Pollinator-Mediated Selection on the Nectar Guide Phenotype in the Andean Monkey Flower, Mimulus Luteus

Abstract

Mimulus luteus (Scrophulariaceae) is a perennial herb occurring in the South American Andes that shows a wide variation in the size and shape of a red spot on the lower lobe of the yellow flower. We describe the preference of four insects (three bees and one butterfly) and one hummingbird species for floral characters, and estimated the strength, direction, and form of pollinator‐mediated selection through female fitness. We applied geometric morphometrics to describe the preference of pollinator species for different guide shapes. Our results revealed striking differences in the floral phenotypes preferred by insects and hummingbirds. Insects visited flowers with corollas 1.25‐fold larger and guides 1.72‐fold larger than the hummingbird species did. While insects preferred flowers with nectar guides pointing toward the corolla tube, the hummingbird preferred flowers with heart‐shaped nectar guides. Most of the floral preferences shown by pollinators translated into significant linear and nonlinear selection coefficients. When selection was analyzed on a per‐flower basis and for female fitness, corolla size was under positive directional selection, and nectar guide size and shape were under disruptive selection. Because the insect and hummingbird pollinators showed a strong segregation in their daily activity time, we suggest that current disruptive selection on the nectar guide phenotype can result from the differential availability of the rewarding floral variants over a day. Our findings suggest that pollinator‐mediated selection favoring extreme phenotypes in M. luteus may not only contribute to high nectar guide variation found in this species, but also can promote divergence of corolla and nectar guide traits.

How plant?animal interactions signal new insights in communication

“…The diverging selection pressures of pollinators and herbivores result in an evolutionary stable flower colour polymorphism [23]. A similar influence of multiple receivers on signal design occurs in the Andean monkeyflower Mimulus luteus, where selection for nectar guides exerted by insect pollinators and by hummingbirds probably leads to the disruptive selection of nectar guide size and shape [24]. Given that intended receivers, such as pollinators, are beneficial to the plant, and unintended receivers, such as Review…”

“…We argue that the evolution of signals is best understood by considering all receivers, especially those with disparate ecologies. Selection pressures by different receivers might result in directional as well as disruptive signal evolution [23,24]. In the wild radish Raphanus sativus, pollinators prefer anthocyanin-recessive white floral colour morphs, but frequencies of anthocyanin-dominant pink morphs remain constant over time.…”

Competition between anthocyanin and flavonol biosynthesis produces spatial pattern variation of floral pigments between Mimulus species

“…Numerous studies have shown that these color patterns are critically important for plant-pollinator interactions (1)(2)(3)(4)(5)(6)(7)(8). Among the most captivating examples are deceptive orchids that display floral pigment patterns remarkably similar to female bees or wasps to lure male counterparts for pseudocopulation, thereby achieving pollination (9)(10)(11).…”

Genetic divergence causes parallel evolution of flower color in ChileanMimulus

“…Their ranges are partially overlapping (vonBohlen, 1995) and they are pollinated by hummingbirds, insects and self-pollination (Medel et al, 2003;Cooley et al, 2008). Mimulus depressus and M. luteus var.…”