Dissertation/Thesis Abstract

Experimental and molecular studies of bryophyte dispersal on alpine summits
by Robinson, Sean Charles, Ph.D., State University of New York at Albany, 2012, 195; 3523653
Abstract (Summary)

A review of bryophyte dispersal studies over the last sixty years revealed that the role of gametophytic fragments in bryophyte population dynamics has not been adequately addressed. In this dissertation, I investigate the dispersal potential of wind blown bryophyte fragments on Adirondack alpine summits using a combination of field and laboratory methods.

In order to establish that bryophyte fragments are disseminating across the summits, airborne diaspores were collected from early spring snow deposits in 2008, 2009, and 2010 from the summit of Mt. Marcy. Additionally, newly designed propagule traps were used to collect material during the summer months of 2009 and 2010 on the summits of Mt. Marcy and Algonquin peak. All fragments collected were subjected to a series of growth experiments to determine reproductive viability. A total of 6130 gametophytic fragments, representing 26 species, were collected. Up to 20% of fragments collected were found to be reproductively viable, with the majority of growth originating from stem tissue. The presence of one hundred spores were detected. These results show that a high number of reproductively viable gametophytic fragments are being disseminated across the summits, while spore production is uncommon to rare.

The importance of vegetative fragments in the dispersal of bryophytes on these summits was further evaluated in parallel comparative studies of Sphagnum pylaesii and S. tenellum using direct and indirect methods. S. pylaesii reproduces primarily by fragmentation, yet it maintains large populations on several of the Adirondack alpine summits. Sphagnum tenellum occupies similar habitats but differs in sexual condition and amount of spore production. Differences in rates of spore production in these two species were confirmed through the examination of contemporary and historic collections of both species. Sporophytes were found in 0.5% and 49% of the S. pylaesii and S. tenellum material, respectively.

As an indirect measure of dispersal between the Adirondack summits, population differentiation (FST), and estimated gene flow (Nm) were calculated from genetic variation at fifteen microsatellite loci. Genetic differentiation (FST) between the Adirondacks and regions outside the Adirondacks was also determined. Molecular data support the hypothesis that Sphagnum pylaesii has dispersed successfully among summits through fragmentation, given a lack of genetic variability (P = 0, A = 0), and consequently no differentiation (FST = 0) and high gene flow (Nm = ∞) between the summits. In contrast, regions outside the Adirondacks showed high levels of genetic variability (P = 7.3, A = 3.1) and high differentiation between regions (FST = 0.46). Sphagnum tenellum, with greater levels of genetic variability in the Adirondacks (P = 6, A = 2.5 (2–4)), and lower levels of differentiation between sampled regions, compared to S. pylaesii (F ST = 0.27), seems to be maintaining its current distribution inside and outside the Adirondacks by the production and dissemination of spores.

To determine dispersal ability experimentally on alpine summits, branch fragments were coated with ultraviolet fluorescent dye and released from specific locations on two alpine summits. Distances traveled by fragments were measured after being located during evening surveys using ultraviolet LED light sources 24 h after initial release. A frequency distribution of fragment dispersal distances fitted a power function showing a high number of fragments near the point of origin followed by a rapid decline and long tail. Fragments dispersed a maximum distance of 26 m and 54 m in Sphagnum tenellum and S. pylaesii, respectively. This is the longest distance measured for wind dispersed bryophyte fragments.

Fragment release in a wind tunnel support field experiments, showing maximum fragment dispersal at wind speeds at and below those measured on the summit of Mt. Marcy during the fall of 2010 using a 2D sonic anemometer.

Together, the results of this study reveal that gametophytic fragments play an important role in the distant dispersal of bryophytes on and between alpine summits.

Indexing (document details)
Advisor: Robinson, George, Miller, Norton
Commitee: Gonder, Mary, Kirchman, Jeremy, Rice, Steven
School: State University of New York at Albany
Department: Biology
School Location: United States -- New York
Source: DAI-B 74/01(E), Dissertation Abstracts International
Subjects: Biology, Plant biology, Ecology
Keywords: Alpine, Bryophytes, Dispersal, Experimental growth, Microsatellites
Publication Number: 3523653
ISBN: 9781267567703