Genome size (C-value) can affect organismal traits across levels of biological organization, from tissue complexity to metabolism. Neotropical salamanders show wide variation in genome and body sizes, including several clades with miniature species. Because miniaturization imposes strong constraints on morphology and development, and genome size is strongly correlated with cell size, we hypothesize that body size has played an important role in the evolution of genome size in bolitoglossine salamanders. If this hypothesis is correct, then genome size and body size should be correlated in this group. Using Feulgen Image Analysis Densitometry (FIAD), we estimated genome sizes for 60 species of neotropical salamanders. We also estimated the “biological size” of species by comparing genome size and physical body sizes in a phylogenetic context. We found a significant correlation between C-value and physical body size using optimal regression with an Ornstein-Uhlenbeck model, and report the smallest salamander genome found to date. Our index of biological size showed that some salamanders with large physical body size have smaller biological body size than some miniature species, and that several clades showed patterns of increased or decreased biological size compared to their physical size. Our results suggest a causal relationship between physical body size and genome size and show the importance of considering the impact of both on the biological size of organisms. Indeed, biological size may be a more appropriate measure than physical size when considering phenotypic consequences of genome size evolution in many groups.

We generated a Sanger sequence dataset by sequencing some taxa of Neotropical salamanders for two mitochondrial genes (cytochrome b and 16S) and combined these data with data from Genbank for these two genes and three nuclear genes (RAG1, SLC8A3, POMC). We concatenated these data and estimated a phylogeny using BEAST. We estimated the maximum clade credibility tree from the posterior distribution of this analysis as well as a file of 100 trees from the posterior distribution of this analysis. We also include a file of measurements of body size and head size taken from museum specimens using Vernier calipers.