Pollinator visitation and female reproductive success in two floral color morphs of Ipomoea aquatica (Convolvulaceae)
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ORIGINAL ARTICLE
Pollinator visitation and female reproductive success in two floral color morphs of Ipomoea aquatica (Convolvulaceae) Piriya Hassa1 · Paweena Traiperm1 · Alyssa B. Stewart1 Received: 21 June 2020 / Accepted: 30 September 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract Differences in floral morphology are often hypothesized to stem from selection by different pollinators. Thus, the presence of multiple floral color morphs within a species might indicate visitation by different pollinator species. To test this prediction, we examined Ipomoea aquatica Forssk., a morning glory species with a “white” morph (all-white flowers) and a “purple” morph (white corolla lobes with purple corolla tubes). We studied this species in Nong Khai, Thailand, where some populations are monomorphic for a single color and others are polymorphic. We compared (a) animal visitation rates to each morph; (b) visitor and pollinator community composition at each morph; and (c) the female reproduction of each morph. Visitation rates were obtained from camcorder footage and used to analyze community composition. Female reproduction was assessed from a pollination experiment with five treatments (open, open emasculation, hand-cross, hand-self, and closed). We found that the main pollinators (bees and butterflies) visited both morphs, and that overall insect community composition to the two floral colors did not differ significantly. Moreover, we found that I. aquatica is capable of spontaneous autogamy but still benefits from pollinators, as flowers in the closed treatment set significantly fewer seeds than flowers in the open and hand cross-pollinated treatments. When comparing female reproduction between morphs, we did not find significant differences for either fruit set or seed set. These findings suggest that floral visitors interact with the two morphs similarly, and that the high-reproductive success experienced by both colors may help maintain the polymorphism in nature. Keywords Bees · Insects · Pollination success · Polymorphism · Thailand
Introduction The enormous diversity of floral forms observed in nature is hypothesized to stem from strong selection imposed by pollinators (Grant 1949; Stebbins 1970; Eriksson and Bremer 1992; but see Ellis and Johnson 2009). Such strong selection is unsurprising given the direct impact that pollinators have on plant reproductive success (Klein et al. 2006; Ollerton et al. 2011). In some instances, we even find diverse floral forms within a single plant species, such as when two or Handling Editor: Thais N. C. Vasconcelos. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00606-020-01716-1) contains supplementary material, which is available to authorized users. * Alyssa B. Stewart [email protected] 1
Department of Plant Science, Faculty of Science, Mahidol University, Bangkok 10400, Thailand
more floral color morphs occur (Rausher 2008). Polymorphism refers to the presence of two or more morphs
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