Hybridizing salamanders experience accelerated diversification

Andrew Storfer,Mark J Margres,Austin H Patton,Jon Eastman,Luke J Harmon,Brendan Epstein

doi:10.1038/s41598-020-63378-w

Abstract

Whether hybridization generates or erodes species diversity has long been debated, but to date most studies have been conducted at small taxonomic scales. Salamanders (order Caudata) represent a taxonomic order in which hybridization plays a prevalent ecological and evolutionary role. We employed a recently developed model of trait-dependent diversification to test the hypothesis that hybridization impacts the diversification dynamics of species that are currently hybridizing. We find strong evidence supporting this hypothesis, showing that hybridizing salamander lineages have significantly greater net-diversification rates than non-hybridizing lineages. This pattern is driven by concurrently increased speciation rates and decreased extinction rates in hybridizing lineages. Our results support the hypothesis that hybridization can act as a generative force in macroevolutionary diversification.

Highlights

Whether hybridization generates or erodes species diversity has long been debated, but to date most studies have been conducted at small taxonomic scales
We suggest that studies at broad phylogenetic and macroevolutionary timescales can help overcome these limitations by providing a phylogenetic context in which to view repeated hybridization events over evolutionary timescales and the consequent impact on lineage diversification rates
We evaluated a total of 14 competing models using HiSSE, half of which represent a model of character-dependent diversification and the remaining half represented models of character independence (Supplementary Tables S2-S9)

Summary

Introduction

Whether hybridization generates or erodes species diversity has long been debated, but to date most studies have been conducted at small taxonomic scales. The prevailing view in the animal literature is that hybridization constrains lineage diversification because hybrid lineages are often documented to be less fit than parentals[4,5,7] Under this scenario, hybridization is predicted to increase extinction rates. Studies of hybridization often occur along different stages of the speciation continuum[29], whereby hybridization can appear as a force that either facilitates or impedes speciation Recent work highlights this uncertainty by demonstrating that the outcomes of hybridization depend on the underlying nature of selection pressures and demography[30]. We suggest that studies at broad phylogenetic and macroevolutionary timescales can help overcome these limitations by providing a phylogenetic context in which to view repeated hybridization events over evolutionary timescales and the consequent impact on lineage diversification rates. Sufficient sequence data are available to resolve the phylogenetic relationships among most (~63%) taxa within this group[32]

Methods

Results

Conclusion