Figure 2
Genome size evolution in sharks and outgroups. Species-level phylogeny (‘Maximum Clade Credibility’ or MCC tree hypothesis) depicting ancestral genome size reconstruction under the best-fitting maximum-likelihood ‘Early-Bust’ (EB) model, with details on geological timescale. Tips are colour-coded, as stated in the inset (bottom-left), by the average genome size of each species (represented in the barplot, right). Internal node colours are based on the most likely ancestral genome size estimates inferred by the model (values reported to two decimal places at nodes). Species names at tips are colour-coded according to the taxonomic order to which they belong, following Fig. 1b colour scheme, with outgroup species in black (left inset). The ancestral genome size state for all extant sharks was estimated at 6.33 pg, and for all extant Chondrichthyes at 3.55 pg. Within Selachii, genome size is differently evolving across higher-level taxa: while galeomorph sharks show a general trend in genome size diminution (with the exception of Heterodontiformes and Scyliorhinidae), most squalomorph sharks (especially Squatiniformes and Squaliformes) exhibit steady genome size increases.
