不同纬度高蔊菜的交配系统和繁殖保障

The mating system and reproductive assurance of Rorippa elata (Brassicaceae) across latitude

高山植物的繁殖适应策略一直是进化生态学研究的热点,但是目前仍缺乏对繁殖适应性状的量化研究。本研究以横断山特有十字花科植物高蔊菜(Rorippa elata)为研究材料,结合野外同质园控制实验,在居群水平探讨了其繁殖适应策略。结果表明,高蔊菜的繁殖能力与纬度呈负相关,而越冬存活率与纬度呈正相关。不同交配方式结实率的显著性差异分析表明,高蔊菜具有混合交配系统,其中自交为主型和中间型的株系各占45.5%和39.4%;不同株系具有不同程度的繁殖保障现象,自交为主型最高(0.163),中间型最低(0.011)。本研究表明高蔊菜在居群水平的繁殖和存活之间存在沿纬度梯度的权衡变化,以自交为主的混合交配系统为其提供不同程度的繁殖保障。

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.Results: Our results showed that the main visitors of R. elata flowers were insects of Syrphidae, Halictus, Musca domestica, and Calliphoridae. Among these, insects of Syrphidae visited flowers most frequently and insects of Calliphoridae had the longest staying time per visiting. According to life history observations in the common garden, we demonstrated that R. elata plants germinated in early spring followed by a long period of reproductive growth throughout the synchronization of both high temperature and precipitation in HDM. They then entered into dormancy with living sprouts belowground during cold and dry winter. Correlation analysis of latitude with seed setting rate and over-winter survival rate showed that latitude was negatively correlated with the reproductive ability but positively correlated with the over-winter survival rate of R. elata. Comparative analysis of seed setting rates among experimental treatments found that R. elata possessed a mixed mating system, with selfing dominant and intermediate types accounting for 45.5% and 39.4% of accessions, respectively. Furthermore, most R. elata accessions showed signs of reproductive assurance, but to different extents, with the highest in selfing dominant accessions(0.163) and the lowest in intermediate accessions(0.011). Conclusions: Our findings reveal the reproductive strategies of R. elata at the population level and underscore a trade-off between reproduction and survival along a latitudinal gradient. The mixed mating system with variable reproductive assurance likely plays an important role in the stability of reproduction. Collectively, our results highlight the important contributions of reproductive strategies for alpine plants during their adaptation to mountain environments.