Plants are boring. They just sit there for photon synthesizing while animals are having fun. Right? Not so much. Take a look at the interactions between ants and plants – plants have been developed specifically to make them attract ants, such as juicy nectar to the insects to eat and hollow roofs for protection. In exchange, plants use ants to spread their seeds and even act as bodyguards. A new study in Negotiations by the National Academy of Sciences breaking down the genetic story of 1700 species of ants and 10,000 plant genera, and the researchers found that the long history of ant and plant development began with ants that fed plants and plants, which later responded to the development of anti-friendly properties.
"My main concern is to study how interactions between organisms have evolved and how these interactions form their evolutionary history. When did ants begin to use plants, and when did plants begin to make ants for ants?" says Matt Nelsen, a field museum after doctoral researcher and the main author of PNAS study.
"There are a number of different structures that make plants that are specific to ant use," explains Nelsen, who led the study with his colleagues Field Museum researchers and co-authors Rick Ree and Corrie Moreau. "Some plants have developed properties that convince ants to defend them from attack from other insects and even mammals. These include hollow tags that ants will live inside or extra nectar on leaves or stalks for the ants to eat. Some ants come just cheating and taking nectar and running, but some will hold on and attack everything that tries to hurt the plant, explains Nelsen. Other plants get ants to help them move their seeds around by replacing them with rich food packages linked to seeds called elaiosomes. "The ant takes up the seed and carries it away, eats the food package and discards the seed – often in a nutritional area where it gets better and because it's farther away from its parent they won't have to compete for resources."
But researchers were not sure how the evolutionary relationship between ants and plants began. If evolution is an arbitration between species that develop ways to benefit from their neighbors, scientists would know if plants or ants kicked the first shot. "It was a matter of chicken and eggs, if it started with ants that develop behaviors to take advantage of plants or plants that develop structures to take advantage of ants," says Ree, plant master at the Field Museum.
The history of ants and plants developed together goes back to the era of dinosaurs, and it is not easy to tell from fossils how the organisms interacted. "There are very few fossil records of these structures in plants, and they do not extend much back in time. And there are lots of bog fossils, but they do not usually show these murder behaviors – we do not necessarily see an ants preserved in amber carrying a seed, says Nelsen.
So, in order to determine the early evolutionary history of anti-interaction, Nelsen and his colleagues turned to large amounts of DNA data and ecological databases. "In our study, we linked these behavioral and physical properties with ants and ants ants to determine when the ants started to eat and live on plants, and when plants developed the ability to produce structures that ants use," explains Moreau, the field's curator of ants.
The team charted the history of the soft properties of the plant and the herb's plant use on these family trees – a process known as the state reconstruction of the ancestors. They could determine when plants began to rely on ants for defense and seed distribution – and it appears that ants have invoked plants longer than plants have directly invoked ants because plants did not develop these specialized structures until long after ants had rely on them for food and habitats.
"Some ants do not use plants too much, while others trust them for food, living habitats and nesting. We found that in order to be fully invested in plant use, the ants first were born with arboreal and then introduced plants into their diet, and then from there began they are arboreal. Although this gradual shift towards increased dependence on plants is intuitive, it still surprised us, says Nelsen.
And while there has been a mutually beneficial relationship between ants and plants over the years, from an evolutionary point of view, groups of ants that eat, feed on or live in plants do not appear to be better than those who do not. "We do not see parts of the ants containing ants based on plants for food or habitat to diversify or grow faster than those parts of the tree that lack these interactions," says Nelsen. "This study is important because it provides an insight into how these widespread and complex interactions were developed."
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