Abstract
Understanding speciation is a central endeavour in Biology. The formation of new species was once thought to be a simple bifurcation process. However, recent advances in genomic resources now provide the opportunity to investigate the role of post-divergence gene flow in the speciation process. The diversification of lineages in the presence of gene flow appears paradoxical. However, with enough time and in the presence of incomplete physical and/or ecological barriers to gene flow, speciation can and does occur. Speciation without complete isolation appears especially likely to occur in highly mobile, wide-ranging marine species, such as cetaceans, which face limited geographic barriers. The toothed whale superfamily Delphinoidea represents a good example to further explore speciation in the presence of interspecific gene flow. Delphinoidea consists of three families (Delphinidae, Phocoenidae, Monodontidae) and within all three families, contemporary interspecific hybrids have been reported. Here, we utilise publicly available genomes from nine species, representing all three Delphinoidea families, to investigate signs of post-divergence gene flow across their genomes, and to shed light on the speciation processes that led to the current diversity of the superfamily. We use a multifaceted approach including: (i) phylogenetics, (ii) the distribution of shared derived alleles, and (iii) demographic inference. We find that the divergence and evolution of lineages in Delphinoidea did not follow a process of pure bifurcation, but were much more complex. Our results indicate multiple ancestral gene flow events within and among families, which may have occurred millions of years after initial divergence.
Competing Interest Statement
The authors have declared no competing interest.