Genetic diversity and the origins of parthenogenesis in the teiid lizard Aspidoscelis laredoensis

Unisexual vertebrates typically form through hybridization events between
sexual species in which reproductive mode transitions occur in the hybrid
offspring. This evolutionary history is thought to have important
consequences for the ecology of unisexual lineages and their interactions
with congeners in natural communities. However, these consequences have
proven challenging to study owing to uncertainty about patterns of
population genetic diversity in unisexual lineages. Of particular interest
is resolving the contribution of historical hybridization events vs.
postformational mutation to patterns of genetic diversity in nature. Here
we use restriction site associated DNA genotyping to evaluate genetic
diversity and demographic history in Aspidoscelis laredoensis, a
diploid unisexual lizard species from the vicinity of the Rio Grande River
in southern Texas and northern Mexico. The sexual progenitor species from
which one or more lineages are derived also occur in the Rio Grande Valley
region, although patterns of distribution across individual sites are
quite variable. Results from population genetic and phylogenetic analyses
resolved the major axes of genetic variation in this species and highlight
how these match predictions based on historical patterns of hybridization.
We also found discordance between results of demographic modelling using
different statistical approaches with the genomic data. We discuss these
insights within the context of the ecological and evolutionary mechanisms
that generate and maintain lineage diversity in unisexual species. As one
of the most dynamic, intriguing, and geographically well investigated
groups of whiptail lizards, these species hold substantial promise for
future studies on the constraints of diversification in unisexual
vertebrates.