Characterization of sympatric Platanthera bifolia and Platanthera chlorantha (Orchidaceae) populations with intermediate plants

Abstract

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...

Biosystematics of Platanthera bifolia s.l. (Orchidaceae): inferences from analysis of Scandinavian population samples

“…Buttler (2011) distinguished the two taxa at species level, and following studies in Belgium (Esposito et al 2016, 2017, 2018, Ambroise et al 2019), his disposition was supported by Tyteca and Esposito (2018). According to Jonsell (2004: 163): ‘Taxa are treated as species if they differ in at least two presumably independent morphological characters and are more or less completely separated by a barrier – geographical and/or ecological, phenological or genetic.…”

“…Thus, the short-spurred and long-spurred taxa can be aptly characterized as less prominent ecological variants that largely differ from each other in a few characters. Moreover, the circumstance that the short-spurred taxon seems to have an incoherent distribution comprising 1) Atlantic NW Europe, 2) the Alps, 3) Portugal and 4) Toscana (Buttler 2011, Tyteca andEsposito 2018) suggests that this taxon might be polyphyletic -especially when taking into account the evolutionary role of pollinator shifts in P. bifolia s.l. (Boberg et al 2014).…”

“…Since then, there has been consensus to separate P. bifolia and P. chlorantha at species level. Both species are diploid with 2n = 42 chromosomes (Heusser 1938, Kliphuis 1963, Averyanov 1979, Alba et al 2003), recent molecular studies have shown them to be highly genetically similar (Pavarese et al 2011, Bateman et al 2012, Esposito et al 2018), and both have nectar‐producing flowers that are almost exclusively pollinated by nocturnal Lepidoptera of the families Noctuidae, Sphingidae and Geometridae (Nilsson 1978, Claessens and Kleynen 2011, Steen 2012, Steen and Mundal 2013, Boberg et al 2014, Sexton 2014, Esposito et al 2017, Steen et al 2019).…”

Orchids from Basilicata: The Scent

“…Another study performed in Sweden showed the presence in the aroma of methyl benzoate, benzyl acetate, benzyl benzoate, benzyl salicylate, and lilac aldehydes Orchids from Basilicata: The Scent [29]. Finally, in a work performed in Belgium, 3,7-dimethyl-1,3,6-octatriene, and santolinatriene were detected in the aroma [30].…”

“…In Switzerland, linalool, methyl benzoate, and geraniol were the components of the aroma [27,28]. In Pays-Bas, lilac aldehydes and linalool were found [28]; in Sweden, methyl benzoate and linalool [28]; and in Belgium, the main components were 3,7-dimethyl-1,3,6-octatriene, 3carene, and lilac aldehyde [30].…”