Queensland University of Technology School of Natural Resource Sciences Seed dispersal, germination and fine-scale genetic structure in the stream lily, Helmholtzia glaberrima (Philydraceae) Peter Prentis B.Sc. (Hons). Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy July 2005 Abstract Seed dispersal in aquatic habitats is often considered to be a complex multistage process, where initial seed shadows are redistributed by water (hydrochory). The roles of hydrochory in seed dispersal and influencing population genetic structure were examined in Helmholtzia glaberrima using both ecological and genetic techniques. Ecological experiments showed that water can redistribute seeds and seedlings over local scales and that hydrochory can provide the potential for very long distance seed and seedling dispersal. Patterns of seedling genetic structure were affected by micro- drainages that direct water flow within populations and influence water-borne seed dispersal on a local scale. Strong non-equilibrium dynamics and persistent founder effects were responsible for the patterns of genetic structure observed among established populations of H. glaberrima. Classical metapopulation models best described dispersal patterns, while water-borne seed dispersal could potentially explain patterns of genetic differentiation within a stream system, it could not explain the distribution of genetic variation among stream systems. The current study found that although hydrochory influenced seed dispersal and seedling genetic structure within a population, it had little effect on the spatial pattern of genetic variation among established populations of H. glaberrima. Moreover, even though prolonged buoyancy and viability in water provide the potential for long-distance hydrochory, results presented here do not support the hypothesis that flowing water is an effective long distance seed dispersal vector for H. glaberrima. Taken together, these results suggest that the relative importance of gene flow via water-born seed dispersal in H. glaberrima may be low compared with that of some other riparian species. 1 Keywords: genetic diversity; Helmholtzia; hydrochory; seed dispersal 2 List of manuscripts 1. Prentis, P. J., A. Vesey, N. M. Meyers, and P. B. Mather 2004. Genetic structuring of the stream lily Helmholtzia glaberrima (Philydraceae) within Toolona Creek, south-eastern Queensland. Australian Journal of Botany 52: 201—207. 2. Prentis, P. J., N. M. Meyers, and P. B. Mather. In press. The significance of post- germination buoyancy in Helmholtzia glaberrima and Philydrum lanuginosum (Philydraceae). Australian Journal of Botany. 3. Prentis, P. J., N. M. Meyers, and P. B. Mather. (In Prep) Seed dispersal and seedling establishment in the riparian plant Helmholtzia glaberrima. Freshwater Biology. 4. Prentis, P. J., N. M. Meyers, and P. B. Mather. (In Review) Micro-geographic landscape features demarcate seedling genetic structure in the stream lily, Helmholtzia glaberrima (Philydraceae)1. American Journal of Botany. 5. Prentis, P. J., N. M. Meyers, AND P. B. Mather. (In Review) Fine-scale patterns of genetic diversity and population structure in the stream lily Helmholtzia glaberrima (Philydraceae) along rainforest streams, south-east Queensland. Freshwater Biology. 3 Table of Contents Abstract 1 List of Manuscripts 3 Table of Contents 4 Statement of Original Authorship 7 Acknowledgments 8 Chapter 1: GENERAL INTRODUCTION Introduction 9 Spatial and temporal dynamics of aquatic habitats 10 Seed dispersal in freshwater habitats 12 Colonisation of isolated habitat patches via long-distance hydrochory 16 Other mechanisms affecting long-distance seed transport 17 Study species and system 22 Account of research progress linking manuscripts 24 References 26 Chapter 2: GENETIC STRUCTURING OF THE STREAM LILY Helmholtzia glaberrima (PHILYDRACEAE) WITHIN TOOLONA CREEK, SOUTH-EAST QUEENSLAND Statement of Joint Authorship 34 Manuscript 1 35 Introduction 37 Materials and Methods 40 Results 43 Discussion 45 References 50 4 Tables and Figures 54 Chapter 3: THE SIGNIFICANCE OF POST-GERMINATION BUOYANCY IN Helmholtzia glaberrima AND Philydrum lanuginosum (PHILYDRACEAE) Statement of Joint Authorship 61 Manuscript 2 62 Introduction 64 Materials and Methods 67 Results 72 Discussion 74 References 78 Tables and Figures 81 Chapter 4: SEED DISPERSAL AND SEEDLING ESTABLISHMENT IN THE RIPARIAN PLANT Helmholtzia glaberrima Statement of Joint Authorship 84 Manuscript 3 85 Introduction 88 Materials and Methods 91 Results 94 Discussion 96 References 100 Tables and Figures 102 Chapter 5: MICRO-GEOGRAPHIC LANDSCAPE FEATURES DEMARCATE SEEDLING GENETIC STRUCTURE IN THE STREAM LILY, Helmholtzia glaberrima (PHILYDRACEAE) Statement of Joint Authorship 105 5 Manuscript 4 106 Introduction 108 Materials and Methods 110 Results 112 Discussion 114 References 118 Tables and Figures 121 Chapter 6: FINE-SCALE PATTERNS OF GENETIC DIVERSITY AND POPULATION STRUCTURE IN THE STREAM LILY Helmholtzia glaberrima (PHILYDRACEAE) ALONG RAINFOREST STREAMS, SOUTH-EAST QUEENSLAND Statement of Joint Authorship 126 Manuscript 5 127 Introduction 129 Materials and Methods 132 Results 134 Discussion 136 References 140 Tables and Figures 143 Chapter 7: GENERAL DISCUSSION General Discussion 147 References 153 6 Statement of Original Authorship This work contains no material which has been accepted for the award of any other degree or diploma in any university or other tertiary institution and, to the best of my knowledge and belief, contains no material previously published or written by another person, except where due reference has been made in the text. Signed Date 7 Acknowledgments Firstly, I would like to thank my supervisors for your guidance and encouragement in helping me complete this project. Many thanks must go both to the ecology and genetics discussion groups for fruitful discussions on sampling designs and data. My parents deserve many thanks for their support of my chosen path and providing guidance during the gloomy PhD blues. A special thankyou to all the people who volunteered to help me with field and lab work, particularly Ana Pavasovic, Cameron Schulz, Mark Schutze, Doug Harding, Alex Wilson and Grant Hamilton. Big thanks must go to Dr Graham Kelly the man whose lectures and infectious enthusiasm are responsible for my interest in plant biology. Lastly and mostly importantly, I have to thank my partner Ana for her support, encouragement and cooking without which I would be a lonely, thin man. 8 CHAPTER 1. General introduction Introduction How seeds disperse among isolated habitat patches, establish and contribute to the genetic pool of new plant populations has long fascinated botanists (Darwin, 1859). This is because dispersal is one of the primary processes that influence population dynamics and evolution of plants (Nathan & Muller-Landau, 2000). In particular the spatial and temporal dynamics of plant populations will be determined chiefly by the movement of seeds within and among populations (Husband & Barrett, 1998). At a broader geographic scale, the range at which seed dispersal is effective will influence the possibility that extirpated populations are recolonised and the probability that new isolated habitat patches are colonised (Cain et al., 2000). Plant species are rarely distributed uniformly in space but often occur as isolated local populations where favourable conditions for successful establishment exist (Edwards & Sharitz, 2000; Ellison & Parker, 2002). Dispersal patterns within and among local populations will determine the extent to which local populations are interconnected via gene flow (Ouborg et al., 1999). Gene flow will only occur however, if the seeds dispersing among populations establish and contribute to future reproduction in the new population (Ouborg et al., 1999). The level of gene flow among patches will determine the distribution of genetic variation within and among local populations and whether they function collectively, or as isolated units (Tero et al., 2003). In situations where dispersal 9 rates among populations are high, gene flow will tend to homogenise gene frequencies among local populations, so they form a single panmictic unit (Ouborg et al., 1999). Alternatively, if gene flow is very low or absent, local populations are likely to diverge and evolve independently due to the diversifying forces of drift and selection (Tero et al., 2003). A number of factors can influence the level of seed dispersal and gene flow that occurs among isolated local populations, including temporal and spatial distribution of favourable habitat patches, the type of vectors that disperse seeds and the individual life-history characteristics of a plant species (Pannell and Charlesworth, 1999, 2000). This review will focus primarily factors acting on aquatic plants restricted to freshwater habitats. Spatial and temporal dynamics of aquatic habitats Many studies have reported that habitat patches are often dispersed heterogeneously across the landscape (Husband & Barrett, 1998; Levins, 1969; McCauley, 1989). Spatial discontinuities, including mountains, valleys or rivers can influence significantly the distribution of many organisms (Lawton, 1993). Most organisms do not exhibit uniform distributions in space (Lawton, 1993). Instead organisms frequently occur as isolated local populations confined to suitable habitat surrounded by a matrix of less favourable habitat (Andrewartha & Birch, 1954; Dejong, 1995; Dupre & Ehrlen, 2002). This is