Longest Tongue of any Insect: New Species is a Prime Example of Coevolution

Sydney Prescott

Many of us are familiar with Charles Darwin’s finches: each species' beak adapted to their unique island's food supplies. This example of evolution, species developing more favorable traits, is a popular one. Coevolution is the reciprocal evolution of interacting species. This often results in species that have become specialized to each other. About 30 years after Darwin’s finch discovery, he received an orchid from Madagascar, known as a Madagascar Star Orchid. With a nectar tube 30 centimeters long, Darwin exclaimed in a letter to a friend: “Good heavens, what insect can suck it!” He theorized that the insect with the ability to pollinate it would be a moth with an extremely long proboscis, or tongue. No moth had yet been discovered, but Dawin was firm in his belief that the orchid had co-evolved with a specific pollinator. Sure enough, in the early 1900s, the Madagascar Star Orchid’s pollinator was discovered. It was classified a subspecies of Xanthopan morganii, an inland species of sphinx moth.

A team of researchers led by Joël Minet, an entomologist at the Institute of Systematics, Evolution, and Biodiversity in Paris examined the genetic and physical differences of this moth. In a September 2021 publication they declared their findings: this moth is not a subspecies of Xanthopan morganii, but its own species, Xanthopan praedicta.

The scientists found a 7.8% difference in the moth’s DNA sequence, proving genetic divergence. They also found 25 physical differences, notably in the wing shape, color patterns, and genitalia shape.

“The underside of the hawkmoth from Madagascar is pinkish, while the underside of the hawkmoth from Africa is whitish or yellowish,” noted David C. Lees, the Natural History Museum curator of moths and one of the study’s authors.

They didn’t find an absolute difference in the proboscis length, but generally, the proboscis of Xanthopan praedicta was much longer than the proboscis of X. morganii, averaging 6.6 cm longer.

This example of an orchid and moth co-evolving is simple and effective proof of Charles Darwin's evolution theory. Over a century after its discovery Xanthopan praedicta, or the predicted Xanthopan, is finally a species in its own right.

References:

Askham, B. (2021, September 30). Moth predicted to exist by Darwin and Wallace becomes a new species. Natural History Museum. https://www.nhm.ac.uk/discover/news/2021/september/moth-predicted-to-exist-by-darwin-and-wallace-becomes-a-new-species.html.

McAlister, Erica (Presenter), Washbourne, Adrian (Producer). (2023, September, 4). Metamorphosis: Jumping fleas and mighty mouthparts [Audio podcast]. Retrieved from https://www.bbc.co.uk/sounds/play/w3ct4nnv.

Minet, J., Basquin, P., Haxaire, J., Lees, D. C., & Rougerie, R. (2021). A new taxonomic status for Darwin’s “predicted” pollinator:Xanthopan praedicta stat. nov. Antenor, French Journal of Lepidopterology, 8(1), 69–86. https://www.researchgate.net/publication/354960755_A_new_taxonomic_status_for_Darwin’s_predicted_pollinator_Xanthopan_praedicta_stat_nov.