FLORAL PAEDOMORPHY LEADS TO SECONDARY SPECIALIZATION IN POLLINATION OF MADAGASCAR DALECHAMPIA (EUPHORBIACEAE)

Authors

  • W. Scott Armbruster,

    1. School of Biological Sciences, University of Portsmouth, Portsmouth PO1 2DY, United Kingdom
    2. Institute of Arctic Biology, University of Alaska, Fairbanks, Alaska 99775
    3. Department of Biology, NTNU, NO-7491 Trondheim, Norway
    4. E-mail: scott.armbruster@port.ac.uk
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  • Joongku Lee,

    1. Department of Integrative Biology and Jepson Herbarium, University of California, Berkeley, California 94720
    2. Current address: Korea Research Institute of Bioscience and Biotechnology, 125 Gwahak-ro, Yuseong-gu, Daejeon 305-806, South Korea
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  • Mary E. Edwards,

    1. Geography and Environment, University of Southampton, Southampton SO17 1BJ, United Kingdom
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  • Bruce G. Baldwin

    1. Department of Integrative Biology and Jepson Herbarium, University of California, Berkeley, California 94720
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Abstract

The traditional evolutionary interpretation of Von Baer's “laws” of embryology is that retention of early developmental forms into adulthood (paedomorphosis) leads to the evolution of simpler or more generalized morphology and ecology. Here we show that paedomorphosis can also be involved in an increase in ecological specialization, in this case of plant–pollinator relationships. A paedomorphic transition from generalized pollination (by several functional types of pollinators) to specialized pollination (by one or a few species in one functional type) occurred in a clade of endemic Madagascar vines (Dalechampia spp., Euphorbiaceae). This evolutionary transition involved staminate flowers that fail to develop “normally,” instead holding mature pollen inside virtually unopened, bud-like flowers. This paedomorphic morphology restricts reward access to “buzz-pollinating” bees, including Xylocopa species (carpenter bees), which can remove pollen by sonication. This is one of very few reports of paedomorphic specialization, and, as far as we are aware, the first documented case of a rapid reversal to specialized pollination in a lineage of plants that had previously switched from specialized to generalized pollination in conjunction with dispersing to a new region.

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