The Park Service ranger called my cell phone three times in ten minutes. He was concerned about my safety of myself and that of my field assistants, noting that my car was still at the trailhead to my research site at 4pm, and temperatures were well into the triple digits.

In fact, we had knocked off earlier than I had planned and were already hiking back, because despite setting up a tarp as a scenic shade ramada, and my constant encouragement to drink more water and more Gatorade, we were overheating.

This was a far cry from my last week, when I attempted to climb Mr. Rainier. With a peak at 14,411 feet and sporting the largest glaciers in the lower 48 states, this mountain tested some very different physiological tolerances. Certainly the 1:30am start was cold, and I wore a layer of wool covered by 1-2 layers of fleece, covered by a wind-proof shell over virtually all part of my body. Plus during breaks I added a down jacket over it all.

But cold was not the only physiological challenge on the mountain. Ultraviolet radiation is more intense because it has less atmosphere to pass through, and is reflected off the snow in every direction. The first day I only put on sunscreen once, and my face was badly burned.

Additionally, the low air pressure and corresponding low oxygen levels present physical challenges in acclimatization and physical exertion. One member of our party started coughing up bloody sputum, which may or may not have been indicative of his having high altitude pulmonary edema (HAPE), a potentially fatal condition. HAPE is, interestingly enough, may stem from the body’s evolved response to fungal infections.

So what a relief to return to the balmy lower latitudes and altitudes, right? Highs are well over 100 degrees Fahrenheit in Tucson, though, and my research revolves around low-elevation (hot), south-facing (hotter) slopes covered in dark volcanic rock.

But the problem of my field crew’s physiological tolerance not withstanding the Sonoran Desert summer is also a solution for an experimental annoyance. Bruchid beetles lay their eggs inside paloverde seeds. Last year, I had gathered a number of paloverde seeds to use in germination and seed removal experiments. Beetles decimated my stores, emerging from up to 75% of the seeds and attacking the rest inside my insect-proof bags.

In the last year, an accomplished naturalist mentioned the observation that those seeds falling outside the shady crown of a parent tree survive better, perhaps because the direct sun kills the beetle larvae. Their lack of physiological tolerance to the direct sun can be used against them. So I am drying the first gathered seeds on my roof: