Immigrant inviability produces a strong barrier to gene flow between parapatric ecotypes of Senecio lautus

Abstract

Speciation proceeds when gene exchange is prevented between populations. Determining the different barriers preventing gene flow can therefore give insights into the factors driving and maintaining species boundaries. These reproductive barriers may result from intrinsic genetic incompatibilities between populations, from extrinsic environmental differences between populations, or a combination of both mechanisms. We investigated the potential barriers to gene exchange between three adjacent ecotypes of an Australian wildflower to determine the strength of individual barriers and the degree of overall isolation between populations. We found almost complete isolation between the three populations mainly due to premating extrinsic barriers. Intrinsic genetic barriers were weak and variable amongst populations. There were asymmetries in some intrinsic barriers due to the origin of cytoplasm in hybrids, which combined with weak selection against hybrids has the potential to facilitate gene flow in the system, specifically from Dune and Headland ecotypes into the This article is protected by copyright. All rights reserved. 3Island ecotype. Overall, these results suggest that reproductive isolation between these three populations is almost complete despite the absence of geographic barriers, and that the main drivers of this isolation are ecologically based, consistent with the mechanisms underlying ecological speciation.

Divergent natural selection drives the evolution of reproductive isolation in an Australian wildflower

“…Previous work also discovered that local adaptation to coastal environments creates strong immigrant inviability between S. lautus ecotypes (Melo et al. ; Richards and Ortiz‐Barrientos ). While ecotypes are genetically differentiated and occur in contrasting ecological conditions, intrinsic barriers to gene flow are weak, (Richards and Ortiz‐Barrientos ), and populations still retain the ability to produce viable hybrid crosses when grown in a common environment (Ali ; Melo et al.…”

Reproductive isolation and the maintenance of species boundaries in two serpentine endemic Jewelflowers

“…), sand dune, and rocky ecotypes of Senecio (Melo et al. ; Richards and Ortiz‐Barrientos ), and serpentine and non‐serpentine ecotypes of Collinsia (Wright and Stanton ; Moyle et al. ).…”

Immigrant and extrinsic hybrid seed inviability contribute to reproductive isolation between forest and dune ecotypes of Epipactis helleborine (Orchidaceae)

“…Second, a fitness advantage of locally adapted ecotypes relative to introduced or immigrant ecotypes can counterbalance the process of gene flow through seed dispersal and maintain reproductive isolation among ecotypes (i.e. immigrant inviability) (Nosil et al , Lowry et al , Melo et al , Richards and Ortiz‐Barrientos ). Third, when two ecotypes are able to hybridize through pollen flow, reduced fitness of the resulting hybrids can occur due to the fact that only one half of the locally adapted alleles can come to expression, a phenomenon known as extrinsic hybrid inviability (Schluter , Rundle and Whitlock , Baack et al ).…”