An intriguing morphological variability of Platanthera s.l.

Efimov, Petr G.

doi:10.14712/23361964.2015.55

Cited by 14 publications

(21 citation statements)

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confidence: 53%

“…Specializations to various methods of pollination by the same type of 541 pollinator was already known in this genus (Efimov 2011). We have, indeed, evidence for rapid 542 morphological evolution of Platanthera genus in connection with pollination shifts (Efimov 2011). Thus, 543 the morphological divergence, in particular the distance between the viscidia, will determine in 544 Platanthera species the attachement of the pollinia on different parts of the pollinator's head (eyes or 545 proboscis).…”

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Supplemental Information 1: Morphological Data From Allopatric Populations (Summarized in Table 2)

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Platanthera bifolia and P. chlorantha are terrestrial and rewarding orchids with a wide Eurasian distribution. Although genetically closely related, they exhibit significant morphological, phenological and ecological differences that maintain reproductive isolation between the species. However, where both species co-occur, individuals with intermediate These results are corroborated also by floral scent analyses, which confirmed a strong similarity in floral scent composition between intermediate morphotypes and P. bifolia. Therefore, this study provided a much more detailed picture of the genetic structure of a sympatric zone between two closely allied species and supports the hypothesis that intermediate morphotypes in sympatry could reflect an adaptive evolution in response to local pollinator-mediated selection. (Nilsson 1983;1985). These two closely related species exhibit not only 67 morphological differences, but also distinct ecological preferences (P. chlorantha favouring dry, 68 calcareous grasslands, while P. bifolia will be typically found in fresh to wet meadows on acidic soil). 80 Recently, a study on some Western-European Platanthera populations composed almost exclusively of 81 intermediate looking individuals, based on morphology and molecular markers, concluded that such 82 individuals were not hybrids, but constitute an independent lineage, distinct from both widespread species 83 (Durka et al. 2017). 84The level of geitonogamy was observed to be higher in P. bifolia than in P. chlorantha because 85 the latter has a pollinarium-bending mechanism that prevents deposition of the pollinia directly after 86 removal (Maad & Nilsson 2004;Maad & Reinhammar 2004). This process may also affect the probability 87 of hybrid formation (Ishizaki et al. 2013). An allopatric P. bifolia population with a high degree (i.e. 88 almost 60%) of self-pollination was found by Brzosko (2003), although self-pollination in Platanthera 89 species is considered generally rare (Nilsson 1983;Maad 2002). 90In the genus Platanthera, floral scent plays a crucial role in guiding pollinators to the flowers 91 (Nilsson 1983;1985;Tollsten & Bergström 1993). A strong fragrance is emitted after dusk, when 92 pollinators (nocturnal moths) are most active (Nilsson 1983;1985;Tollsten & Bergström 1993; Hapeman 93 & Inoue 1997;Plepys et al. 2002a;2002b). Floral fragrances of Platanthera have been classified into 94 linaloolic, lilac, geraniolic and benzenoic chemotypes depending on the main class of compounds present 95 in the blend (Tollsten & Bergström 1993;Plepys et al. 2002a;2002b (Plepys et al. 2002a;2002b). Furthermore, a change in floral scent composition has been suggested 98 by Nilsson (1983;1985) to prevent effective cross-pollination between both species (Nilsson 1978; 99 Tollsten & Bergström 1993), by acting as a reproductive barrier via ethological mechanisms. Tollsten & 100 Bergström (1993) discovered that important inter-individual and inter-population variation in floral scent 101 exists, and may act as an adapta...

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Supplemental Information 1: Morphological Data From Allopatric Populations (Summarized in Table 2)

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“…was surveyed by Efimov (2011). Within Section Platanthera , some details of P. bifolia , P. chlorantha and P. holmboei were illustrated by Claessens & Kleynen (2011) and Bateman, James & Rudall (2012), and later were compared with the three Azorean species plus P. algeriensis by Bateman, Rudall & Moura (2013).…”

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“…Their overall length can be calculated from the empty thecae, and appropriately placed depressions at the base of the thecae suggest that the viscidia were near-circular in outline (mirroring the single viscidium of P. convallariifolia illustrated in Fig. 2D of Efimov, 2011, though the viscidia of P. hyperborea were described as “linear to linear-oblong” by Sheviak, 2002) and as presented were inclined only slightly relative to the horizontal (Figs. 13A, 14A–14C).…”

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“…Vegetatively, P. hyperborea and its close relatives differ from Section Platanthera in having narrower tubers (e.g., Sundermann, 1980; Currah, Smreciu & Hambleton, 1990; Sheviak, 2002; Sheviak & Jennings, 2006; Colwell, Sheviak & Moore, 2007; Efimov, 2011) that arguably are better described as filiform than fusiform. Rather than showing a clear distinction between oval basal leaves and lanceolate bracteoidal leaves, those of the P. hyperborea group pass gradually from broadly lanceolate lower leaves to bracteoidal upper leaves.…”

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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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Can phenotypic selection on floral traits explain the presence of enigmatic intermediate individuals in sympatric populations of Platanthera bifolia and P. chlorantha (Orchidaceae)?

Ambroise

Esposito

Scopece

et al. 2019

Plant Species Biology

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Pollinators represent one of the main agents of selection on floral traits. Here, we estimated phenotypic selection on floral morphology and phenology in a sympatric population of two orchid species, Platanthera bifolia and P. chlorantha, including enigmatic individuals with intermediate column morphology (as reflected by the distance between viscidia and caudicle length, two traits involved in assortative mating and reproductive isolation among Platanthera species), but genetically indistinguishable from P. bifolia. Our aim was to clarify whether the occurrence of intermediate phenotypes could be explained by the presence of selective pressures exerted by pollinators. Simple linear and quadratic regressions together with univariate and multivariate analyses were used to evaluate the strength of directional, disruptive and stabilizing selection. We found that selection on phenotypic traits varied between groups and sex functions. Contrary to our hypothesis, selection on the viscidia distance and caudicle length appeared to be consistent in the two P. bifolia groups. Interestingly, the viscidia distance was under significant stabilizing selection through female reproductive success in intermediate individuals. Based on these results, we conclude that, despite a significant selective pressure on some phenotypic traits, the presence of individuals with intermediate phenotype is not due to selection. Stabilizing selection on distance between viscidia in intermediate individuals may suggest that assortative mating play a role in the maintenance of this phenotypic polymorphism.

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An intriguing morphological variability of Platanthera s.l.

Cited by 14 publications

References 10 publications

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

Can phenotypic selection on floral traits explain the presence of enigmatic intermediate individuals in sympatric populations of Platanthera bifolia and P. chlorantha (Orchidaceae)?

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