Reproduction and Development in Echinodermata and Prochordata (Reproduction and Development in Aquatic Invertebrates)

"Echinoderms and prochordates occupy a key position in vertebrate evolution. The genomes of sea urchin share 70% homology with humans. Researches on cell cycle in sea urchin and phagocytosis in asteroids have fetched Nobel Prizes. In this context, this book assumes immense importance. Echinoderms are unique, as their symmetry is bilateral in larvae but pentamerous radial in adults. The latter has eliminated the development of an anterior head and bilateral appendages. Further, the obligate need to face the substratum for locomotion and acquisition of food has eliminated their planktonic and nektonic existence. Egg size, a decisive factor in recruitment, increases with decreasing depths up to 2,000-5,000 m in lecithotrophic asteroids and ophiuroids but remains constant in their planktotrophics. Smaller ( 110 mm) asteroids generate planktotrophic eggs only. Publications on sex ratio of echinoderms indicate the genetic determination of sex at fertilization but those on hybridization, karyotype and ploidy induction do not provide evidence for heterogametism. But the herbivorous echinoids and larvacea with their gonads harboring both germ cells and Nutritive Phagocytes (NPs) have economized the transportation and hormonal costs on gonadal function. Despite the amazing potential just 2 and 3% of echinoderms undergo clonal reproduction and regeneration, respectively. Fission is triggered, when adequate reserve nutrients are accumulated. It is the most prevalent mode of clonal reproduction in holothuroids, asteroids and ophiuroids. However, budding is a more prevalent mode of clonal reproduction in colonial hemichordates and urochordates. In echinoderms, fission and budding eliminate each other. Similarly, autoregulation of early development eliminates clonal reproduction in echinoids and solitary urochordates. In pterobranchs, thaliaceans and ascidians, the repeated and rapid budding leads to colonial formation. Coloniality imposes reductions in species number and body size, generation time and life span, gonad number and fecundity as well as switching from gonochorism to simultaneous hermaphorditism and oviparity to ovoviviparity/viviparity."--Provided by publisher Cover 1 Half title 2 Title 4 Copyrights 5 Preface to the Series 6 Preface 8 Acknowledgements 12 Contents 14 Section I Non-Chordate-Deuterostomia 18 Section Ia Echinodermata 18 1. Introduction 20 1.1 Taxonomy and Structural Diversity 23 1.2 Distribution, Locomotion and Dispersal 26 1.3 Population Density and Microhabitats 33 1.4 Energy Budget and Reproduction 35 1.5 Gonad Index and Fecundity 40 1.5.1 Gonad Index 40 1.5.2 Fecundity 41 1.6 Egg Size and its Implications 49 1.6.1 Maternal Investment 51 1.6.2 Egg Size and Fertilizability 56 1.6.3 Endogenous and Exogenous Nutrients 58 1.6.4 Egg Size Manipulations 60 1.6.5 Ontogenetic Pathways 64 1.7 Larval Developments and Thyroid Hormones 69 1.8 Brooding and Viviparity 72 1.9 Size and Life Span 74 2. Fisheries and Aquaculture 76 Introduction 76 2.1 Capture Fisheries 77 2.2 Aquaculture 79 2.2.1 Sea Urchins 80 2.2.2 Sea Cucumbers 87 3. Sexual Reproduction 93 Introduction 93 3.1 Sexuality 93 3.2 Gonochorism 94 3.2.1 Sex Ratio 94 3.2.2 Reproductive Systems 96 3.2.3 Gametogenesis 99 3.3 Parthenogenesis 104 3.4 Hermaphroditism 105 3.5 Reproductive Cycle 108 4. Asexual Reproduction 111 Introduction 111 4.1 Types and Characteristics 112 4.2 Fission and Reproduction 115 4.3 Clonal and Sexual Reproduction 119 4.4 Induced Fission 131 4.5 The Trigger 136 4.6 Clonal Autotomy 140 4.7 Larval Cloning 142 4.8 Eggs and Embryos 147 4.9 Searching Stem Cells 149 5. Regeneration 153 Introduction 153 5.1 Incidence and Prevalence 154 5.2 Induction of Autotomy 161 5.3 Causes and Consequences 163 5.4 Growth and Differentiation 171 5.5 Growth Factors and Genes 176 6. Sex Determination 180 Introduction 180 6.1 Species and Fidelity 180 6.2 Karyotypes and Heteromorphism 183 6.3 Ploidy Induction 183 6.4 Genome and Sequencing 186 7. Sex Differentiation 187 Introduction 187 7.1 Asteroid Model 188 7.2 Echinoid Model 192 7.3 Induction of Spawning 192 7.4 Endocrine Disruption 193 7.5 Parasitic Disruption 197 Section Ib Hemichordata 200 8. Reproductive Biology 202 Introduction 202 8.1 Life Cycles 202 8.2 Gonads and Consequences 204 8.3 Regeneration in Enteropneusts 204 Section II Chordate Deuterostomia 208 9. Cephalochordata 210 Introduction 210 9.1 Reproductive Biology 210 10. Urochordata 212 Introduction 212 10.1 Pelagic Tunicates 212 10.2 Benthic Tunicates 218 10.3 Germline Lineage 226 11. New Findings and Highlights 231 Introduction 231 11.1 Structure and Distribution 231 11.2 Fecundity, Size and Depth 232 11.3 Aquaculture: Sea Urchins and Cucumbers 232 11.4 Intromittent Organ 233 11.5 Gonad and Hormonal Economy 233 11.6 Regenerative Potential 234 11.7 Gonads of Cloners 234 11.8 Clonal Reproduction 235 11.9 Autoregulation and Stem Cells 236 11.10 Cloning and Coloniality 238 12. References 242 Author Index 270 Species Index 277 Subject Index 285 Content: Cover Half title Title Copyrights Preface to the Series Preface Acknowledgements Contents Section I Non-Chordate-Deuterostomia Section Ia Echinodermata 1. Introduction 1.1 Taxonomy and Structural Diversity 1.2 Distribution, Locomotion and Dispersal 1.3 Population Density and Microhabitats 1.4 Energy Budget and Reproduction 1.5 Gonad Index and Fecundity 1.5.1 Gonad Index 1.5.2 Fecundity 1.6 Egg Size and its Implications 1.6.1 Maternal Investment 1.6.2 Egg Size and Fertilizability 1.6.3 Endogenous and Exogenous Nutrients 1.6.4 Egg Size Manipulations 1.6.5 Ontogenetic Pathways1.7 Larval Developments and Thyroid Hormones 1.8 Brooding and Viviparity 1.9 Size and Life Span 2. Fisheries and Aquaculture Introduction 2.1 Capture Fisheries 2.2 Aquaculture 2.2.1 Sea Urchins 2.2.2 Sea Cucumbers 3. Sexual Reproduction Introduction 3.1 Sexuality 3.2 Gonochorism 3.2.1 Sex Ratio 3.2.2 Reproductive Systems 3.2.3 Gametogenesis 3.3 Parthenogenesis 3.4 Hermaphroditism 3.5 Reproductive Cycle 4. Asexual Reproduction Introduction 4.1 Types and Characteristics 4.2 Fission and Reproduction 4.3 Clonal and Sexual Reproduction 4.4 Induced Fission4.5 The Trigger 4.6 Clonal Autotomy 4.7 Larval Cloning 4.8 Eggs and Embryos 4.9 Searching Stem Cells 5. Regeneration Introduction 5.1 Incidence and Prevalence 5.2 Induction of Autotomy 5.3 Causes and Consequences 5.4 Growth and Differentiation 5.5 Growth Factors and Genes 6. Sex Determination Introduction 6.1 Species and Fidelity 6.2 Karyotypes and Heteromorphism 6.3 Ploidy Induction 6.4 Genome and Sequencing 7. Sex Differentiation Introduction 7.1 Asteroid Model 7.2 Echinoid Model 7.3 Induction of Spawning 7.4 Endocrine Disruption 7.5 Parasitic DisruptionSection Ib Hemichordata 8. Reproductive Biology Introduction 8.1 Life Cycles 8.2 Gonads and Consequences 8.3 Regeneration in Enteropneusts Section II Chordate Deuterostomia 9. Cephalochordata Introduction 9.1 Reproductive Biology 10. Urochordata Introduction 10.1 Pelagic Tunicates 10.2 Benthic Tunicates 10.3 Germline Lineage 11. New Findings and Highlights Introduction 11.1 Structure and Distribution 11.2 Fecundity, Size and Depth 11.3 Aquaculture: Sea Urchins and Cucumbers 11.4 Intromittent Organ 11.5 Gonad and Hormonal Economy 11.6 Regenerative Potential11.7 Gonads of Cloners 11.8 Clonal Reproduction 11.9 Autoregulation and Stem Cells 11.10 Cloning and Coloniality 12. References Author Index Species Index Subject Index This book discusses the sexual and asexual modes of reproduction of solitary echinoderms, colonial hemichordates, and ascidians. It focuses on the study of the primordial and embryonic stem cells found in echinoderms as early models for gene therapy in vertebrates.