Pollen competition and environmental effects on hybridization dynamics between Phlox drummondii and Phlox cuspidata

Abstract

Pollen competition between species strongly influences hybridization dynamics in plants. By performing single-and mixed-donor pollinations, we show that soil Ca alters the outcome of interspecific pollen competition in the annual Phlox hybrid system of Phlox cuspidata and P. drummondii. In the absence of interspecific pollen competition, heterospecific pollen siring success of both species was influenced most strongly by the maternal growth environment, such that hybridization was facilitated when heterospecific pollen was deposited on stigmas of maternal plants growing in high Ca soils. When heterospecific pollen was forced to compete against conspecific pollen, however, the maternal growth environment did not influence hybridization, but the environmental origin of heterospecific pollen did, and this effect depended on the maternal species. Pollen of P. drummondii was more effective at outcompeting P. cuspidata pollen and preventing hybridization in P. drummondii dams when P. cuspidata pollen was derived from low Ca. Pollen competition within pistils of P. cuspidata was unaffected by pollen Ca environment. In situations in which P. cuspidata grows in lower soil Ca than P. drummondii, as has been documented in one population, these results suggest that the competitive ability of heterospecific pollen will be diminished by environmental effects of soil Ca. Thus, the environment in which pollen develops can influence interspecific pollen competition and hybridization frequency.

Reinforcement in plants

“…Some studies just assume that hybrids are maladapted as a result of apparent differential local adaptation of the parents (McNeilly & Antonovics, 1968;Silvertown et al, 2005;Zeng et al, 2011). In the Phlox system, hybrids between P. cuspidata and P. drummondii are vigorous, but suffer low fertility (0-30% compared with nonhybrid individuals), indicating a high cost to hybridization (Ruane & Donohue, 2008).…”

Molecular Signatures of Selection on Reproductive Character Displacement of Flower Color In phlox Drummondii

“…It has been suggested that this pattern is caused by reinforcement (Levin 1985). Hybrids between the two species are largely, though not completely, sterile (Levin 1967;Ruane and Donohue 2008), thus allowing for some introgression between the species (Levin 1975). Moreover, there is experimental evidence indicating that dark-red-flowered P. drummondii experience less interspecific hybridization than light-blue-flowered individuals (Levin 1985).…”

Pollen performance of Raphanus sativus (Brassicaceae) declines in response to elevated [CO2]

“…While effects on male function are less studied, evidence is accumulating that both individual components of male reproductive success (Rao et al 1992;Havens et al 1995;Demchik and Day 1996;Agrawal et al 1999;Lehtila and Strauss 1999;Galen 2000;Pendleton 2000;Galloway 2001;Poulton et al 2001aPoulton et al , b, 2002Etterson and Galloway 2002;Avila-Sakar et al 2003;Galen and Stanton 2003;Hedhly et al 2005;Kravetz et al 2008) and overall ability to sire seeds (Young and Stanton 1990;Lau and Stephenson 1993;Quesada et al 1995;Delph et al 1997;Johannsen and Stephenson 1998;Poulton et al 2001a;Pasonen et al 2002;Hersch 2006;Ruane and Donohue 2008) vary as environments change.…”

“…ability of pollen donors to sire seeds. Seed paternity has been shown to be significantly affected by soil nutrient composition (Young and Stanton 1990;Lau and Stephenson 1993;Poulton et al 2001a;Ruane and Donohue 2008), the presence of mycorrhizae (Poulton et al 2001a), variation in temperature (Johannsen and Stephenson 1998;Pasonen et al 2002), and herbivory (Quesada et al 1995;Avila-Sakar et al 2003;Hersch 2006; but see Strauss et al 2001).…”