P-elements strengthen reproductive isolation within the Drosophila simulans species complex

Determining mechanisms that underlie reproductive isolation is key to
understanding how species boundaries are maintained in nature.
Transposable elements (TEs) are ubiquitous across eukaryotic genomes.
However, the role of TEs in modulating the strength of reproductive
isolation between species is poorly understood. Several species of
Drosophila have been found to harbor P-elements (PEs), yet only D.
simulans is known to be currently polymorphic for their presence in wild
populations. PEs can cause reproductive isolation between PE-containing
(P) and PE-lacking (M) lineages of the same species. Here, we use the
simulans species complex to assess whether differences in PE status
between D. simulans and its sister species, which do not harbor PEs,
contribute to multiple barriers to gene flow between species. We show that
crosses involving a P-D. simulans father and an M-mother from a sister
species exhibit lower F1 female fecundity than crosses involving an M-D.
simulans father and an M-sister-species mother. We also find that another
TE, I-element, might play a minor role on determining the frequency of
dysgenesis between species. Our results suggest that the presence of PEs
in a species can strengthen isolation from its sister species, providing
evidence that TEs can play a role in isolation. --