Effect of historical factors on genetic variation in three terrestrial Cephalanthera species (Orchidaceae) with different breeding system on the Korean Peninsula

Abstract

Previous studies have shown that levels of genetic diversity in species of the genus Cephalanthera covary with the breeding system. In the southern part of the Korean Peninsula, the three self‐compatible terrestrial orchids Cephalanthera erecta, C. falcata and C. longibracteata flower synchronously in sympatric populations. The food‐deceptive C. falcata with bright yellow flowers is predominantly outcrossing, whereas autogamy is the dominant strategy in both C. erecta and C. longibracteata, whose white flowers do not open fully. We examined genetic diversity (by means of allozymes) of the three species in sympatric populations (600 × 600 m area) in the Yeonwhasan Provincial Park (YPP) and in non‐sympatric populations outside YPP, South Korea. Thirteen out of 20 putative loci were variable across the three species, but there was a complete lack of allozyme variation within each species and we found no evidence of hybridisation. Our results suggest that historical factors, i.e. the Quaternary climate oscillations, have played a major role in determining levels of genetic diversity in the three Cephalanthera species. The Korean populations of C. erecta (a warm‐temperate/temperate element) and C. falcata (a warm‐temperate element) may have been established by a single introduction from a genetically depauperate ancestral population, likely located outside the Korean Peninsula. On the other hand, since C. longibracteata is a boreal/temperate element, it may have survived the Last Glacial Maximum in microrefugia located in low elevation regions within the Peninsula where it has been subjected to population bottlenecks reducing its genetic diversity.

Evaluation of the taxonomic rank of the terrestrial orchid <i>Cephalanthera subaphylla</i> based on allozymes

“…The nearly neutral allozyme markers have been useful for identifying species boundaries in a variety of plant groups (Crawford, 1989;Arduino et al, 1996;Harris and Abbott, 1997;Chung et al 2005;Hedrén and Nordström, 2009;López-Pujol et al 2012;Chung et al, 2018). A review on orchid allozyme-based genetic diversity studies revealed that most orchid species examined so far have 'diagnostic' or unique alleles for species delimitation at several isozyme loci (reviewed in Chung and Chung, 2012).…”

“…A review on orchid allozyme-based genetic diversity studies revealed that most orchid species examined so far have 'diagnostic' or unique alleles for species delimitation at several isozyme loci (reviewed in Chung and Chung, 2012). The more recent study of Chung et al (2018), focused on three Cephalanthera species in South Korea (C. erecta [three populations], C. falcata [five populations], and C. longibracteata [three populations]), revealed no allozyme variation within any of the species using 20 putative loci; all populations of each species were fixed for one allele at all loci (expected heterozygosity at population level and sample as a whole, H e P and H e S = 0). However, there was considerable genetic variation between species, with 13 loci being useful for the three Cephalanthera species delimitation.…”

“…However, there was considerable genetic variation between species, with 13 loci being useful for the three Cephalanthera species delimitation. Among the 30 alleles harbored by these 13 loci, each of the three alleles at four loci were unique ('diagnostic') to a single species (Chung et al, 2018). The presence of these species-specific alleles was the reason for the relatively low Nei's (1978) genetic identities found between species pairs: 0.400 for Cephalanthera erecta vs. C. falcata; 0.500 for C. erecta vs. C. longibracteata; and 0.600 for C. falcata vs. C. longibracteata (Chung et al, 2018).…”

“…Among the 30 alleles harbored by these 13 loci, each of the three alleles at four loci were unique ('diagnostic') to a single species (Chung et al, 2018). The presence of these species-specific alleles was the reason for the relatively low Nei's (1978) genetic identities found between species pairs: 0.400 for Cephalanthera erecta vs. C. falcata; 0.500 for C. erecta vs. C. longibracteata; and 0.600 for C. falcata vs. C. longibracteata (Chung et al, 2018). Chung et al (2018) also found no hybrids in sympatric populations at the landscape level in Yeonwhasan Provincial Park (YPP, 600 × 600-m area [36 ha]; altitude, 230 m asl).…”

“…The presence of these species-specific alleles was the reason for the relatively low Nei's (1978) genetic identities found between species pairs: 0.400 for Cephalanthera erecta vs. C. falcata; 0.500 for C. erecta vs. C. longibracteata; and 0.600 for C. falcata vs. C. longibracteata (Chung et al, 2018). Chung et al (2018) also found no hybrids in sympatric populations at the landscape level in Yeonwhasan Provincial Park (YPP, 600 × 600-m area [36 ha]; altitude, 230 m asl). Thus, it seems relatively easy or simple to use alleles at several loci to identify species.…”