Living Low and Dry: Costs of and Resilience to Soil Hydric Stress in a Fossorial Amphisbaenian Reptile

The physiological traits of animals can be strongly influenced by climatic fluctuations, and future climate changes may have negative impacts. However, the magnitude of these effects likely depends on the type of animal and its specific environment. In fossorial animals, soil alterations can affect their physiological traits, but adaptations to fossoriality may lead to different effects when compared to epigeal animals. We experimentally examined the hydric physiology and the effects of soil hydric stress (i.e., a simulated drought) on the physiological state of the amphisbaenian Blanus cinereus, a strictly fossorial reptile. Individuals selected substrates with moderately low moisture levels in a laboratory gradient but avoided the wettest substrates. The evaporative water loss rates of amphisbaenians were temperature-dependent, but notably low compared to other epigeal reptiles of similar size and climatic niche. In the hydric stress experiment, amphisbaenians buried in dry substrates did not gain body weight and showed increased glucocorticoid (GC) levels, whereas those in wet substrates gained weight without an increase in GC levels. However, immune response was unaffected by the drought or elevated GC levels, and individuals exposed to hydric stress recovered their weight after a subsequent recovery period under normal conditions. Additionally, amphisbaenians compensated for drought conditions behaviorally, more often selecting soils under rocks where conditions could be more favorable. These results suggest that soil drought imposes moderate, temporary costs, but that amphisbaenians can cope with, at least, moderately short droughts, likely as a result of their adaptations to the underground environment.