UVM Theses and Dissertations
Format:
Print
Author:
McHenry, Monique A.
Dept./Program:
Plant Biology
Year:
2012
Degree:
PhD
Abstract:
Uplift of the tropical Andes had a significant impact on the diversification of flora and fauna in South America. The connection between geologic history and modern biodiversity patterns is supported by phylogenetic data, divergence time estimations, and reconstruction of ancestral geographic areas. However, these inquiries have been limited to fauna and angiosperms; investigations based on seedfree vascular plants are scant. An investigation of tropical Andean ferns in the genus Polystichum Roth (Dryopteridaceae) provides the first insight into the timing of diversification of Andean seed-free vascular plant lineages in the context of the known sequence of geologic events, including their origin and spatiotemporal patterns of diversification. This dissertation begins with a review of the literature, followed by two chapters of original investigation intended for simultaneous submission as peer-reviewed manuscripts, and ends with a comprehensive bibliography.
The origin and patterns of divergence within exindusiate Andean Polystichum species were investigated using genetic material from specimens from Mexico, Central America, and South America. Plastid DNA sequence comparisons confirmed a monophyletic group within the fern genus Polystichum Roth (Dryopteridaceae). This clade was found to be rich in endemic species from the northern and central Andes and to be supported by a morphological synapomorphy, the lack of an indusium. The exindusiate Andean Polystichum clade diverged from a lineage rich in endemics from Mexico during the middle Miocene, based on divergence-time estimations. An ancestral area reconstruction suggested a central Andean diversification for most of the exindusiate species with radiation to the northern Andes and the southeastern South American highlands. From these results we hypothesize that the divergence events of the exindusiate Andean Polystichum lineage corresponded with episodes of uplift in the tropical Andes.
A systematic revision of the exindusiate Andean Polystichum clade was informed by the examination of over 2,000 herbarium specimens. Taxonomically informative characters (58) were identified and scored for 160 accessions. The most informative characters were found to be perispore morphology, leaf dissection, indument color and shape, and bulbil presence. Based on the morphological revision in combination with the phylogenetic data, 26 taxa of exindusiate Andean Polystichum were recognized including two new varieties and two new species. Results from a morphological character reconstruction suggested that the most recent common ancestor of exindusiate Andean Polystichum had twice-pinnate laminar dissection and lacked a bulbil.
In conclusion, phylogenie, biogeographic, and sytematic inquiry of the widespread and species-rich exindusiate Andean Polystichum clade has provided an abundance of new data, that support the impact ofgeological events on the evolution of biodiversity in the Andes.
The origin and patterns of divergence within exindusiate Andean Polystichum species were investigated using genetic material from specimens from Mexico, Central America, and South America. Plastid DNA sequence comparisons confirmed a monophyletic group within the fern genus Polystichum Roth (Dryopteridaceae). This clade was found to be rich in endemic species from the northern and central Andes and to be supported by a morphological synapomorphy, the lack of an indusium. The exindusiate Andean Polystichum clade diverged from a lineage rich in endemics from Mexico during the middle Miocene, based on divergence-time estimations. An ancestral area reconstruction suggested a central Andean diversification for most of the exindusiate species with radiation to the northern Andes and the southeastern South American highlands. From these results we hypothesize that the divergence events of the exindusiate Andean Polystichum lineage corresponded with episodes of uplift in the tropical Andes.
A systematic revision of the exindusiate Andean Polystichum clade was informed by the examination of over 2,000 herbarium specimens. Taxonomically informative characters (58) were identified and scored for 160 accessions. The most informative characters were found to be perispore morphology, leaf dissection, indument color and shape, and bulbil presence. Based on the morphological revision in combination with the phylogenetic data, 26 taxa of exindusiate Andean Polystichum were recognized including two new varieties and two new species. Results from a morphological character reconstruction suggested that the most recent common ancestor of exindusiate Andean Polystichum had twice-pinnate laminar dissection and lacked a bulbil.
In conclusion, phylogenie, biogeographic, and sytematic inquiry of the widespread and species-rich exindusiate Andean Polystichum clade has provided an abundance of new data, that support the impact ofgeological events on the evolution of biodiversity in the Andes.