Essential for mimicry is the production of a false signal (visual, olfactory and/or tactile) that is used to mislead the operator, resulting in a gain in fitness of the mimic. One of the deceptive strategies is mimicry, defined as the close resemblance of one living organism, ‘the mimic’, to another, ‘the model’, leading to misidentification by a third organism, ‘the operator’. Pollinators can either receive nectar, oil, pollen or shelter in return for pollen transfer in a rewarding relationship, or nothing at all in a deceptive relationship. These genetic changes are not incorporated in current models and urge for a rethinking of the evolution of deceptive flowers.įlowering plants interact with a wide range of other organisms including pollinators. pusilla to mimic an unrelated rewarding flower for pollinator attraction. Duplications, diversifying selection and changes in spatial expression of different MADS-box genes shaped these organs, enabling the rewardless flowers of E. pusilla appear to be derived from a sepal, a stamen that gained petal identity, and stamens, respectively. The median sepal, callus and stelidia of E. Another copy of AGAMOUS, EpMADS20, and the single copy of SEEDSTICK, EpMADS23, are most highly expressed in the stelidia, suggesting EpMADS22 may be required for fertile stamens.
Out of three copies of AGAMOUS and four copies of SEPALLATA, EpMADS22 and EpMADS6 are most highly expressed in the stamen. AGAMOUS is not expressed in the callus, consistent with its sterilization. Six vascular bundles, indicating a stamen-derived origin, lead to the callus, stelidia and stamen. AGL6 EpMADS5 and APETALA3 EpMADS13 are most highly expressed in lip and callus, consistent with current models for lip identity. A vascular bundle indicating second whorl derivation leads to the lip. Expression of AGL6 EpMADS4 and APETALA3 EpMADS14 is low in the median sepal, possibly correlating with its petaloid appearance. The vascular bundle of the median sepal indicates it is a first whorl organ but its convex epidermal cells reflect convergence of petaloid features.
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The evolutionary origin of these organs was investigated using a combination of morphological, molecular and phylogenetic techniques to a developmental series of floral buds of E. Different hypotheses exist about the evolutionary origin of the median sepal, callus and stelidia of orchid flowers. pusilla has a ‘callus’ that, together with winged ‘stelidia’, mimics these glands. These bees also forage on similar looking but rewarding Malpighiaceae flowers that have five unequally sized petals and gland-carrying sepals. Rewardless flowers of the orchid Erycina pusilla have an enlarged median sepal and incised median petal (‘lip’) to attract oil-collecting bees. Thousands of flowering plant species attract pollinators without offering rewards, but the evolution of this deceit is poorly understood.