You wouldn’t typically find orb-weaver spiders inhabiting one specific plant.
Usually, these common garden inhabitants are not host plant-specific; they just look for favorable architecture for their spiral, wheel-shaped webs.
But for the acacia plants in the rainforests of Panama, that is not the case.
“As far as we can tell, they seem to be specific to the acacia [plant]; that’s the only place they’re found, but we haven’t done an exhaustive survey to see if they really are in other places,” said University of Lynchburg Biology Professor John Styrsky.
Styrsky said the acacia plant is a small tree that can be “real shrubby” in the understory of the rainforest. The trunks aren’t big, and the plants have big leaves with lots of leaflets.
The professor said the plants in Panama look a lot like the mimosa trees in the Lynchburg area.
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Those plants also are the home of the acacia ants, which depend on the plant for food and habitat.
With the help of a grant, the “incredibly rare” relationship and interaction between orb-weaver spiders, acacia ants and acacia plants will be studied further.
The grant was awarded by the National Secretariat of Science and Technology and Innovation, or SENACYT, in the amount of $120,000, in collaboration with Styrsky; Thomas Hesselberg, of Oxford University; and Dumas Galvez, of the University of Panama.
Acacias provide the ants with a form of sugar water, also called extrafloral nectar, as well as big thorns the ants hollow out and use as “little nursery chambers” for their babies,” Styrsky said.
In return, the ants patrol the plant and protect it from predators such as caterpillars that eat their leaves.
The ants are aggressive and will sting anything that comes in contact with the plant.
For some reason, however, orb-weaver spiders are able to live on these acacia plants without being harmed.
Styrsky said there’s two things he doesn’t know: how the spiders manage to live on the plants without getting attacked by the ants, and how the spiders manage to find these acacia plants, because the plants are spread out.
He believes part of the reason the spiders have managed to live on these plants, in the presence of the ants, is they have behaviorally adapted to just sit there and not move when the ants are around.
He believes the spiders get a form of protection also from predators, because of the ants.
“So, what’s interesting about this whole system is that the ants typically will not tolerate anything else being on the plant, they’re very protective of it, but somehow these spiders have managed to sort of infiltrate the system,” Styrsky said.
Hesselberg said in an email the project directly builds on the discoveries he and Styrsky made independently in Panama almost 15 years ago.
“It is therefore very exciting that we, in collaboration with the excellent Panamanian researcher Dumas Galvez, who adds tremendous knowledge to this project, got the generous funding from SENACYT to get more detailed and quantitative data to answer many of these questions,” Hesselberg said in an email.
Styrsky first became aware of the relationship between the three organisms while in graduate school in 2000 during a trip to Panama, where he traveled to study birds.
He thought birds would be the area of study on which he would entirely focus, until one day he was out in the rainforest helping his now-wife — who he met while on the trip — with her research on birds when he came across the acacia plants.
Through additional research following the discovery, he realized no one had ever documented the spiders that lived on the plant.
The research continued from there.
“The spiders themselves had been discovered 100 years ago, but nobody had ever talked about or done any work with the fact that the spiders lived on these plants. That was very weird and so that got me very interested,” Styrsky said.
The new grant will cover research costs and help support some of the Panamanian students. It also will cover airfare and lodging for the student Styrsky takes.
The group will consist of a student from Oxford University, students from the University of Panama and a student from the University of Lynchburg.
The team will investigate how the spiders coexist with the aggressive plants and how the spiders are able to find these plants, through the collection of samples the team will collect while in the field.
A hypothesis Styrsky has is the spiders employ a chemical camouflage where they may assimilate the odors of the ants or the plant into their own exoskeleton, which allows them to smell like the ants or the plants. This helps them when encountered by the ants, because they have a similar odor.
Hesselberg said he is looking forward to continuing this research with the group.
“I am particularly thrilled that the grants come with very generous funding for students allowing us to involve undergraduate and postgraduate students from Panama, Oxford and Lynchburg, and thus hopefully igniting the passion for spiders and tropical biology in a new generation of researchers,” Hesselberg said.