Data from: Components of reproductive isolation between Orchis mascula and O. pauciflora

Studies of the strength and nature of reproductive isolation (RI) between
species can greatly contribute to our understanding of speciation.
Although the role of RI in speciation is well recognized, there is a
dearth of information on the contributions of different barriers between
related plant species. Here, we estimated multiple components of RI
between two Mediterranean orchid sister species (Orchis mascula and Orchis
pauciflora), disentangling the strength and absolute contributions of
seven different isolating mechanisms. Our survey includes one
prepollination, two postpollination prezygotic (pollen–stigma
incompatibility, conspecific pollen precedence), two intrinsic postzygotic
(embryo mortality and hybrid sterility) and two extrinsic postzygotic
(hybrid habitat differentiation and hybrid pollination) isolating
mechanisms. We found strong RI between the investigated species, although
none of the barriers were able to completely impede gene flow. Five
isolating mechanisms contributed positively to the maintenance of species
boundaries. Contrary to most surveys of isolating mechanisms, our data
speak against a clear predominance of prepollination or of prezygotic
barriers but confirm the emerging pattern of multiple barriers
contributing to the maintenance of species integrity. These findings
suggest an allopatric condition during early phases of species divergence.
We discuss our data in the wider context of previous studies carried out
in this orchid group by using a comparative approach.