Exploring natural hybridizations among <i>Asplenium ruprechtii</i> and related taxa in Korea

Abstract

The purported four hybrid origins of Asplenium in Korea were tested based on morphological, cytological and DNA sequence data. Asplenium castaneo-viride, A. × uiryeongse, A. × montanus, and A. × kitazawae share several morphological characteristics with the Asian walking fern A. ruprechtii and related taxa as parents and show a sympatric distribution with the putative parents, raising the possibility of hybrid origins: A. castaneo-viride (A. ruprechtii and A. incisum), A. × uiryeongse (A. ruprechtii and A. pekinense), A. × montanus (A. ruprechtii, A. trichomanes, and A. incisum), and A. × kitazawae (A. ruprechtii and A. sarelii). We investigated flow cytometry and chloroplast DNA sequence data (rbcL, rps4-trnS, and rps4-trnS intergenic spacer) to clarify the hybridization and origin of each hybrid. In the flow cytometry analyses, A. ruprechtii shows diploid (2x) only, whereas A. castaneo-viride (3x, 4x), A. × uiryeongse (3x), A. × montanus (3x, 4x), and A. × kitazawae (2x, 4x) exhibit polyploidy, suggesting hybrid events along speciation. The rbcL and rps4-trnS and rps4-trnS intergenic spacer data suggest that A. ruprechtii is one the maternal ancestors of all four hybrids. In addition, the rps4-trnS and rps4-trnS intergenic spacer data indicate that A. incisum is also the maternal ancestor of A. × kitazawae and A. × montanus, proposing multiple hybridization events for these two hybrids. In A. × montanus, morphological features such as the leaf forms and sympatric distributions of the species also support the multimaternal hypothesis, but the morphological features of A. × kitazawae must be examined with consideration of hybrid events. To clarify the complex hybrid evolutionary lineages of the four Asplenium hybrids, further research with taxon sampling and molecular markers should be conducted.

Dynamic hybridization between two spleenworts, Asplenium incisum and Asplenium ruprechtii in Korea

“…In contrast to the results of Lee et al. (2019) , the plastome of A. bimixtum was clearly A. ruprechtii -type and not belonging to A. incisum -type.…”

“…According to them, the obligately inbreeding taxon may have difficulty playing the role of a maternal parent in the hybridization process because of the synchronous maturity of male and female gametes. Based on the length variation due to the large deletion of rpoC2-rps2 in Buramsan populations of A. ruprechtii and tetraploid A. castaneoviride and their capacity to hybridize with other species in the same genus ( Lee et al., 2019 ), it is suggested that A. ruprechtii is an outbreeding taxon. In contrast, A. incisum has hybridized with species other than A. ruprechtii and acts as a maternal parent ( Ebihara, 2016 ).…”

“…bimixtum ranged within those of the allotetraploid A. castaneoviride in their results as well as in this study. Lee et al. (2019) also argued that A. bimixtum has two types of plastid genes: A. ruprechtii -type rbcL and A. incisum -type rps4 .…”

“…Based on morphological features, multiple hybridization has been suggested for the development of A. bimixtum ( Lee et al., 2015 ). After the first report of this hybrid, Lee et al. (2019) argued the origin of this new species based on morphological characteristics, genome size, and phylogenetic relationships.…”

“…However, the origin and status of A. bimixtum require reconsideration since morphological features of A. bimixtum are almost identical to those of A. castaneoviride . In their cytometric study, some of the genome size data had a high standard deviation, since they ran the sample without any reference plant having the standard genome size, which generally runs together with the target sample for measuring accuracy ( Lee et al., 2019 ). Additionally, the authors described that A. bimixtum has two different types of plastid genes originating from A. ruprechtii and A. incisum and suggested a multi-maternal hypothesis to explain their results.…”