Mating system and pollination biology of a high-mountain perennial plant, Rhodiola dumulosa (Crassulaceae)

Abstract

Rhodiola dumulosa is a perennial herb growing in a naturally fragmented habitat of high-mountain rocks. This research aims to (i) investigate the mating system characteristics and pollination biology of R. dumulosa, (ii) study the effects of ecological factors on the mating system and pollination biology of R. dumulosa and (iii) assess the relationship between its pollination and mating system. Mating system parameters were analysed using allozyme markers. Growth of pollen tubes from artificial self- and cross-pollination was also examined. Field investigations were conducted on insect flower visitation during the blooming period of R. dumulosa. Relationships among mating system, insect flower visitation frequency and environmental factors were assessed. The results showed that (i) R. dumulosa has a mixed-mating system: it is self-compatible and primarily outbreeding, with the multilocus outcrossing rate (tm) ranging from 0.589 ± 0.078 (± standard deviation) to 0.846 ± 0.077; inbreeding coefficients of maternal parents (F) were zero, indicating that inbreeding depression was intense. (ii) Light intensity and temperature impacted the visitation of the principal pollinators, the syrphid Eristalis tenax and the bumblebee Bombus pyrosoma. (iii) Population size plays an important role in the mating system and pollination. Populations received more frequent visits by the principal pollinators usually had higher outcrossing rates. Pollination to some extent affects the mating system of R. dumulosa and it is important to maintain large populations to prevent further inbreeding and to maintain pollinators to facilitate outcrossing.