Two free hours in the afternoon, and what to do? Take a walk, take a nap, journal my experiences? Why not play?
At Palo Verde, there is a large diversity of Acacia trees and acacia ants that form mutualisms with these trees. In exchange for housing and food provided by the tree, the ants defend the tree from herbivory. Some ant species will even eradicate any plants or seedlings that grow too close to the acacia tree so that it does not have to deal with excessive competition for light, space, and nutrients.
Dr. Kaspari and colleagues found an interesting pattern of salt limitation as one moves in an ecosystem from coastal to inland (Kaspari et. al 2008 PNAS). To investigate these patterns, Kaspari et. al used ant communities and bait traps of NaCl or sucrose. They found that, the further inland ant communities were, the more frequently they chose the NaCl baits over the sucrose baits.
At Palo Verde, we were given the opportunity to go into the field, make observations, and design a hypothetical research project. My group designed a proposal about the acacia ant system, to see whether acacia ants close to the gulf [salt water] were less salt limited than ants further inland. We designed two series of ‘salinity gradients’ – one from the coast inward at three distances, and then using sampling sites at three distances from brackish water and fresh water [the river] as well. We wanted to do both a field and lab component in which we presented ants with NaCl solution and sucrose solution, and count the number of visitations to each. If our hypothesis, that ants further from salt water [gulf/ocean] would be salt limited, was true, then we would expect to find ants further from salt water having a higher number of visitations to the salt baits versus the sugar baits.
Of course, this was just a hypothetical proposal – even if we had time to do independent projects at Palo Verde, one as complex as this would not be completed in time. As part of the feedback we got from our proposal, it was suggested that we do a pilot study first. So, when we suddenly had two free hours one afternoon, I decided to do just that.
I had it in my head to visit three to five patches of acacia trees, and do two salt/sugar trials at each patch. Suffice to say, the pilot study did not go exactly as planned, but I learned a ton in the process. This leads me to the importance of play.
After visiting two trees, I realized that I was working with two different species of acacia ants. Not being a myrmecologist, I will simply describe them as the black ants and the red ants. At first I thought that the black ants were the more active and aggressive ones [thus being better for my study], because they had an immediate reaction to my disturbance of their tree. However, after an initial flurry of activity when their branch or domatia were disturbed, they calmed down and retreated into hiding. It was all for show!! Whose show? I don’t know. Is a flurry of timid ants enough to ward off potential herbivores? When I repeatedly disturbed their branch, the flurries of activity became smaller and less frequent, until it was simply a little ant head peeking out from a domatia hole, or nothing at all.
So, first lesson learned, it was time to try the red ants. They were, on the whole, more aggressive and active. Even so, there were decided differences among different populations of the red ants [different trees with red ants in them]. Some were very active, but barely reacted to my disturbance of their tree, whereas a tree that looked totally empty suddenly had aggressive ants ready for battle when I brushed past a branch. This was the tree where I got the most observations in [oh yeah, remember I’m doing a pilot study about sucrose versus sodium solution preference?]. It is also where I got bit by an angry red Acacia ant. Let me tell you, it hurts! I would certainly be warded off if I was an herbivore [but not warded off as a tenacious scientist, haha!]. The pain is immediate and intense, but then dissipates. Oh, what a cool adaptive strategy, I though to myself, to invest only enough to inflict immediate annoyance. Silly scientist…about twenty four hours the pain came back along with oober intense itching!! Aha, so they invest in immediate deterrence followed by a delayed reminder of just what a bad idea it was to mess with acacia trees and their ants.
[Above: Acacia ants visit sugar (blue) and salt (orange) solution vials.
But back to my study – ahem, I mean, play. In total I checked out three different acacia trees. The black ants, during ten minutes of observation, made one visit to the vial with sugar solution and one visit to the vial with salt solution. I visited two trees with red ants, with very different personalities [or, if you will, behavioral patterns]. On the “too busy to be bothered” tree, the red ants made, well, zero visitations to either vial, even when vials were placed directly in their path. On the “curious and rapid defense” tree, the red ants made 12 visits to the sugar solution and 6 visits to the salt solution. One thing I realized as I observed them [play!!] was that the vials were so large that the ants, though curious, would only investigate solution on the lid and rim of the vial but would not go in. So I ran back to the classroom and put the solution into smaller vials, brought it back out to my star students. During the smaller vial trial, the red ants made 1 visit to the sugar solution and 3 visits to the salt solution.
My results are of course inconclusive, but do support an idea of doing a lab experiment prior to a complex field experiment, and I learned a lot more about my potential study subjects in the process. Playing with acacia ants – a great way to spend two free hours in the afternoon!
What questions will lead you to play today? 🙂