrub (Ochradenus baccatus ssp.delete (Resedaceae)). Israel J. Pl. Sci.43: 325–337.
Wyatt, R. 1982. Inflorescence architecture: How flower number, arrangement and phenology affect pollination and fruit set. Amer. J. Bot.69:585–594.
Yeo, P. F. 1975. Some aspects of heterostyly. New Phytol.75:147–153.
Yin, T. &J. A. Quinn. 1992. A mechanistic model of a single hormone regulating both sexes in flowering plants. Bull. Torrey Bot. Club119:431–441.
——. 1994. Effects of exogenous growth regulators and a gibberellin inhibitor on the sex expression and growth form of buffalograss (Buchloe dactyloides) and their ecological significance. Bull. Torrey Bot. Club1221:170–179.
——. 1995. Tests of a mechanistic model of one hormone regulating both sexes inBuchloe dactyloides (Poaceae). Amer. J. Bot.82:745–751.
Zaharan, M. A. &A. J. Willis. 1992. The vegetation of Egypt. Chapman & Hall, London.
Zimmerman, J. K. &M. J. Lechowicz. 1982. Responses to moisture stress in male and female plants ofRumex acetosella L. (Polygonaceae). Oecologia53:305–309.
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Freeman, D.C., Doust, J.L., El-Keblawy, A. et al. Sexual specialization and inbreeding avoidance in the evolution of dioecy. Bot. Rev 63, 65–92 (1997). https://doi.org/10.1007/BF02857918
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DOI: https://doi.org/10.1007/BF02857918