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

Abstract

Plant mating systems rapidly respond to pollen limitation in changing environments. However, whether and how floral traits are involved in a mating system shift requires further investigation. A widely distributed and bumblebee‐pollinated lousewort, Pedicularis siphonantha D. Don was studied. We investigated pollination systems, reproductive success, and floral traits in four large populations growing from 3200 m to 4300 m. Pollinator activity in low altitude populations was lower and these populations had a decreased fruit set and seed number per capsule compared to populations at high altitudes. Supplemental hand pollination with outcross pollen significantly increased seed production per capsule for plants from high altitudes but not for those from lower altitudes. We also found that bumblebees visited more flowers within an inflorescence in a single foraging bout in high altitudes compared with low altitudes, which caused a high possibility of geitonogamous mating. These differences may be pollination‐dependent rather than inheritance‐based because hand pollination on bagged flowers did not cause a difference in seed production across populations. Compared to plants from low altitudes, high‐altitude plants had increased flower longevity, larger floral displays, higher pollen production per flower, and shorter corolla tubes, which were found to be well in accordance with changes in both pollination environment and mating system. Plasticity in floral traits might help plants to adjust their resource allocation strategies in response to their habitat, which might be linked with pollination environment. The variability among these populations might be beneficial for this widely distributed species to cope with environmental changes.

Reproductive strategies of animal‐pollinated plants on high mountains: A review of studies from the “Third Pole”

“…It seems that as elevation increases, pollen limitation may be more severe, because in the alpine zone above the treeline, flower visitation rates declined with increasing elevation (Arroyo et al, 1982, 1985; Bingham & Orthner, 1998). In four large populations of Pedicularis siphonantha (Orobanchaceae) from 3200 to 4300 m, pollinator activity, fruit set and seed number were lower in high‐altitude populations (Dai et al, 2017b).…”

Effects of environmental heterogeneity on phenotypic variation of the endemic plant Lilium pomponium in the Maritime and Ligurian Alps

“…In general, floral traits are found to be less variable and less affected by environmental heterogeneity than vegetative traits because variation in floral morphology may have negative effects on fitness (Berg 1960 ; Frazee and Marquis 1994 ). Nevertheless, population variation has been detected in stigma–anther separation (Griffin and Willi, 2014 ; Papuga et al 2015 ), floral display (Dai et al 2017 ; Lambrecht et al 2017 ), and pollen–ovule ratio (Guo et al 2010 ; Dai et al 2017 ). This variation in floral traits is usually related to variation in the pollination environment (Aigner 2004 ) and some studies have detected increased pollen limitation at the distributional edges (Moeller et al 2012 ), although others do not record any increase in pollen limitation, presumably due to increase in resource constraints or self-pollination (Totland 2001 ; Hargreaves et al 2015 ).…”

Spatio-Temporal Variations in Pollen Limitation and Floral Traits of an Alpine Lousewort (Pedicularis rhinanthoides) in Relation to Pollinator Availability

“…The number of ovules is a more conservative floral trait than pollen production in the evolution of flowering plants’ breeding systems [ 51 ]. This was proven in a series of taxa [ 10 , 52 , 53 ]. In this study, the number of pollen grains per flower differed in space and time, while the ovules per flower remained unchanged.…”

“…tibetica (Bonati) Tsoong has a very short raceme in which all flowers open on the same plane; an appropriate corolla-tube length is essential for a flower to display on the plane. For P. siphonantha , the long raceme allows the flowers with varied corolla-tube lengths to open at different positions on the inflorescence [ 52 ].…”

“…Therefore, it is proposed that this lousewort species’ three floral traits were highly phenotypically plastic [ 27 , 35 , 36 ]. The stigma–anther distance is thought to be linked with the pollen release and body size of the visiting bumble bee [ 52 ]. The variations could be adapted to the differences in the pollination environment among the different flowering stages across the populations.…”