Abstract
Levels of outcrossing were compared in two sympatric weedy species of Carduus, C. nutans and C. acanthoides and their hybrid swarms from Grey County, Ontario, Canada in order to determine whether: (i) a departure from random outcrossing could be demonstrated in the Grey County populations; (ii) there were species differences in outcrossing rates and selfing potential; (iii) differences were evident between pure populations of the parental taxa and the hybrid swarms; and (iv) there was evidence for spatial substructuring of the populations or inter-plant variation in outcrossing rates. Self-fertilization studies, conducted in the greenhouse on individuals of both species, indicated varying degrees of self-fertility, up to 60 per cent among plants of each species. Two estimates of outcrossing, t and tH, were obtained from analyses of three polymorphic enzyme loci, for three populations of each species and three hybrid swarms. Outcrossing rates, tH, were based on Wright's inbreeding coefficient, F, calculated from the observed levels of heterozygosity pooled over all progeny per population, whereas outcrossing rates, t, were obtained from analyses of progeny genotype arrays using maximum likelihood estimation procedures. Both multilocus estimates of the outcrossing rate t and tH averaged over all loci, were significantly less than 1ยท0 for all nine populations studied, indicating significant departures from random outcrossing. No consistent differences in outcrossing rates were detected for populations of the two parental species and the three hybrid swarms. However, considerable inter-plant variation in values of t were observed in both Carduus species, although the data did not provide evidence for population substructuring.
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Brown, A H D, and Allard, R W. 1970. Estimation of the mating system in open-pollinated maize populations using isozyme polymorphisms. Genetics, 66, 133โ145.
Brown, A H D, and Burdon, N J. 1988. Mating systems and colonising success in plants. In Gray, A. J., Crawley M. J. and Edwards, P. J. (eds) Brit Ecol Soc Symposium, 26, 115โ132.
Clegg, M T. 1980. Measuring plant mating systems. Bioscience, 230, 814โ818.
Desrochers, A M. Bain, J F, and Warwick, S I. 1988โ89a. The biology of Canadian weeds. Carduus nutans L. and C. acanthoides L. Can J PI Set, 68, 1053โ1068.
Desrochers, A M. Bain, J F, and Warwick, S I. 1988b. A biosystematic study of the Carduus nutans L. complex in Canada. Can J Bot, 66, 1621โ1631.
Hamrick, J L. 1982. Plant population genetics and evolution. Amer J Bot, 69, 1685โ1693.
Moore, R J, and Mulligan, G A. 1956. Hybridization between Carduus acanthoides and Carduus nutans in Ontario. Can J Bot, 34, 71โ85.
Moore, R J, and Mulligan, G A. 1964. Further studies on natural selection among hybrids of Carduus acanthoides and Carduus nutans. Can J Bot, 42, 1605โ1613.
Phillips, M A, and Brown, A H D. 1977. Mating system and hybridity in Eucalyptus pauciflora. Aust J Biol Set, 39, 337โ344.
Richards, A J. 1986. Plant Breeding Systems. Allen and Unwin. London.
Ritland, K. 1983. Estimation of mating systems. In Tanksley, S. D. and Orton, T. J. (eds) Isozymes in Plant Genetics and Breeding, Part A, Elsevier Science Publishers, New York, pp. 289โ302.
Ritland, K. 1986. Joint maximum likelihood estimation of genetic and mating structure. Biometrics, 42, 25โ44.
Ritland, K, and Jain, S K. 1981. A model for the estimation of outcrossing rate and gene frequencies using n independent loci. Heredity, 47, 35โ52.
Schemske, D W, and Lande, R. 1985. The evolution of self-fertilization and inbreeding depression in plants. II. Empirical observations. Evolution, 39, 42โ52.
Smyth, C A, and Hamrick, J L. 1984. Variation in estimates of outcrossing in musk thistle populations. J Hered, 75, 303โ307.
Smyth, C A, and Hamrick, J L. 1987. Realized gene flow via pollen in artificial populations of musk thistle. Evolution, 41, 613โ619.
Sokal, R R, and Rohlf, F J. 1969. Biometry. W. H. Freeman. San Francisco.
Warwick, S I, and Bain, J F. 1987. Hybridization and introgression in Carduus nutans and C acanthoides. Amer J Bot, 74, 764 [Abst.].
Warwick, S I. Bain, J F. Wheatcroft, R, and Thompson, B K. 1989. Hybridization and introgression in Carduus nutans and C. acanthoides. Syst Bot, 14, 476โ494.
Wright, S. 1969. Evolution and Genetics of Populations, Volume II The Theory of Gene Frequencies. University of Chicago Press, Chicago.
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Warwick, S., Thompson, B. The mating system in sympatric populations of Carduus nutans, C. acanthoides and their hybrid swarms. Heredity 63, 329โ337 (1989). https://doi.org/10.1038/hdy.1989.106
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DOI: https://doi.org/10.1038/hdy.1989.106
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