Abstract
Experimental hand pollinations have revealed that the Australian proteaceous shrub Grevillea barklyana is fully self-compatible, although one study suggested that when both self- and outcross pollen were presented to different flowers on the same inflorescence significantly greater seed set resulted from the outcrossed flowers. This study used single-locus electrophoretic surveys of maternal plants and their progeny arrays to test the prediction that this apparent 'preference' for outcross pollen would produce high levels of outcrossing within natural populations. We found instead that plants within three of four populations were almost completely selfed. Outcrossing rates (t) in each of these populations (based on the progeny arrays of a minimum of nine plants) ranged from 0.07 ± 0.03 to only 0.33 ± 0.08 and showed little variation among years, ranging from 0.07 ± 0.03 to 0.10 ± 0.03 for a population sampled in each of two breeding seasons. Furthermore, examination of the progeny arrays from plants in the most intensively studied population revealed virtually no exchange of genes between immediately adjacent plants. Three pairs of alternative homozygotes were near neighbours (separated by less than 2 m) and yet detectable outcrosses comprised only seven of the 108 seeds sampled. In contrast, the fourth population of G. barklyana appeared highly outcrossed (t = 0.85 ± 0.2) which is typical of the realized mating system reported for other Australian Proteaceae. These data show that the realized mating system may vary widely among populations and may often be less than optimal. The occurrence of very low outcrossing rates within some populations may reflect the presence of introduced pollinators or other disturbances.
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Ayre, D., Whelan, R. & Reid, A. Unexpectedly high levels of selfing in the Australian shrub Grevillea barklyana (Proteaceae). Heredity 72, 168–174 (1994). https://doi.org/10.1038/hdy.1994.24
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