Repeated hybridization between incipient lineages is a common feature of ecological speciation and ecomorphological diversification. However, computational constraints currently limit our ability to reconstruct network radiations from gene-tree data. Available methods are limited to level-1 networks wherein reticulations do not share edges, and higher-level networks may be non-identifiable in many cases. We present a heuristic method to recover information from higher-level networks across a range of potentially identifiable empirical scenarios, supported by a theorem and success in simulated data. When extrinsic information indicating the location and direction of recent or ancestral hybridization events is available, our method can yield successful estimates of non-level-1 networks, or at least a reduced possible set thereof. We apply this technique to the Pisgah clade of Desmognathus salamanders, which contains four to seven species exhibiting two discrete phenotypes, aquatic “shovel-nosed” and semi-aquatic “black-bellied” forms in the southern Appalachian Mountains of the eastern United States. Phylogenomic data strongly support a single backbone topology with up to five overlapping hybrid edges. These results suggest an unusual mechanism of ecomorphological hybrid speciation, wherein a binary threshold trait causes hybrids to shift between two microhabitat niches, promoting ecological divergence between sympatric hybrids and parentals. This contrasts with other well-known systems in which hybrids exhibit intermediate, novel, or transgressive phenotypes. Geographically proximate populations of both phenotypes exhibit admixture, and at least two black-bellied lineages have been produced via reticulations between shovel-nosed parentals, suggesting complex transmission dynamics. The genetic basis of these phenotypes is unclear and further data are needed to clarify the nature of selection and speciation in the group.

Morphological measurements from specimens, data for specimens collected in the wild, AHE data (NEWICK-format trees) from Pyron et al. (2022; Ecol. & Evol.), and GBS data assembled using ipyrad (Eaton & Overcast 2020).

Zip files; csv spreadsheets