Disentangling the bindweeds: hybridization and taxonomic diversity in BritishCalystegia(Convolvulaceae)

Abstract

Calystegia is taxonomically complex. More than 65 taxa are currently recognized, but species circumscription is problematic, geographical intergradation between taxa is common and hybridization between species is known to occur. In this study, the nuclear ribosomal internal transcribed spacer 1 region (ITS1) was used to investigate the extent to which interspecific hybridization has contributed to the generation of taxonomic diversity in the C. sepium complex of the genus. Focusing principally on taxa that occur in Britain and their putative relatives, patterns of infra-individual ITS1 variation were examined by direct sequencing and cloning. Direct sequencing of the ITS region of 58 accessions representing 11 taxa and one hybrid revealed 22 variable positions that collectively defined 14 ribotypes. Diagnostic and invariant ribotypes lacking polymorphisms were found in C. sepium ssp. sepium, C. sepium ssp. limnophila, C. silvatica ssp. silvatica, C. pellita, C. pubescens and C. soldanella. Three ribotypes were recovered in C. sepium ssp. americana, two of which lacked polymorphisms, whereas the third exhibited two polymorphic sites. Calystegia sepium ssp. roseata, C. sepium ssp. spectabilis, C. silvatica ssp. disjuncta, C. pulchra and C. ¥ howittiorum were each characterized by taxon-specific polymorphisms in the ITS1 region. In each case, the polymorphisms observed were consistent with the co-occurrence in the genome of nonpolymorphic ribotypes that were observed in other taxa. This observation is supported by cloning of the ITS region and is consistent with a hybrid origin for the taxa in which they occur. The hypotheses of hybridity proposed are further shown to be congruent with other data, notably morphology. This study suggests that taxonomic diversity within the C. sepium

Factors affecting germination of great bindweed (<i>Calystegia silvatica</i>) seeds

“…Seedling germination occurred most rapidly at temperatures between 15 and 25°C. Germination did occur down to temperatures of 5°C, a temperature at which seed germination of field bindweed is also known to occur (Brown et al 2009). However, germination was slower for temperatures lower than 15°C.…”

“…Field bindweed seeds are known to germinate at a wide range of temperatures from 5˚C to 40˚C, with the highest reported germination rate occurring when temperatures alternated between 20˚C and 35˚C (Brown et al 2009). However, limited information is available about great bindweed seeds and the conditions under which they can germinate.…”

Lucky morning glory, Calystegia felix (Convolvulaceae): a new species from Southern California, with notes on the historical ecology of the Chino ciénega belt

“…It is a taxonomically difficult complex that may include over twenty Calystegia sepium subtaxa, some additional closely related species, and their subtaxa (Stace 1961, Brown et al 2009). So defined, all of the original material for Convolvulus binghamiae , including the lectotype at UC (Brummitt et al 2012), is clearly referable to this complex.…”

Asymmetric hybridization between <i>Calystegia japonica</i> Choisy and <i>C. hederacea</i> Wall in Matsumoto, Nagano, central Japan

“…。そのた め，分布域が接触し，同所的に両親種が存在する地域では， 種間雑種が生み出される交雑帯が生じやすい。この交雑帯の 構造と安定性は，両親種の遺伝的・生態的特性，交雑帯への 分散能力，そして交雑帯で生じた雑種の適応度などに依存し ている (Barton and Hewitt 1981;Harrison 1993) 。一般に，交 雑帯は種間雑種が両親種に比べ適応度が低いこと，強化や遺 伝子流動が起こることにより，消失しやすく，一時的なもの になりやすい (Harrison 1986) 。しかしながら，直接的な証拠 はないが (Harrison 1986) ，長期間にわたって安定的に維持さ れてきた交雑帯も存在することが示唆されている (Graham et al 1995) 。 ヒルガオ属(Calystegia)における種間雑種は，人工的， 並びに自然条件下で容易に形成されることが知られており， 属 内 の 多 様 化 に 大 き く 貢 献 し て き た と 考 え ら れ て い る (Brown et al 2009 (Nason et al 1992;Carney et al 2000;Burgess et al 2005) 。例えば，Nason et al(1992…”