Trait-dependent resemblance of the flowering phenology and floral morphology of the allopolyploid Cardamine flexuosa to those of the parental diploids in natural habitats

Abstract

Allopolyploids possess complete sets of genomes derived from different parental species and exhibit a range of variation in various traits. Reproductive traits may play a key role in the reproductive isolation between allopolyploids and their parental species, thus affecting the thriving of allopolyploids. However, empirical data, especially in natural habitats, comparing reproductive trait variation between allopolyploids and their parental species remain rare. Here, we documented the flowering phenology and floral morphology of the allopolyploid wild plant Cardamine flexuosa and its diploid parents C. amara and C. hirsuta in their native range in Switzerland. The flowering of C. flexuosa started at an intermediate time compared with those of the parents and the flowering period of C. flexuosa overlapped with those of the parents. Cardamine flexuosa resembled C. hirsuta in the size of flowers and petals and the length/width ratio of petals, while it resembled C. amara in the length/width ratio of flowers. These results provide empirical evidence of the trait-dependent variation of allopolyploid phenotypes in natural habitats at the local scale. They also suggest that the variation in some reproductive traits in C. flexuosa is associated with self-fertilization. Therefore, it is helpful to consider the mating system in furthering the understanding of the processes that may have shaped trait variation in polyploids in nature.

Keywords: Cardamine; Floral morphology; Flowering phenology; Polyploid; Reproductive traits; Trait variation.

Fig. 1

Proportion of flowering individuals of Cardamine amara, C. flexuosa, and C. hirsuta in all study sites in Switzerland in 2014. The circles represent weekly census on marked individuals (C. amara, N = 113; C. flexuosa, N = 136; C. hirsuta, N = 195), while triangles represent census on all individuals at the study sites on April 10 (C. amara, N = 4,275; C. flexuosa, N = 812; C. hirsuta, N = 8,140) and May 21 (C. amara, N = 2,920; C. flexuosa, N = 418; C. hirsuta, N = 188) (Table S1)

Fig. 2

Dimension, length/width ratio of flowers and petals, and schematic drawings of flower and petal morphology of Cardamine amara (hermaphrodite and male), C. flexuosa, and C. hirsuta. a Flower length, b petal length, c flower width, d petal width, e length/width ratio of the flowers, f length/width ratio of the petals, g schematic drawing of flower shape based on the mean length and width of the flowers, and h schematic drawing of petal shape based on the mean length and width of the petals. For a–f, the dots and vertical lines within violin plots indicate the mean and SD, and the lowercase letters in each figure indicate statistical differences based on Tukey’s HSD test