Reproductive Ecology and Severe Pollen Limitation in the Polychromic Tundra Plant, Parrya nudicaulis (Brassicaceae)

Abstract

Pollen limitation is predicted to be particularly severe in tundra habitats. Numerous reproductive patterns associated with alpine and arctic species, particularly mechanisms associated with reproductive assurance, are suggested to be driven by high levels of pollen limitation. We studied the reproductive ecology of Parrya nudicaulis, a species with relatively large sexual reproductive investment and a wide range of floral pigmentation, in tundra habitats in interior montane Alaska to estimate the degree of pollen limitation. The plants are self-compatible and strongly protandrous, setting almost no seed in the absence of pollinators. Supplemental hand pollinations within pollinator exclusion cages indicated no cage effect on seed production. Floral visitation rates were low in both years of study and particularly infrequent in 2010. A diversity of insects visited P. nudicaulis, though syrphid and muscid flies composed the majority of all visits. Pollen-ovule ratios and levels of heterozygosity are consistent with a mixed mating system. Pollen limitation was severe; hand pollinations increased seed production per plant five-fold. Seed-to-ovule ratios remained low following hand pollinations, indicating resource limitation is likely to also be responsible for curtailing seed set. We suggest that pollen limitation in P. nudicaulis may be the result of selection favoring an overproduction of ovules as a bet-hedging strategy in this environmental context of highly variable pollen receipt.

Pollen limitation, plasticity in floral traits, and mixed mating system in an alpine plant Pedicularis siphonantha (Orobanchaceae) from different altitudes

“…The phenomenon that pollinator limitation was more serious in high altitudes than low altitudes has been found in many species of alpine plants (Tate & Simpson, 2004;Arroyo et al, 2006;Zhang et al, 2006;Fulkerson et al, 2012;Zhao & Wang, 2015). Our results revealed that in P. siphonantha plants growing at high altitudes were mainly limited by quality (outcross) pollen rather than by the quantity of pollen deposited.…”

Transcriptome Analysis of a Petal Anthocyanin Polymorphism in the Arctic Mustard, Parrya nudicaulis

“…Since the frequency of white individuals is positively correlated with the length of the growing season, we suspect climatic factors (or correlated, non-pollinator selective agents) interacting with the petal color contribute to the maintenance of this polymorphism [13]. We have also detected selection against individuals with lighter colored petals along the Arctic Coastal Plain, but not in interior Alaska where the climate during the growing season is more benign [14].…”

Ovule bet‐hedging at high elevation in the South American Andes: Evidence from a phylogenetically controlled multispecies study

“…Acceptance of ovule bet-hedging as deeply engrained in flowering plants would be greatly strengthened by empirical evidence coming from comparisons of ovule number in plant communities differing in levels of pollination stochasticity. In general, alpine and Arctic habitats are characterized by strongly stochastic pollination as evidenced by variable visitation rates, erratic visitation, wide variation in numbers of pollen grains deposited on stigmas, and large differences in seed set per flower (Ai, Zhou, Xu, Wang, & Li, 2013;Bergman et al, 1996;Eriksen, Molau, & Svensson, 1993;Fulkerson, Whittall, & Carlson, 2012;Hocking, 1968;Kasagi & Kudo, 2003;Kudo, Hirao, & Kawai, 2011;Ladinig & Wagner, 2007;Ladinig, Hacker, Neuner, & Wagner, 2013;Lundemo & Totland, 2007;McCall & Primack, 1992;Tiusanen, Hebert, Schmidt, & Roslin, 2016;Torres-Diaz et al, 2007;Totland, 1994Totland, , 1997Tur, Sáez, Traveset, & Aizen, 2016;Waites & Ågren, 2004). Progressively shorter growing seasons with increasing elevation and latitude place further restrictions on pollination and seed set by limiting the amount of time available for flowering and seed maturation (Körner, 2003).…”

“…Alpine areas and the Arctic thus are prime candidates for ovule bet-hedging (Burd et al, 2009). However, although the possibility of ovule oversupply has been mentioned by some authors (Fulkerson et al, 2012;Wagner, Lechleitner, & Hosp, 2016), no study has explicitly tested the ovule bet-hedging hypothesis in these harsh environments for animal pollinators.…”

“…Andes, a major alpine area characterized by some of the lowest pollination rates recorded among alpine and terrestrial ecosystems in general (Primack & Inouye, 1993; see also Fulkerson et al, 2012).…”