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.
Highlights
Allopolyploids exhibit large variation in traits (Ramsey and Ramsey 2014)
The flowering phenology of C. flexuosa was intermediate compared with C. amara and C. hirsuta
The census on all plants showed that, on Julian date 100 (April 10), the proportion of plants with open flowers was highest for C. hirsuta, followed by C. flexuosa and C. amara, and that this order was reversed on Julian date 141 (May 21) (Fig. 1)
Summary
Allopolyploids (organisms possessing complete sets of genomes derived from different parental species) exhibit large variation in traits (Ramsey and Ramsey 2014). The phenotypes of synthetic neoallopolyploids and natural allopolyploids were either similar, intermediate, or transgressive compared with those of the parental species (Abbott and Lowe 2004; Alexander-Webber et al 2016; Davis 1943; Schranz and Osborn 2004). Such findings do not necessarily translate to natural allopolyploids. The influence of inheritance and polyploidization should be prominent in allopolyploids shortly after emergence, while natural selection should affect trait variation over a longer time. Allopolyploidization may confer large organ size and delayed flowering (Garbutt and Bazzaz 1983; Stebbins 1971; te Beest et al 2012), such effects may diminish after several generations (Gaeta et al 2007)
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