Genome size and evolutionary diversification in vertebrates

Abstract

The possibility that the accumulation and amplification of excess non-coding DNA may adversely affect the ability to evolve (evolvability) has been suggested for various organisms. In particular, an inverse correlation between genome size and number of species, and a direct correlation between genome size and extinction risk, have recently been established in plants, and in plants and vertebrates, respectively. The present study of a broad sample of vertebrates also evidenced an inverse correlation between genome size, percentage of repetitive DNA and number of species in this subphylum. This correlation is significant only at the higher taxonomic levels and exhibits a different trend in groups with DNA content greater than 5 pg/nucleus compared with those exhibiting lower values. Large genomes may influence the evolvability in multiple ways. Indeed, different correlations have been obtained between genome size, amount of repetitive DNA and various morphological and functional cell parameters with different roles in vertebrate evolution subject to different hierarchical levels of selection. The trend of the correlation between genome size and species number observed in the present study is similar to the one between genome size and extinction risk, and suggests that genome size is not the sole factor exerting a constraint on evolvability, but rather that it is one of a number of factors in a complex hierarchical system within which various evolutionary phases would have been influenced by the interaction among various genomic, cellular and organismic factors.