Does the Platanthera dilatata (Orchidaceae) complex contain cryptic species or continuously variable populations?

Adhikari, Binaya; Wallace, Lisa E.

doi:10.1007/s00606-013-0974-8

Cited by 9 publications

(9 citation statements)

References 45 publications

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“…We maximised the number of populations sampled rather than individuals per population because population structure of cytogenomes is typically high (e.g. Tarayre & Thompson, ; Petit et al ., ; McCauley & Ellis, ; Adhikari & Wallace, ; Bergero et al ., ). Furthermore, our sampling strategy provides a sufficient estimate of within‐population diversity to document differentiation of mitotypes among populations that vary in sex ratio.…”

Section: Methodsmentioning

confidence: 99%

Beyond balancing selection: frequent mitochondrial recombination contributes to high‐female frequencies in gynodioecious Lobelia siphilitica (Campanulaceae)

2019

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Gynodioecy is a sexual system in which females and hermaphrodites co-occur. In most gynodioecious angiosperms, sex is determined by an interaction between mitochondrial malesterility genes (CMS) that arise via recombination and nuclear restorer alleles that evolve to suppress them. In theory, gynodioecy occurs when multiple CMS types are maintained at equilibrium frequencies by balancing selection. However, some gynodioecious populations contain very high frequencies of females. High female frequencies are not expected under balancing selection, but could be explained by the repeated introduction of novel CMS types.To test for balancing selection and/or the repeated introduction of novel CMS, we characterised cytoplasmic haplotypes from 61 populations of Lobelia siphilitica that vary widely in female frequency.We confirmed that mitotype diversity and female frequency were positively correlated across populations, consistent with balancing selection. However, while low-female populations hosted mostly common mitotypes, high-female populations and female plants hosted mostly rare, recombinant mitotypes likely to carry novel CMS types.Our results suggest that balancing selection maintains established CMS types across this species, but extreme female frequencies result from frequent invasion by novel CMS types. We conclude that balancing selection alone cannot account for extreme population sex-ratio variation within a gynodioecious species.

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Section: Methodsmentioning

confidence: 99%

Beyond balancing selection: frequent mitochondrial recombination contributes to high‐female frequencies in gynodioecious Lobelia siphilitica (Campanulaceae)

2019

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“…Hapeman and Inoue, 1997; Bateman et al, 2003, 2009; see also Efimov, 2011). Other DNA‐based studies have used genetic data to help explore speciation and hybridization in more narrowly defined groups of Platanthera , most notably the P. dilatata–hyperborea group (section Limnorchis ) in North America (e.g., Wallace, 2006; Adhikari and Wallace, 2014) and the P. bifolia–chlorantha group (section Platanthera ) in Eurasia in general and England in particular (Bateman et al, 2009, 2012; Pavarese et al, 2011). The P. bifolia–chlorantha group is of particular significance because it generated one of the classic textbook examples of presumed selection‐mediated coevolution between orchids and their pollinating insects (e.g., Nilsson, 1983, 1985; Maad and Nilsson, 2004; reviewed by Hapeman and Inoue, 1997; Bateman et al, 2012).…”

Section: Comparison Of the Orchid Floras Of The Three Northern Macaromentioning

confidence: 99%

Speciation via floral heterochrony and presumed mycorrhizal host switching of endemic butterfly orchids on the Azorean archipelago

Bateman

Rudall

Bidartondo

et al. 2014

American J of Botany

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• Premise of the study: Most orchid species native to the Macaronesian islands reflect immigration from western Europe or North Africa followed by anagenesis. The only putative exception is the butterfly orchids (Platanthera) of the Azores, where three species apparently reflect at least one cladogenetic speciation event. This multidisciplinary study explores the origin, speciation, phenotypic, and genotypic cohesion of these Azorean species and their mainland relatives.• Methods: Plants of Platanthera from 30 localities spanning all nine Azorean islands were compared with those of four continental European relatives for 38 morphometric characters; substantial subsets were also analyzed for plastid microsatellites, and for nrITS of both the orchids and their mycorrhizae.• Key results: Although the three Azorean and four mainland species are all readily distinguished morphometrically using several floral characters, and hybridization appears rare, divergence in ITS and especially plastid sequences is small. Despite occupying similar laurisilva habitats, the Azorean species differ radically in the identities and diversity of their mycorrhizal partners; specialism apparently increases rarity.• Conclusions: Although morphological evidence suggests two invasions of the islands from NW Africa and/or SW Europe, ITS data imply only one. As the molecular data are unable to distinguish among the potential mainland ancestors, two scenarios of relationship are explored that imply different ancestors. Both scenarios require both anagenetic and cladogenetic speciation events, involving homoplastic shifts in overall flower size and (often substantial) changes in the relative dimensions of individual floral organs. Limited genotypic divergence among the three species compared with greater phenotypic divergence suggests comparatively recent speciation. Mycorrhizae may be the most critical factor dictating the respective ecological tolerances, and thus the relative frequencies, of these species. The recent IUCN Red-List amalgamation of Azorean Platanthera taxa into a single species urgently requires reappraisal, as P. micrantha is an excellent indicator species of seminatural laurisilva forest and P. azorica is arguably Europe's rarest orchid.

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“…Unfortunately, all of the morphometric matrices gathered on North American members of the P. dilatata-hyperborea group have consisted entirely of a compartively small number of continuous metric characters employed to describe floral parts. Nonetheless, it proved possible (just) to use these characters to discriminate between P. dilatata , P. aquilonis and their F1 hybrids or their allotetraploid product P. huronenesis (Catling & Catling, 1997; Wallace, 2006; Sears, 2008), and between two of the three varieties of P. dilatata (Adhikari & Wallace, 2014). …”

Section: Resultsmentioning

confidence: 99%

Floral miniaturisation and autogamy in boreal-arctic plants are epitomised by Iceland’s most frequent orchid,Platanthera hyperborea

Bateman

Sramkó

Rudall

2015

PeerJ

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Background and Aims. This paper concludes our series of publications comparing island and mainland speciation in European butterfly-orchids, by studying the morphology, phylogenetics and reproductive biology of the controversial circum-arctic species Platanthera (Limnorchis) hyperborea—the most frequent of seven Icelandic orchids. We draw particular attention to its phylogenetic placement, remarkable reproductive biology and morphological convergence on other Platanthera lineages through floral miniaturisation.Methods. Five populations of P. hyperborea in southwest Iceland were measured for 33 morphological characters and subjected to detailed multivariate and univariate analyses, supported by light and scanning electron microscopy of selected flowers. Representative samples from six populations were sequenced for nrITS and placed in a taxonomically broader phylogenetic matrix derived from previous studies.Key Results . Section Limnorchis consists of three distinct ITS-delimited clades based on P. stricta, P. sparsifolia–limosa–aquilonis and P. dilatata–hyperborea. Within the latter group, supposed species boundaries overlap; instead, the data indicate a crude stepwise series of ribotypic transitions extending eastward from North America to Iceland. Morphometric data failed to identify any taxonomically meaningful partitions among Icelandic P. hyperborea populations, despite the presence of a distinct and apparently plesiomorphic ribotype at the most glacially influenced habitat sampled. Microscopic study of the flowers revealed several distinguishing features (some not previously reported), including resupinate lateral sepals, toothed bract margins, club-shaped papillae shared by both the interior of the labellar spur and the stigmatic surface, and an exceptionally adhesive stigma that is reliably covered in disaggregated pollen masses prior to anthesis; auricles are absent.Conclusions. Ribotypes suggest that Icelandic P. hyperborea represents the terminus of a migration route that may have begun in East Asia before passing through North America and presumably Greenland. The incohesive pollinia, rapidly desiccating anther locules, weakly developed rostellum, exceptionally adhesive stigma and the close juxtaposition of compact male and female reproductive organs together conspire to cause routine autogamy and frequent cleistogamy, despite the continued production of substantial nectar reservoirs in the spur and consequent ongoing attraction to the flowers of insects, including mosquitoes. When considered in combination with independently derived lineages of Platanthera on the Azorean and Hawaiian archipelagos also bearing small green flowers, our observations show allometric and paedomorphic reductions in flower size as the primary evolutionary driver, but also indicate strong developmental and functional constraints.

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Does the Platanthera dilatata (Orchidaceae) complex contain cryptic species or continuously variable populations?

Cited by 9 publications

References 45 publications

Beyond balancing selection: frequent mitochondrial recombination contributes to high‐female frequencies in gynodioecious Lobelia siphilitica (Campanulaceae)

Beyond balancing selection: frequent mitochondrial recombination contributes to high‐female frequencies in gynodioecious Lobelia siphilitica (Campanulaceae)

Speciation via floral heterochrony and presumed mycorrhizal host switching of endemic butterfly orchids on the Azorean archipelago

Floral miniaturisation and autogamy in boreal-arctic plants are epitomised by Iceland’s most frequent orchid,Platanthera hyperborea

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