Divergence of thermal physiological traits in terrestrial breeding frogs along a tropical elevational gradient

Abstract

Critical thermal limits are thought to be correlated with the elevational distribution of species living in tropical montane regions, but with upper limits being relatively invariant compared to lower limits. To test this hypothesis, we examined the variation of thermal physiological traits in a group of terrestrial breeding frogs (Craugastoridae) distributed along a tropical elevational gradient. We measured the critical thermal maximum (CT max; n = 22 species) and critical thermal minimum (CT min; n = 14 species) of frogs captured between the Amazon floodplain (250 m asl) and the high Andes (3,800 m asl). After inferring a multilocus species tree, we conducted a phylogenetically informed test of whether body size, body mass, and elevation contributed to the observed variation in CT max and CT min along the gradient. We also tested whether CT max and CT min exhibit different rates of change given that critical thermal limits (and their plasticity) may have evolved differently in response to different temperature constraints along the gradient. Variation of critical thermal traits was significantly correlated with species’ elevational midpoint, their maximum and minimum elevations, as well as the maximum air temperature and the maximum operative temperature as measured across this gradient. Both thermal limits showed substantial variation, but CT min exhibited relatively faster rates of change than CT max, as observed in other taxa. Nonetheless, our findings call for caution in assuming inflexibility of upper thermal limits and underscore the value of collecting additional empirical data on species’ thermal physiology across elevational gradients.

Elevational and microclimatic drivers of thermal tolerance in Andean Pristimantis frogs

“…This hypothesis predicts a stronger response of cold tolerance limits than heat tolerance limits with increasing elevation and latitude (Bishop, Robertson, Van Rensburg, & Parr, 2017;Gaston & Chown, 1999;von May et al, 2017;Muñoz et al, 2014;Sunday et al, 2014). The lower spatial variation in heat tolerance is argued to be due to intrinsic and extrinsic mechanisms.…”

“…In addition, they occupy a wide array of forested habitats, such as moist lowland and montane forest, but are also widespread in open habitats -pasture, grassland and páramos (Lynch & Duellman, 1997). Former studies in Strabomantidae frogs revealed elevational variation in CTmax (Catenazzi, Lehr, & Vredenburg, 2014;Christian, Nunez, Clos, & Diaz, 1988;Heatwole, Mercado, & Ortiz, 1965), and more recently, von May et al (2017) showed elevational variation in thermal tolerance limits, with faster rates of change for cold than for heat tolerances, with lowland species being more prone to suffer heat impacts. The latter study only included forest Pristimantis species; thus, we build on this previous work by considering microhabitats as potential drivers of thermal tolerance diversity.…”

Elucidating the functional evolution of heat sensors among Xenopus species adapted to different thermal niches by ancestral sequence reconstruction

“…Previous studies showed that the thermal tolerances (lower and upper thermal limits for survival) of species correlate with their respective thermal niches, although a weak correlation was found between the upper thermal limits and selected thermal niches of some species (Araujo et al, 2013;von May et al, 2017;Snyder & Weathers, 1975). However, to date, the involvement of thermal perception in environmental adaptation has not been well studied.…”

Peer Review #2 of "Evolutionary radiation of earless frogs in the Andes: molecular phylogenetics and habitat shifts in high-elevation terrestrial breeding frogs (v0.1)"

“…Our analyses only depend on the relative branch lengths of the tree, but we preferred to illustrate our tree in approximate units of time. Therefore, we used an uncorrelated relaxed molecular clock with the rate of nucleotide substitution for 16S set at 1% per million years as done in a recent study (von May et al 2017). However, as in von May et al (2017), we note that the dates associated with the tree should only be viewed as very approximate and that there can be multiple sources of error when calibrating phylogenies (Arbogast et al 2002).…”