New Zealand Journal of Botany abstracts

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Does competition-dependent incompatibility provide reproductive assurance in Phormium tenax?

Linley K. Jesson*
Lesley D. Milicich
Sarah C. Newman

School of Biological Sciences
Victoria University of Wellington
PO Box 600
Wellington 6140, New Zealand

*Present address: Department of Biology, University of New Brunswick, PO Bag Service 45111, Fredericton, New Brunswick, Canada E3B 6E1. jesson@unb.ca

Abstract  New Zealand flax (Phormium tenax) has a reproductive system in which the early abscission of selfed flowers is determined by the degree of competition with crossed fruits on the same plant. It has been suggested that this functions as a form of reproductive assurance, allowing for high levels of outcrossing when pollinators are abundant, while ensuring seedset when pollinators are scarce. We performed experimental crosses and mating system estimation in natural populations to determine whether P. tenax can set seed in the absence of pollinators, and how pure and mixed pollen loads influence reproductive success and population-level selfing rates. Phormium tenax can set seed autonomously, although if other flowers on the plant are available for outcrossing, resources are preferentially allocated to maturing those fruits. Experimental crosses suggest that flowers pollinated with mixtures of selfed and outcrossed pollen can result in fruitset, although fruitset is reduced if flowers pollinated with mixed pollen loads compete with cross-pollinated flowers. Despite the potential for geitonogamy in P. tenax, outcrossing rates from five populations showed that these populations were universally outcrossing (t = 0.83–1.06). In P. tenax, self-compatibility in the absence of competition from outcrossed pollen can provide some reproductive assurance, but in large populations, selfing and mixed mating rarely occur.

Keywords  cryptic incompatibility; inbreeding depression; Phormium tenax; reproductive assurance; outcrossing rates

B06004; Received 16 February 2006; accepted 25 May 2006; Online publication date 7 September 2006
New Zealand Journal of Botany, 2006, Vol. 44: 249–259
0028–825X/06/4403–0249 © The Royal Society of New Zealand 2006

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