Multiple pre‐ and postzygotic components of reproductive isolation between two co‐occurring Lysimachia species

• Published in: The New phytologist Vol. 238; no. 2; pp. 874 - 887
• Main Authors: Jiménez‐López, Francisco Javier, Arista, Montserrat, Talavera, María, Cerdeira Morellato, Leonor Patrícia, Pannell, John R., Viruel, Juan, Ortiz Ballesteros, Pedro L.
• Format: Journal Article
• Language: English
• Published: England Wiley Subscription Services, Inc 01-04-2023
• Subjects: Allopatry; backcrosses; Divergence; F2 hybrids; Fitness; flowering phenology; Gene flow; Genetic Speciation; Hybridization, Genetic; Hybrids; Life cycle; Life cycles; Lysimachia; Lysimachia arvensis; Offspring; Phenotype; Pollinators; pollinator‐isolation; Progeny; Reproduction; Reproductive behaviour; Reproductive fitness; Reproductive Isolation; speciation; Sympatry; gene flow; Lysimachia arvensis; F2 hybrids; pollinator-isolation; flowering phenology; backcrosses; speciation
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/nph.18767

Summary
Genetic divergence between species depends on reproductive isolation (RI) due to traits that reduce interspecific mating (prezygotic isolation) or are due to reduced hybrid fitness (postzygotic isolation). Previous research found that prezygotic barriers tend to be stronger than postzygotic barriers, but most studies are based on the evaluation of F1 hybrid fitness in early life cycle stages.
We combined field and experimental data to determine the strength of 17 prezygotic and postzygotic reproductive barriers between two Lysimachia species that often co‐occur and share pollinators. We assessed postzygotic barriers up to F2 hybrids and backcrosses.
The two species showed near complete RI due to the cumulative effect of multiple barriers, with an uneven and asymmetric contribution to isolation. In allopatry, prezygotic barriers contributed more to reduce gene flow than postzygotic barriers, but their contributions were more similar in sympatry.
The strength of postzygotic RI was up to three times lower for F1 progeny than for F2 or backcrossed progenies, and RI was only complete when late F1 stages and either F2 or backcrosses were accounted for. Our results thus suggest that the relative strength of postzygotic RI may be underestimated when its effects on late stages of the life cycle are disregarded.