Climate and amphibian body size: a new perspective gained from the fossil record

Abstract

In recent years several studies have been carried out to test the validity of Bergmann's rule for amphibians, and have generated varying results. Due to the lack of agreement on this topic, here we examine the relationship between climate and body size for one anuran species (Bufo calamita, commonly known as the natterjack toad) with a new methodological approach that uses the fossil record as the data source. We analysed bones from two archaeo-paleontological sites located close to each other in the Sierra de Atapuerca (Burgos, Spain) that together encompass more than one million years from Early to Late Pleistocene. We used ordinary least squares (OLS) simple regression models to integrate body size and palaeoclimatic data (temperature and precipitation) and describe the relationship between the amphibian's body size and climate along the entire temporal gradient. We found the body size of B. calamita to be negatively related to the mean annual temperature and the mean temperature of the coldest month, and positively related to December-to-February precipitation. The climatic influence was stronger in females, which were smaller than males in most cases, and therefore an inverse sexual size dimorphism pattern was found. Juvenile individuals or the limited sexual size dimorphism of this species may be causes of this unusual pattern. Bufo calamita populations showed a clear Bergmann cline during the Pleistocene period, and winter stands out as the most influential season. Although this new methodology can only be used to describe patterns, we discuss several mechanisms that could explain our results. We propose that starvation resistance and delayed maturation are the main causes for this increase in size in periods with cooler winters, and a fecundity-related hypothesis to explain why climate has a greater influence on female body size.

Dwarfism in close continental amphibian populations despite lack of genetic isolation

“…Increased temperatures often accelerate larval development resulting in smaller body sizes at metamorphosis (Kingsolver and Huey 2008), but our E. calamita populations from Doñana did not show reduced size at metamorphosis compared to the other study localities. Nevertheless, the inverse relationship between ambient temperature and body size is commonly observed across taxa and holds true for natterjack toads throughout their evolutionary history (Martínez-Monzón et al 2017). This common phenomenon in line with the current global warming is already causing reductions in body size worldwide in diverse taxa (Sheridan andBickford 2011, Caruso et al 2015).…”

Influence of phylogenetic structure and climate gradients on geographical variation in the morphology of Mexican flycatcher forests assemblages (Aves: Tyrannidae)

“…The use of different environmental variables to elucidate patterns of morphological change in lineages, with distinct levels of phylogenetic signal, and varied patterns of lineage composition across space provides greater explanatory power than only taking into account species richness or abundance, or simply presence/absence distributional data (Olson et al, 2009; Maestri et al, 2016; Lawing et al, 2017). Several authors have noticed that morphological variation is best explained by a varied set of variables, given that the effect of a single climatic variable, most of the time explains variation only at one scale (taxonomic or geographic, James, 1970; Dial, Greene & Irschick, 2008; Olson et al, 2009; Martínez-Monzón et al, 2017). Assessing the distribution of ecomorphological traits of organisms is the best way to predict change over an environmental gradient (Olson et al, 2009; Santos, Cianciaruso & Marco, 2016) and consequently, regression models representing variation of functional traits provide new insights into elucidating the general mechanisms that relate biodiversity across environmental and geographical changes (Violle et al, 2014).…”

Iberian Quaternary as a scenario for the study of global biogeographic and macroecological patterns in amphibians and reptiles

“…Este hecho constituye un nuevo dato a favor del cumplimiento de dichas reglas en ectotermos y concretamente en anfibios, además de reforzar la validez de esta nueva metodología basada en el registro fósil para el estudio de reglas y patrones en macroecología. Por otro lado, dado que ninguna de dichas reglas contempla la humedad como factor determinante a la hora de explicar las variaciones de tamaño, en este caso concreto, el mecanismo propuesto consiste en la combinación de una maduración retrasada en climas fríos unido a una mayor disponibilidad de recursos en climas húmedos, lo cual se traduce en un aumento de tamaño en climas fríos y húmedos (principalmente en invierno) permitiendo así un mayor acumulo de grasa y un aumento de la fertilidad de las hembras con las ventajas adaptativas que esto supone (Martínez-Monzón 2017).…”