Recurrent hybridization without homoeologous chromosome paring in the <i>Dryopteris varia</i> complex (Dryopteridaceae)

Abstract

ABSTRACT:Controlling combining chromosomes in meiosis is necessary to maintain genome constitutions. The Dryopteirs varia complex is one of the apogamous fern groups which perform recurrent hybridization with unequal meiosis, and produce spores after meiosis of the genome doubling in spore mother cells. We analyzed five low-copy nuclear markers (AK1, EST, GapCp, G6PD, and PgiC) and three regions of plastid DNA (rbL, ndhF and trnL-F). The genetic constitution of the five nuclear markers was the same in the D. varia complex. Therefore, recurrent hybridization seemed to be occurred without homoeologous chromosome paring. KEYWORDS: Apogamous ferns, Homoeologous, Hybridization, Unequal meiosisControlling combining chromosomes in meiosis is necessary to maintain genome constitutions (Riley and Chapman 1958; Wall et al. 1971;Griffiths et al. 2006). Especially, meiosis of hybrids does not succeed because appropriate partners to pair are absent (Hirabayashi 1969(Hirabayashi , 1970. To solve this problem, allopolyploid has doubled set of chromosomes originated from progenitors to pair (Kihara 1924(Kihara , 1930 Wagner 1954; Riley and Chapman 1958;Ebihara et al. 2005;Griffiths et al. 2006; Sessa et al. 2012). Furthermore, allopolyploids can get more genome from other progenitors through recurrent hybridizations. In this case, the set of chromosomes originated from a parental allopolyploid and another parental diploid are also saved (Kihara 1924(Kihara , 1930 Riley and Chapman 1958;Griffiths et al. 2006; Sessa et al. 2012).Many apogamous ferns also have to control behaviors of their chromosomes because they produce spores through delicate mechanism called 'Döpp-Manton scheme' (Döpp 1939;Manton 1950). In this mechanism, disomic chromosome pairing and meiosis is occurred after genome doubling of spore mother cells. However, if homoeologous chromosomes pair randomly, offspring may have various morphological characteristics because genome constitutions of them are edited, but it does not seem to be occurred in regular shaped spores (Manton 1950). In fact, if homoeologous chromosome pairing is occurred in spore mother cells, the offspring get difficulty to survive (Otsuki et al. 2012).Otherwise, apogamous ferns get genetic diversity through hybridization between sexual species (Grusz et al. 2009;Ebihara et al. 2012;Dyer et al. 2012;Hori et al. 2014). Apogamous ferns get genetic variation through hybridization maintaining maturity of their spores in three patterns: (1) tetraploid apogamous hybrid between triploid apogamous species and diploid sexual species (Walker 1962; Watano and Iwatsuki 1988;Grusz et al. 2009;Dyer et al. 2012); (2) tetraploid apogamous hybrid between diploid apogamous species and tetraploid sexual species (Walker 1962); (3) triploid apogamous hybrid between diploid apogamous species and diploid sexual species (Walker 1962; Suzuki and Iwatsuki 1990;Chao et al. 2012;Jaruwattanaphan et al. 2013); (4) triploid apogamous hybrid between triploid apogamous species and diploid sexual species (Hori et al. 2014); (...

Asymmetric hybridization in Central European populations of the Dryopteris carthusiana group

“…Hybridization is considered to be common in ferns (Barrington et al., ; Sigel, ); however, surprisingly, no accurate estimation of hybridization rates in natural populations has been published for ferns. Many studies have described fern hybrid taxa, including intergeneric ones (e.g., Brownsey, ; Reichstein, ; Knobloch et al., ; Rothfels et al., ), or studied the presence of hybrids in natural fern populations (Zhang et al., ; Testo et al., ; Ekrt and Koutecký, ; Hori et al., ; Hanušová et al., ). However, hybridization rates have only been described qualitatively in these studies, without any precise evaluation.…”

Genome Constitution of the <i>Dryopteris atrata</i> Complex (Dryopteridaceae)

“…We counted chromosomes from living plants of D. dickinsii and D. tsutsuiana collected and their localities were in Appendix 1. The methods are followed by Hori et al (2018). To estimate the reproductive mode of each sample or herbarium specimen, the spores in each sporangium were counted.…”

“…For molecular analyses, total DNA was extracted from the silica-dried leaves by using cetyltrimethylammonium bromide solution, according to the method of Doyle and Doyle (1990). ndhF was used as the maternal inherited cpDNA marker (Kuo et al 2016, Hori et al 2018, Table 1. Taxa (cytotypes reported in the previous study with references and newly reported in this study with asterisks), voucher, cytotype in this study and allele constitution of the Dryopteris atrata complex.…”

“…DNA data accession numbers of the obtained nucleotide sequences used for the construction of molecular phylogenetic trees in this study. Data quoted from Hori et al (2018) are marked by asterisks.…”

“…Such allopolyploid has undergone alternation of generation continuously because they can produce fertile offspring with maintaining their genome constitution (Kihara 1924, 1930, Wagner 1954, Riley and Chapman 1958, Ebihara et al 2005, Griffiths et al 2006, Sessa et al 2012. Apogamous ferns also have much genetic variation because they can get allele from sexual species through hybridization (Morita et al 1990, Ebihara et al 2012, Jaruwattanaphan et al 2013, Hori et al 2018. If they cannot maintain their genome constitutions, they will lose their genetic variation.…”