A New Behavioral Experiment using Computerized Shape Analysis of Actual Flowers

摘要

Variation in corolla shape has been widely observed at inter- and intra-specific levels in entomophilous plants. Many ecologists have focused on this variation in the context of co-evolution of wild plants and their pollinators. The corolla shape is considered to be an important visual cue that attracts their pollinators. However, the ability of pollinators to discriminate among the corolla shapes under natural conditions has not yet been supported by a large body of evidence. This study demonstrates the efficacy of combining a traditional' behavioral experiment with computerized shape analysis of actual flowers. Elliptic Fourier descriptors were used to describe these shapes by transforming coordinate information of the contours into coefficients. Principal components analysis then transformed these coefficients to a smaller number of variables called principal components. Using these methods, artificial flowers were created based on the natural diversity of petal shape in Primula sieboldii and Brassica rapa. Dual-choice tests were then performed to investigate the ability of bumblebees (Bombus ignitus) to detect differences in the aspect ratio of petals. The insects showed significant ability to detect differences in the aspect ratio when the morphological distance increased. Moreover, the bumblebees showed a significant preference for narrow petals in P. sieboldii. The insects also detected differences in this parameter of the B. rapa flowers at close range. The effectiveness of this behavioral experiment was demonstrated using the actual variation present in the corolla shapes of the two plant species. Whether pollinators can discriminate among flowers based on the variation in corolla shape and whether the variation affects pollinator behavior remain fundamental questions regarding the mechanisms responsible for the formation and maintenance of diversity in these characteristics of entomophilous plants. The method proposed here could be useful in answering these questions for many other plants.