Allometric and seasonal variation in the species-specific tissue masses. A: Allometric slopes between the mass of each tissue and cubed snout-vent length (SVL3) so that proportionate scaling follows a slope of 1 on a log-log scale. Each point represents a species-specific mean value in breeding condition (N = 116). Relationships deviating from proportionate scaling (based on bootstrapped 95% confidence intervals) are highlighted in blue (steeper than unity) or red (shallower than unity). B: Mean percent change with 95% confidence interval for body mass and each individual tissue of 50 anuran species with data from both shortly before and after brumation (= breeding), based on absolute tissue masses between stages and log-transformed to maintain symmetry and additivity (Törnqvist et al., 1985): log(post-brumation / pre-brumation) × 100. The transparent grey dots depict species-specific values. C: Relationship between brumation period and percent mass change in the amount of body fat. D: Relationship between brumation period and percent mass change in testis mass. Each point indicates a species.

Effects of brumation duration on the relative tissue sizes. Relationships between brumation duration and the relative mass of the brain (A), body fat (B), and testes (C) across males of 116 anuran species in breeding (post-brumation) condition. All axes are controlled for the snout-vent length and phylogeny.

Effects of brumation duration on the relative tissue sizes. Panels A-D depict the phylogenetic correlations (shown as phylomorphospace plots; Revell, 2012) between the relative masses of (A) brain and body fat, (B) brain and testes, (C) testes and body fat, and (D) testes and hindlimb muscles, respectively, across the 116 species (results in Table S14). The relative tissue masses represent the centered log ratios of the compositional data, and the lines connect the nodes of the underlying phylogeny, indicating that phenotypic correlations are not simply the result of phylogenetic clustering. The correlation coefficients and 95% confidence intervals are indicated. The loadings from a phylogenetic principal component analysis (Revell, 2012) on the same variables are also mapped as vectors onto biplots between (E) the first and second or (F) the second and third principal components. In all panels, the point colors reflect the species-specific brumation periods (see legend in panel A). Generally, where brumation was relatively shorter or absent, species also tended to have relatively larger brains, less body fat and smaller testes, respectively, consistent with the univariate analyses (Fig. 2).

Results of the averaged phylogenetic path model. Visual representation of the average phylogenetic path model across 116 anuran species. Arrows reflect the direction of the path, with their widths being proportional to the standardized regression coefficients and colors indicating the sign (blue = positive, red = negative). Paths with 95% confidence intervals excluding 0 (i.e., arrows highly probable) are drawn as solid arrows, all others as dashed, semi-transparent arrows. For simplicity and to avoid over-parameterization, other organs were omitted in path models as they showed little covariation with brumation duration or brain size. All phenotypic traits were log-transformed, and all variables were controlled for body size via additional paths from log SVL. Although SVL had a strong effect on all variables (all β > 0.37), its thick blue arrows to each box are omitted in this figure only for visual clarity, but all path coefficients are presented with their 95%CI in Fig. S7, with further details in Fig. S6 and Table S16.