Evolutionary arms race stretches hawkmoths and flowers to extremes

Hawkmoths have evolved different feeding strategies. While some species have long proboscises they use to drink nectar from specialized flowers, others have short ones that give them access to a wider variety of floral food sources. Some have no proboscises and rely entirely on energy stored during their larval stage.
In a new study, researchers determined how and when these structures evolved by sequencing DNA and measuring the proboscises of 310 hawkmoth species. The results show that proboscises have repeatedly grown and shrunk over the last 44 million years in response to environmental pressures and latitudinal gradients.
Hawkmoths have historically been remarked upon by naturalists like Charles Darwin and Alfred Russel Wallace because of an evolutionary arms race that sometimes forms between them and the flowers they rely on for food. As the moths develop longer proboscises to feed on nectar, flowers evolve deeper nectar tubes to ensure the moth continues to pick up pollen, driving both toward an extreme and mutual dependence.

Long before his days of research, Christian Couch was just a kid marveling at the butterflies in the Florida Museum of Natural History’s Butterfly Rainforest. Years later, after enrolling as an undergraduate student at the University of Florida, that same sense of wonder led him back to the museum, first as a volunteer in the Kawahara Lab and eventually as a master’s student studying the insects that first inspired him.

“When I started college, I knew I wanted to volunteer in the Florida Museum because I thought it was a really special place,” Couch said. “When I found out I could do research with butterflies and moths, I was even more excited.”

Couch recently published the results of his master’s thesis in the Royal Society Open Science journal, in which he and his colleagues map out the evolutionary history of hawkmoths. This group is well known for their unusually long proboscises, the strawlike tube that many moths and butterflies use to drink nectar from flowers. One species, Darwin’s Hawkmoth (Xanthopan praedicta), has evolved to feed on a particular orchid in Madagascar using a specialized, foot-long proboscis, which is longer than that of any other known species.

But other hawkmoth species have opted for a more measured approach.

“There are different strategies of survival. Some species of hawkmoths have an extraordinary long tongue that is very important for gaining nectar and pollinating the plant, but other hawkmoths have almost no proboscis,” said the study’s senior author, Akito Kawahara, director of the Florida Museum’s McGuire Center for Lepidoptera and Biodiversity.