Distribution patterns and driving factors of mixed-ploidy Actinidia species in China

Polyploidization is an important driver for species formation and adaptive evolution, which results in mixed-ploidy species in the nature, i.e., one species contains at least two cytotypes. Understanding the driving factors of mixed-ploidy species offer unique insights into unraveling the evolutionary mechanisms of polyploid species. Here we investigated the distribution patterns and driving factors of 40 Actinidia species in China. Polyploid Actinidia species formed from whole-genome duplication (WGD). Actinidia species showed a mosaic geographic pattern. The potential range of mixed-ploidy Actinidia species is significantly larger than diploid and polyploid species, with higher ecological amplitude of longitude, latitude and elevation. Mixed-ploidy species showed wider temperature and water niches than diploid and polyploid species, and the tolerate capacity of mixed-ploidy species to climate extremes increased with ploidy diversity. Polyploid Actinidia species occupied niches of high altitude, low temperature and drought, supporting the niche shift hypothesis to explain the survival of polyploids. Ploidy diversity and mixed-ploidy effect was positively correlated with the ecological amplitude of temperature. Our results support that the formation and distribution of polyploidy species are associated with climate factors and adaptation capacity to abiotic stresses, and highlight the importance of mixed-ploidy species in the species formation and adaptive evolution.