Radiation with reproductive isolation in the near-absence of phylogenetic signal

According to the genic view, species are characterized by the genes that
underlie functional divergence. Here, we take a
phylogenomic approach to assess this view at the scale of a whole
radiation. The hamlets (Hypoplectrus spp.) represent a recent radiation of
reef fishes from the Greater Caribbean that are reproductively
isolated through assortative mating. A total of 335 genomes from 15
locations revealed a single well-supported phylogenetic split
among species, with a large share of the radiation unresolved.
The polytomic nature of the hamlet radiation is extreme compared
to other recent radiations such as Lake Victoria cichlids. At the
gene-tree level we identified just one genomic region, centered
around the casz1 transcription factor, with a topology that
reflects species differences. These results show that phenotypic
diversification and reproductive isolation—two major attributes of
species—may unfold in the near-absence of phylogenetic signal,
both genome-wide and at the gene-tree level.