Previous studies have examined an association between reproductive success and pollination biology of rare versus widespread species through pair-wise comparisons of native and invasive congeners or rare and common congeners. To determine the importance of reproductive success and pollination biology for an invasive thistle, Cirsium vulgare, we compared it in its invaded range to five, co-occurring native Cirsium species that range from rare to common. Native study species include C. fontinale var. fontinale, C. andrewsii, C. brevistylum, C. occidentale, and C. quercetorum. We compared all species' reproductive success, insect visitation rate and composition, autonomous selfpollination, and level of pollen limitation in multiple populations. Species differed in their reproductive success; the invasive C. vulgare produced more flower heads per plant than most native species. C. vulgare attracted more visitors than its congeners. In addition, reproductive success and insect visitation significantly varied between populations within species, mainly due to aphid infestation in one population of C. occidentale. Unlike the rare species (C. fontinale and andrewsii), C. vulgare did not require a pollinator for high-levels of seed production. The remaining native species set fewer seeds than C. vulgare without a pollinator. However, differences in insect visitation and autonomous selfpollination did not lead to differences in pollen limitation across species or between populations. This result suggests that factors other than pollination biology determine the difference in reproductive success of these species. However, high levels of autonomous self-pollination and generalist insect visitation may allow the invasive C. vulgare to easily establish new populations from low numbers of propagules. Our study provides one contrast that should build towards a larger comparative analysis to examine general patterns in the relationship between reproductive success, pollination biology, rare and invasive species, and our ability to predict biological invasions in introduced species.
The long-recognized genus Gaura was shown recently to be deeply nested within one of two major clades of Oenothera. New molecular data indicate further taxonomic changes are necessary in Oenothera sect. Gaura. We make these changes here, including three new combinations, in advance of the Onagraceae treatment for the Flora of North America. The new phylogenetic studies show that several pairs of taxa treated as subspecies in the most recent revision by Raven and Gregory (1972) had independent origins within sect. Gaura, and are here elevated to species level (Oenothera nealleyi for Gaura suffulta subsp. nealleyi; Oenothera dodgeniana for Gaura neomexicana subsp. neomexicana; and Oenothera podocarpa for Gaura hexandra subsp. gracilis). Also, a nomenclatural problem in Oenothera sect. Calylophus is corrected by adopting the name Oenothera capillifolia Scheele for the species known previously, and nomenclaturally correct, as Calylophus berlandieri Spach. This problem necessitates a new combination Oenothera capillifolia subsp. berlandieri.
Pollinators are considered a major selective force in shaping the diversification of angiosperms. It has been hypothesized that convergent evolution of floral form has resulted in “pollination syndromes” - i.e. suites of floral traits that correspond to attraction of particular pollinator functional groups. Across the literature, the pollination syndrome concept has received mixed support. This may be due to studies using different methods to describe floral traits and/or the pollination syndrome concept being supported more often in species highly reliant on pollinators for reproduction. Here, we assess the predictive ability of pollination syndromes in Oenothera, a species rich clade with pollination systems existing on a gradient of specialization, and in which species are either self-compatible or self-incompatible. We ask the following questions: Do Oenothera species follow the pollination syndrome concept using traditional, categorical floral trait descriptions and/or quantitative floral trait measurements? And, are floral traits more predictive of primary pollinators in species with specialized pollination systems and/or species that are self-incompatible? Mapping floral traits of 54 Oenothera species into morphospace, we do not find support for the pollination syndrome concept using either categorical or quantitative floral trait descriptions. We do not find support for specialization or breeding system influencing the prediction of primary pollinators. However, we find pollination syndromes were more predictive in Oenothera species with moth pollination systems. Collectively, these results suggest that the pollination syndrome concept cannot be generally applied across taxa and that evolutionary history is important to consider when evaluating the relationship between floral form and contemporary pollinators.
brackenridgei A. Gray, was investigated on Kauai, HI. The presence of extra floral nectar appears to maintain the beetle presence on the plant. Because coccinellid beetles are predators on insects that are damaging to plants, beetle presence may increase plant fitness. Beetles were found feeding heavily on the extra floral nectaries of the Hibiscus. An examination of the beetle mouth parts with scanning electron microscopy revealed no structures specifically adapted for the consumption of nectar. The sensory ability of the coccinellids was tested to determine if they respond to visual or olfactory cues to detect the nectar. Studies with an eight-armed air-flow olfactometer concluded there was no olfactory cue. Tracing the pathways of beetles in laboratory experiments yielded results that suggest a visual cue. The extra floral nectaries are concluded to be a potential mechanism to maintain beetle presence on a plant to provide defense against herbivores.
Experimental hand pollinations of the endangered, Hawaiian, endemic, Gossypium tomentosum Nutt. Ex. (Malvaceae) showed that it was self-compatible, but self-pollination resulted in reduced reproductive output. Field observations and pollen tube analyses using fluorescence microscopy showed that mechanical self-pollination in this species included a mechanism known as bending stigmas. A receptive stigma bent backwards and contacted dehiscent anthers in 7% of flowers found on 17 G. tomentosum plants. The yellow flowers were nectarless and were not visited by most anthophilous insects in situ except for the introduced, nitidulid beetle, Aethina concolor Macleay. Collections and insect GI-tract dissections showed that A. concolor carried and ate the pollen of the host flower. Field observations recorded regular contact between beetles and stigma lobes as these insects exited the flowers effecting selfpollination. Behavioral experiments showed that the beetles responded positively to a yellow visual cue. Under some circumstances, an introduced pollen vector may help maintain a low level of reproductive success in an insular endemic.
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