Acacia Tree Ants Symbiotic Relationship

A founding queen acacia-ant cuts her outset archway hole into the swollen thorn in which she volition showtime her colony, the first thorn made by this immature bulb pismire-acacia in Veracruz, United mexican states, 1962.

Dan Janzen

During his doctoral studies in the 1960s, Dan Janzen, now Thomas M. and Louise E. DiMaura Term Chair in the Section of Biology, re-described what has become a archetype instance of biological mutualism: the obligate relationship between acacia-ants and their host acacia trees. The acacia trees produce specialized structures to shelter and feed the emmet colony, and the ants, in turn, defend the tree against herbivores.

In a recent study in Proceedings of the National Academy of Sciences, colleagues of Janzen'due south in the biology section uncover a genetic machinery that programs the institute side of the ant-acacia relationship. Scott Poethig, the John H. and Margaret B. Fassitt Professor of Biology, and Aaron Leichty, GR'18, showed that these species of acacia develop the traits necessary to feed the ant colony—hollow swollen thorns to firm them, and nectaries and food-rich leaflet tips chosen Beltian bodies to feed them—equally part of an historic period-dependent miracle in institute development.

"At that place is a cost associated with making these traits," says Poethig, senior writer on the report, "simply the found needs them, otherwise it's a goner. Then in that location's a tradeoff happening. And what we constitute is that these traits seem to accept evolved on the back of a preexisting pathway that governs a developmental transition in plants."

Leichty, now a postdoctoral researcher at the University of California, Davis, says, "When nosotros dug into the literature, we found that a lot of establish defense force strategies are age-dependent. It's counterintuitive because you lot think the immature plants would want to commencement making these structures right abroad so they wouldn't go eaten, but our findings too as profound logic advise there are biological constraints on making them."

To study the traits in the context of establish development, Poethig and Leichty gathered acacia seeds from online sellers in Belize and from Janzen himself. They observed what Janzen had seen in the wild a half-century before.

"Sure enough, the traits announced, but not right away," Leichty says.

Later on obtaining the commencement genome sequence of a Vachellia species, the researchers looked specifically at certain microRNAs —short, not-coding sections of the genome—miR156 and miR157, which they had previously found to exist associated with controlling the developmental timing of traits in other found species.

As the bloated thorn and other ant- attracting traits began to appear in the acacia, levels of miR156 and miR157 declined, and the levels of unlike protein transcription factors repressed by these microRNAs increased.

To get a sense of how the regulation of these traits may accept arisen evolutionarily, the researchers explored other acacia species that do not make Beltian bodies or swollen thorns but exercise make nectaries on their leaves. In these species, equally in the ant-acacias, miR156's decline coincided with the advent of the nectaries. The similarity among the acacias in this regard suggests that the existing pathway was coopted to regulate the other traits that are required for a good for you bodyguard—swollen thorns and good nutrient—the researchers say.

To Janzen, the finding is supportive of his field discoveries, making a instance for the blending of field and lab investigations.

"I watched and asked why," says Janzen. Of Poethig and Leichty, he notes, "They watched and asked how."