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The Evolutionary Ecology of Lampreys (Petromyzontiformes)

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The Evolutionary Ecology of Lampreys (Petromyzontiformes) Hume, John B. (2013) The evolutionary ecology of lampreys (Petromyzontiformes). PhD thesis http://theses.gla.ac.uk/4125/ Copyright and moral rights for this thesis are retained by the author A copy can be downloaded for personal non-commercial research or study, without prior permission or charge This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the Author The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the Author When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given. Glasgow Theses Service http://theses.gla.ac.uk/ [email protected] The Evolutionary Ecology of Lampreys (Petromyzontiformes) John B. Hume Scottish Centre for Ecology & the Natural Environment, Institute of Biodiversity, Animal Health & Comparative Medicine, College of Medical, Veterinary & Life Sciences Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy November 2012 “A parasite for instance, is a shocking and a baneful monster, yet still Nature has infused into his blandishments a not unpolished charm.” Plato ii ABSTRACT Lampreys (Petromyzontiformes) are an ancient vertebrate group, comprising 40 currently recognised species that range throughout the Northern and Southern Hemispheres. Despite a conserved morphology, lampreys nevertheless express a diverse range of life history strategies. Unusually for vertebrates larval lampreys are filter-feeding organisms prior to undergoing an extensive anatomical reorganisation, and the adoption of either a parasitic or a non-parasitic adult life. Parasitic lampreys consume the flesh and blood of actinopterygian fishes, either in marine or freshwater environments, while non-parasitic lampreys do not feed following their metamorphosis from the larval form. Morphological and genetic similarities between pairs of parasitic and non-parasitic lampreys have led to taxonomic confusion regarding the specific status of many non-parasitic forms, and the suggestion that the loss of the trophic adult phenotype is the result of a single species capable of producing alternative life history strategies. In this thesis it is argued that at least some paired species of lampreys do not comprise two distinct evolutionary lineages; rather, that non-parasitic lampreys represent one extreme in a continuum of life history variation expressed by a parasitic species. Some lamprey species, such as the European river lamprey Lampetra fluviatilis, are morphologically variable, exhibiting divergent phenotypes in response to ecological pressures, such as alternative foraging environments. Loch Lomond, Scotland contains a population of L. fluviatilis that feeds exclusively in the lake and exhibits a reduced body size and an overall morphology distinct from the typical anadromous form. Its foraging strategy indicates that it may be capable of switching hosts in the face of declining numbers of a presumed favoured and formerly abundant host, suggesting a certain amount of plasticity in its trophic ecology that may have ensured its survival in this freshwater lake. This freshwater-resident form, as well as anadromous L. fluviatilis and the non- parasitic species L. planeri, were found to spawn in a single river system within the Loch Lomond basin, and this site is crucial for the continued presence of this life history variant in Loch Lomond. The appearance of sexually mature specimens of three discrete phenotypes in this river, each representing an alternative life history strategy that may, or may not, belong to a single species, provides a crucial opportunity to test the strength of assortative mating between lamprey species pairs. Within this system the strength of assortative mating was iii found to be weak, and points to the possibility that freshwater-resident L. fluviatilis are mitigating gene flow between large anadromous parasitic L. fluviatilis, and small, non- parasitic L. planeri. As well as weak behavioural isolation, inter-specific sneak male mating tactics were documented among these populations, and represents the first time this phenomenon has been observed between paired lamprey species. Such behaviour indicates a lack of species-specific cues acting between L. fluviatilis and L. planeri, and suggests that hybrid offspring could be common in some systems. Testing hybrid viability (survivorship) between Loch Lomond’s two L. fluviatilis life history strategies and the sympatric L. planeri revealed no post-zygotic barriers to gene flow, at least in the form of gamete incompatibility. Perhaps more convincingly though, when comparing traditional morphometrics and body shape variation, as well as mitochondrial DNA sequences, between L. fluviatilis expressing different foraging strategies with populations of L. planeri, no robust species specific differentiation was observed. In fact, species delimitation between L. fluviatilis and L. planeri appears to be related solely to overall body size, which is itself a function of life history strategy. However, life history strategy was not correlated with current species designation as relationships among mtDNA haplotypes indicate non-parasitic populations have evolved independently multiple times throughout the geographic range of L. fluviatilis in Europe. Therefore, L. planeri should not be considered as a distinct species, either morphologically or genetically. Instead, L. fluviatilis appears capable of expressing a range of life history strategies; from parasitic anadromous populations through to non-parasitic stream-resident populations. The overall research approach employed in this thesis, i.e., the combination of ecological, behavioural, taxonomic and molecular studies, could be used to robustly examine the evolutionary ecology of parasitic and non-parasitic lampreys elsewhere. iv CONTENTS Abstract………………………………………………………………………….....................iii List of Tables………………………………………………………………………………….xi List of Figures………………………………………………………………………………..xv List of Publications………………………………………………………………………….xxi Appendices………………………………………………………………………………….xxii Acknowledgments………………………………………………………………………….xxiii Author’s Declaration…………………………………………………………….................xxiv CHAPTER ONE An introduction to the biology of lampreys (Petromyzontiformes), with particular reference to paired species……………………………………………….....1 1.1 GENERAL INTRODUCTION……………………………………………………………1 1.2 LARVAL STAGE…………………………………………………………………………3 1.2.1 Early Development………………………………………………………………….....5 1.2.2 Burrowing……………………………………………………………………………...6 1.2.3 Habitat…………………………………………………………………………………7 1.2.4 Density…………………………………………………………………………………8 1.2.5 Movement…………………………………………………………………………….10 1.2.6 Diet…………………………………………………………………………………...11 1.2.7 Growth………………………………………………………………………………..12 1.2.8 Larval Duration……………………………………………………………………....14 1.2.9 Teratology……………………………………………………………………………16 1.3 METAMORPHOSIS……………………………………………………………………..17 1.3.1 Anatomical Rorganisation............................................................................................18 1.3.2 Timing & Causes……………………………………………………………………..19 1.3.3 Migration……………………………………………………………………………..22 1.4 POST-METAMORPHIC FEEDING…………………………………………………….23 v 1.4.1 Feeding Location on Hosts…………………………………………………………..25 1.4.2 Duration of Feeding Attachments……………………………………………………26 1.4.3 Host Size……………………………………………………………………………...27 1.4.4 Diversity of Host Species……………………………………………………………..28 1.4.5 Locating Hosts………………………………………………………………………..29 1.4.6 Growth………………………………………………………………………………..30 1.4.7 Duration of the Juvenile Period……………………………………………………...31 1.4.8 Alternative Foraging Strategies……………………………………………………...32 1.5 ADULT STAGE………………………………………………………………………....33 1.5.1 Spawning Migration………………………………………………………………….34 1.5.2 Pheromones…………………………………………………………………………..37 1.5.3 Barriers to Migration………………………………………………………………...38 1.5.4 Energetics…………………………………………………………………………….39 1.5.5 Sexual Maturation……………………………………………………………………39 1.5.6 Sex Ratio……………………………………………………………………………...40 1.5.7 Spawning Behaviour…………………………………………………………………41 1.5.8 Fecundity……………………………………………………………………………..45 1.5.9 Death…………………………………………………………………………………46 1.6 PAIRED SPECIES……………………………………………………………………….48 1.6.1 Morphological & Life History Differences…………………………………………..49 1.6.2 Molecular Ecology…………………………………………………………………...52 1.7 THESIS AIMS…………………………………………………………………………...54 CHAPTER TWO Evidence of a recent decline in lamprey parasitism of a nationally rare whitefish Coregonus lavaretus in Loch Lomond, Scotland: is there a diamond in the ruffe?................................................................................................................................63 2.1 ABSTRACT……………………………………………………………………………...63 2.2 INTRODUCTION……………………………………………………………………….63 2.3 MATERIALS & METHODS……………………………………………………………65 vi 2.4 RESULTS………………………………………………………………………………...66 2.5 DISCUSSION……………………………………………………………………………66 2.6 FIGURES & TABLES…………………………………………………………………...70 CHAPTER THREE Pre-spawning migration of lampreys, Lampetra spp., in the Loch Lomond basin, Scotland……………………………………………………………………………………..74 3.1 ABSTRACT……………………………………………………………………………...74 3.2 INTRODUCTION……………………………………………………………………….74 3.3 MATERIALS & METHODS…………………………………………………………….77 3.4 RESULTS………………………………………………………………………………...78 3.5 DISCUSSION……………………………………………………………………………81 3.6 FIGURES & TABLES…………………………………………………………………...86 CHAPTER FOUR No evidence of behavioural barriers
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