In self-compatible plants, small populations may experience reduced outcrossing owing to decreased pollinator visitation and mate availability. We examined the relation between outcrossing and population size in eastern Ontario populations of Aquilegia canadensis. Experimental pollinations showed that the species is highly self-compatible, and can achieve full seed-set in the absence of pollinators via automatic self-pollination. We estimated levels of outcrossing (t) and parental inbreeding coefficients (F) from allozyme variation in naturally pollinated seed families for 10 populations ranging in size from 32 to 750 reproductive individuals. The proportion of seeds produced through outcrossing was generally low (mean = 0.29 ± 0.02 SE) and varied widely among populations (range = 0.00–0.83). Accordingly, estimates of F were large (mean = 0.26 ± 0.05) and significantly greater than zero in seven populations. As expected, four small populations (N < 40) outcrossed less (0.17 ± 0.03) than six large populations (N > 90; 0.38 ± 0.03). However, parental plants were not significantly more inbred in small than large populations (P= 0.18). There was no difference in the germination of seeds from hand self- and cross-pollinations. However, population genetic estimates of inbreeding depression for survival expressed from seed to reproductive maturity were very high (mean δ = 1 − relative fitness of selfed seed = 0.88 ± 0.14). The combination of self-compatibility and automatic self-pollination makes the mating system of A. canadensis sensitive to variation in ecological factors that affect the likelihood of cross-pollination.
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We thank Grace Lo, Blandine Massonnet, Pascal Thomas and especially Greg Grabas for help with the fieldwork; the Queen’s University Biological Station and the Saint Lawrence Islands National Park for logistic support in the field and access to study sites; Marcel Dorken, Vicki Friesen and Brian Husband for comments on the manuscript; Queen’s University School of Graduate Studies for graduate awards to K.M.; and the Natural Sciences and Engineering Research Council of Canada (NSERC) for a research grant to C.G.E.
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Routley, M., Mavraganis, K. & Eckert, C. Effect of population size on the mating system in a self-compatible, autogamous plant, Aquilegia canadensis (Ranunculaceae). Heredity 82, 518–528 (1999) doi:10.1038/sj.hdy.6885220
- Aquilegia canadensis
- inbreeding depression
- mating systems
- population size
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