Pollen competition as an asymmetric reproductive barrier between two closely relatedSilenespecies

Abstract

Reproductive barriers are important determinants of gene flow between divergent populations or species. We studied pollen competition as a post‐mating reproductive barrier between Silene dioica and S. latifolia. Gene flow between these species is extensive, but early‐generation hybrids are rare. In an experiment with conspecific, heterospecific and 50 : 50 mixed pollinations in the two species, pollination treatments did not significantly affect seed set and seed weight. However, molecular determination of siring success after mixed pollinations showed that fewer than expected hybrids were produced in S. latifolia (18% hybrids) but not in S. dioica (51% hybrids). This constitutes an asymmetric post‐mating reproductive barrier and likely contributes to the rarity of early‐generation hybrids. Our study shows that pollen competition can be an effective barrier to hybridization between closely related species that likely acts in concert with other reproductive barriers.

Cryptic gametic interactions confer both conspecific and heterospecific advantages in the Chrysochus (Coleoptera: Chrysomelidae) hybrid zone

“…Until recently, the great majority of research in reproductive barriers has examined the nature and evolution of either premating barriers or late-acting postzygotic barriers such as hybrid sterility and inviability (Markow 1997;Howard 1999;Coyne and Orr 2004). However, cryptic barriers that are realized within the reproductive systems of hybridizing females have received increasing attention (e.g., Rieseberg et al 1995;Howard et al 1998;Price et al 2000;Chang 2004;Fricke and Arnqvist 2004a;Rahmé et al 2009). As a result, it is now clear that cryptic post-mating barriers can take a variety of forms (Eberhard 2009), including the failure of heterospecific sperm (or pollen) to survive or remain motile (Price et al 2000), the incompatibility of heterospecific sperm and eggs (Palumbi and Metz 1991), the tendency for conspecific sperm to outcompete heterospecific sperm in fertilizing the eggs of multiply-mated females (Howard 1999), the reduced fecundity of females that mate with heterospecific males (Nosil and Crespi 2006), and the early abortion of F1 embryos (Matsubayashi and Katakura 2009).…”

Plastid DNA Analysis Reveals Cryptic Hybridization in Invasive Dalmatian Toadflax (Linaria dalmatica) Populations

“…Possible causes of asymmetric gene flow in plants include the relative abundance of each parent species at the hybrid site (e.g., as reported in Magnolia by Muranishi et al 2013), differences in flower morphology (e.g., as described in Eucalyptus by Field et al 2011), pollinator behavior (e.g., as reported in Yucca by Starr et al 2013), and postmating reproductive barriers resulting in differential pollen success (e.g., as described in Silene by Rahme et al 2009). In a series of controlled, reciprocal hybridizations between YT and DT, carried out by Ward et al (2009), a greater proportion of hand-pollinated crosses with YT as the female parent produced viable seed (49.1%) compared with those with DT as the female parent (10.1%).…”

Sistema Reproductivo de Trichloris (Poaceae, Chloridoideae, Chlorideae)

“…El aumento en la cantidad de polen debió favorecer una mayor competencia polínica. Antecedentes sobre el efecto de la competencia polínica para el adecuado desarrollo de frutos fueron presentados, para diversas especies, por Schlichting et al (1987), Winsor et al (2000) y Rahme et al (2009), entre otros.…”