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Poecilogony, the production of both feeding (planktotrophic) and non-feeding (lecithotrophic) larvae, occurs in five species of sea slugs in clade Sacoglossa, but only two other animal species. Dispersive planktotrophic sea slugs have little genetic structure across the Caribbean or Indo-Pacific, but non-dispersive lecithotrophic species can be highly structured, with up to 80% of genetic covariance distributed among populations. However, exceptions include over-dispersed lecithotrophs (E. velutinus, E. subornata) and under-dispersed planktotrophs (E. pusilla). Here, we present three new cases of poecilogony: E. velutinus, E. subornata and E. papillosa were exclusively lecithotrophic in oligotrophic central Caribbean waters, but produced 90-100% planktotrophic clutches in higher productivity waters of coastal Panama. Larvae were cultured to metamorphosis in three weeks, and were genetically confirmed as conspecific to lecithotrophic egg-layers. Populations of E. velutinus and E. papillosa from coastal South America had higher genetic diversity and connectivity than in low-productivity sites, indicating local expression of planktotrophy as an explanation for anomalous population-genetic patterns. Conversely, E. pusilla was highly genetically structured across the Indo-Pacific; populations were highly divergent in mitochondrial DNA despite producing primarily planktotrophic larvae. Expression of eyespots at one week and early onset of downward swimming and crawling behavior typical of settling larvae suggest precompetent larvae of E. pusilla avoid advection from natal sites during planktonic development, increasing genetic isolation. Variable development and larval behavior may create unusual patterns of genetic population structure in tropical sea slugs. Quantifying larval behavior can ultimately improve oceanographic models and predictions of larval dispersal and connectivity to aid management and conservation efforts.
Many marine species produce larvae that disperse and develop into post-larvae in the open ocean over a period of weeks to months. However, the patterns and potential of larvae to disperse across long geographic distances are poorly understood. Here genetic variation found at the mitochondrial locus, cytochrome C oxidase subunit I, in adult ghost shrimp, Neotrypaea californiensis, was used as a proxy to infer dispersal potential of ghost shrimp larvae found in estuaries along the west coast of the United States. Multiple haplotypes were shared among 346 adult ghost shrimp specimens collected from estuaries in Washington, Oregon, and California indicated that larvae of this species are transported across great distances during the pelagic dispersal phase of development. Interestingly, extreme population structure (F[subscript]ST ranged from 0.062 to 0.98) was observed among sampling sites located in close proximity to one another. Phylogenetic analyses and analysis of molecular variance revealed that the cause of population structure was in part attributed to the presence of three putative cryptic species that were deeply divergent from N. californiensis. Qualitative and quantitative morphological measurements commonly employed for shrimp species identification were inconsistent among putative cryptic species groups but did show that the newly identified cryptic species were not undiagnosed individuals of the closest relative of N. californiensis, N. gigas.
This richly illustrated book presents the diversity and natural history of sea snail groups. By integrating aspects of morphology, ecology, evolution and behaviour, it describes how each group copes with problems of defence, locomotion, nutrition, reproduction and embryonic development. First come general characteristics of the Mollusca, to which snails belong; and next, characteristics by which snails (Gastropoda) differ from other molluscs. Then a broad, panoramic view of all major sea snail groups, from the primitive to the more advanced, is presented, including both the more abundant and some remote ones of special interest. In detailing primitive sea snails, first limpets (Patellogastropoda) are described, followed by brush snails (Vetigastropoda: top-shells, turbans and allies) and nerites (Neritimorpha), a small group with remarkably high variation in shell colour and in habitats. In looking at advanced-snails (Caenogastropoda), it details the herbivorous grazers and filter-feeders and the many voracious predators, some which use venomous darts. The book also covers sea slugs (Opisthobranchia), which have shifted from mechanical to chemical defence; some are herbivores, some use their food to harness solar energy, others are predators that gain stinging cells and poisonous compounds from their food. In addition, readers will learn about aspects of sea snails in human culture, including use as sacred artefacts and objects of magic and money, as a source of the royal and sacred dyes of purple and blue and as holy ceremonial trumpets. The text, in which scientific terms are accompanied by parallel common ones, is accompanied by over 200 illustrations (mostly in colour). This comprehensive, insightful portrait of sea snails will appeal to marine biologists, zoology lecturers and students, biology teachers, field-school instructors, nature reserve wardens, amateur naturalists, as well as to lecturers and learners of human culture.
This book presents a broad overview of the current state of knowledge regarding the Red Sea, from its geological formation and oceanographic development to the environmental influences on its ecology and the changes it is experiencing due to the rapid development of its coastlines and role as one of the world’s major transport routes. The book gathers invited contributions from researchers with an interest in the geology, geophysics, oceanography and environment of the Red Sea, while also providing comprehensive new data and a complete review of the literature. It will be of interest not only to researchers actively studying the sea and its surroundings, but will also appeal to all those involved in planning and managing the Red Sea, its environment, its resources and the countries which rely on its existence.