Data from: Profound genetic divergence and asymmetric parental genome contributions as hallmarks of hybrid speciation in polyploid toads

The evolutionary causes and consequences of allopolyploidization, an
exceptional pathway to instant hybrid speciation, are poorly investigated
in animals. In particular, when and why hybrid polyploids versus diploids
are produced, and constraints on sources of paternal and maternal
ancestors, remain underexplored. Using the Palearctic green toad radiation
(including bisexually reproducing species of three ploidy levels) as
model, we generate a range-wide multi-locus phylogeny of 15 taxa and
present four new insights: (i) At least five (up to seven) distinct
allo-triploid and allo-tetraploid taxa have evolved in the Pleistocene;
(ii) All maternal and paternal ancestors of hybrid polyploids stem from
two deeply diverged nuclear clades (6 Mya, 3.1-9.6 Mya), with distinctly
greater divergence than the parental species of diploid hybrids found at
secondary contact zones; (iii) Allotriploid taxa possess two conspecific
genomes and a deeply-diverged allospecific one, suggesting that genomic
imbalance and divergence are causal for their partly clonal reproductive
mode; (iv) Maternal vs. paternal genome contributions exhibit asymmetry,
with the maternal nuclear (and mitochondrial) genome of polyploids always
coming from the same clade, and the paternal genome from the other. We
compare our findings with similar patterns in diploid/polyploid
vertebrates, and suggest deep ancestral divergence as a precondition for
successful allopolyploidization.