A few issues back Martin Epstein wrote:
It is generally assumed that orchids and their pollinators co-evolve and therefor orchids come to rely on a single pollinator, or a few related pollinators, to propagate in their native habitats.
Actually, I don't think that many, if any, orchids and their pollinators co-evolve. Most orchids are pollinated by deception. They trick the pollinator by appearing to provide a reward when in fact they don't. Some orchids look and smell quite similar to other flowering plants that live nearby and do offer a reward. They get pollinated because the bee or other pollinator mistakes them for the rewarding flower. Others appear to provide a good spot for laying eggs - prominent bumps that look like previously deposited eggs (Paphs? Maybe someone can help me with this). Others, and we've all heard about these, lure male bees or flies with the promise of sex - but no reward is actually awaiting the duped males! If these cases are correctly understood, the insects can't co-evolve with the orchids. They get no advantage from being more easily tricked. The pollinators actually make their living from visiting rewarding flowers or real egglaying sites or real females.
Since a few orchids do reward their pollinators with nectar or fragrant oils there is a possibility of co-evolution. One could imagine, for example, that the long-tongued moth that Darwin predicted would pollinate Angraecum sesquipedale would be at an advantage because it has a long enough tongue to reach the tip of the spur on A. sesquipedale. The only evidence I know of shows that the long spur is, in fact, advantageous to the orchid, but I don't know that anyone has tested whether the long tongue (proboscis) is advantageous to the moth because it can drink from A. sesquipedale. It might be that the long tongue is beneficial to the moth because it works well for other food sources. In any case, a noted orchid biologist once admonished me that there is no evidence for orchid-pollinator co-evolution.
Steve Beckendorf -- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Steven K. Beckendorf Professor of Genetics and Development Department of Molecular and Cell Biology University of California 16 Barker Hall Berkeley, California 94720-3204 USA
Phone (510) 642-7906 Fax (510) 643-6334 Email [EMAIL PROTECTED]
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