Abstract Detail

Mycology

McCormick, Melissa [1], Hartvig, Ida [2], Evans, Simone [2], Whigham, Dennis [2].

Mycorrhizal fungus association and speciation in North American fringed orchids (Platanthera).

The Orchidaceae is one of the most species-rich plant families, with nearly 10% of flowering plant species. Orchids depend on associations with particular mycorrhizal fungi for nutrition throughout their life cycle. Orchid distribution is influenced by the availability of compatible mycorrhizal fungi, particularly when orchids require specific fungi. Specificity of orchids for mycorrhizal fungi remains controversial, with no clear patterns determining the range of fungi that are compatible with different orchid species, but when it occurs, specialization on different fungi may have implications for orchid speciation. Different fungi may grow in different environments, so associations with fungi may also influence whether orchid species co-occur or are environmentally segregated. Hybridization is a major driver of speciation for many plants, and for orchids in particular. If hybrids use different fungi than their parent species, then spatial segregation driven by the availability of appropriate mycorrhizal fungi could influence whether hybrids evolve into new species. We studied the role of hybridization and fungal use in the speciation patterns of the most species rich genus of terrestrial orchids in North America, Platanthera. We focused on species complexes that include both contemporary hybrids and recently described species of proposed hybrid origin in two subgenera. We also considered additional species within and outside of these hybrid complexes. We used a combination of fungal cultivation and direct sequencing to test the hypotheses that 1) the identity of fungal associates reflects plant phylogenetic relatedness, and 2) specificity in fungal associations differs among orchid species, as well as between hybrids and parent species. We sequenced the internal transcribed spacers of the nuclear ribosomal repeat from fungi in or cultured from >200 Platanthera roots and found that phylogenetically distinct orchids associated with different fungi. Orchids in section blephariglottis were associated primarily with Tulasnella fungi, while those in section fimbriella associated primarily with Ceratobasidum fungi. Within each section, some species associated with a narrow group of fungi and others were generalists. Contemporary hybrids associated with diverse fungi but favored the fungal assemblage of the parent they were co-occurred with. The newly described species that were thought to be of hybrid origin were more specific than contemporary hybrids. This suggests that fungal associations may affect orchid speciation and co-existence. This information has implications for species delimitation and conservation planning, as well as for setting conservation priorities and conserving threatened Platanthera species.

Related Links:
Project website for Platanthera speciation and mycorrhizal associations

1 - Smithsonian Institution, SERC, 647 Contees Wharf Rd, Edgewater, MD, 21037, United States
2 - Smithsonian Environmental Research Center, 647 Contees Wharf Rd, Edgewater, Maryland, 21037, United States

Keywords:
Orchidaceae
Mycorrhizae
Speciation
host specificity
Mycology.

Presentation Type: Oral Paper
Session: MY3, Mycology: Fungus-Plant Interactions - Ectomycorrhizae and Orchid Mycorrhizae
Location: /
Date: Tuesday, July 20th, 2021
Time: 4:30 PM(EDT)
Number: MY3007
Abstract ID:934
Candidate for Awards:None