Effect of pollen load, self-pollination and plant size on seeds and germination in the endangered pink-lipped spider orchid, Caladenia behrii
Sophie Petit A D , Manfred Jusaitis B and Doug Bickerton CA School of Natural and Built Environments, Sustainable Environments Research Group, University of South Australia, Mawson Lakes, SA 5095, Australia.
B Botanic Gardens of Adelaide, Department for Environment and Heritage, North Terrace, Adelaide, SA 5000, Australia.
C Science and Conservation Directorate, Department for Environment and Heritage, GPO Box 1047, Adelaide, SA 5001, Australia.
D Corresponding author. Email: sophie.petit@unisa.edu.au
Australian Journal of Botany 57(4) 307-314 https://doi.org/10.1071/BT08117
Submitted: 1 July 2008 Accepted: 3 February 2009 Published: 29 July 2009
Abstract
Caladenia behrii Schltdl. (Orchidaceae) (syn. Arachnorchis behrii) is a sexually deceptive, endangered orchid that produces aggregated pollen as pollinia. It is pollinated by a thynnine wasp, and may also be pollinated incidentally by other insects. Pollinator effectiveness may depend on the number of pollinia that pollinators carry and deposit, and on whether they mediate cross-pollination or self-pollination. To understand the role of pollinators and guide conservation programs, we determined the effect of pollen load (one pollinium v. two pollinia) and self-pollination on seed number, seed (embryo) size and germination at 35 days. We also examined the effect of plant size on seed size and seed number. By using partial correlations with leaf width, seed size, seed number, capsule volume and stem length, we found that leaf width was a good predictor for seed number, and that seed size was not correlated with any of the variables examined. Flowers pollinated with one pollinium and two pollinia did not produce seeds that differed in size or number. Cross-pollinated flowers produced fewer but larger seeds, which germinated faster than did seeds from self-pollinated flowers. We conclude that seed production in the field may be estimated from leaf size, that pollinators carrying one pollinium are as effective as those carrying two pollinia and that selfing affects germination negatively, partly because of the smaller size of selfed seeds. Conservation programs aiming to perform hand-pollination of this species should use crossing with a single pollinium.
Acknowledgements
We thank profusely Damian Morrant and David Wilson, whose seed-counting and measuring abilities we revere. Catherine Dickson also contributed to field and laboratory work; Simon Cheers helped with germination trials. This research was sponsored by Early Career Grants to S. Petit from the Division of Information Technology, Engineering and the Environment (University of South Australia), an Australian Technology Network Grant to S. Petit, and several grants from the Native Vegetation Council of South Australia. The University of South Australia also provided transport to the field site. We thank Erik Dahl for facilitating access to the field site (E 24836 permit series). Denise Noack assisted with locating the references. Catherine Dickson, Helen Waudby and three anonymous reviewers provided useful comments on the manuscript.
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