Rudolf von May - Eco-physiology & habitat shifts

Eco-physiology and habitat shifts across Andes-Amazon elevational gradients—The Tropical Andes exhibit extraordinary levels of amphibian diversity and endemism. However, many areas remain largely unexplored and contain range-restricted species. This study investigates the diversity, distribution, and thermal physiology of terrestrial-breeding frogs (Strabomantidae) in Peru to better understand why species live at different elevations and how they respond to environmental change. While much attention has been given to modeling and predicting species distributions, especially in the context of climate change, the underlying evolutionary mechanisms and physiological characteristics determining species’ ranges remain poorly understood. This is particularly important in tropical montane regions because they are unique centers of diversification. My collaborators and I have been conducting field surveys at both known and previously unexplored areas in Peru to determine species’ habitat use across elevations, to obtain empirical data on their tolerance to heat and water loss, and to collect specimens and tissues for genetic analyses. The genetic data, along with morphological and thermal physiological data, allowed us to examine patters of niche evolution across elevations (e.g., von May et al. 2018, Ecology and Evolution 7: 3257–67). Ongoing collaborations with Alessandro Catenazzi and other colleagues focus on physiological thermal traits of many lowland species. Additionally, this work has resulted in the discovery of new species described in collaboration with Edgar Lehr and other colleagues (e.g., Lehr & von May 2017, ZooKeys; Serrano-Rojas et al. 2017, Zootaxa).

Elevational divergence in terrestrial breeding frogs along a tropical montane gradient in southern Peru (Manu NP). The species tree (top) depicts the relationship among 22 species and their elevational distribution along the study transect (bottom); species are color-coded according to genus (von May et al. 2018, Ecology and Evolution 7: 3257–67).

Thermal physiology is relevant in determining where species live, and species' critical thermal limits are correlated with elevation. Left: correlation between critical thermal maximum (CTmax) and elevational midpoint. Right: correlation between critical thermal minimum (CTmin) and elevational midpoint. Species are color-coded according to genus. The slopes of the regression lines reflect the phylogenetic corrections in each model (von May et al. 2018, Ecology and Evolution 7: 3257–67).

The operative warming tolerance of terrestrial breeding frogs increases with elevation, suggesting that species living at high elevations might be more buffered from increased temperatures. In contrast, species living in the lowland might be more sensitive to increased temperatures because they live at ambient conditions that are closer to their critical thermal limits.

Evaporative water loss—My ongoing research also focuses on evaporative water loss (EWL), or cutaneous water loss, which is a mechanism involved in thermoregulation in amphibians. Researchers have shown that EWL can aid in thermoregulation through evaporative cooling, and different rates of EWL within and among species vary in correlation with local climate, individuals’ behavior, habitat use, and various micro-environmental conditions experienced by the species in their natural habitats. It has been hypothesized that frogs with low EWL rates are more tolerant to desiccation than frogs with high EWL rates. This hypothesis has not been tested at high elevations in the Tropical Andes, where distinct habitats co-occur above 3000 m. In particular, open habitats such as the Andean grasslands experience higher maximum daily temperatures than forest habitats located at the same elevation, and it remains unclear whether frogs living in these distinct habitats exhibit different EWL rates. In an ongoing study, I am measuring EWL in terrestrial-breeding frogs (Strabomantidae) living at high elevations in Peru to test the hypothesis that open-habitat species have lower EWL rates than forest-habitat species. My preliminary data indicate that closely related species exhibit similar EWL rates despite living in different habitats.

Evaporative water loss (EWL, i.e., mass of water lost per hour) in three species of terrestrial-breeding frogs living at 3000 m in relationship to their body mass. Two closely related species, Bryophryne cophites and B. hanssaueri, exhibit similar EWL rates despite living in different habitats (grassland vs. forest, respectively). A third species of frog included in the study, Psychrophrynella usurpator, remained more active during the experiment and lost more water (von May et al., in review).