Ant have been eating plants for millions of years, but eventually, plants developed a feature system that allowed them to use ants for profit.
Over time, plants have evolved to produce nectar that attracts ants and hollow spines that ants can use to shelter. Sometimes, the ants will even keep the plant against the attack or help spread the seeds of the plant.
This is a mutually beneficial relationship and an example of how complex interactions between two organisms evolve over time.
Researcher from Field Museum do research to better understand this evolutionary relationship and to find out which organisms begin interactions, plant features or find ants.
"This is a chicken-and-egg question, whether things start with ants developing behavior to take advantage of plants, or plants that evolve structures to take advantage of ants," said Rick Ree, a study author.
This study was published in the journal Proceedings of the National Academy of Sciences and the researchers reviewed the genetic history of 1,700 ant species and 10,000 plant genera.
Ants and plants return to the age of dinosaurs, but studying ancient interactions is difficult because there is little evidence of fossil relationships between plants and ants.
"There are only a few fossil records of these structures in plants, and they don't extend far into the past. And there are a lot of ant fossils, but they don't usually show the behavior of these ants – we don't need to see ants preserved in amber carrying seeds, "said Matt Nelsen, lead author of the study.
To help improve the information gap, researchers examined and analyzed DNA and ecological databases to retrace the genetic history of various plant features.
Mapping the history of ant-friendly properties in plants, the researchers found that plants evolved this interesting feature in response to foraging ants. It turns out that ants have relied on plants for longer than plants rely on ants.
"Some ants don't directly use plants for much, while others depend on them for food, habitat foraging, and nesting," Nelson said. "We found that to be fully invested in the use of plants, the ants first began to forage around them, then put the plants into their food, and then from there, they began to nest in the stomach. While a gradual shift towards increasing dependence on plants is intuitive, it still surprises us. "
Plants seem to benefit more from this relationship, because the researchers found that ants that depend on plants are no better, evolutionarily, than other ant species that do not forage or nest in plants.
"We don't see part of the ant family tree that includes ants that depend on plants for diverse food or habitat or grow faster than parts of the tree that do not have this interaction," Nelsen said. "This study is important because it provides a glimpse of how this vast and complex interaction evolved."
By Kay Vandette, Earth.com Staff Writer
Image Credit: (c) Field Museum, Corrie Moreau