Direct selection at the blossom level on floral reward by pollinators in a natural population of Dalechampia schottii: full-disclosure honesty? Geir H. Bolstad, W. Scott Armbruster, Christophe Pélabon, Rocío Pérez-Barrales and Thomas F. Hansen
Summary Author for correspondence: Geir H. Bolstad Tel: +47 92 03 76 65 Email: geir.bolstad@bio.ntnu.no
New Phytologist (2010) 188: 370–384 doi: 10.1111/j.1469-8137.2010.03429.x
KEYWORDS: Dalechampia schottii, fitness function, euglossine bees, multivariate selection, natural selection, pollination, selection gradient.
Both floral rewards and advertisements can be important in the attraction of pollinators, but few studies have separated the individual contributions of rewards and advertisements to fitness. Here, we investigated selection by pollinators on individual blossoms in Dalechampia schottii. This Neotropical vine, endemic to the Yucatán Peninsula, rewards bees by secreting fully visible, deep-blue resin from a gland subtended by two conspicuous petaloid bracts that may play the role of advertisement. We used contextual analysis to build a fitness function for four morphological traits of individual blossoms: the amount of the reward as measured by gland area; the size of the advertisement trait as measured by bract length; the flower-pollinator fit as measured by the shortest distance between reward and stigma; and the potential for self-pollination as measured by the shortest distance between anthers and stigma. Larger gland area and increased potential for self-pollination directly increased the seed production of individual blossoms. However, bract size or flower-pollinator fit did not influence the number of seeds produced by blossoms. Therefore, in this Dalechampia species, pollinators seem to select directly on the reward of individual blossoms but not on the advertising bracts.