Sonoran Desert amphibians in isolated waters: Investigating threats posed by drought and pathogens

Amphibians are undergoing unprecedented global declines and are currently the most threatened class of vertebrates in the world. Many recent declines have been attributed to two novel threats, climate change and the pathogen Batrachochytrium dendrobatidis (Bd). As novel threats, questions remain about their potential impacts, such as where and to what degree they will harm amphibian populations. In the Sonoran Desert of North American, threats from both climate change and the pathogen Bd are present, but their impacts on amphibians in the region are largely unknown. To fill the knowledge gap regarding the effects of these threats on Sonoran Desert amphibians, I examined the threats posed by drought, which is projected to increase in severity and frequency with climate change, and the pathogen Bd to amphibians in isolated waters of the Sonoran Desert. In chapter two, I examined if an existing drought mitigation strategy for wildlife, the use of constructed waters, supported red-spotted toad breeding effort during drought. I found that the breeding effort of male red-spotted toads decreased at constructed sites during drought but remained high at natural water sites, which indicates that current constructed waters may not be sufficient to support amphibians through the projected increase in drought from climate change. In my third chapter, I investigated the presence of the pathogen Bd in isolated Sonoran Desert waters, where it was previously not anticipated to persist due to its sensitivity to hot and dry conditions. I found that Bd was widespread, occurring in the majority of waters, but had low infection rates on amphibian hosts. I determined that Bd is persisting in the Sonoran Desert at temperatures that were previously thought to be lethal to it, showing that amphibians in hot deserts are not as safe from Bd as previously assumed. The findings of this thesis indicate that continued monitoring of these threats and planning of mitigation strategies may be required to maintain the health of amphibian populations in the region.