Abstract
Salamanders (Urodela) have among the largest vertebrate genomes, ranging in size from 10 to 120 pg. Although changes in genome size often occur randomly and in the absence of selection pressure, non-random patterns of genome size variation are evident among specific vertebrate lineages. Here we report i) an unexpected relationship between genome size (C-value) and species richness at the family taxonomic level in salamander clades; ii) C-value and species richness both correlate with clade crownage but not with diversification rates; iii) C-value is strongly associated with geographical area. Consistent with this observation we found that iv) genome size in salamanders is also strongly related to climatic niche rate. Finally, we report a relationship between C-value diversity and family-level species diversity as measured by the coefficient of variation of genome size within clades. Based on these results we propose that variation in C-value and genomic organization (heterochromatin content and gene synteny) might underlie variation in species richness in agreement with the Geographical Area Hypothesis. These observations suggest that changes in C-value, and hence changes in the amount and/or organization of non-coding DNA in the vertebrate genome, are associated with the allelic incompatibility believed to drive reproductive isolation and speciation in salamanders.