Geographic body size variation of a tropical anuran: effects of water deficit and precipitation seasonality on Asian common toad from southern Asia

Abstract

BackgroundTwo previous studies on interspecific body size variation of anurans found that the key drivers of variation are the species’ lifestyles and the environments that they live in. To examine whether those findings apply at the intraspecific level, we conducted a study of the Asian common toad (Duttaphrynus melanostictus), a terrestrial anuran distributed in tropical regions. The body size of toads from 15 locations, covering the majority of their geographic range, and local environmental data were summarized from published literature. We used a model selection process based on an information-theoretic approach to examine the relationship between toad body size and those environmental parameters.ResultsWe found a positive correlation between the body size of the Asian common toad and the water deficit gradient, but no linkage between body size and temperature-related parameters. Furthermore, there was a positive correlation between the seasonality of precipitation and body size of females from different sampled populations.ConclusionsAs a terrestrial anuran, the Asian common toad should experience greater pressure from environmental fluctuations than aquatic species. It is mainly distributed in tropical regions where temperatures are generally warm and stable, but water availability fluctuates. Therefore, while thermal gradients are not strong enough to generate selection pressure on body size, the moisture gradient is strong enough to select for larger size in both males and females in dryer regions. Larger body size supports more efficient water conservation, a pattern in accordance with the prediction that lifestyles of different species and their local habitats determine the relationship between body size and environment. In addition, larger females occur in regions with greater seasonality in precipitation, which may happen because larger females can afford greater reproductive output in a limited reproductive season.

Does spatial sorting occur in the invasive Asian toad in Madagascar? Insights into the invasion unveiled by morphological analyses

“…In the study population, females were significantly larger than males which, instead, had proportionally longer limbs (Figure 2), a common pattern in toads and other amphibians (Wells, 2010). The marked female-biased sexual dimorphism in body size is well known in this and several other toad species (Guo et al, 2019;Ngo & Ngo, 2013;Wells, 2010). The observed sexual dimorphism index of the invasive toad of Madagascar (SDI = 0.12) stands among the lowest recorded for this species, where the median is 0.201 (range = −0.033-0.353; Guo et al, 2019).…”

“…The marked female-biased sexual dimorphism in body size is well known in this and several other toad species (Guo et al, 2019;Ngo & Ngo, 2013;Wells, 2010). The observed sexual dimorphism index of the invasive toad of Madagascar (SDI = 0.12) stands among the lowest recorded for this species, where the median is 0.201 (range = −0.033-0.353; Guo et al, 2019). This is due to the larger average size of males in Madagascar (SVL = 72.5 mm; Table S1) with respect to native populations (SVL = 66.4 mm; Guo et al, 2019), whereas females are only slightly bigger than the native ones (SVL = 81.1 vs. 79.9 mm; Table S1; Guo et al, 2019).…”

“…The observed sexual dimorphism index of the invasive toad of Madagascar (SDI = 0.12) stands among the lowest recorded for this species, where the median is 0.201 (range = −0.033–0.353; Guo et al, 2019). This is due to the larger average size of males in Madagascar (SVL = 72.5 mm; Table ) with respect to native populations (SVL = 66.4 mm; Guo et al, 2019), whereas females are only slightly bigger than the native ones (SVL = 81.1 vs. 79.9 mm; Table ; Guo et al, 2019). Variation of sexual size dimorphism could be determined by age differences between sexes (Liao et al, 2013).…”

“…This terrestrial, lentic‐breeding amphibian is an ecological generalist and thrives in human‐dominated landscapes (van Dijk et al, 2004). Females reproduce seasonally, producing over 9500 eggs per clutch (Ngo & Ngo, 2013), and, as in most anurans, are larger than males, but size and sexual dimorphism can vary considerably across populations (range of average body size across populations: females = 58.0–107.1 mm; males = 50.8–90.6 mm; Guo et al, 2019). The invasive population established in Madagascar originates from an area between Vietnam and Cambodia (Vences et al, 2017) and was likely introduced via accidental stowaway in commercial containers around 2010 (Moore et al, 2015).…”

For neither heat nor water conservation: Body size variation in Atlantic Forest frogs does not follow a general mechanism

“…According to this hypothesis, differences in environmental water availability may explain body size variation in some species of tropical anurans (Ashton, 2002;Gouveia et al, 2019;Nevo, 1973;Olalla-Tárraga et al, 2009). Additionally, by exploring this hypothesis, it was proposed that tropical anurans with specific sets of morphological and life-history traits occurring across several morphoclimatic domains tend to exhibit body size variation associated with water availability (Gouveia et al, 2019;Guo et al, 2019).…”