Pollination ecology and the floral reward of Vaccinium myrtilloides and V. vitis-idaea (Ericaceae)
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The goals of this research project were to investigate aspects of pollination biology of two native boreal species: Vaccinium myrtilloides (Canadian blueberry) and Vaccinium vitis-idaea (lingonberry) in central Saskatchewan. Accordingly, surveys of insect taxa visiting the flowers were performed, and determination of the effectiveness of these insect taxa to serve as pollinators was measured through pollen deposition and pollen tube growth in the style. Accompanying fieldwork, and morphological and anatomical studies were done for the two food rewards offered by flowers of both Vaccinium species: pollen released through poricidal anthers and nectar secreted from the nectary atop the inferior ovary. Pollen-ovule (P/O) ratios were determined for the two study species in Saskatchewan (V. myrtilloides, V. vitis-idaea) as well as for five other Vaccinium species from eastern Canada (Nova Scotia – V. angustifolium, V. boreale, V. caespitosum, V. corymbosum, and V. uliginosum). Pollen, released at maturity as tetrads, were converted to total pollen grains per flower to yield P/O ratios ranging from 238 (V. caespitosum) to 2,008 (V. vitis-idaea), but 736 for the latter in Saskatchewan. These P/O ratios are indicative of a breeding system ranging from facultative autogamy to facultative xenogamy. Additionally, the structure of mature stamens and pollen tetrads was studied in V. myrtilloides and V. vitis-idaea. Each anther was functionally bilocular; had a single-cell thickness (i.e., epidermis) with regularly occurring papillae; lacked an endothecium; and possessed two distal, hollow tubules each terminating in a pore. Overall pollen grain viability was 76-97% (V. myrtilloides) and 51-93% (V. vitis-idaea), with about 20% of tetrads having only 1-3 grains viable, and 12% and 27% of tetrads entirely non-viable in V. myrtilloides and V. vitis-idaea, respectively. Pollen tetrads occasionally were connected by a sticky substance resembling pollenkitt, but viscin threads were absent. One instance of precocious (in situ) germination of tetrads was recorded within anthers of V. myrtilloides. The floral nectary was a disk of secretory tissue situated between the stamens and the style. The epidermis possessed solitary stomata that were variable in number, but not different between V. myrtilloides and V. vitis-idaea. The nectary was vascularized by phloem alone; many traces were found for V. myrtilloides throughout the nectary, whereas V. vitis-idaea had few traces at the nectary base, concentrated at the inner side of the disk closest to the style base. Young sclerenchyma cells were found throughout the nectary parenchyma. Nectar production started on the day of anthesis for both species, although many flowers of V. vitis-idaea appeared to have no measureable nectar at that time. V. myrtilloides produced a larger range of nectar solutes per flower (0 - 3684.1 μg), than V. vitis-idaea iii (1.29 to 1147.62 μg) over both years; nectar volumes per flower never exceeded 5 μL. Nectar was measured daily in flowers aged 1 – 4 days in 2010 and 1 – 6 days in 2011, however, over the two years at the same study site there was no clear pattern of secretion and reabsorption throughout flower life for V. myrtilloides, and only a gradual increase for V. vitis-idaea as flowers aged. Insect visitors to flowers surveyed in 2010 included a large proportion of honeybees (Apis mellifera) as visitors to both species, whereas in 2011 there were no honeybees present at the field site. There was a larger proportion of hoverflies (Syrphidae) found on the flowers of V. vitis-idaea than on V. myrtilloides. Other visitors to V. myrtilloides were bees (Bombus, Andrena, Osmia, Colletes) and wasps (Vespidae), whereas flowers of V. vitis-idaea were visited by bees (Bombus, Andrena, Osmia, Lasioglossum, Colletes, Hylaeus), an ant (Formicidae) and a butterfly (Lycaenidae). Bombus spp. were shown to be pollinators of V. myrtilloides. Andrena spp. were probable pollinators, whereas honeybees appeared to be poor pollinators. Bombus spp. seemed probable pollinators of V. vitis-idaea and hoverflies to be barely more than visitors, though small sample sizes did not allow for conclusive evidence. The time that an insect spent on a virgin flower had no relationship to the pollination result. Among individuals of various Bombus spp. that did or did not sonicate flowers of V. myrtilloides, the action of “buzz pollination” was shown to result in an increase in the number of pollen tetrads deposited and in pollen tube growth.
DegreeMaster of Science (M.Sc.)
CommitteeSawhney, Vipen; Gray, Jack; St. Pierre, Richard
Copyright DateJune 2012
poricidal anther structure