The nonlinear change in pollinator assemblages and self-mating syndromes of Primula atrodentata along elevation gradients

Abstract

The reproductive strategies of alpine plants are often altered by environmental changes caused by changes in the spatial distribution of the gradient. However, few studies have investigated whether reproductive patterns of the same species vary with elevation. Three natural populations of Primula atrodentata, which are distributed in the eastern Himalayas and have a long flowering period, were selected along the elevation gradients in Shergyla Mountain, Tibet, China. Morph ratio investigation, floral trait measurement, pollinator observation, and manipulated pollination experiments were conducted to explore the changes in self-compatibility and floral traits associated with the selfing syndrome along elevation gradients. We found that the breeding system of the S-morph is facultative outcrossing, and that of the L-morph is obligatory outcrossing. We further found that with increasing elevation, the number of pollen and ovules, anther-stigma distance, and inbreeding depression index first increased and then decreased, whereas the seeds per fruit and seed setting rate under hand self-pollination, pollen limitation, and self-incompatibility index tended to decrease first, but then increased. In addition, pollinator diversity and visiting frequency were the highest at the middle elevation (4050 population), which can better explain the non-linear change in self-fertility with elevation. Our findings provide insights into the evolutionary pattern of self-compatibility in alpine plants along elevational gradients.