ABSTRACT BRYOPHYTE INFLUENCE ON TERRESTRIAL AND EPIPHYTIC FERN GAMETOPHYTES by Mirabai R. McCarthy The climate and structural complexity of tropical forests enable vertical habitat differentiation between epiphytic and terrestrial communities. Because fern spores are copiously released one might expect to find species growing in both habitats, yet taxa are typically confined to one particular habitat type. The goal of this study was to better understand how development of epiphytic and terrestrial fern species is restricted by habitat, by observing gametophyte growth on various substrates. Experiments revealed that terrestrial gametophytes were malformed, significantly reduced in size and did not reach sexual maturity or failed to germinate when sown directly on top of, or in close proximity to epiphytic bryophyte substrates. In contrast, epiphytic species developed uniformly regardless of distance to bryophyte substrates. These observations indicate that epiphytic bryophytes have a negative impact on terrestrial gametophyte development, perhaps through allelopathy, and this interaction appears to represent a limiting factor for the establishment of terrestrial species in epiphytic communities. BRYOPHYTE INFLUENCE ON TERRESTRIAL AND EPIPHYTIC FERN GAMETOPHYTES A Thesis Submitted to the Faculty of Miami University in partial fulfillment of the requirements for the degree of Master of Science Department of Botany by Mirabai Rachel McCarthy Miami University, Oxford, Ohio 2007 Advisor_____________________________ R. James Hickey Reader______________________________ John Z. Kiss Reader______________________________ Nicolas P. Money TABLE OF CONTENTS Introduction…………………………..……………………………..………………….….1 Materials and methods for substrate cultures………......….……….……….......................6 Materials and methods for substrate/agar cultures…..………..………………….…........11 Results from substrate cultures..…...……..……………………………..............…….…12 Results from substrate/agar cultures…..………………..………………………...……...24 Discussion………………..……………………………………………………...…….…33 Literature cited…………………..…………………………..…………………...……....38 ii LIST OF TABLES Table 1. Collection and voucher data for plant material used in this study……………….8 Table 2. Mean developmental gametophyte stages and P-values……………………….20 iii LIST OF FIGURES Figure 1. Map of Andros Island………………..………………………………................7 Figure 2. Stages of gametophyte development…..……………………………………...10 Figure 3. Phlebodium aureum and Neurodium lanceolatum development.…………….14 Figure 4. Platycerium bifurcatum and Thelypteris augescens development....................16 Figure 5. Adiantum tenerum and Pteris bahamensis development……………..............18 Figure 6. Development on hepatic and epiphytic soil substrates………….....………….19 Figure 7. Mean gametophyte stages on various substrates …..........................................22 Figure 8. Epiphytic vs. terrestrial mean gametophyte stages on various substrates……………………………………………………………………...23 Figure 9. Proportion of gametophyte stages across distances on hepatic/agar cultures..…………………………………..….………………..……………...25 Figure 10. Adiantum tenerum and Neurodium lanceolatum development on hepatic/agar cultures......….......………………..………….………………….26 Figure 11. Proportion of gametophyte stages across distances on moss/agar cultures……..………………………………………………...……………....27 Figure 12. Phlebodium aureum and Adiantum tenerum development on moss/agar cultures………………………………………….………………...28 Figure 13. Mean gametophyte sizes on agar………………..…………………………...29 Figure 14. Mean gametophyte sizes on moss……………………..……………………..29 Figure 15. Proportion of gametophyte stages across distances on lichen/agar cultures…………………..………………………………………………...…31 iv Figure 16. Asplenium nidus and Pteris bahamensis development on lichen/agar cultures…………………..…..………………………….…………………....32 v ACKNOWLEDGEMENTS I would like to thank… Barb Wilson and Vickie Sandlin for absolutely everything you do. You are the glue that holds us all together! Barbara Thiers, at the New York Botanical Garden and Bruce Allen, at the Missouri Botanical Garden, for their time and help with identification of moss and liverwort species. The Department of Botany at Miami University, and the Ohio Academic Challenge grant program for providing financial support for my research. Dr. Nic Money and Dr. John Kiss for their time and excellent feedback about my research. All of my wonderful friends in the botany department, especially my lab mates, Susan Sprunt and Melanie Link-Perez, for their encouragement and support. You have all made my time here so much more enjoyable by sharing your passion for botany, some great laughs and unforgettable experiences! Thanks for bringing the feeling of a community into the department. My mountain biking buddies in Heuston Woods. I seriously don’t think I would have survived life in Ohio without your company on the trails. Biking provides the perfect outlet for stress, and the opportunity to clear my thoughts. Your friendships have helped motivate me to get out there and ride. Thanks for all the great times, and the scars to remind me! Dave Conant for sparking my interest in botany, and particularly ferns! His encouragement and guidance have greatly influenced my decision to pursue graduate school, and ultimately my direction in life. Thank you for being an excellent mentor, friend and role model. My family; especially my mom for providing love and support every step of the way. Thanks for keeping me grounded and focused on the things that truly matter in life. I love you so much! I would especially like to thank Jim Hickey for taking the time to provide thoughtful advice about my research, helping strengthen my knowledge about ferns, and further develop my passion for botany. Despite all of the jokes about your “nurturing” capabilities, you really have been a tremendous support and an excellent advisor! I sincerely appreciate the freedom you’ve granted me in the process of creating and exploring my research. That freedom has allowed me to develop a sense of independence and confidence about my abilities as a researcher and teacher. I can’t thank you enough for all that you do! vi INTRODUCTION The unique climate and structural complexity of tropical forests enable vertical habitat differentiation between terrestrial and epiphytic plant communities. Understanding the relationship between habitat type and species type, and when or how habitat selection occurs have been subjects of great interest and debate (Ranal, 1999; Hietz, et al., 2002; Cardelus et al., 2006; Watkins et al., 2007). Variations in plant morphology, species ranges, and community structure are the products of complex interactions among plants, animals, microbes and their surroundings (Ponge, 2002); however, the dynamics of these interactions are poorly understood. Tropical ecosystems contribute significantly to biodiversity worldwide. Epiphytes encompass about 10% of all vascular plants (Nieder et al., 2001; Callaway et al., 2002), of which pteridophytes are the second largest group (Hooper and Haufler, 1997). Epiphytes are either holo-epiphytic (where they grow on a host tree for their entire life cycle) or hemi-epiphytic (where a portion of their life cycle occurs on the ground; Nieder et al., 2001). Hemi-epiphytes are the least common form of epiphytism and account for less than 1% of all vascular plants (Nieder et al., 2001). In this study, the term “epiphyte” is used in a restrictive sense to include only holo-epiphytes. Species typically inhabit strictly epiphytic or terrestrial communities, but the ecological separation between habitats is not always clear. Occasionally species are found growing in opposing habitats, which implies that the mechanisms controlling habitat selection may not always be as stringent, or perhaps do not limit both gametophyte and sporophyte generations. Sillett (1999), and Mehltreter et al. (2005) discovered terrestrial fern species growing at the base of trees and in tree crotches where deep layers of humus have formed. These ferns were found exclusively in their juvenile form, and it was suggested that they remained fixed in the juvenile form as a response to growth in the wrong habitat (Mehltreter et al., 2005). Epiphytic ferns have been grown successfully from spore to sporophyte on manufactured terrestrial humus in a laboratory (Page, 1 2002), but they are rarely found growing on terrestrial soil in nature. These observations (Page, 2002) indicate that mechanisms preventing the establishment of epiphytic ferns in terrestrial communities are not likely the result of nutrient deficiencies in soil substrates, but rather are the result of other mechanisms in natural terrestrial communities, such as biochemical influences, attack by fungi or microherbivores, or space limitations. Epiphytic and terrestrial ferns rarely become established in alternate habitats, and the mechanisms that control their distribution are largely unknown. Epiphytism has evolved from terrestrial ancestors numerous times and in numerous families (Benzing, 1987), possibly as early as the Eocene era in ferns (Poole and Page, 2000). Although epiphytic ferns lack a common phylogenetic history, they do share some common traits. Most epiphytic fern species are members of the Polypodiaceae, Elaphoglossaceae, Vittariaceae, Grammitidaceae, and Hymenophyllaceae, five of the most derived fern families. Many sporophytes in these families have a climbing habit with surface clinging ability, reduced root systems, and many have rhizomes that are fine to filiform with