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Flies (Diptera) as pollinators of two dioecious plants: behaviour and implications for plant mating

Published online by Cambridge University Press:  02 April 2012

Christopher J. Borkent*
Affiliation:
Department of Natural Resource Sciences, McGill University, Macdonald Campus, 21, 111 Lakeshore Road, Sainte-Anne-de-Bellevue, Quebec, Canada H9X 3V9
Lawrence D. Harder
Affiliation:
Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada T2N 1N4
*
1Corresponding author (e-mail: cborkent@alumni.uvic.ca).

Abstract

We consider the role of generalist Diptera in the pollination of two dioecious plant species, Clematis ligusticifolia Nutt. (Ranunculaceae) and Shepherdia canadensis (L.) Nutt. (Elaeagnaceae). In particular, we assess (i) whether or not generalist pollinators are unable to distinguish between the sexes of dioecious species and so visit the sexes at equivalent rates, and (ii) the number of flowers that generalist flies visit and revisit during a foraging bout, which would affect self-pollination if plants were hermaphroditic. We determined the visitation rate to each plant species during 10 min periods and recorded the number of flowers that individual pollinators visited and revisited per foraging bout. Diptera were the main pollinators, visiting both sexes at similar rates for both plant species. The main visitors to C. ligusticifolia were muscoid flies (small and large), Culicidae, and halictid bees. The number of flowers visited in this species varied with pollinator group, but groups did not differ in the frequency of revisits. Visitors to S. canadensis were primarily Syrphidae and Empididae. Neither the number of flowers visited nor the number of revisits differed between these two pollinator groups. The results for each plant species are discussed and contrasted, particularly with other studies of the behaviour of generalist and specialist pollinators. We compare the observed pollinator behaviours, and their implications for plant mating, with the various theories of the role of pollinators in the evolution of the dioecious breeding system in plants.

Résumé

Nous étudions le rôle des diptères généralistes dans la pollinisation de deux espèces de plantes dioïques, Clematis ligusticifolia Nutt. (Ranunculaceae) et Shepherdia canadensis (L.) Nutt. (Eleagnaceae). En particulier, (i) nous déterminons si les pollinisateurs généralistes sont capables ou non de distinguer les sexes des plantes dioïques et, en conséquence, de visiter les deux sexes à des fréquences équivalentes et (ii) nous évaluons le nombre de fleurs que les mouches généralistes visitent une première fois et visitent de nouveau durant un même épisode de recherche de nourriture, ce qui affecterait l'auto-pollinisation si les plantes étaient hermaphrodites. Nous avons déterminé la fréquence des visites à chacune des espèces durant des périodes de 10 minutes et nous avons noté le nombre de fleurs que chaque pollinisateur visite et visite de nouveau au cours d'un même épisode d'alimentation. Les diptères constituent les pollinisateurs principaux qui visitent les deux sexes des deux espèces de plantes à des fréquences similaires. Les visiteurs principaux de C. lusticifolia sont des mouches muscoïdes, petites et grandes, ainsi que des Culicidae et des abeilles Halictidae. Chez cette espèce, le nombre de fleurs visitées varie d'un groupe de pollinisateurs à un autre, mais il n'y a pas de différences entre les groupes dans la fréquence des visites subséquentes. Les visiteurs de S. canadensis sont surtout des Syrphidae et des Empididae. Ni le nombre de fleurs visitées, ni le nombre de visites subséquentes aux mêmes fleurs ne diffèrent chez ces deux groupes de pollinisateurs. Nous comparons les résultats obtenus avec chacune des espèces de plantes et nous en discutons, particulièrement en regard d'autres études sur les comportements des pollinisateurs généralistes et spécialistes. Nous confrontons les comportements que nous avons observés chez les pollinisateurs et leurs conséquences sur la reproduction des plantes aux diverses théories sur le rôle des pollinisateurs dans l'évolution des systèmes dioïques de reproduction chez les plantes.

[Traduit par la Rédaction]

Type
Articles
Copyright
Copyright © Entomological Society of Canada 2007

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