Intraspecific variation in reproductive barriers between two closely related Arabidopsis sister species

Abstract

Reproductive isolation (RI) is a critical component of speciation and varies strongly in timing and strength among different sister taxa, depending on, for example the geography of speciation and divergence time. However, these factors may also produce variation in timing and strength among populations within species. Here we tested for variation in the expression of RI among replicate population pairs between the sister taxa Arabidopsis lyrata subsp. lyrata and A. arenicola. While the former is predominantly outcrossing, the latter is predominantly selfing. We focused on intrinsic prezygotic and postzygotic RI as both species occur largely in allopatry. We assessed RI by performing within‐population crosses and interspecific between‐population crosses, and by raising offspring. RI was generally high between all interspecific population pairs, but it varied in timing and strength depending on population history. Prezygotic isolation was strongest between the closest‐related population pair, while early postzygotic isolation was high for all other population pairs. Furthermore, the timing and strength of RI depended strongly on cross direction. Our study provides empirical support that reproductive barriers between species are highly variable among population pairs and asymmetric within population pairs, and this variation seems to follow patterns typically described across species pairs.

Recent speciation associated with range expansion and a shift to self-fertilization in North American Arabidopsis

“…14). Gene flow after budding may have led to the buildup of reproductive isolation, given the high to complete (depending on cross direction) intrinsic reproductive isolation between Lake Superior A. lyrata and southern A. arenicola found in a crossing experiment 29 . Later, the two species might have become separated by ecological succession of the vegetation to boreal forests between Lake Superior and the Hudson Bay.…”

“…Recent genomic verification revealed that A. arenicola and North American A. lyrata are sister taxa 27,28 . Intrinsic reproductive isolation between the two species is quite strong, with artificial crossing resulting in high failure in fruit and seed set, and in seed germination 29 . Apart from morphology, the species also differ in latitudinal distribution.…”