Abstract Detail

Hybrids and Hybridization

Keller, Barbara [1], De Vos, Jurriaan [2], James, Thomson [3], Conti, Elena [4].

Reproductive barriers between heterostylous primroses.

The interaction between floral traits and reproductive isolation is crucial to explaining the extraordinary diversity of angiosperms. Flowers enable the evolution of complex relationships with pollinators, promoting reproductive isolation and diversification. Distinct features of corollas (e.g., color, scent, texture, shape, tube length) and reproductive organs (e.g., position, form, pollen/stigma ultrastructure and proteins) can facilitate isolating mechanisms by attracting different pollinators, restricting interspecific pollen transfer, or rejecting interspecific pollen. Heterostyly, a complex floral polymorphism that optimizes outcrossing, evolved repeatedly in angiosperms and has been shown to accelerate diversification in primroses. However, no experimental study has evaluated its possible effects on reproductive isolation. We quantify multiple reproductive barriers between the heterostylous Primula elatior (oxlip) and P. vulgaris (primrose), elucidate the relative importance of pre- vs. postmating barriers, and test whether traits of heterostyly contribute to individual barriers. We find that premating isolation is key for both species, while postmating isolation is more pronounced in P. vulgaris. More specifically, ecogeographic isolation is important for both species, but stronger in P. elatior than in P. vulgaris, while phenological, seed developmental, and hybrid sterility barriers are stronger in P. vulgaris than in P. elatior. Consequently, reproductive isolation under sympatry is highly asymmetric between species, thus gene flow is expected to be higher from P. vulgaris into P. elatior than vice versa. Furthermore, we document for the first time that, in addition to widely occurring species-dependent asymmetries, morph-dependent asymmetries affect reproductive barriers between heterostylous species. Indeed, the interspecific decrease of reciprocity between high sexual organs of complementary morphs limits interspecific pollen transfer from S-morph anthers to L-morph stigmas, while higher reciprocity between low sexual organs favors introgression over isolation from L-morph anthers to S-morph stigmas. Therefore, patterns of pollen movement across species boundaries are likely affected by morph composition of adjacent populations. As small populations of heterostylous species often have unbalanced morph ratios, human-mediated habitat fragmentation that progressively reduces population sizes likely affects the permeability of species boundaries. Finally, intra-morph incompatibility persists across species boundaries, but is weakened in L-flowers of P. elatior, opening a possible backdoor to gene flow through intra-morph pollen transfer between species. 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.

1 - University of Zurich, Department of Systematic and Evolutionary Botany, Zürich, Switzerland
2 - Royal Botanic Gardens, Kew, Richmond, UK
3 - University of Toronto, Ecology and Evolutionary Biology Department, Toronto, Canada
4 - University of Zurich, Department of Systematic and Evolutionary Botany, Zürich, 8008, Switzerland

Keywords:
floral heteromorphism
heterostyly
hybridization
mechanical isolation
morph- and species-dependent asymmetry
Primula elatior (oxlip)
Primula vulgaris (primrose)
reciprocal herkogamy.

Presentation Type: Oral Paper
Session: 50, Hybrids and Hybridization
Location: 102/Savannah International Trade and Convention Center
Date: Wednesday, August 3rd, 2016
Time: 5:00 PM
Number: 50006
Abstract ID:458
Candidate for Awards:None