Published: Feb. 2, 2014

CU-Boulder researchers lead breakthrough study on microbes in butterfliesRed postman butterfly

Red postman butterfly (Courtesy photo / University of Colorado)

The internal bacterial makeup of a butterfly species through its three major life stages has been genetically sequenced for the first time by a team led by a University of Colorado researcher. "Everyone is familiar with butterflies; everyone knows butterflies," said Tobin Hammer, a doctoral student at the University of Colorado in the department of ecology and evolutionary biology. "This study was coming from the perspective that butterflies are also habitats for communities of bacteria, fungi, viruses and other kinds of microbial life that we don't know anything about." Hammer added, "I think there is a lot of potential for insect microbiomes as a good model system for studying how the human microbiome works." And in general, microbial research on insects could ultimately lead to breakthroughs in treating crop infestation in more effective and environmentally friendly ways, Hammer said. Hammer's research marks the first time anyone has sequenced the internal bacterial makeup of the three major life stages of a butterfly species — from caterpillar to chrysalis to butterfly — and it showed some surprising events occur during metamorphosis.

Microbial changes matched insect's own evolution

A paper on the study by Hammer and his associates of the red postman butterfly, an abundant tropical butterfly found in Central and South America, was published in the Jan. 23 issue of the journal PLOS ONE. Tobin and his colleagues found that as the postman butterfly evolved from caterpillar to pupa to butterfly, the microbial community in the insect went through its own evolution. 

"When the caterpillar becomes the chrysalis, a lot of the internal anatomy is broken down ... and the adults are kind of made from scratch — the host anatomy is kind of simplifying into something new. And that is basically analogous to what's going on in the microbiome," Hammer said. "The microbes simplify in terms of the diversity drops to about half, while the host is undergoing metamorphosis and when the adult emerges from the chrysalis, the diversity has kind of turned back, or returned to the caterpillar. The number of species present in the adult butterflies is about the same as caterpillars, but the types are different — that's the key distinction there."

One of the study co-authors on the paper was Noah Fierer, also of CU's ecology and evolutionary biology department. Fierer is traveling outside of the country, but in a news release, he likened butterflies to "airborne microbial habitats."

"The main question raised by this research is what these microbes are doing inside caterpillars and butterflies to influence their health and behavior," Fierer said. "Now we know that the dramatic shift that occurs as caterpillars turn into active butterflies is matched by large changes in their microbial communities."

Hammer compared the sequencing of the butterfly-associated bacterial DNA to the process used to tag grocery store products. Using powerful gene sequencing techniques, his team collected bacterial DNA from the individual caterpillar, pupa and butterfly stages of the red postman, then used a bar coding method to identify the bacterial DNA sequences.

'Single father to 150 caterpillar children'

He collected the red postman butterflies the old-fashioned way — using a butterfly net, as he rode a bicycle from the research station in Gamboa, Panama, to promising areas of the surrounding rainforest. The data analysis was performed at CU.

"Collecting the butterflies was fun," Hammer said, "but raising the caterpillars was a lot of work, keeping them all fed and happy and clean. They eat a lot of plant material, and they produce a lot of excrement, a lot more than you might imagine. A big part of it is just cleaning up after them."

He added, "At times I felt like I was a single father to 150 caterpillar children. That was a little overwhelming."

Hammer said one reason insects offer rich potential for microbial research is that "there is a whole big mix of the kinds of research approaches that you can do with insects that you can't do with people because of ethical considerations," such as genetic engineering.

He added, "I have heard rumors that there are calls for more regulation for research on invertebrates because honestly right now, you can do whatever you want. With vertebrates, there are really rigorous guidelines."

Co-authors on the paper also included W. Owen McMillan of the Smithsonian Tropical Research Institute in Panama City, Panama.

CU and the National Science Foundation funded the study.