We caressed the lichen-coated rocks with the limp ends of our butterfly nets, walking back and forth. It may not seem to be an efficient way of catching anything, but it caused the grasshoppers to fly. Then, if we watched carefully, we could see where they landed and catch them. Well, that was the idea, anyway, but it didn’t work well for me until I came up with an alternate netting technique, I’ll reveal below.
Why catch grasshoppers on a warm Sunday morning two hours south of St. Louis in an Ozark glade? These lichen grasshoppers, Trimerotropis saxatlis, are special. They are found only in acidic glades on volcanic rhyolite rocks and they don’t eat the lichens, just hang out on them when they are resting, taking advantage of their amazing camouflage. At this late August date these grasshoppers had mated and laid their eggs, so they were dead grasshoppers walking from an evolutionary perspective, making our harvest unlikely to impact the next generation.
This is as delightful a bit of hidden nature as you could imagine and Alan Templeton was willing to share it with me and jeff smith. There were other, larger grasshoppers in the area, brown and visible. We’ve all seen grasshoppers and may well fail to appreciate their wonder, or we may fail to find the more cryptic ones. Or we may even fear these relentless munchers. But go in the field with an expert and you will see something new, hear the back story, get out of town into hidden nature. (Wonder where the other Hidden Nature entries are? Check out my other blog, Goodbye Houston.)
I’ve just moved here from Texas, so I am still learning about the magic of Ozark glades. So often we love what is rich, the cheesecake, not the fat-free yogurt. But there is also a wonder in the impoverished, the desert. A glade is nutrient poor, a place where rock comes closer to the surface, so soils are thin, too thin for trees. A glade is a gap in the forest, an island of habitat separated from other glades by intervening forests. Glades can be acidic or basic, depending on whether the rocks that underlie them are acid volcanic rhyolite, or basic limestone or dolomite. These pH differences are subtle, nothing as acid as vinegar or as basic as ammonia, but plants work in tight limits, making the small differences enough to impact them, and the animals that they attract.
Glades are habitat islands in a sea of forest, so the ecological and evolutionary truths about islands, described long ago by Robert MacArthur, and Ed Wilson, should hold. They are quite simple. Larger islands should have more species. Islands closer to the mainland should have more species. The beauty comes in the exceptions and in how the patterns vary with species; there is much beauty in the lichen grasshopper story.
You see, the big secret about Ozark glades is that they are variable islands in some respects. The glades we sampled sure did look like habitat islands, but what if the intervening forest is not so much of a barrier as an ocean is? How might that be? After all, the habitats are different, and it is hard to survive in a new place. Well, it turns out that the big variable for an Ozark glade is fire. The forests naturally surrounding acid glades are made up of pine trees, or were before human fire suppression. And one thing about pines is that they are fire adapted. I’m talking about cool, frequent fires that clear out the understory and pop open the pine cones, releasing the next generation of seeds, not the destructive infernos that result from fire after suppression when toomuch fuel has built up. A fire does something equivalent to joining all the glade islands, turning an archipelago into a continent, for a short time.
Really? How do you know it has this impact on the animals? Well, if it does, then the current populations of grasshoppers in glades where humans have suppressed fires for many grasshopper generations should be genetically more isolated and differentiated than those in glades where there were recent fires. So it is a simple matter of collecting grasshoppers in multiple glades with fire, and without fire, chosen in an area where other things are as equal as possible. Three is the minimum number of glades in each treatment to answer this kind of question. Twenty is the minimum number of grasshoppers per glade, so that is what we had to collect.
That meant 7 grasshoppers each since there were three of us, but it turned out Alan wanted 40 grasshoppers from the easier-to-collect glades and we complied. We were doing the unburned glades. Alan assembled a different team for the burned glades, collected the next day while we were being oriented as new faculty at Washington University in St. Louis. We were happy to get the right number of grasshoppers, for the three of us scientists well understand the importance of sample size, and that analyses are much easier with balanced sampling designs.
Another cool thing about this project is that it is beginning undergraduates in biology that get to do the actual DNA analyses. We have a great biology department with a lot of care going into teaching, and part of this is making the learning that students do count, right from the beginning. So instead of learning PCR, sequencing, and DNA isolation on something ordered from a catalog just for teaching, our wonderful undergraduates get to participate in a research project. All of them. And some will be sufficiently intrigued to join a research laboratory and do more.
I was just glad to participate in the field angle, and wander around the hot glades, dipping and sweeping my net, walking carefully through lichen beds that crunched and squeaked like very cold snow. I had long ago decided to accompany field biologists on their projects whenever I could. Even as a graduate student, extremely busy myself in the field, I took time to see what my colleagues were doing, following them to hummingbird flowers, to pigeon roosts, and elsewhere. Few things are more fun than getting a biologist to explain how they see a corner of our planet.
Oh, about that grasshopper-catching technique I developed, it’s easy. Instead of actually going for the grasshopper and plopping my net over him or her, I just swung wildly in the air just above the grasshopper. The usually fly, and this would catch them. It was a great feeling to fill my tube and hand it over to Alan for cool storage. I can’t wait to get back to a glade!
Sorry, you’ll have to wait for the answer to the burn/no burn genetic differentiation question because the students have not finished grinding up those grasshoppers and analyzing the data!
I bet you are looking at the large brown mating grasshoppers in the foreground, but right behind and slightly to the left is our hero, Trimerotropis saxatlis. See how hidden in the lichens it is? Try to say Trimerotropis saxatlis five times! It’s fun!
I love lichen on rocks, the first colonizer of new habitats.
Alan Templeton looks just like he did at 28 when we celebrated his birthday in Austin, Texas some decades ago. He’s caught a grasshopper and is taking it out of the net, but clearly has his eye on another!
jeff smith came along and proved to be an excellent grasshopper hunter.
It just looks like a patch in the forest, but the underlying soil is thinner, more rocky.
We saw some other social insects, these lovely tent caterpillars.
A very nice wasp, Polistes metricus, got caught in the web, unable to hunt these caterpillars.
jeff found this praying mantis. Has she produced all her egg cases, or is she looking for another male to consume during the mating act?