Seasonal Decline in Male-Phase Duration in a Protandrous Plant: A Response to Increased Mating Opportunities?

1. We examined the effects of pollinator visitation and time of season on male- and female-phase duration, using experimental manipulation and survey data from naturally occurring populations of Chamerion (= Epilobium) angustifolium (L.) J. Holub (Onagraceae). 2. Based on the observation that male m...

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Bibliographic Details
Published in:Functional ecology 2000-08, Vol.14 (4), p.484-489
Main Authors: Sargent, R. D., Roitberg, B. D.
Format: Article
Language:English
Subjects:
Animal and plant ecology
Animal, plant and microbial ecology
Autoecology
Biological and medical sciences
Chamerion angustifolium
dichogamy
Epilobium
Epilobium angustifolium
Flowers
Fundamental and applied biological sciences. Psychology
hermaphrodite
Human ecology
Mating behavior
Ovules
Plants
Plants and fungi
Pollen
Pollinating insects
Pollination
pollinator visitation
Pollinators
Sex ratio
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Summary:1. We examined the effects of pollinator visitation and time of season on male- and female-phase duration, using experimental manipulation and survey data from naturally occurring populations of Chamerion (= Epilobium) angustifolium (L.) J. Holub (Onagraceae). 2. Based on the observation that male mating opportunity (numbers of female flowers/numbers of male flowers) increases seasonally, we predicted that individual flowers should spend more time in the male phase early in the season when mating opportunity is low. We predicted that if seasonal changes in mating opportunity select for phase duration, male-phase duration should decline when pollinator effects are experimentally controlled. 3. A comparison of phase duration in naturally pollinated and pollinator-excluded plants supported this prediction: male-phase duration in the pollinator-exclusion treatment was longer and declined faster than in the naturally pollinated group. 4. A population survey revealed that once the effects of temperature were controlled for, male-phase duration was negatively correlated with date, while female-phase duration was positively correlated with date. 5. These findings suggest that seasonal variation in mating opportunity, and not just pollination rate or temperature, may play a significant role in phase duration in dichogamous plants.
ISSN:0269-8463
1365-2435
DOI:10.1046/j.1365-2435.2000.00453.x