While studying the genome of the Heliconius genus of butterflies, researchers at UC Irvine found information not only relating to their abilities to smell and taste, but also the unusual source of their colorful wings. Different species of the Heliconius genus, a brightly colorful family, are able to acquire superior wing colors through crossbreeding.
By studying the way these butterflies use crossbreeding to acquire superior wing colors, researchers hope to learn more about hybridization. Hybridization, which is considered extremely rare in the wild, occurs when members of different species interbreed.
“This study is important because it now suggests that hybridization may be much more widespread than we thought and that it provides a much faster way for species to adapt than by evolving similar traits from scratch,” said Adriana Briscoe, UC Irvine associate professor of ecology and evolutionary biology and study co-author. “The study might prompt other investigators to look for evidence of trait-sharing in other species.”
According to Arthur M. Shapiro, UC Davis professor of evolution and ecology, hybridization can be a creative force in evolution, producing genetic novelties.
“In plants we have long known of and studied, [there is] a phenomenon called ‘introgression’ or ‘introgressive hybridization,’” Shapiro said. “In this case even a very small amount of hybridization can introduce genes from one species into the other, where they act like new mutations; if advantageous, they will spread and increase in frequency.”
This spread of advantageous mutations can thus improve the overall fitness of the recipient species, which is what is happening in the case of the Heliconius butterfly.
“This study is thus a spectacular animal example of something previously known almost entirely in plants,” Shapiro said.
The crossbreeding found in this genus wasn’t the only important finding in their genome. Because the Heliconius butterflies are active in the day and use their wing colors to attract mates and ward off predators, researchers predicted that the butterflies’ senses other than visual would be weakened. Instead, they found that the butterflies’ senses of smell and taste were similar in strength to night-flying moths, which rely strongly on the recognition of pheromones.
“One of the most obvious morphological differences between a moth and a butterfly is in the shape of the antennae, where on a moth there are vastly more hairs for catching odors than on a butterfly,” Briscoe said. “We were surprised when we found similar numbers of genes for smell and taste in both.”
The olfactory similarity between these butterflies and night-flying moths could be considered a backup or supplemental method to the butterflies’ usual visual cues.
“If you are a mimetic butterfly you may also have to rely on smell to identify potential mates when you are surrounded by other butterflies that look like you,” Briscoe said. “Another likely reason is that butterflies have long been in a chemical arms race with their host plants so finding the right kind of food to eat [by using their sense of smell] is crucial for their survival.”
In addition to its implications for hybridization in other species, this study also establishes a precedent in research methods due to the researchers’ use of genomes.
“We were particularly excited by the fact that we were able to sequence the butterfly genome by pooling our money together rather than by obtaining major grant funding for the project,” Briscoe said. “This suggests that it will soon be possible for small research groups to study biodiversity on a genome-wide scale.”
Because genome sequences can show the fundamental genetics of a species, they are especially important in learning about creatures across all natural populations, according to Robert Reed, article co-author and UC Irvine assistant professor of ecology and evolutionary biology, whose lab produced the online database server and genome browser.
“We can learn which genes are involved [in the evolution of ecological traits], how those genes change, and how the genes can even move between populations and species!” Reed said. “This is one of the great frontiers in biology right now — hunting for the specific genetic changes that drive evolutionary change.”
RACHEL KUBICA can be reached at science@theaggie.org.
