Floral isolation is the major reproductive barrier between a pair of rewarding orchid sister species

AimWe test for spatial and climatic patterns of diversification in the Orchidaceae, an angiosperm family characterized by high levels of species diversity and rarity. Globally, does orchid diversity correlate with land area? In Australia, does diversity correlate with herbarium collecting effort, range size, or climate niche breadth? Where are Australia's orchids distributed spatially, in protected areas, and in climate space?LocationGlobal, then Australia.MethodsWe compared orchid diversity with land area for continents and recognized orchid diversity hotspots. Then, we used cleaned herbarium records to compare collecting effort (for Australian Orchidaceae vs. all other plant families, and also among orchid genera). Spatial and climate distributions were mapped to determine orchids’ coverage in the protected area network, range sizes, and niche breadths.ResultsGlobally, orchid diversity does not correlate with land area (depauperate regions are the subantarctic: 10 species, and northern North America: 394 species). Australian herbarium records and collecting effort generally reflect orchid species diversity (1,583 spp.), range sizes, and niche breadths. Orchids are restricted to 13% of Australia's landmass with 211 species absent from any protected areas. Species richness is the greatest in three biomes with high general biodiversity: Temperate (especially southwest and southeast Australia), Tropical, and Subtropical (coastal northern Queensland). Absence from the Desert is consistent with our realized climate niche—orchids avoid high temperature/low rainfall environments. Orchids have narrower range sizes than nonorchid species. Highly diverse orchid genera have narrower rainfall breadths than less diverse genera.Main conclusionsHerbarium data are adequate for testing hypotheses about Australian orchids. Distribution is likely driven by environmental factors. In contrast, diversification did not correlate with increases in range size, rainfall, or temperature breadths, suggesting speciation does not occur via invasion and local adaptation to new habitats. Instead, diversification may rely on access to extensive obligate symbioses with mycorrhizae and/or pollinators.

Section: Discussionmentioning

confidence: 99%

Orchid diversity: Spatial and climatic patterns from herbarium records

Gaskett

Gallagher

2018

“…Among-population variation in interactions with pollinators may result in divergent selection on floral traits, promoting floral diversification (Grant, 1949(Grant, , 1994Stebbins, 1970;Van der Niet & Johnson, 2012; Van der Niet, Peakall, & Johnson, 2014), and the formation of pollination ecotypes (Anderson, Alexandersson, & Johnson, 2010;Johnson, 1997;Van der Niet, Pirie, Shuttleworth, Johnson, & Midgley, 2014). However, ecotypes (e.g., Armbruster, 1985;Boberg et al, 2014;Van der Niet, Pirie, et al, 2014) and closely related species (e.g., Campbell, Waser, & Melendez-Ackerman, 1997;Sun, Schlüter, Gross, & Schiestl, 2015) commonly differ in multiple traits that can be strongly correlated within and across populations, and the relative contribution of different traits to adaptive differentiation is usually poorly known. Because of strong trait correlations, experimental approaches are required to determine the independent and combined effects of individual traits on pollination success and plant fitness (Campbell, 2009;Castellanos, Wilson, & Thomson, 2004;Schemske & Bradshaw, 2008).…”

Section: Introductionmentioning

confidence: 99%

The independent and combined effects of floral traits distinguishing two pollination ecotypes of a moth‐pollinated orchid

Trunschke

Sletvold

Ågren

2019

Identifying traits and agents of selection involved in local adaptation is important for understanding population divergence. In southern Sweden, the moth‐pollinated orchid Platanthera bifolia occurs as a woodland and a grassland ecotype that differ in dominating pollinators. The woodland ecotype is taller (expected to influence pollinator attraction) and produces flowers with longer spurs (expected to influence efficiency of pollen transfer) compared to the grassland ecotype. We examined whether plant height and spur length affect pollination and reproductive success in a woodland population, and whether effects are non‐additive, as expected for traits influencing two multiplicative components of pollen transfer. We reduced plant height and spur length to match trait values observed in the grassland ecotype and determined the effects on pollen removal, pollen receipt, and fruit production. In addition, to examine the effects of naturally occurring variation, we quantified pollinator‐mediated selection through pollen removal and seed production in the same population. Reductions of plant height and spur length decreased pollen removal, number of flowers receiving pollen, mean pollen receipt per pollinated flower, and fruit production per plant, but no significant interaction effect was detected. The selection analysis demonstrated pollinator‐mediated selection for taller plants via female fitness. However, there was no current selection mediated by pollinators on spur length, and pollen removal was not related to plant height or spur length. The results show that, although both traits are important for pollination success and female fitness in the woodland habitat, only plant height was sufficiently variable in the study population for current pollinator‐mediated selection to be detected. More generally, the results illustrate how a combination of experimental approaches can be used to identify both traits and agents of selection.

“…left aside because it has been suggested that the (relative) amount of scent compounds is highly affected by environmental (nongenetic) effects and is relatively evolutionarily labile (e.g., highly adaptive) to be used in phylogenetic studies (Barkman 2001;Levin et al 2003). Indeed, floral scents can be different between closely related species, not only through particular ratios of more widespread compounds, but also through specific key compounds (Schiestl and Ayasse 2002;Raguso 2008;Waelti et al 2008;Ayasse et al 2011;Okamoto et al 2015;Sun et al 2015). Moreover, both specific key compounds and a specific ratio of (common) compounds may be exposed to phenotypic selection (Andersson 2003;Galen et al 2011;Schiestl et al 2011;Parachnowitsch et al 2012).…”

Section: Introductionmentioning

confidence: 99%

Comparative analyses of flower scent inSileneaereveal a contrasting phylogenetic signal between night and day emissions

Prieto‐Benítez

Millanes

Dötterl

et al. 2016

Flower scents are complex blends of volatile compounds often shaped by selection pressures exerted by mutualistic and antagonistic interaction partners, but also by phylogenetic constraints. So far, little is known about the relative effect of selection and phylogenetic signal on scent patterns, and no study to date analyzed the phylogenetic signal in multivariate semiquantitative scent patterns. We analyzed the phylogenetic signal in qualitative and semi-quantitative patterns of flower scents in 47 Sileneae (Caryophyllaceae) species using phylogenetic principal component analysis (pPCA) and several indices of univariate and multivariate phylogenetic signal. As previous results showed that Sileneae species are visited by diurnal and nocturnal pollinators and flower scents also vary along the day, we compared the phylogenetic signal between night and day. Multivariate pPCA analyses identified compounds that correlate with the phylogeny at both night and day; however, multivariate Bloomberg 0 s K detected phylogenetic signal in the dataset of night scents, but not of day scents. In multivariate qualitative datasets, phylogenetic signal was neither found for day nor for night scents. In univariate analyses, phylogenetic signal was detected for some compounds both for day and night scents. Overall, we found that the phylogenetic signal is stronger in night compared to day scents, which might be owed to the different guilds of pollinators at day and night. At day, the phylogenetic resemblance of Sileneae scents might be masked by or disappear due to divergent selective pressures exerted by a diverse guild of pollinators on the different species. In contrast, we hypothesize that the nocturnal moth pollinators exert similar selective pressures; thus, the phylogenetic similarity of scent profiles might be conserved. Future studies of scent phylogenetic signal must consider not only the usage of qualitative measures but also semiquantitative analyses.