I stopped in a slot canyon in Capitol Reef National Park to let the scenery and experience sink in.
At this point, the floor of the canyon was about 20 feet wide, and the walls soared several hundred feet, nearly vertically.
Desert varnish streaked the shady and north-facing walls, while the south-facing walls were baked, dried and bleached by the sun, so desert varnish could not accumulate.
It was quiet, without a whisper of wind, when something moved on the sand in front of me — a small toad with red spots was walking in my direction.
Red-spotted toads, Bufo punctatus, are creatures of the desert — they live on the Colorado Plateau, in the Mojave, Sonoran and Chihuahuan deserts, and Baja California. Red-spotted toads are small and, indeed, they have red or reddish-orange spots.
While they live in deserts, they are tied to ephemeral creeks and pools, for they must lay their eggs in water.
Genetic analyses of mitochondrial DNA in red-spotted toads have revealed three distinct lineages.
The eastern lineage is on the Colorado Plateau and in the Chihuahuan Desert, the western lineage is in the Mojave and Sonoran deserts, and the peninsular lineage occupies the full length of Baja.
These three lineages are equally differentiated from each other, suggesting that they arose simultaneously. Their degrees of genetic differentiation suggest that they arose at the same time that the Colorado Plateau was rising, approximately 5.3 million years ago.
In a very real sense, these toads are as old as the hills.
Water is a perennial challenge for species that live in the desert and it is particularly a problem for toads, which do not drink water.
You might suppose that it is good that red-spotted toads do not drink water, because deserts don't have any water anyway. But that is not true — deserts can be as dry as dust, but the slot canyons have been cut by swiftly flowing floodwaters in the wake of thunderstorms.
At the time that I was in the slot canyon, it contained one large pool and several moist areas, but no running water. A month later the slot canyon might have been, literally, as dry as dust.
Toads are remarkably resistant to desiccation. A human who has lost 10 percent of his or her weight begins to develop dangerous symptoms, but toads survive repeated desiccations that decrease body weight by 30 percent. Nevertheless, sooner or later, the toad has to take on water.
A thirsty toad that has no access to a stream or pool goes walking about, looking for moist earth.
Well, more feeling than looking — a toad uses its back feet to sense the moisture in the soil. A toad walks with its body held above the soil, but when the back feet detect adequate moisture, the toad stops to press its stomach and pelvic area to the soil. If the soil has little water, the toad will wiggle from side to side to make intimate contact with the moisture.
Toads literally absorb water through the skin on its ventral surface.
Physiologists have determined that the skin on a red-spotted toad's belly is better able to absorb water than the skin on its back. In addition, a toad is able to sense water absorption and osmosis, so if it has absorbed as much water as it can from a patch of sand, it will move to another spot.
And they will not dally with soil containing salty water, for osmosis is changed by salt solutions, making it more difficult for a toad to absorb water.
When the canyon becomes as dry as dust, toads retire to their burrows in the soil, and do not appear until water flows or at least collects into pools again.
Given that red-spotted toads live in deserts, their offspring hasten through development, so that tadpoles metamorphose to the adult form before their ephemeral water supply disappears. Their eggs hatch and then larvae grow, develop and metamorphose in just 16 to 20 days.
While this is quite fast, a sympatric species, the western spade foot toad, completes development in 13 to 14 days. In contrast, boreal toads take about 3 months from egg laying to metamorphosis, or about six times as long.
A toad in the desert has to be fast.
Jeff Mitton, email@example.com, is a professor in the Department of Ecology and Evolutionary Biology at the University of Colorado.