Minimum size threshold of visiting bees of a buzz‐pollinated plant species: consequences for pollination efficiency

Abstract

PREMISE Flowering plants with poricidal anthers are commonly visited by buzzing bees, which vibrate flowers to extract pollen. However, not all flower visitors are in fact pollinators, and features such as body size and duration of flower visits are important factors in determining pollination effectiveness. We tested whether bee‐to‐flower size relationships predict the pollination effectiveness of flower visitors of a buzz‐pollinated species (Chamaecrista ramosa, Fabaceae). METHODS We sorted 13 bee taxa into three groups: smaller than, equivalent to (“fit‐size”), and larger than flower herkogamy (spatial separation between anthers and stigma). We expected the latter two groups to touch the stigmas, which would be an indicator of pollination effectiveness, more frequently than the first group. To test this hypothesis, we assessed contact with stigmas, foraging behavior, and duration of visits for the three size groups of bees. RESULTS Our data reveal that small bees scarcely touched the stigmas, while large and fit‐size bees were the most efficient pollinators, achieving high stigma‐touching rates, conducting much shorter flower visits, and visiting flowers and conspecific plants at high rates during foraging bouts. CONCLUSIONS The results did not show size‐matching among bees and flowers, as expected, but rather a minimum size threshold of efficient pollinators. The finding of such a threshold is a nonarbitrary approach to predicting pollination effectiveness of visitors to herkogamous flowers with poricidal anthers.

Anther cones increase pollen release in buzz‐pollinated Solanum flowers

“…Bees that are relatively large compared to the flower they visit should be capable of such manipulation, although quantitative evidence of this behavior remains scarce. At the same time, the evolution of loosely held anthers might be favored when buzzing bees can remove pollen from only one or a few anthers but only infrequently contact the stigma, such as when the bees are relatively small compared to the flower (Li et al 2015;Solis-Montero and Vallejo-Marin 2017;Telles et al 2020;Mesquita-Neto et al 2021). In this context, loosely held anthers that reduce vibrations being transmitted to nonfocal anthers (as shown in our study) would simultaneously reduce pollen wastage and pollen theft.…”

“…2020; Mesquita‐Neto et al. 2021). In this context, loosely held anthers that reduce vibrations being transmitted to nonfocal anthers (as shown in our study) would simultaneously reduce pollen wastage and pollen theft.…”

Heteromorphic stamens are differentially attractive in Swartzia (Fabaceae)

“…The stamens and carpels of S. simplex are larger than those of S. flaemingii , being hard to the smaller bees to have body contact with the stigma when collecting pollen. The separation distance between stigma and anthers seems to impose a threshold of minimum size on the bee’s body so that it can be effective in the role of pollinator (see Mesquita-Neto et al 2021 ). Thus, Pinheiro et al (2018) consider that only large bees (>20 mm, e.g.…”

Stigmas arrangement, reproductive system, and maternal reproductive success in two species of Stigmaphyllon (Malpighiaceae): does pollinator size matter?

“…According to Ne'eman et al (2010) the efficiency of a pollinator is based on how much it contributes to reproductive success and for this it is necessary to consider seed set under the given resource constraints of the plant. In addition, different species of pollinators can vary in effective pollen deposition and removal (Schemske and Horvitz 1984;Herrera 1987;Young and Stanton 1990;Wilson and Thomson 1991), with large pollinators being expected to have high visitation rates according to their energy requirements (Casey et al 1985;Harder and Barclay 1994;Mesquita-Neto et al 2021). In general, the size of a pollinator seems to be a particularly strong determinant of their efficiency (Mesquita-Neto et al 2021).…”

“…In addition, different species of pollinators can vary in effective pollen deposition and removal (Schemske and Horvitz 1984;Herrera 1987;Young and Stanton 1990;Wilson and Thomson 1991), with large pollinators being expected to have high visitation rates according to their energy requirements (Casey et al 1985;Harder and Barclay 1994;Mesquita-Neto et al 2021). In general, the size of a pollinator seems to be a particularly strong determinant of their efficiency (Mesquita-Neto et al 2021). However, although numerous studies showed that Malpighiaceae species are pollinated by several species of oil-collecting bees (Vogel 1974;Sazima and Sazima 1989;Barros 1992;Sigrist and Sazima 2004;Vilas Boas et al 2013;Sazan et al 2014;Torretta et al 2017;Aliscioni et al 2018among others), few studies reported any information regarding about differences in pollinator body size (Vilas Boas et al 2013;Sazan et al 2014;Baro ˆnio and Torezan-Silingardi 2017;Torretta et al 2017;Aliscioni et al 2018).…”