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Accueil du site → Doctorat → États-Unis → 2009 → Ecology and Molecular Phylogenetics of Hydnora (Hydnoraceae) in Southern Africa

Old Dominion University (2009)

Ecology and Molecular Phylogenetics of Hydnora (Hydnoraceae) in Southern Africa

Bolin Jay Francis

Titre : Ecology and Molecular Phylogenetics of Hydnora (Hydnoraceae) in Southern Africa

Auteur : Bolin Jay Francis

Université de soutenance : Old Dominion University

Grade : Doctor of Philosophy (PhD) 2009

Résumé
The Hydnoraceae are a clade of root holoparasitic angiosperms that contain two small genera, Hydnora and Prosopanche. This study, focused on Hydnora, presents novel data regarding the pollination biology, germination ecology, parasite-host nutritional relationships, and the molecular systematics of this group. Experimental addition of the primary pollinator, Dermestes maculatus to Hydnora africana chamber flowers demonstrated beetle imprisonment during the carpellate stage. Changes in the inner surfaces of the androecial chamber allowed beetle escape after pollen release. Most beetles escaped, dusted with viable pollen, three days after pollen release. To investigate germination ecology, aqueous root extracts of host and non-host Euphorbia spp. were applied to seeds of Hydnora triceps which germinated only in response to root extracts of its exclusive host, Euphorbia dregeana, and not for co-occurring non-host Euphorbia spp. This pattern of host specific germination suggests that germination response to host-root cues may be responsible for host partitioning. There are large gaps in our understanding of holoparasitic plant-host nutrient relationships and the mechanisms of solute uptake. Transdermal water loss, parasite-host mineral relationships, and heterotrophy were evaluated for Hydnora . Transdermal water loss in Hydnora ranged from 0.14±.02 to 0.38±.04 mg cm-2 hr-1, comparable to transpiration rates recorded for xerophytes. Concentrations of P and K were higher in Hydnora relative to their CAM (Crassulacean acid metabolism) hosts ; other mineral concentrations were significantly lower in the parasite or were not different. Stable isotope fractionation in host tissues dictated significant differences between parasite and host δ 13C signatures. A phylogeny of the Hydnoraceae was generated using plastid (rpoB) and nuclear ITS (internal transcribed spacer) DNA sequences. The analyses supported the monophyly of Hydnora and Prosopanche, their relationship as sister genera, and validated subgeneric sections of Hydnora. Optimization of the character of host preference suggests the Fabaceae as the ancestral state of Prosopanche and Hydnora. A well resolved Hydnora clade parasitizing Fabaceae was resolved as sister to a clade parasitizing exclusively Euphorbia, indicating a single host shift. In order to examine the specific limits of H. africana phylogenetic and morphological data were compared. In the section Euhydnora, floral morphometric data was congruent with phylogenetic data, revealing three cryptic taxa within Hydnora africana sensu lato, Hydnora africana, Hydnora longicollis, and a new Hydnora species.

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