| Several factors may limit the production of fruit in plants, including insufficient levels of pollination or nutrient resource availability, negative climatic effects, herbivory or seed predation. In the context of this thesis, the pollination ecology of two economically important fruiting crops in Quebec were studied, the wild cloudberry (Rubus chamaemorus L.) and the cultivated cranberry (Vaccinium macrocarpon Ait.). Cloudberry is a perennial, dioecious plant with a circumpolar distribution in sub-arctic bogs. We studied the interaction between its flowers and the guild of insect pollinators that visited them during 4 field seasons on the North Shore of Quebec in order to (i) determine the most important insect pollinators in this system and (ii) test the hypothesis that pollination occurred via the deception of the insect pollinators. Through sweep net sampling and controlled experiments we showed that four insect Families (Hymenoptera: Apidae, Halictidae; Diptera: Muscidae, Syrphidae) were the most frequent and effective flower visitors to cloudberry. Furthermore, due to their high relative abundances, the two groups of flies were determined to be the most important pollinators in this system. Despite floral sex ratios and a flowering phenology that supports the model---mimic hypothesis, we found that the female cloudberry flowers produced significantly more nectar than the males. These small amounts of nectar were exploited by small flies, who were physically excluded from accessing the food rewards in co-flowering plants due to their small size and short lapping mouthparts. Cloudberry seems to have evolved a floral attraction that is economically tailored to small flies, with simple, open flowers and quantities of pollen and nectar that are ideal for the nutritional and energetic needs of these insects.; Cranberry is a perennial plant with a native distribution in the sub-arctic bogs of North-Eastern North America. Because the cranberry plant produces more flowers than eventually develop into fruit, it is often assumed by farmers that pollination is limiting. We showed via manual pollination experiments that the cranberry plant produces more flowers than develop into fruit in order to be able to replace fruit lost early in the season. These results support the hypothesis that cranberry plants employ a reproductive strategy that optimizes reproductive effort, allowing for the selection of an optimal size and number of fruit and seeds, as well as to increase the reproductive success via paternal siring of fruit and seeds. Also, for a plant that has evolved in sub-arctic bogs, where springtime climatic conditions can be variable and sometimes extreme, an over-production of flowers may allow for a compensation for fruit lost due to unpredictable events, such as pollination failure, limiting nutrient resources, climatic effects or predation. Our results on cranberry pollination ecology allow us to view cranberry reproduction from an ecological and evolutionary perspective, rather than from its traditionally agricultural interpretation. |
