Molecular Phylogenetics and Biogeography of Hawaiian Members of the Pteridophyte Genus Cibotium (Dicksoniaceae)
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Molecular phylogenetics and biogeography of Hawaiian members of the pteridophyte genus Cibotium (Dicksoniaceae) Submitted in partial fulfillment of the requirements for graduation with honors from the Department of Natural Sciences at Carroll College, Helena, Montana Annabelle Catherine Kleist April 3, 2006 This thesis for honors recognition has been approved for the Department of Biology. Dr. Gerald Shields, Reader Date 4--S-eC, Date Acknowledgements The author thanks her thesis director, Dr. Jennifer Geiger, for research advice, encouragement, and editing; her professor, Dr. Gerald Shields, for writing inspiration and editing; Christine Nelson and Kris Christensen, her co-researchers, for their advice and help in the lab; Dr. Tom Ranker from UC-Boulder for plant material, pictures, and collaboration; and Carroll College MT for lab space. Financial support was provided by the National Science Foundation. ii Table of Contents Acknowledgements.....................................................................................................................................ii Abstract.........................................................................................................................................................iv List of Tables................................................................................................................................................v List of Figures............................................................................................................................................. vi Introduction....................................................................................................................................................1 Materials and Methods.................................................................................................................................5 Results............................................................................................................................................................ 7 Discussion....................................................................................................................................................10 Figure Captions...........................................................................................................................................16 References....................................................................................................................................................19 in Abstract Although ferns comprise a significant proportion of Hawaii’s native vascular-plant flora, few phylogenetic studies have been performed to infer relationships among taxa and to deduce their biogeographical origins. Species from the pteridophyte genus Cibotium can be found among the canopy in the Island’s montane regions and were the focus of this study. Four species of Cibotium are endemic to the Hawaiian Archipelago and ten species exist worldwide. The goal of this study was to determine whether Hawaiian Cibotium is monophyletic and to discover the biogeographical origins of the species. Two chloroplast DNA fragments, trnL-F IGS and rbcL, were sequenced and maximum parsimony, maximum likelihood, and neighbor joining analyses were performed. These analyses support a South American origin for a monophyletic Hawaiian Cibotium. This supports the hypothesis that the ancestor of Hawaiian Cibotium colonized Hawaii by wind dispersal of spores via a combination of the ICTZ, Hadley Cells, and trade winds. iv List of Tables Table 1. Species list, collector, and collection number.......................................................................14 Table 2. Primers, components, and cycling conditions for PCR amplification.............................. 15 v List of Figures Figure 1. trnL-F consensus tree............................................................................................................. 17 Figure 2. rbcL consensus tree................................................................................................................ 18 vi Introduction The current high islands of the Hawaiian Archipelago are located approximately 4000 km from the nearest continent, North America, and 1600 km from the nearest archipelago, the islands of Polynesia. The Hawaiian Island chain is only about 80 million years old and was produced in a conveyer-belt-like manner by a transfixed volcanic hotspot beneath the Pacific Ocean. Islands are removed from the hotspot as the Pacific tectonic plate moves to the northwest. Geological evidence suggests that the islands’ separation from the mainland has been relatively constant (Carson and Clague, 1995) and their extreme isolation has formed an imposing barrier to colonization by terrestrial organisms. Due to this continual isolation and young geological age, the Hawaiian Islands provide an ideal setting to study plant speciation, diversification, and evolutionary origins. In an isolated island environment, evolution leading to remarkable morphological diversity can occur within a short amount of time (Hiramatsu et al., 2001). The Hawaiian Islands have the highest levels of species endemism of any regional flora in the world (Wagner et al., 1999), which can be explained by the continual opening of new habitats accompanied by geographic dispersal through the developing islands. Of the 188 species of pteridophytes native to Hawaii, 77% are endemic to the archipelago (Palmer, 2003). Pteridophytes comprise nearly 15% of the native vascular-plant species of the Hawaiian Archipelago, although they constitute only about 3% of the vascular-plant flora of the world (Wagner et al., 1999). Despite the abundance of native ferns on the Hawaiian Islands, only seven phylogenetic studies that included Hawaiian pteridophytes had been published as of spring 2006 (Haufler and Ranker, 1995; Hennequin et al., 2003; Ranker et al., 2003, 2004; Schneider et al., 2004, 2005; Geiger and Ranker, 2005). These studies represent only a fraction of the diversity present in Hawaiian pteridophytes. In addition, few studies have sampled widely enough outside of the Hawaiian Islands to resolve the biogeographical origins of native Hawaiian ferns or fern groups. 1 It has been estimated that extant species living in Hawaii’s habitats could not have colonized the islands before about 23 Ma. This may have been due to a 10 million-year lull in new island formation that necessitated completely new colonization and evolution at this time (Price and Clague, 2002). In addition, montane taxa, including most of the ferns, probably arrived from outside the Hawaiian archipelago or evolved after the formation of Kauai approximately 5.2 Ma because appropriate mid- and high-elevation montane habitats did not exist on islands older than Kauai by the time Kauai was high enough to support these habitats (Price and Clague, 2002). One of the first successful colonists of the newly emerging montane habitats in the Hawaiian Archipelago was the ancestor of the genus Diellia, a group of ferns endemic to Hawaii. The estimated time of the radiation of the extant species of Diellia is approximately 2 Ma (Schneider et al., 2005). Biogeographical histories of Hawaiian ferns tend to be more complex and obscure than those of pteridophytes from other volcanic archipelagos (Kim et al., 1998). This is largely due to their long distances from source populations. Spores are regularly transported by wind and some species can survive exposure to high altitudes and UV radiation (Gradstein and van Zanten, 2001). There are three climate-based pathways that may explain the airborne dispersal of fern spores to Hawaii. The first is the jetstream, a wave-like band of fast moving air that flows from west to east at up to 485 kph and approximately 5,500 to 17,000 m in altitude. The jetstream accelerates as it moves eastward from Southeast Asia and decelerates as it moves over the Hawaiian Islands. Spores could enter the jetstream during storms in SE Asia/Malaysia and be dropped onto Hawaii two to four days later. The combined activity of storms and the jetstream may account for colonizing species from Southeast Asia/Malaysia, and Fosberg (1948) hypothesized that the ancestors of the majority of Hawaiian plants are of Indo-Malaysian origins. Many of the Hawaiian species of the fern genus Dryopteris are closely related to Dryopteris 2 species in SE Asia, and the jetstream is the proposed mechanism for their dispersal to Hawaii (Geiger and Ranker, 2005). The second weather-based pathway for spores migrating to Hawaii is the trade winds. The high islands are within the northern trade-wind belt, while, for most of the year, 90% of the low elevation and surface winds are from the north-northeast. Northerly air masses are drawn towards the equator by the North Pacific anticyclone, so the trade winds could account for the dispersal of spores from the Americas. The third method of air-borne dispersal of spores to Hawaii is the combination of the trade winds, the effects of Hadley cells, and a seasonal shift southward of the inter-tropical convergence zone (ITCZ). The ITCZ marks a discontinuity between the northern and southern hemispheres and normally lies north of the equator at 5-10°N. This tends to limit both the movement of low altitude air masses across the equator and the dispersal of wind-blown organisms. During the austral late summer/early fall, the ITCZ can form south of the equator at 5-10° S (Wright et al., 2001). This southerly position of the ITCZ periodically