A gradient of pollination specialization in three species of Bolivian Centropogon

Abstract

Premise Closely related plant species with overlapping ranges often experience competition for pollination services. Such competition can select for divergence in floral traits that attract pollinators or determine pollen placement. While most species in Centropogon (Campanulaceae: Lobelioideae) have flowers that suggest adaptation to bat or hummingbird pollination, actual pollinators are rarely documented, and a few species have a mix of traits from both pollination syndromes. We studied the pollination biology of a “mixed‐syndrome” species and its co‐occurring congeners to examine the relationship between floral traits and visitation patterns for Centropogon. Methods Fieldwork at two sites in Bolivian cloud forests involved filming floral visitors, quantifying pollen transfer, and measuring floral traits. Stamen exsertion, which determines pollen placement, was measured from herbarium specimens across the geographic range of these species to test for character displacement. Results Results show a generalization gradient, from primarily bat pollination in white‐flowered Centropogon incanus, to bat pollination with secondary hummingbird pollination in the cream‐flowered C. brittonianus, to equal reliance on both pollinators in the red‐flowered, mixed‐syndrome C. mandonis. Pollen transfer between these species is further reduced by differences in stamen exsertion that are accentuated in zones of sympatry, a pattern consistent with character displacement. Conclusions Our results demonstrate that key differences in floral color and shape mediate a gradient of specialization in Bolivian Centropogon. Interspecific pollen transfer is further reduced by potential character displacement of a key trait. Broadly, our results have implications for understanding the hyper‐diversity of Andean cloud forests, in which multiple species of the same genus frequently co‐occur.

Pollination syndromes in the 21stcentury: where do we stand and where may we go?

“…An exciting and unanswered question in this context is whether some pollinator combinations (e.g. hummingbirds and bats, see Lagomarsino & Muchhala, 2019; Dellinger et al ., 2019b) are more likely to evolve into stable bimodal systems (i.e. systems with intermediate adaptations to two distinct functional pollinator groups sensu Goldblatt and Manning, 2006) than others (e.g.…”

Reproductive character displacement and underlying drivers in a species-rich and florally diverse lineage of tropical angiosperms (Ruellia; Acanthaceae)

“…The contribution of RCD to Floral Diversity. In plants, a pattern of increased floral divergence among sympatric compared to allopatric populations of species is well-documented (Whalen 1978;Armbruster et al 1994;Fishman and Wyatt 1999;Coyne and Orr 2004;Muchhala and Potts 2007;Norton et al 2015;Gögler et al 2015;Koski and Ashman 2016;Lagomarsino and Muchhala 2019). In this study, we document clear patterns of reproductive character displacement (RCD) in sympatric species of a diverse lineage of Neotropical plants.…”

Reproductive character displacement and potential underlying drivers in a species‐rich and florally diverse lineage of tropical angiosperms (Ruellia; Acanthaceae)

“…In plants, a pattern of increased floral divergence among sympatric compared to allopatric populations of species has now been shown for various clades (Armbruster et al, 1994;Coyne & Orr, 2004;Fishman & Wyatt, 1999;Gögler et al, 2015;Koski & Ashman, 2016;Lagomarsino & Muchhala, 2019;Muchhala & Potts, 2007;Norton et al, 2015;Whalen, 1978). In this study, we document clear patterns of reproductive character displacement (RCD) in sympatric species of a diverse lineage of Neotropical plants.…”