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Both morph ‐ and species ‐ dependent asymmetries affect reproductive barriers between heterostylous species

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ABSTRACT

The interaction between floral traits and reproductive isolation is crucial to explaining the extraordinary diversity of angiosperms. Heterostyly, a complex floral polymorphism that optimizes outcrossing, evolved repeatedly and has been shown to accelerate diversification in primroses, yet its potential influence on isolating mechanisms remains unexplored. Furthermore, the relative contribution of pre‐ versus postmating barriers to reproductive isolation is still debated. No experimental study has yet evaluated the possible effects of heterostyly on pre‐ and postmating reproductive mechanisms. We quantify multiple reproductive barriers between the heterostylous Primula elatior (oxlip) and P. vulgaris (primrose), which readily hybridize when co‐occurring, and test whether traits of heterostyly contribute to reproductive barriers in unique ways. We find that premating isolation is key for both species, while postmating isolation is considerable only for P. vulgaris; ecogeographic isolation is crucial for both species, while phenological, seed developmental, and hybrid sterility barriers are also important in P. vulgaris, implicating sympatrically higher gene flow into P. elatior. We document for the first time that, in addition to the aforementioned species‐dependent asymmetries, morph‐dependent asymmetries affect reproductive barriers between heterostylous species. Indeed, the interspecific decrease of reciprocity between high sexual organs of complementary floral morphs limits interspecific pollen transfer from anthers of short‐styled flowers to stigmas of long‐styled flowers, while higher reciprocity between low sexual organs favors introgression over isolation from anthers of long‐styled flowers to stigmas of short‐styled flowers. Finally, intramorph incompatibility persists across species boundaries, but is weakened in long‐styled flowers of P. elatior, opening a possible backdoor to gene flow through intramorph pollen transfer between species. Therefore, patterns of gene flow across species boundaries are likely affected by floral morph composition of adjacent populations. To summarize, our study highlights the general importance of premating isolation and newly illustrates that both morph‐ and species‐dependent asymmetries shape boundaries between heterostylous species.

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Distributional ranges of Primula elatior (blue), Primula vulgaris (yellow), and their overlap (green) in Europe. Distributional maps were generated from data compiled from Global Biodiversity Information Facility (GBIF: http://data.gbif.org/), Info Flora (www.infoflora.ch), Flora Web Deutschland (http://www.floraweb.de), Flora Europaea (Valentine and Kress 1972), Flora of the USSR (Komarov 1963), and Richards (2003, personal communication). Highlighted in red is Switzerland, where occurrences records of both species were used to estimate ecogeographic barriers (RIecogeo) and the experimental part of our study was conducted (see text).
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ece32293-fig-0002: Distributional ranges of Primula elatior (blue), Primula vulgaris (yellow), and their overlap (green) in Europe. Distributional maps were generated from data compiled from Global Biodiversity Information Facility (GBIF: http://data.gbif.org/), Info Flora (www.infoflora.ch), Flora Web Deutschland (http://www.floraweb.de), Flora Europaea (Valentine and Kress 1972), Flora of the USSR (Komarov 1963), and Richards (2003, personal communication). Highlighted in red is Switzerland, where occurrences records of both species were used to estimate ecogeographic barriers (RIecogeo) and the experimental part of our study was conducted (see text).

Mentions: Widespread in Europe, P. elatior and P. vulgaris occur in both allopatric and sympatric populations within their largely overlapping distributional ranges (Taylor and Woodell 2008; Jacquemyn et al. 2009), including in Switzerland, where our study was conducted (B. Keller, pers. obs; Fig. 2). Primula elatior prefers moister habitats and tolerates colder winter/spring temperatures, spanning a broader altitudinal range than P. vulgaris (e.g., Hegi 1935; Valentine 1948; Woodell 1969). Both species flower in spring (P. elatior: March–May; P. vulgaris: March–April [‐May]; Lauber and Wagner 2007; Taylor and Woodell 2008; Jacquemyn et al. 2009) and are visited by the same generalist insects (Christy 1922; Woodell 1960b; Richards 2003). Thus, ethological barriers are unlikely to contribute significantly to reproductive isolation.


Both morph ‐ and species ‐ dependent asymmetries affect reproductive barriers between heterostylous species
Distributional ranges of Primula elatior (blue), Primula vulgaris (yellow), and their overlap (green) in Europe. Distributional maps were generated from data compiled from Global Biodiversity Information Facility (GBIF: http://data.gbif.org/), Info Flora (www.infoflora.ch), Flora Web Deutschland (http://www.floraweb.de), Flora Europaea (Valentine and Kress 1972), Flora of the USSR (Komarov 1963), and Richards (2003, personal communication). Highlighted in red is Switzerland, where occurrences records of both species were used to estimate ecogeographic barriers (RIecogeo) and the experimental part of our study was conducted (see text).
© Copyright Policy - creativeCommonsBy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5016645&req=5

ece32293-fig-0002: Distributional ranges of Primula elatior (blue), Primula vulgaris (yellow), and their overlap (green) in Europe. Distributional maps were generated from data compiled from Global Biodiversity Information Facility (GBIF: http://data.gbif.org/), Info Flora (www.infoflora.ch), Flora Web Deutschland (http://www.floraweb.de), Flora Europaea (Valentine and Kress 1972), Flora of the USSR (Komarov 1963), and Richards (2003, personal communication). Highlighted in red is Switzerland, where occurrences records of both species were used to estimate ecogeographic barriers (RIecogeo) and the experimental part of our study was conducted (see text).
Mentions: Widespread in Europe, P. elatior and P. vulgaris occur in both allopatric and sympatric populations within their largely overlapping distributional ranges (Taylor and Woodell 2008; Jacquemyn et al. 2009), including in Switzerland, where our study was conducted (B. Keller, pers. obs; Fig. 2). Primula elatior prefers moister habitats and tolerates colder winter/spring temperatures, spanning a broader altitudinal range than P. vulgaris (e.g., Hegi 1935; Valentine 1948; Woodell 1969). Both species flower in spring (P. elatior: March–May; P. vulgaris: March–April [‐May]; Lauber and Wagner 2007; Taylor and Woodell 2008; Jacquemyn et al. 2009) and are visited by the same generalist insects (Christy 1922; Woodell 1960b; Richards 2003). Thus, ethological barriers are unlikely to contribute significantly to reproductive isolation.

View Article: PubMed Central - PubMed

ABSTRACT

The interaction between floral traits and reproductive isolation is crucial to explaining the extraordinary diversity of angiosperms. Heterostyly, a complex floral polymorphism that optimizes outcrossing, evolved repeatedly and has been shown to accelerate diversification in primroses, yet its potential influence on isolating mechanisms remains unexplored. Furthermore, the relative contribution of pre‐ versus postmating barriers to reproductive isolation is still debated. No experimental study has yet evaluated the possible effects of heterostyly on pre‐ and postmating reproductive mechanisms. We quantify multiple reproductive barriers between the heterostylous Primula elatior (oxlip) and P. vulgaris (primrose), which readily hybridize when co‐occurring, and test whether traits of heterostyly contribute to reproductive barriers in unique ways. We find that premating isolation is key for both species, while postmating isolation is considerable only for P. vulgaris; ecogeographic isolation is crucial for both species, while phenological, seed developmental, and hybrid sterility barriers are also important in P. vulgaris, implicating sympatrically higher gene flow into P. elatior. We document for the first time that, in addition to the aforementioned species‐dependent asymmetries, morph‐dependent asymmetries affect reproductive barriers between heterostylous species. Indeed, the interspecific decrease of reciprocity between high sexual organs of complementary floral morphs limits interspecific pollen transfer from anthers of short‐styled flowers to stigmas of long‐styled flowers, while higher reciprocity between low sexual organs favors introgression over isolation from anthers of long‐styled flowers to stigmas of short‐styled flowers. Finally, intramorph incompatibility persists across species boundaries, but is weakened in long‐styled flowers of P. elatior, opening a possible backdoor to gene flow through intramorph pollen transfer between species. Therefore, patterns of gene flow across species boundaries are likely affected by floral morph composition of adjacent populations. To summarize, our study highlights the general importance of premating isolation and newly illustrates that both morph‐ and species‐dependent asymmetries shape boundaries between heterostylous species.

No MeSH data available.


Related in: MedlinePlus