A number of hybrid species has been recently detected in orchids of the genus Dacylorhiza, by the use of codominant single copy nuclear markers (e.g. enzyme loci). They differ in ploidy level, mode of reproduction, genetic variation and single versus multiple origin. The Allotetraploid Marsh Orchids (D. elata s.l.) show sexual reproduction and have 4x=80; their parental species are D. saccifera s.l. (2n=40) and D. incarnata s.l. (2n=40), as suggested on chromosome basis by Heslop-Harrison (1953, 1954, 1957) and assessed on allozyme basis (Hedrén, 1996a, b; Bullini et al., 2002). Genetic comparison of various AMO taxa from Europe and Caucasus showed their multiple origin, both in time and space; the maternal species was generally D. saccifera s.l., as shown by cpDNA. Other hybrid Dactylorhiza species are allotriploid and reproduce by apomixis. Among marsh orchids, four triploid apomictic taxa, as yet undescribed, have been evidenced: three of them show 2 genomes from D. incarnata and 1 from D. saccifera, the fourth has 2 saccifera and 1 incarnata genomes. Their origin from occasionally fertile backcrosses of AMOs with either parental species has been suggested; according to the taxon, cpDNA was contributed from either D. saccifera or D. incarnata (Bullini et al., in press). The Western Mediterranean orchid D. insularis (3x=60) shows sporophytic polyembriony; this species derived from hybridization between D. romana (2n=40) and D. sambucina (2n=40), which contributed two and one genomes, respectively, as assessed by allozyme markers; the maternal species was D. romana. D. insularis had a single, recent origin and shows limited clonal variation (Bullini et al., 2001). Genetic relationships between Dactylorhiza hybrid taxa and their parental species, as inferred from cpDNA, are generally similar to those reported for nuclear ribosomal intergenic spacer (ITS; Bateman et al., 1997; Bateman, 2001). These findings suggest that concerted evolution, i.e. homogenization towards one parental species, has occurred in hybrid Dactylorhiza taxa at ITS level, highly biased towards the maternal parent.
Speciation by hybridization in European orchids: evidence by nuclear and chloroplastic markers / Cianchi, Maria Rossella; Mosco, M. C.; Bullini, Luciano. - ELETTRONICO. - (2002). (Intervento presentato al convegno Plant species-level systematics: patterns, processes and new applications - NHN Symposium tenutosi a Leiden nel 13 - 15 Novembre 2002).
Speciation by hybridization in European orchids: evidence by nuclear and chloroplastic markers
CIANCHI, Maria Rossella;BULLINI, Luciano
2002
Abstract
A number of hybrid species has been recently detected in orchids of the genus Dacylorhiza, by the use of codominant single copy nuclear markers (e.g. enzyme loci). They differ in ploidy level, mode of reproduction, genetic variation and single versus multiple origin. The Allotetraploid Marsh Orchids (D. elata s.l.) show sexual reproduction and have 4x=80; their parental species are D. saccifera s.l. (2n=40) and D. incarnata s.l. (2n=40), as suggested on chromosome basis by Heslop-Harrison (1953, 1954, 1957) and assessed on allozyme basis (Hedrén, 1996a, b; Bullini et al., 2002). Genetic comparison of various AMO taxa from Europe and Caucasus showed their multiple origin, both in time and space; the maternal species was generally D. saccifera s.l., as shown by cpDNA. Other hybrid Dactylorhiza species are allotriploid and reproduce by apomixis. Among marsh orchids, four triploid apomictic taxa, as yet undescribed, have been evidenced: three of them show 2 genomes from D. incarnata and 1 from D. saccifera, the fourth has 2 saccifera and 1 incarnata genomes. Their origin from occasionally fertile backcrosses of AMOs with either parental species has been suggested; according to the taxon, cpDNA was contributed from either D. saccifera or D. incarnata (Bullini et al., in press). The Western Mediterranean orchid D. insularis (3x=60) shows sporophytic polyembriony; this species derived from hybridization between D. romana (2n=40) and D. sambucina (2n=40), which contributed two and one genomes, respectively, as assessed by allozyme markers; the maternal species was D. romana. D. insularis had a single, recent origin and shows limited clonal variation (Bullini et al., 2001). Genetic relationships between Dactylorhiza hybrid taxa and their parental species, as inferred from cpDNA, are generally similar to those reported for nuclear ribosomal intergenic spacer (ITS; Bateman et al., 1997; Bateman, 2001). These findings suggest that concerted evolution, i.e. homogenization towards one parental species, has occurred in hybrid Dactylorhiza taxa at ITS level, highly biased towards the maternal parent.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
