Patterns of genome size evolution in tetraodontiform fishes.

We used flow cytometry to measure genome size in 15 species from seven families and subfamilies of tetraodontiform fishes. Previous studies have found that smooth pufferfishes (Tetraodontidae) have the smallest genome of any vertebrate measured to date (0.7-1.0 picograms diploid). We found that spiny pufferfishes (Diodontidae, sister group to the smooth puffers) possess a genome that is about two times larger (1.6-1.8 pg). Mola mola, a member of the sister group to Diodontidae and Tetraodontidae, also has a relatively large genome (1.7 pg). Parsimony analysis of this pattern indicates that the plesiomorphic condition for Molidae (Diodontidae, Tetraodontidae) is a genome size of 1.6-1.8 pg, and that tiny genome size is a derived character unique to smooth puffers. However, an alternative explanation is that the ancestor of Tetraodontidae acquired a heritable tendency toward decreasing genome size, such as a new or modified deletion mechanism, and genome size in all of the tetraodontid lineages has been decreasing in parallel since the split from Diodontidae. Small genome size (1.1-1.3 pg) also appears to have evolved independently in some members of Balistoidea (triggerfishes and filefishes) within Tetraodontiformes.