Characterization of sympatric Platanthera bifolia and Platanthera chlorantha (Orchidaceae) populations and study of phenotypic selection.
(2017)
Files
Fabiana_Esposito_phd_thesis.pdf
Restricted Access - Adobe PDF
- 11.42 MB
Details
- Authors
- Supervisors
- Abstract
- Two terrestrial and rewarding Platanthera species, Platanthera bifolia and Platanthera chlorantha are widespread throughout Europe. Though very closely genetically related, they exhibit significant morphological, phenological and ecological differences. Specific floral characteristics are likely to prevent effective cross-pollination between both species, which generally attract distinct moth species through the emission of different fragrances. However, situations in which both species come into contact are not rare and individuals with intermediate gynostemium morphology are frequently observed. In this thesis I investigated two Belgian mixed populations of P. bifolia and P. chlorantha where individuals with intermediate column morphology co-occurred. I have explored the occurrence of natural hybridization/introgression in these populations by carrying morphological analyses, investigated the genetic profiles and floral scent composition of both P. bifolia and P. chlorantha and intermediate morphotypes. I also have examined their mycorrhizal associations and observed night flowers visitors. Moreover, I have estimated phenotypic selection and reproductive compatibility between species in order to test the presence of reproductive isolation in sympatry. The results of AFLP genetic markers did not separate intermediate plants from P. bifolia group. This result was also corroborated by the floral scent analysis (headspace samples), which revealed a similar chemical composition of intermediate morphotypes in relation with P. bifolia. Manual cross-pollination has demonstrated that P.bifolia and P. chlorantha are interfertile, and fruit set analysis showed a significantly higher female reproductive success of P. chlorantha compared to P. bifolia and morphologically intermediate individuals. Moreover, observations on insect flower visitors conducted in both mixed populations using light traps revealed that two Noctuidae species Cucullia umbratica and Autographa gamma were carrying pollinaria of both Platanthera species, by suggesting that these two moths species might be responsible for interspecific pollen transfer. To explain the degrees of morphological divergence and the molecular similarity observed between intermediate individuals and the sympatric P. bifolia species, we investigated directional selection on phenological and morphological characters. A multiple regression analysis was conducted to estimate the phenotypic selection acting on floral characters in both studied species and intermediate morphotypes. I have observed that phenotypic selection on pollination traits in P. bifolia and P. chlorantha varied between species and sex functions. I detected inflorescence length for both Platanthera species undergoing positive selection gradients through male and female functions. Specifically, regression analysis showed positive selection gradients for a longer spur length a longer labellum and for early flowering individuals in P. bifolia. On the other hand, in P. chlorantha a positive directional selection was observed for a larger distance between the viscidia and for later flowering individuals. Nevertheless, since directional selection on floral column in P. bifolia was not observed I concluded that the presence of intraspecific individuals of P. bifolia with intermediate phenotype is not due to selection for the more efficient pollinator. However, only more detailed studies focused on the strength of reproductive barriers and on genomic analyses and ecology of these intermediate phenotypes in a larger scale, will shed light on the reasons that lay at the basis of their presence and persistence.
- Affiliations
Citations
Esposito, F. (2017). Characterization of sympatric Platanthera bifolia and Platanthera chlorantha (Orchidaceae) populations and study of phenotypic selection. https://hdl.handle.net/2078.5/177827