Above: Mating in Anurogryllus. arboreus -- the male (lower) continues to sing (note elevated forewings) as he passes a spermatophore to the female.
Above: Calling male Anurogryllus arboreus. The forewings are elevated from the body at roughly 45 degrees and specialized structures on the two wings engage and ultimately transform the energy of the closing wing movement into sound.
My research follows two related paths, both having to do with energetics.
1. The importance of energy in acoustic communication in animals. In particular, I am interested in the what are often termed "mating calls". These calls, which are generally produced only by males, are often very loud and are produced at a high rate over a long period of time. I have been able to show that such calls can seem to be very expensive energetically.
In ectothermic ("cold-blooded") animals such as some insects and frogs, the metabolic expense of producing these calls (energy and/or power) may, in cases where the calls are very loud and repeated at a high rate and/or an extended period of time, rival or exceed that of terrestrial locomotion. In other cases, the energy or power requirements for calling appear to be quite trivial. Perhaps one way to think about it is the difference in requirements for a human to run a 4-minute mile vs. a slow walk over the same (or shorter!) distance. Much of my recent work has had to do with trying to understand metabolic costs within the context of an animal's condition and/or its ability to perform at high power levels and/or replace energy stores depleted by calling. In some cases at least, expensive calls appear to be less demanding than might be expected.
There has been a tendency to for workers to look at either the energy and/orpower of calls and other displays or to look at the aerobic metabolism associated with producing the calls (as I have in much of my work). There has been an untested assumption that the two are related in a predictable manner within a given population of signalers. However, this assumes that the mechanisms used for producing the signal (for example, the muscles, stridulatory apparatus and radiation surfaces in the crickets shown at left) are the same in all individuals. The efficiency of signaling behaviors is a composite phenotypic trait defined by the ratio of the power (or energy) of a signal divided by the metabolic power (or energy) required to produce it. In general, we have found that animals do not convert their metabolic energy into sound very efficiently. For instance, efficiency of locomotion such as walking, running, swimming or flying is typically 10 to 20% while the efficiency of sound production is generally less than 1%. Moreover, at least in some species there is individual variation in signal production efficiency with most values tending to cluster together but, as should be expected, with some individuals showing considerably lower efficiencies. This discovery has led me and my students to investigate anatomical factors which actually determine the efficiency of sound production -- for instance features of the forewings (tegmina) of crickets.
2. Understanding the limitations of the locomotory system of arachnids, especially as related to their respiratory systems. Most arachnids are superbly adapted predators. Their hunting styles vary from ambush, to cornering prey in burrows, to active pursuit and, of course, in spiders, the use of a bewildering variety of webs. Each species has its own particular morphological, physiological and behavioral traits that correlate the type of prey capture it uses. In my lab we look at the energetic consequences of these different approaches to prey capture. For instance, we have studied the amount of energy required to build different types of webs. We have tried to estimate the amount of energy required to capture different types of prey using different methods.
We are especially interested in understanding the limits (constraints) imposed on a arachnid's ability to move about rapidly. We compare species in terms of the their oxygen consumption, heart rates, and reliance on anaerobic and phosphagen metabolism during different types of exercise and recovery from that exercise. Over the years, a picture has emerged of arachnids that rely on book lungs as also having a high reliance on anaerobic metabolism during especially vigorous activity (such as escape from a predator) and likely also during some courtship behaviors. By contrast, other arachnids such as solifuges, some spiders and others, that use extensive tracheal systems (albeit coupled to their hemolymph and not directly connected to cells as in insects/myriapods) seem to be much more aerobic.
Hogna lenta, a wolf spider possesses both a pair of booklungs and pair of trachea but it seems to rely mainly on the booklung system for gas exchange. Routine activities are primarily aerobic but vigorous activity in largely fueled by phosphagen stores and anaerobic metabolism.
A solifugid, Eremobates sp. These arachnids can sustain high rates of activity for long periods of time. They rely on "tracheal lungs" -- well-developed tracheal systems that exchange oxygen and carbon dioxide with the hemolymph (as with lungs). This is in contrast to the tracheal systems of insects and their close allies. Solifugids do not seem to have the reliance on anaerobic metabolism that is seen in many other groups of arachnids.