title: Where the lake meets the sea: strong reproductive isolation is associated with adaptive divergence between lake resident and anadromous three-spined sticklebacks.
abstract: Contact zones between divergent forms of the same species are often characterised by high levels of phenotypic diversity over small geographic distances. What processes are involved in generating such high phenotypic diversity? One possibility is that introgression and recombination between divergent forms in contact zones results in greater phenotypic and genetic polymorphism. Alternatively, strong reproductive isolation between forms may maintain distinct phenotypes, preventing homogenisation by gene flow. Contact zones between divergent freshwater-resident and anadromous stickleback (Gasterosteus aculeatus L.) forms are numerous and common throughout the species distribution, offering an opportunity to examine these contrasting hypotheses in greater detail. This study reports on an interesting new contact zone located in a tidally influenced lake catchment in western Ireland, characterised by high polymorphism for lateral plate phenotypes. Using neutral and QTL-linked microsatellite markers, we tested whether the high diversity observed in this contact zone arose as a result of introgression or reproductive isolation between divergent forms: we found strong support for the latter hypothesis. Three phenotypic and genetic clusters were identified, consistent with two divergent resident forms and a distinct anadromous completely plated population that migrates in and out of the system. Given the strong neutral differentiation detected between all three morphotypes (mean FST = 0.12), we hypothesised that divergent selection between forms maintains reproductive isolation. We found a correlation between neutral genetic and adaptive genetic differentiation that support this. While strong associations between QTL linked markers and phenotypes were also observed in this wild population, our results support the suggestion that such associations may be more complex in some Atlantic populations compared to those in the Pacific. These findings provide an important foundation for future work investigating the dynamics of gene flow and adaptive divergence in this newly discovered stickleback contact zone.
authors: School of Biological Sciences, Queen's University Belfast, Belfast, United Kingdom.
authors: Mark
authors: M
authors: Ravinet
authors: School of Biological Sciences, Queen's University Belfast, Belfast, United Kingdom; Institute for Global Food Security, School of Biological Sciences, Queen's University Belfast, Belfast, United Kingdom.
authors: Rosaleen
authors: R
authors: Hynes
authors: Marine Institute, Furnace, Newport, County Mayo, Ireland.
authors: Russell
authors: R
authors: Poole
authors: Aquaculture, Fisheries and Development Centre, School of Biological, Earth & Environmental Sciences, University College Cork, Cork, Ireland.
authors: Tom F
authors: TF
authors: Cross
authors: Aquaculture, Fisheries and Development Centre, School of Biological, Earth & Environmental Sciences, University College Cork, Cork, Ireland.
authors: Phil
authors: P
authors: McGinnity
authors: School of Biological Sciences, Queen's University Belfast, Belfast, United Kingdom.
authors: Chris
authors: C
authors: Harrod
authors: School of Biological Sciences, Queen's University Belfast, Belfast, United Kingdom; Institute for Global Food Security, School of Biological Sciences, Queen's University Belfast, Belfast, United Kingdom.
authors: Paulo A
authors: PA
authors: Prodöhl
mesh_terms: D000222:Adaptation, Physiological; D025041:Animal Migration; D000818:Animals; D001267:Atlantic Ocean; D001499:Bayes Theorem; D049628:Body Size; D016000:Cluster Analysis; D017753:Ecosystem; D051456:Gene Flow; D056726:Genetic Association Studies; D014644:Genetic Variation; D006824:Hybridization, Genetic; D007494:Ireland; D060106:Lakes; D018895:Microsatellite Repeats; D058974:Phylogeography; D040641:Quantitative Trait Loci; D060047:Reproductive Isolation; D045483:Rivers; D012641:Selection, Genetic; D023701:Smegmamorpha / Q000033:anatomy & histology / Q000145:classification / Q000235:genetics* / Q000502:physiology; D013045:Species Specificity