  Salamanders (urodela) have among the largest vertebrate genomes, ranging in
size from 10 to over 80 pg. The urodela are divided into ten extant families
each with a characteristic range in genome size. 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 that genome size in salamander families varies
inversely with species richness and other ecological factors: clades that began
radiating earlier (older crown age) tend to have smaller genomes, higher levels
of diversity and larger geographical ranges. These observations support the
hypothesis that urodel families with larger genomes either have a lower
propensity to diversify or are more vulnerable to extinction than families with
smaller genomes.
