Genetic differentiation and habitat preference of flowering-time variants within Gymnadenia conopsea

Abstract

Using fast-evolving microsatellites, more slowly evolving ITS markers and performing habitat analyses, we demonstrated a drastic genetic divergence and significant habitat differentiation between early- and late-flowering variants of plants morphologically belonging to Gymnadenia conopsea ssp conopsea. The two phenological variants can either be found in separate or in mixed populations. Information from microsatellite markers and ITS sequences indicated the occurrence of an early historical split between the two flowering-time variants, a split that has been maintained until the present time even within sympatric populations. Early-flowering variants were also far more genetically diverse, had more alleles per microsatellite locus and a wider habitat amplitude than late-flowering variants. As a comparison, we included G. odoratissima in the sequencing study. We found G. odoratissima to be most closely related to the early-flowering type. This indicates a more ancient divergence event between the two flowering-time variants within G. conopsea ssp conopsea than between the two different species G. odoratissima and the early-flowering variant of G. conopsea. Possible explanations to the results arrived at and possible mechanisms maintaining the genetic separation are discussed.

Absence of pollinator-mediated premating barriers in mixed-ploidy populations of Gymnadenia conopsea s.l. (Orchidaceae)

“…differing in morphologic and scent characteristics has been reported repeatedly for many areas of its distribution (Heusser 1938;Gustafsson and Lönn 2003;Vöth and Sontag 2006). Recently, Marhold et al (2005) suggested that the variability in Gymnadenia complex might be underlined by differences in the ploidy level.…”

Frequency-Dependent Selection and the Evolution of Assortative Mating

“…Host races of phytophagous insects are thought to have evolved because individuals group together and mate on their preferred plant host (Berlocher and Feder 2002), as exemplified by the poster child of sympatric speciation: the apple maggot fly, Rhagoletis pomonella, in which a new host race formed on apples in the mid-1800s (Filchak et al 2000). Cases of sympatric speciation in plants are often associated with shifts in flowering time (Gustafsson and Lonn 2003;Silvertown et al 2005;Antonovics 2006;Savolainen et al 2006) or shifts in pollen placement (Maad and Nilsson 2004), such that mating tends to occur within groups of similar plants. Similarly, grouping by location or timing during mating has been implicated in the evolution of assortative mating in salmon and birds (Hendry et al 2007).…”

Land use affects flowering time: seasonal and genetic differentiation in the grassland plant Scabiosa columbaria

“…Considering the evolutionary impact of grassland management practices, especially the effect of mowing must be taken into account, since mowing cuts off the plants every year during more or less the same time period. This reduces the seed production of those plants that can neither tolerate the damage nor have finished their reproduction before mowing (Gustafsson and Lönn 2003). The early flowering of S. columbaria can, therefore, be considered as an adaptation to land use, avoiding to be cut off before seed set (Grossmann 1975).…”

“…Different flowering times within the same species have been reported for several plant genera (Karlsson 1984;Lennartsson 1997;Gustafsson and Lönn 2003), and phenological variants of the same taxon, called seasonal ecotypes, are considered to result from adaptation to environmental conditions or particular habitats (Turesson 1922). Selective factors contributing to the evolution of such flowering time ecotypes can be climate (Stinchcombe et al 2004), competition for light and nutrients, increased pollination through flowering synchrony, competition for pollinators or dispersal agents (Janzen 1967), reduced inbreeding (Barrett and Kohn 1991) or management practices (Wettstein 1895;Warwick and Briggs 1979;van Tienderen and van der Toorn 1991;Theaker and Briggs 1993).…”