Data for: Tracking hybrid viability across life-stages in a natural avian contact zone

Hybrid inviability is an important post-zygotic reproductive barrier
between species, but emerging signs of reduced viability can be difficult
to study across the lifespan of natural hybrids. We use a combination of
long-term monitoring, extra-pair paternity and mitochondrial DNA
identification in a natural hybrid zone of Ficedula flycatchers to detect
emerging signs of intrinsic hybrid inviability across their entire
lifespan. We evaluate possible evidence of Darwin’s corollary to Haldane’s
rule, predicting asymmetries in inviability between hybrids resulting from
reciprocal crosses, due to incompatible genetic factors with sex-specific
inheritance patterns. We found higher hatching failure among mixed-species
pairs, possibly indicating early developmental impairments associated with
specific parental genetic combinations. Adult hybrids had a higher basal
mortality rate than both parental species, and different age-specific
mortality trajectories. There were signs of differences in age-independent
mortality rates between the reciprocal hybrid crosses: hybrids with a pied
flycatcher mother experienced slightly increased mortality later in life.
Using an exceptional dataset with many natural hybrids tracked across life
stages, we provide evidence for several emerging signs of reduced hybrid
viability. Incompatibilities between alleles located on autosomes and
uniparentally inherited factors such Z-linked and/or mitochondrial genes
are strong candidates underlying intrinsic hybrid dysfunction in this
system.