Year of the Sphingidae – Co-Evolution

Co-evolution is a term to describe what happens when two (or more) species influence one another’s evolutionary pathways. Plants and pollinators represent a classic case of co-evolution. One of the most famous examples of co-evolution of all time involves an orchid, a hawkmoth and none other than Charles Darwin.

First, the orchid: 

Angraecum sesquipedale, the Madagascan star orchid, is a species endemic to Madagascar. It was first discovered in 1798 by French botanist Louis-Marie Aubert du Petit-Thouars. The flower is bright white and has a nectar spur that is nearly a foot long. A nectar spur is a long tubular part of a flower that houses nectar at the very bottom. In flowers that feature nectar spurs, only pollinators with beaks or probosces long enough to reach to the bottom are able to drink nectar and pollinate the flower.

A. sesquipedale, note the long, curved green nectar spur. Photo via Wikimedia commons

In 1862, years after Thouars discovered it, Darwin was sent a specimen of the orchid. He famously wrote in a letter to a friend, “Good heavens, what insect can suck it?!” Then in his book, On the Various Contrivances by which British and Foreign Orchids are Fertilised by Insects, he predicted that there must exist an insect with a proboscis long enough to reach to the base of the nectar spur. He had no idea what insect but he thought a sphingid would be a likely candidate given that many species possess long probosces.

Now, the moth:

X. morganii praedicta with proboscis extended. Photo via Wikimedia commons.

In the 1830s, entomologists had discovered a sphinx moth in Africa with a very long proboscis, but it wasn’t until 1903 that one was discovered from Madagascar. The entomologists describing it named the moth Xanthopan morgani praedicta in honor of Darwin’s prediction.

BUT an interaction between the orchid and hawmoth had not yet been witnessed by humans. In 1992 an X. morganii praedicta was found carrying A. sesquipedale pollinia (orchid pollen packets) confirming it as a visitor to the orchid. That same year – one hundred and thirty years after Darwin’s original prediction, a team of entomologists led by L.T. Wasserthal of the University of Erlangen (Germany) witnessed the moth visiting the orchid. In 2004, the interaction was captured on video by Philip DeVries of the University of New Orleans.

National Moth Week 2015 (July 18-26) is just around the corner! Register a public or private event here.

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