1
|
Coppola U, Kamal AK, Stolfi A, Ristoratore F. The Cis-Regulatory Code for Kelch-like 21/30 Specific Expression in Ciona robusta Sensory Organs. Front Cell Dev Biol 2020; 8:569601. [PMID: 33043001 PMCID: PMC7517041 DOI: 10.3389/fcell.2020.569601] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2020] [Accepted: 08/17/2020] [Indexed: 12/18/2022] Open
Abstract
The tunicate Ciona robusta is an emerging model system to study the evolution of the nervous system. Due to their small embryos and compact genomes, tunicates, like Ciona robusta, have great potential to comprehend genetic circuitry underlying cell specific gene repertoire, among different neuronal cells. Their simple larvae possess a sensory vesicle comprising two pigmented sensory organs, the ocellus and the otolith. We focused here on Klhl21/30, a gene belonging to Kelch family, that, in Ciona robusta, starts to be expressed in pigmented cell precursors, becoming specifically maintained in the otolith precursor during embryogenesis. Evolutionary analyses demonstrated the conservation of Klhl21/30 in all the chordates. Cis-regulatory analyses and CRISPR/Cas9 mutagenesis of potential upstream factors, revealed that Klhl21/30 expression is controlled by the combined action of three transcription factors, Mitf, Dmrt, and Msx, which are downstream of FGF signaling. The central role of Mitf is consistent with its function as a fundamental regulator of vertebrate pigment cell development. Moreover, our results unraveled a new function for Dmrt and Msx as transcriptional co-activators in the context of the Ciona otolith.
Collapse
Affiliation(s)
- Ugo Coppola
- Biology and Evolution of Marine Organisms, Stazione Zoologica Anton Dohrn Napoli, Naples, Italy.,School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, United States
| | - Ashwani Kumar Kamal
- Biology and Evolution of Marine Organisms, Stazione Zoologica Anton Dohrn Napoli, Naples, Italy
| | - Alberto Stolfi
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, United States
| | - Filomena Ristoratore
- Biology and Evolution of Marine Organisms, Stazione Zoologica Anton Dohrn Napoli, Naples, Italy
| |
Collapse
|
2
|
Liberti A, Bertocci I, Pollet A, Musco L, Locascio A, Ristoratore F, Spagnuolo A, Sordino P. An indoor study of the combined effect of industrial pollution and turbulence events on the gut environment in a marine invertebrate. MARINE ENVIRONMENTAL RESEARCH 2020; 158:104950. [PMID: 32217300 DOI: 10.1016/j.marenvres.2020.104950] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2019] [Revised: 02/25/2020] [Accepted: 03/07/2020] [Indexed: 06/10/2023]
Abstract
Natural storms are able to determine reworking of seabed up to considerable depths and favour suspension of sediment-associated chemicals. Yet, a direct link between exposure to resuspended contaminants and the biological effects on marine organisms have to be fully established. We exposed adults of a suspension feeder, the ascidian Ciona robusta, to polluted sediment (e.g., containing mixtures of polycyclic aromatic hydrocarbons and heavy metals) from the industrial area of Bagnoli-Coroglio under two temporal patterns ('aggregated' vs. 'spaced') of turbulence events. Then, we assessed the impact of resuspended pollutants on the ascidian gut environment via four broad categories: oxidative stress, innate immunity, host-microbiota interactions, and epithelium. An early oxidative stress response was seen after a week of exposure to static sediment. Instead, water turbulence had no effect on the antioxidant defence. The first episode of turbulent suspension induced a minimal pro-inflammatory response in the 'spaced' pattern. Mucus overproduction and a complete occlusion of the crypt lumen were found following sediment reworking. This study suggests a protective response of the gut environment in marine invertebrates exposed to environmental extremes, leading to increased susceptibility to disease and to concerns on the combined effects of chronic environmental contamination and acute disturbance events possibly associated with climate change.
Collapse
Affiliation(s)
- Assunta Liberti
- Department of Biology and Evolution of Marine Organisms, Stazione Zoologica Anton Dohrn, Naples, Italy.
| | - Iacopo Bertocci
- Department of Integrated Marine Ecology, Stazione Zoologica Anton Dohrn, Naples, Italy; Department of Biology, University of Pisa, CoNISMa, Pisa, Italy
| | | | - Luigi Musco
- Department of Integrated Marine Ecology, Stazione Zoologica Anton Dohrn, Naples, Italy
| | - Annamaria Locascio
- Department of Biology and Evolution of Marine Organisms, Stazione Zoologica Anton Dohrn, Naples, Italy
| | - Filomena Ristoratore
- Department of Biology and Evolution of Marine Organisms, Stazione Zoologica Anton Dohrn, Naples, Italy
| | - Antonietta Spagnuolo
- Department of Biology and Evolution of Marine Organisms, Stazione Zoologica Anton Dohrn, Naples, Italy
| | - Paolo Sordino
- Department of Biology and Evolution of Marine Organisms, Stazione Zoologica Anton Dohrn, Naples, Italy.
| |
Collapse
|
3
|
Kourakis MJ, Smith WC. An organismal perspective on C. intestinalis development, origins and diversification. eLife 2015; 4. [PMID: 25807088 PMCID: PMC4373457 DOI: 10.7554/elife.06024] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2014] [Accepted: 03/10/2015] [Indexed: 11/13/2022] Open
Abstract
The ascidian Ciona intestinalis, commonly known as a 'sea squirt', has become an important model for embryological studies, offering a simple blueprint for chordate development. As a model organism, it offers the following: a small, compact genome; a free swimming larva with only about 2600 cells; and an embryogenesis that unfolds according to a predictable program of cell division. Moreover, recent phylogenies reveal that C. intestinalis occupies a privileged branch in the tree of life: it is our nearest invertebrate relative. Here, we provide an organismal perspective of C. intestinalis, highlighting aspects of its life history and habitat-from its brief journey as a larva to its radical metamorphosis into adult form-and relate these features to its utility as a laboratory model.
Collapse
Affiliation(s)
- Matthew J Kourakis
- Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, Santa Barbara, United States
| | - William C Smith
- Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, Santa Barbara, United States
| |
Collapse
|
4
|
Crocetta F, Marino R, Cirino P, Macina A, Staiano L, Esposito R, Pezzotti MR, Racioppi C, Toscano F, De Felice E, Locascio A, Ristoratore F, Spagnuolo A, Zanetti L, Branno M, Sordino P. Mutation studies in ascidians: a review. Genesis 2014; 53:160-9. [PMID: 25395385 DOI: 10.1002/dvg.22837] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2014] [Revised: 11/06/2014] [Accepted: 11/11/2014] [Indexed: 12/21/2022]
Abstract
Historically, mutations have had a significant impact on the study of developmental processes and phenotypic evolution. Lesions in DNA are created by artificial methods or detected by natural genetic variation. Random mutations are then ascribed to genetic change by direct sequencing or positional cloning. Tunicate species of the ascidian genus Ciona represent nearly fully realized model systems in which gene function can be investigated in depth. Additionally, tunicates are valuable organisms for the study of naturally occurring mutations due to the capability to exploit genetic variation down to the molecular level. Here, we summarize the available information about how mutations are studied in ascidians with examples of insights that have resulted from these applications. We also describe notions and methodologies that might be useful for the implementation of easy and tight procedures for mutations studies in Ciona.
Collapse
Affiliation(s)
- Fabio Crocetta
- Laboratory of Cellular and Developmental Biology, Stazione Zoologica Anton Dohrn, Villa Comunale, Naples, Italy
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
5
|
Esposito R, Racioppi C, Pezzotti MR, Branno M, Locascio A, Ristoratore F, Spagnuolo A. The ascidian pigmented sensory organs: structures and developmental programs. Genesis 2014; 53:15-33. [PMID: 25382437 DOI: 10.1002/dvg.22836] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2014] [Revised: 11/03/2014] [Accepted: 11/04/2014] [Indexed: 01/25/2023]
Abstract
The recent advances on ascidian pigment sensory organ development and function represent a fascinating platform to get insight on the basic programs of chordate eye formation. This review aims to summarize current knowledge, at the structural and molecular levels, on the two main building blocks of ascidian light sensory organ, i.e. pigment cells and photoreceptor cells. The unique features of these structures (e.g., simplicity and well characterized cell lineage) are indeed making it possible to dissect the developmental programs at single cell resolution and will soon provide a panel of molecular tools to be exploited for a deep developmental and comparative-evolutionary analysis.
Collapse
Affiliation(s)
- R Esposito
- Cellular and Developmental Biology Department, Stazione Zoologica Anton Dohrn, Villa Comunale, 80121, NAPOLI, Italy
| | | | | | | | | | | | | |
Collapse
|
6
|
Karaiskou A, Swalla BJ, Sasakura Y, Chambon JP. Metamorphosis in solitary ascidians. Genesis 2014; 53:34-47. [PMID: 25250532 DOI: 10.1002/dvg.22824] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2014] [Revised: 09/15/2014] [Accepted: 09/19/2014] [Indexed: 12/19/2022]
Abstract
Embryonic and postembryonic development in ascidians have been studied for over a century, but it is only in the last 10 years that the complex molecular network involved in coordinating postlarval development and metamorphosis has started to emerge. In most ascidians, the transition from the larval to the sessile juvenile/adult stage, or metamorphosis, requires a combination of environmental and endogenous signals and is characterized by coordinated global morphogenetic changes that are initiated by the adhesion of the larvae. Cloney was the first to describe cellular events of ascidians' metamorphosis in 1978 and only recently elements of the molecular regulation of this crucial developmental step have been revealed. This review aims to present a thorough view of this crucial developmental step by combining recent molecular data to the already established cellular events.
Collapse
Affiliation(s)
- Anthi Karaiskou
- Sorbonne Universités, UPMC Univ Paris 06, UMR7622-Biologie du Développement, Paris, France
| | | | | | | |
Collapse
|
7
|
Sorrenti G, Bagnoli A, Miraglia V, Crocetta F, Vitiello V, Ristoratore F, Cirino P, Sansone G, Sordino P. Investigating sperm cryopreservation in a model tunicate, Ciona intestinalis sp. A. Cryobiology 2013; 68:43-9. [PMID: 24269530 DOI: 10.1016/j.cryobiol.2013.11.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2013] [Revised: 11/11/2013] [Accepted: 11/12/2013] [Indexed: 10/26/2022]
Abstract
In cryopreservation procedures, the capacity to protect the cells from freezing and thawing processes is sensitive to the choice of the cryoprotective agent (CPA) and to its optimal concentration. The advancement of research on Tunicate model species has raised interest in liquid nitrogen cryopreservation for the storage and distribution of genetic resources. Ciona intestinalis (Linnè, 1767) consists of a complex of cryptic taxa that are central to several areas of investigation, from comparative genomics to invasive biology. Here we investigated how five CPAs, three chilling rates and two freezing rates influence semen cryopreservation in C. intestinalis sp. A. By using larval morphology and motility as endpoints, we estimated that long term semen storage requires 10% dimethyl sulfoxide as a protective agent, -1°C/min chilling rate (18°C to 5°C) and -13°C/min freezing rate (5°C to -80°C), followed by immersion in liquid nitrogen.
Collapse
Affiliation(s)
- Gerarda Sorrenti
- Stazione Zoologica Anton Dohrn, Villa Comunale, I-80121 Naples, Italy
| | - Anna Bagnoli
- Laboratory of Cryobiology, Department of Biological Sciences, University of Naples "Federico II", Via Mezzocannone 16, I-80134 Naples, Italy
| | | | - Fabio Crocetta
- Stazione Zoologica Anton Dohrn, Villa Comunale, I-80121 Naples, Italy
| | - Valentina Vitiello
- Laboratory of Cryobiology, Department of Biological Sciences, University of Naples "Federico II", Via Mezzocannone 16, I-80134 Naples, Italy; CRIAcq, Interdepartmental Research Center for Acquaculture, University of Naples "Federico II", Via Università 100, Portici, I-80055 Naples, Italy
| | | | - Paola Cirino
- Stazione Zoologica Anton Dohrn, Villa Comunale, I-80121 Naples, Italy
| | - Giovanni Sansone
- Laboratory of Cryobiology, Department of Biological Sciences, University of Naples "Federico II", Via Mezzocannone 16, I-80134 Naples, Italy; CRIAcq, Interdepartmental Research Center for Acquaculture, University of Naples "Federico II", Via Università 100, Portici, I-80055 Naples, Italy
| | - Paolo Sordino
- Stazione Zoologica Anton Dohrn, Villa Comunale, I-80121 Naples, Italy; CNR ISAFOM - Institute for Agricultural and Forest Systems in the Mediterranean, National Research Council, Str. le Lancia, Blocco Palma I, Zona Industriale, I-95121 Catania, Italy.
| |
Collapse
|
8
|
ANDREAKIS NIKOS, LUTER HEIDIM, WEBSTER NICOLES. Cryptic speciation and phylogeographic relationships in the elephant ear spongeIanthella basta(Porifera, Ianthellidae) from northern Australia. Zool J Linn Soc 2012. [DOI: 10.1111/j.1096-3642.2012.00848.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
|
9
|
Zhan A, Darling JA, Bock DG, Lacoursière-Roussel A, MacIsaac HJ, Cristescu ME. Complex genetic patterns in closely related colonizing invasive species. Ecol Evol 2012; 2:1331-46. [PMID: 22957143 PMCID: PMC3434944 DOI: 10.1002/ece3.258] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2012] [Revised: 03/16/2012] [Accepted: 03/16/2012] [Indexed: 11/30/2022] Open
Abstract
Anthropogenic activities frequently result in both rapidly changing environments and translocation of species from their native ranges (i.e., biological invasions). Empirical studies suggest that many factors associated with these changes can lead to complex genetic patterns, particularly among invasive populations. However, genetic complexities and factors responsible for them remain uncharacterized in many cases. Here, we explore these issues in the vase tunicate Ciona intestinalis (Ascidiacea: Enterogona: Cionidae), a model species complex, of which spA and spB are rapidly spreading worldwide. We intensively sampled 26 sites (N = 873) from both coasts of North America, and performed phylogenetic and population genetics analyses based on one mitochondrial fragment (cytochrome c oxidase subunit 3–NADH dehydrogenase subunit I, COX3-ND1) and eight nuclear microsatellites. Our analyses revealed extremely complex genetic patterns in both species on both coasts. We detected a contrasting pattern based on the mitochondrial marker: two major genetic groups in C. intestinalis spA on the west coast versus no significant geographic structure in C. intestinalis spB on the east coast. For both species, geo-graphically distant populations often showed high microsatellite-based genetic affinities whereas neighboring ones often did not. In addition, mitochondrial and nuclear markers provided largely inconsistent genetic patterns. Multiple factors, including random genetic drift associated with demographic changes, rapid selection due to strong local adaptation, and varying propensity for human-mediated propagule dispersal could be responsible for the observed genetic complexities.
Collapse
Affiliation(s)
- Aibin Zhan
- Great Lakes Institute for Environmental Research, University of Windsor401 Sunset Avenue, Windsor, Ontario N9B 3P4, Canada
| | - John A Darling
- National Exposure Research Laboratory, US Environmental Protection Agency109 T. W. Alexander Drive, Durham, North Carolina 27711, USA
| | - Dan G Bock
- Great Lakes Institute for Environmental Research, University of Windsor401 Sunset Avenue, Windsor, Ontario N9B 3P4, Canada
| | | | - Hugh J MacIsaac
- Great Lakes Institute for Environmental Research, University of Windsor401 Sunset Avenue, Windsor, Ontario N9B 3P4, Canada
| | - Melania E Cristescu
- Great Lakes Institute for Environmental Research, University of Windsor401 Sunset Avenue, Windsor, Ontario N9B 3P4, Canada
| |
Collapse
|
10
|
Zhan A, Macisaac HJ, Cristescu ME. Invasion genetics of the Ciona intestinalis species complex: from regional endemism to global homogeneity. Mol Ecol 2010; 19:4678-94. [PMID: 20875067 DOI: 10.1111/j.1365-294x.2010.04837.x] [Citation(s) in RCA: 98] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Determining the degree of population connectivity and investigating factors driving genetic exchange at various geographical scales are essential to understanding population dynamics and spread potential of invasive species. Here, we explore these issues in the highly invasive vase tunicate, Ciona intestinalis, a species whose invasion history has been obscured by its poorly understood taxonomy and population genetics. Recent phylogenetic and comparative genomic studies suggest that C. intestinalis is a cryptic species complex consisting of at least three species. We reconstructed phylogenies based on both mitochondrial (cytochrome c oxidase subunit 3--NADH dehydrogenase subunit 1 region and NADH dehydrogenase subunit 4 gene) and nuclear (internal transcribed spacer 1) sequences, results of which support four major phylogroups corresponding to the previously reported spA, spB and Ciona spp. (spC) as well as an undescribed cryptic species (spD). While spC and spD remain restricted to their native ranges in the Mediterranean Sea and Black Sea, respectively, the highly invasive species (spA and spB) have disjunct global distributions. Despite extensive interspecific divergences, we identified low phylogeographical structure within these two invasive species. Haplotype network analyses revealed comparatively limited mutation steps among haplotypes within each species. Population genetic analyses based on two mtDNA fragments and eight unlinked microsatellites illustrated relatively low population differentiation and high population connectivity at both regional and continental scales in the two invasive species. Human-mediated dispersal coupled with a high potential for natural dispersal is probably responsible for the observed genetic homogeneity.
Collapse
Affiliation(s)
- Aibin Zhan
- Great Lakes Institute for Environmental Research, University of Windsor, 401 Sunset Avenue, Windsor, Ontario, Canada.
| | | | | |
Collapse
|
11
|
Sasakura Y, Inaba K, Satoh N, Kondo M, Akasaka K. Ciona intestinalis and Oxycomanthus japonicus, representatives of marine invertebrates. Exp Anim 2010; 58:459-69. [PMID: 19897929 DOI: 10.1538/expanim.58.459] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
The study of marine invertebrates is useful in various biological research fields. However, genetic analyses of these animals are limited, mainly due to difficulties in culturing them, and the genetic resources of marine invertebrates have not been organized. Recently, advances have been made in the study of two deuterostomes, an ascidian Ciona intestinalis and a feather star Oxycomanthus japonicus. The draft genome sequence of Ciona intestinalis has been determined, and its compact genome, which has less redundancy of genes compared with vertebrates, provides us with a useful experimental system for analyzing the functions of genes during development. The life cycle of Ciona intestinalis is approximately 2-3 months, and the genetic techniques including a perfect inland culture system, germline transformation with a transposon Minos, enhancer detection and insertional mutagenesis, have been established. The feather star Oxycomanthus japonicus conserves the characteristics of the basic echinoderm body plan with a segmented mesoderm, which is a fascinating characteristic for understanding the evolution of echinoderms. Oxycomanthus japonicus shows strong regeneration ability and is a suitable subject for analysis of the mechanisms of regeneration. In consideration of these features, the National BioResource Project (NBRP) has started to support the supply of wild-types, transgenic lines and inbred lines of Ciona intestinalis and Oxycomanthus japonicus.
Collapse
Affiliation(s)
- Yasunori Sasakura
- Shimoda Marine Research Center, University of Tsukuba, Shimoda, Shizuoka, Japan
| | | | | | | | | |
Collapse
|
12
|
Christiaen L, Wagner E, Shi W, Levine M. The sea squirt Ciona intestinalis. Cold Spring Harb Protoc 2009; 2009:pdb.emo138. [PMID: 20150076 DOI: 10.1101/pdb.emo138] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
INTRODUCTIONSea squirts (Ciona intestinalis) are tunicates (or urochordates), the closest living relatives of the vertebrates. Although the adults are simple, sessile filter feeders, the embryos and larvae possess clear chordate features including a prominent notochord and dorsal, hollow neural tube. Tail-bud-stage embryos and mature swimming tadpoles are composed of approximately 1000 and 2600 cells, respectively, with complete lineage information. This cellular simplicity is coupled with a streamlined genome that has not undergone the duplications seen in vertebrates. A variety of molecular tools have been applied to understanding Ciona embryogenesis. Comparisons of the C. intestinalis genome and the related but divergent Ciona savignyi genome have facilitated the identification of conserved non-coding DNAs, including regulatory DNAs such as tissue-specific enhancers. Systematic in situ hybridization assays and gene-disruption experiments using specific morpholino antisense oligonucleotides have led to the elaboration of provisional gene regulatory networks underlying the specification of key chordate tissues, including the notochord, neural tube, and beating heart. These networks provide a foundation for understanding the mechanistic basis of more complex cell-specification processes in vertebrates, and for understanding the evolutionary origins of distinctive vertebrate characteristics such as the neural crest. Because tunicates and vertebrates are sister groups, there is every indication that the developmental mechanisms revealed in the simple Ciona model will be applicable to comparable processes in vertebrates.
Collapse
Affiliation(s)
- Lionel Christiaen
- Molecular and Cell Biology Department, University of California, Berkeley, California 94720, USA.
| | | | | | | |
Collapse
|
13
|
Dupont L, Viard F, Dowell MJ, Wood C, Bishop JDD. Fine- and regional-scale genetic structure of the exotic ascidian Styela clava (Tunicata) in southwest England, 50 years after its introduction. Mol Ecol 2009; 18:442-53. [PMID: 19161467 DOI: 10.1111/j.1365-294x.2008.04045.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Styela clava, an ascidian native to the northwest Pacific, was first recorded in the Atlantic at Plymouth, southwest England, in 1953. It now ranges in the northeast Atlantic from Portugal to northern Denmark, and has colonized the east coast of North America. Within the region of first introduction, we aimed to characterize current genetic diversity in the species, elucidate the respective roles of human-aided vs. natural dispersal, and assess the extent of larval dispersal by looking for genetic differentiation at very small scales. Eight sites, mostly marinas, were studied along c. 200 km of coast in southwest England encompassing Plymouth. Five microsatellite loci were genotyped in 303 individuals to analyse gene flow at regional (among sites) and fine (within sites) scales. F-statistics and assignment tests were used to investigate regional genetic structure. At the fine scale, deviation from mutation-drift equilibrium was tested, and isolation by distance and genetic clustering analyses were undertaken. Significant genetic differentiation existed between sites, unrelated to geographical separation; migration between geographically distant marinas was inferred, highlighting the likely importance of human-mediated dispersal in range expansion and occupancy by S. clava. Fine-scale population structure was present within at least four sites, which may be explained by the limited dispersal ability of this ascidian and recruitment from differentiated pools of larvae. Populations in enclosed marinas had higher self-recruitment rates than those in open sites. Some marinas might therefore function as reservoirs of propagules for subsequent spread, whereas others might be sinks for migrants.
Collapse
Affiliation(s)
- L Dupont
- Marine Biological Association, Citadel Hill, Plymouth PL12PB, UK.
| | | | | | | | | |
Collapse
|