Tuesday, August 7, 2007

PS 35-171: Is selfing more advantageous than sex in Drosera due to the pollinator-prey conflict?

Amber R. Sciligo1, Jon J. Sullivan1, Linley K. Jesson2, Taina Witt3, Andreas Juergens3, Roddy J. Hale1, and Linda Newstrom4. (1) Lincoln University, (2) University of New Brunswick, (3) Hortresearch Canterbury, (4) Landcare Research Lincoln

The debate on why sex is usually more beneficial for reproductive fitness than selfing has been continuing for years.  The carnivorous plant genus Drosera is an ideal study system because there is additional cost to sexual reproduction when pollinators are captured as prey. To define this pollinator-prey conflict and dependence on insects as pollinators, we measured selfing and outcrossing rates, and pollinator/prey overlap for two morphologically different species: D. arcturi and D. spatulata. In montane and alpine bogs in New Zealand, D. arcturi may depend on insect pollination less than D. spatulata.  There is a large overlap in floral visitor and prey taxa for D. arcturi, and high variation is exhibited in separation of traps and flowers including complete overlap, suggesting potential for pollinator-prey conflict. Floral visitor taxa are never found in traps of D. spatulata and trap-flower separation is much greater and less variable.  Seedset varied greatly for all treatments of D. arcturi flowers, however high seedset is common for bagged flowers, which implies a large amount of selfing.  Phenological observations suggest pseudo-cleistogamy, prior and delayed selfing are the predominant mechanisms for D. arcturi, while only delayed selfing was observed in D. spatulata. Emasculated flowers tend to abort fruits or produce very few seeds, suggesting low pollinator efficiency for outcrossing in D. arcturi. In addition, flower opening of D. arcturi is not reliant on weather conditions; flowers open on bad weather days when pollinators are absent, while D. spatulata flowers only open with good weather, when pollinators are most abundant. We suspect that plants with more pollinator-prey conflict depend on selfing instead of sex for reproduction. The benefits of capturing pollinators may outweigh the costs of selfing for D. arcturi, whereas selfing may be too costly for D. spatulata. Determining selfing costs is the next stage for this study.

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