Abstract
We investigated whether stochastic processes influence the frequency of mating types within populations of tristylous Eichhornia paniculata in northeastern Brazil. The importance of genetic drift as a result of small populations was evaluated using survey data on spatial and temporal variation in style morph frequencies in natural populations. The patterns expected when morph variation is due entirely to stochastic forces in finite populations were determined by computer simulation of tristylous populations, for various sampling schemes. Surveys of a total of 167 populations, censused during 1982–1989, indicated that morph structure was negatively correlated with population size. Populations with three style morphs were significantly larger than those containing two or one morph, suggesting that evolutionary processes in small populations may account for morph loss. In 88 populations surveyed for either 2 or 3 consecutive years, 33 per cent showed significant changes in morph frequency. There were no consistent patterns in the direction of morph frequency change and the magnitude of change was largest in small populations (N<50). Among the 12 trimorphic populations that lost morphs during the survey period, the L, M and S morphs were lost 2, 6 and 11 times respectively, a pattern consistent with stochastic morph loss under the two-locus inheritance pattern for tristyly. Simulation results indicated that the observed proportion of populations with significant morph frequency change and the magnitude of this change could be accounted for by random processes alone. Collectively, these findings are consistent with the hypothesis that genetic drift plays an important role in influencing morph frequencies in populations of E. paniculata.
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References
Barrett, S C H. 1977. Tristyly in Eichhornia crassipes (Mart.) Solms (Water Hyacinth). Biotropica, 9, 230–238.
Barrett, S C H. 1985a. Floral trimorphism and monomorphism in continental and island populations of Eichhornia paniculata (Spreng.) Solms (Pontederiaceae). Biol J Linn Soc, 25, 41–60.
Barrett, S C H. 1985b. Ecological genetics of breakdown in tristyly. In: Haeck, J. and Woldendorp, J. W. (eds) Structure and Functioning of Plant Populations, II Phenotypic and Genotypic Variation in Plant Populations, North-Holland, Amsterdam, pp. 267–275.
Barrett, S C H, Brown, A H D, and Shore, J S. 1987. Disassortative mating in tristylous Eichhornia paniculata (Pontederiaceae). Heredity, 58, 49–55.
Barrett, S C H, and Husband, B C. 1990. Variation in outcrossing rates in Eichhornia paniculata: the role of demographic and reproductive factors. Plant Sp Biol, 5, 41–55.
Barrett, S C H, and Kohn, J R. 1991. Genetic and evolutionary consequences of small population size in plants: implications for conservation. In: Falk. D. A. and Holsinger, K. E. (eds) Genetics and Conservation of Rare Plants, Oxford University Press, New York. pp. 3–30.
Barrett, S C H, Morgan, M T, and Husband, B C. 1989. The dissolution of a complex genetic polymorphism: the evolution of self-fertilization in tristylous Eichhornia paniculata (Pontederiaceae). Evolution, 43, 1398–1416.
Billington, H L. 1991. Effect of population size on genetic variation in a dioecious conifer. Con Biol, 5, 115–119.
Charlesworth, D. 1979. The evolution and breakdown of tristyly. Evolution, 33, 486–498.
Eckert, C G, and Barrett, S C H. 1992. Stochastic loss of style morphs from populations of tristylous Lythrum salicaria and Decodon verticillatus (Lythraceae). Evolution, (in press).
Epling, C, and Dobzhansky, T. 1942. Genetics of natural populations. VI. Microgeographical races in Linanthus parryae. Genetics, 27, 317–332.
Fisher, R A. 1944. Allowance for double reduction in the calculation of genotype frequencies with polysomic inheritance. Ann Eugen, 11, 31–38.
Hanski, I. 1985. Colonization of ephemeral habitats. In: Pickett, S. T. A. and White, P. S. (eds) The Ecology of Natural Disturbance and Patch Dynamics, Academic Press, NY. pp. 155–183.
Harrison, S, Murray, D D, and Ehrlich, P R. 1988. Distribution of the bay checkerspot butterfly, Euphydryas editha bayensis: evidence for a metapopulation model. Am Nat, 360–382.
Heuch, I. 1979. Equilibrium populations of heterostylous plants. Theor Pop Biol, 15, 43–57.
Heuch, I. 1980. Loss of incompatibility types in finite populations of the heterostylous plant: Lythrum salicaria. Hereditas, 92, 53–57.
Heuch, I, and Lie, R T. 1985. Genotype frequencies associated with incompatibility systems in tristylous plants. Theor Pop Biol, 27, 318–336.
Husband, B C. 1992. Stochastic processes and the evolution of self-fertilization in Eichhornia paniculata (Spreng) Solms (Pontederiaceae). PhD Thesis, University of Toronto, Toronto, Canada.
Husband, B C, and Barrett, S C H. 1992a. Effective population size and genetic drift in tristylous Eichhornia paniculata (Pontederiaceae). Evolution (in press).
Husband, B C, and Barrett, S C H. 1992b. Pollinator visitation to populations of tristylous Eichhornia paniculata (Pontederiaceae) in northeastern Brazil. Oecologia, 89, 365–371.
Lande, R, and Barrowclough, G F. 1987. Effective population size, genetic variation and their use in population management. In: Soulé, M. E. (ed.) Viable Populations for Management, Cambridge University Press, Cambridge, pp. 87–124.
McClenaghan, L R Jr, and Beauchamp, A C. 1986. Low genic differentiation among isolated populations of the California fan palm (Washingtonia filifera). Evolution, 40, 315–322.
Moran, G F, and Hopper, S D. 1983. Genetic diversity and the insular population structure of Eucalyptus caesia. Beuth. Aust J Bot, 31, 161–172.
Morgan, M T, and Barrett, S C H. 1988. Historical factors and anisoplethic population structure in tristylous Pontederia cordata: a reassessment. Evolution, 42, 496–504.
Olivieri, L, Couvet, D, and Gouyon, P. 1990. The genetics of transient populations: research at the metapopulation level. Trends Ecol Evol, 5, 207–210.
Oxford, G S, and Shaw, M W. 1986. Long-term variation in colour-morph frequencies in the spider Enoplognatha ovata (Clerk) (Araneae: Theridiidae): natural selection, migration and intermittent drift. Biol J Linn Soc, 27, 225–249.
Waples, R S. 1989. Temporal variation in allele frequencies: testing the right hypothesis. Evolution, 43, 1236–1251.
Waples, R S. 1990. Conservation genetics of Pacific Salmon I. Temporal changes in allele frequency. Con Biol, 4, 144–156.
Wright, S. 1931. Evolution in Mendelian populations. Genetics, 16, 97–159.
Wright, S. 1938. Size of population and breeding structure in relation to evolution. Science, 87, 430–431.
Wright, S. 1943. An analysis of local variability of flower color in Linanthus parryae. Genetics, 28, 139–156.
Wright, S. 1951. The genetical structure of populations. Ann Eugen, 15, 323–354.
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Husband, B., Barrett, S. Genetic drift and the maintenance of the style length polymorphism in tristylous populations of Eichhornia paniculata (Pontederiaceae). Heredity 69, 440–449 (1992). https://doi.org/10.1038/hdy.1992.148
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DOI: https://doi.org/10.1038/hdy.1992.148
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