Body size variation and sexual size dimorphism across climatic gradients in the widespread treefrog Scinax fuscovarius (Anura, Hylidae)

Abstract

Variation in body size represents one of the crucial raw materials for evolution. However, at present, it is still being debated what is the main factor affecting body size or if the final body size is the consequence of several factors acting synergistically. To evaluate this, widespread species seem to be suitable models because the different populations occur along a geographical gradient and under contrasted climatic and environmental conditions. Here we describe the spatial pattern of variation in body size and sexual size dimorphism in the snouted treefrog Scinax fuscovarius (Anura, Hylidae) along a 10°range in latitude, 25°longitude, and 2000 m in altitude from Argentina, Brazil and Paraguay using an information-theoretic approach to evaluate the support of the data for eight a priori hypotheses proposed in the literature to account for geographical body size, and three hypotheses for sexual size dimorphism variation. Body size of S. fuscovarius varied most dramatically with longitude and less so with latitude; frogs were largest in the northwestern populations. Body size was positively related with precipitation seasonality, and negatively with annual precipitation. Furthermore, the degree of sexual size dimorphism was greatest in the western populations with less annual precipitation, as the increase in body size was stronger for females. Our results on body size variation are consistent with two ecogeographical hypotheses, the starvation resistance and the water availability hypotheses, while our results on sexual size dimorphism in S. fuscovarius supports the differential-plasticity hypothesis but the inverse to Rensch's rule and the parental investment hypothesis. Due to the weak association between environmental variables and body size and sexual size dimorphism variation, we stress that there are other factors, mainly those related to the life history, driving the geographical variation of S. fuscovarius.

Environmental variation predicts patterns of phenotypic and genomic variation in an African tropical forest frog

“…First, intraspecific amphibian body size has been shown to increase with decreasing temperatures, consistent with the heat balance hypothesis which predicts a negative relationship between body size and measures of energy availability (Boaratti & Da Silva, 2015;Ficetola et al, 2010;Rivas et al, 2018), although this has been found to not always be the case (Goldberg et al, 2018;Guo et al, 2019). Second, several studies have shown that larger bodied animals are found in drier areas (Goldberg et al, 2018;Guo et al, 2019;Olalla-Tárraga et al, 2009) providing support for the water availability hypothesis which predicts that larger bodied animals are less prone to desiccation due to reduced surface-to-volume ratio. In contrast, the converse water availability hypothesis argues that body size is positively related to water availability such that larger animals will be found in areas with greater precipitation (Zug et al, 2001).…”

Seasonality drives body size variation in a widely distributed Neotropical treefrog

“…An interspecific study in the Cerrado ecoregion also found a positive relationship between anurans’ body sizes and water deficit, with larger species inhabiting areas with higher water deficit (Olalla–Tárraga et al , 2009). At the intraspecific level, the same pattern was found in Dendropsopohus minutus (Oyamaguchi et al , 2016) and Scinax fuscovarius (Goldberg et al , 2017), whereas the inverse relationship was found in Boana faber and no relationship was found in Physalaemus cuvieri (Boaratti & da Silva, 2015). According to Gouveia et al (2019), increasing body size to avoid desiccation is a more effective strategy in small size anuran species, because a little increase of size in small species results in a much larger water economy in comparison to large size ones, for which investing in mechanisms to increase skin resistance may be a better strategy.…”

“…This hypothesis is based on the association among the activity of amphibians and high levels of water availability (Ficetola et al , 2010) and contradicts the water conservation hypothesis. A large body in amphibians is advantageous in both, dry climates and also in wet areas (Trochet et al , 2019); however, in this specific case, the analyses support a clearly stronger influence of seasonality over body sizes (Table 1) being in concordance with other Neotropical species (Oyamaguchi et al , 2016; Goldberg et al , 2017).…”

A new maximum body size record for the Berry Cave Salamander (Gyrinophilus gulolineatus) and genus Gyrinophilus (Caudata, Plethodontidae) with a comment on body size in plethodontid salamanders

“…Larger body size in such species is in accordance with the 'starvation hypothesis' that predicts that greater mass is positively correlated to seasonality and periods of low resource availability (Lundberg 1986), because larger individuals can persist through low-resource events by having greater energy stores and typically more efficient metabolism owing to positive allometry. The starvation hypothesis has received recent support in multiple amphibian taxa, where body size is positively related to extended inactivity (Valenzuela-Sánchez et al 2015) and increased precipitation seasonality (Goldberg et al 2018).…”