The mating system and reproductive assurance of <i>Rorippa elata</i> (Brassicaceae) across latitude

Abstract

Aim: The strategies of reproductive adaptation for alpine plants have long been a hot topic in evolutionary ecology, but there is still a lack of quantitative measures for reproductive traits under natural conditions. Here, we investigated reproductive adaptation of Rorippa elata, an endemic Brassicaceae species in one of the world's temperate biodiversity hotspots, the Hengduan Mountains (HDM). Methods: We established a field-based common garden experiment at Shangri-La Alpine Botanical Garden in Yunnan. During 2019-2020, we transplanted a total of 633 R. elata plants for 150 accessions across latitudes and performed manipulative field experiments. First, we collected several life history-related traits of R. elata, including germination rate, flowering time, over-winter survival rate, and pollination-relevant characteristics. We then carried out a set of four experimental treatments to characterize natural variation of the mating system in R. elata, including (1) strict selfing rate by bagging inflorescences before flowering; (2) common outcrossing rate by emasculation and open pollination; (3) strict outcrossing rate by emasculation and artificial pollination among accessions; and (4) natural reproductive rate under open pollination. For each treatment, we counted seed setting rate per fruit per accession and used this information to assign a mating system type for each R. elata accession. Furthermore, we also quantified the extents of pollen limitation and reproductive assurance.