271 — Gene Duplication and Gene Expression Changes Play a Role in the Evolution of Candidate Pollen Feeding Genes in Heliconius Butterflies

Seriously. This is like my favorite recent paper from the lab and I’m retweeting it because I don’t think anyone’s read it. The butterfly proboscis expresses digestive enzymes people!!! It’s not just a straw!!! https://t.co/kdWa4jlEUb pic.twitter.com/7gsUNm8SJW

— Adriana Briscoe (@AdrianaBriscoe) May 16, 2018

I’ve read it!!

Of the many varieties of butterfly, the Heliconius genus is unique in that its adult members commonly eat pollen. Not only do they eat it — the individuals that eat pollen tend to live longer, and stay healthier. Much like the prolonged human expression of lactase, which (sometimes) enables even adults to digest the lactose in milk — these adult butterflies changed something about the way they digest material in order to better glean nutrients from their food.

To better understand this adaptation, the researchers looked to the butterfly genome.

Butterflies tend to produce their digestive enzymes in their salivary glands, wheres several types of moths produce at least one main enzyme — cocoonase — along their proboscis. But this research demonstrates that Heliconius butterflies produce cocoonase across their probosces as well! Using RNA sequencing of both feeding-related and non-feeding-related body parts of both Heliconius and non-_Heliconius_ butterflies, the authors found that there were hundreds of genes that were upregulated in adult pollen-feeding butterflies, many of which appear to code for variants of previously-known digestive enzymes whose expression, in most butterflies, does not persist into adulthood.

Totally unrelated to the thrust of this research, but fascinating to me: I never thought previously about fat tissue in insects. Of course, it makes perfect sense that insects would want to have energy reserves just like other animals, but I never picture fat! Evidently, many species of insects that feed on pollen as larvae convert that protein-rich pollen into fat stores to tap into during adulthood!