Resource Competition Triggers the Co-Evolution of Long Tongues and Deep Corolla Tubes

Abstract

BackgroundIt is normally thought that deep corolla tubes evolve when a plant's successful reproduction is contingent on having a corolla tube longer than the tongue of the flower's pollinators, and that pollinators evolve ever-longer tongues because individuals with longer tongues can obtain more nectar from flowers. A recent model shows that, in the presence of pollinators with long and short tongues that experience resource competition, coexisting plant species can diverge in corolla-tube depth, because this increases the proportion of pollen grains that lands on co-specific flowers.Methodology/Principal FindingsWe have extended the model to study whether resource competition can trigger the co-evolution of tongue length and corolla-tube depth. Starting with two plant and two pollinator species, all of them having the same distribution of tongue length or corolla-tube depth, we show that variability in corolla-tube depth leads to divergence in tongue length, provided that increasing tongue length is not equally costly for both species. Once the two pollinator species differ in tongue length, divergence in corolla-tube depth between the two plant species ensues.Conclusions/SignificanceCo-evolution between tongue length and corolla-tube depth is a robust outcome of the model, obtained for a wide range of parameter values, but it requires that tongue elongation is substantially easier for one pollinator species than for the other, that pollinators follow a near-optimal foraging strategy, that pollinators experience competition for resources and that plants experience pollination limitation.

The long and the short of it: a global analysis of hawkmoth pollination niches and interaction networks

“…This behavioural hedge may be important when long‐tubed flowers are scarce, for example, during seasonal changes and migration (Haber & Frankie ; Amorim, Wyatt & Sazima ) or when competition for long‐tubed flowers becomes significant. Longer proboscis lengths are correlated with larger body size and lower abundance, so that long‐proboscid species may be at a disadvantage in scramble competition with the more species‐rich and individually abundant short‐proboscid species (Rodríguez‐Gironés & Llandres ).…”

The ecological role of extremely long-proboscid Neotropical butterflies (Lepidoptera: Hesperiidae) in plant-pollinator networks

“…Many scientists have pondered over the evolutionary processes that led to the development of particularly elongate proboscides in flower-visiting insects (Darwin 1862;Johnson 1997;Johnson and Anderson 2010;Muchhala and Thomson 2009;Nilsson 1988Nilsson , 1998Pauw et al 2009;Rodríguez-Gironés and Llandres 2008;Rodríguez-Gironés and Santamaría 2007;Wasserthal 1997Wasserthal , 1998Whittall and Hodges 2007). The most widely accepted hypothesis for the evolution of extreme mouthpart lengths is that they coevolved with long nectar spurs of angiosperms.…”

Passive partner choice through exploitation barriers

“…Most existing models of pollen transfer assume that, within a foraging bout, pollinators visit flowers of a single plant species (Galen and Rotenberry 1988;Harder and Thomson 1989;Thomson and Thomson 1992;de Jong et al 1993;Harder and Wilson 1998;LeBuhn and Holsinger 1998;Sánchez-Lafuente et al 2012). Although some computer simulation models study the effect of pollinator flower choices on pollen transfer (Rodríguez-Gironés and Santamaría 2007;Rodríguez-Gironés and Llandres 2008;Muchhala et al 2010), the results of computer simulations are not easily generalised: to predict the effect of using different parameter values it is often necessary to run the simulation again. We therefore derive an analytical expression for the relationship between foraging strategy and pollen flow using as the starting point Sargent and Ottos's (2006) model.…”