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Genetic diversity and population structure of Caribbean marine invertebrates

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Abstract
Natural populations of many marine invertebrates are under pressure by fisheries due to the increasing demand and unit prices leading to overexploitation. I examined the genetic variation of two marine invertebrates: the corallimorpharian Ricordea florida and the emerald crab Mithraculus sculptus both of which are heavily traded by the marine aquarium industry. A third species studied, the commensal barnacle Chelonibia caretta, was not under direct fishing pressure, but its host is an endangered species, the hawksbill sea turtle (Eretmochelys imbricata). Using direct sequencing of mitochondrial genes (COI and 16S) and the nuclear the ITS region (ITS1, 5.8S, and ITS2), the phylogeography and genetic population structure of these invertebrates were characterized. The genetic diversity in C. caretta was low compared to published sequences from populations of barnacles attached to fixed substrata. However, genetic diversity values from C. caretta were comparable to those reported from C. testudinaria, an epibiont barnacle on loggerhead turtles. Analysis of molecular variance and phylogenetic analysis of the sampled turtle epibionts indicated that they are genetically homogeneous, irrespective of the host or host gender. In contrast, the phylogeography of the ITS region of the coral R. florida uncovered two partial sympatric genetic lineages. These lineages showed two highly supported monophyletic groups when they were compared phylogenetically against published nuclear ribosomal sequences of other genera of Corallimorpharia (Actinodiscus, Amplexidiscus, Corynactis, and Rhodactis). Similarly to R. florida, the phylogeographic analysis of M. sculptus based on 16S revealed two distinct lineages distributed throughout the sampled region. The analysis of molecular variance and the phylogeography of the sampled populations of M. sculptus reflected that most of the specimens within each lilneage were collected from demographically open populations within the western Caribbean. In general, the three species studied are consistent with the prediction that higher rates of dispersal reduce population divergence and estimates of nucleotide diversity. As in previous studies, the absence of genetic differentiation between geographical distant populations of these species suggests high connectivity between all sampled areas. Additionally, the presence of cryptic lineages confirms concerns regarding that biodiversity can be vastly understudied for marine environment.
Las poblaciones naturales de muchos invertebrados estĂ¡n bajo presiĂ³n por las pesquerĂ­as debido a su creciente demanda y valor comercial, que conducen a su sobreexplotaciĂ³n. Yo examinĂ© la variaciĂ³n genĂ©tica de dos especies de invertebrados marinos: el corallimorfario Ricorea florida y el cangrejo esmeralda Mithraculus sculptus, ambos cosechados extensamente para la industria de acuarios marinos. Una tercera especie fue estudiada, la bayoca comensalista Chelonibia caretta, la cual no estĂ¡ bajo presiĂ³n directa de la pesquerĂ­a, pero su hospedero, el carey de concha (Eretmochelys imbricata), es una especie de tortuga marina amenazada. Utilizando amplificaciones directas de genes mitocondriales (COI y 16S) y nucleares (ITS1, 5.8S y ITS2) se caracterizĂ³ la filogeografĂ­a y estructura genĂ©tica poblacional de estos invertebrados. La diversidad genĂ©tica de Chelonibia caretta fue baja al compararla con secuencias publicadas de otras especies de bayocas sobre substratos fijos. Sin embargo, los valores de la variabilidad genĂ©tica para C. caretta son comparables con aquellos publicados para C. testudinaria, bayoca epibionte de la tortuga marina cabezona. AnĂ¡lisis de variaciĂ³n molecular y anĂ¡lisis filogenĂ©tico de los epibiontes muestreados de la tortuga indicaron que Ă©stos son genĂ©ticamente homogĂ©neos, independientemente del hospedero o del gĂ©nero del hospedero. En contraste, los anĂ¡lisis de la regiĂ³n del ITS de R. florida revelaron dos linajes genĂ©ticos parcialmente solapados. Estos linajes fueron comparados filogenĂ©ticamente contra secuencias ribosomales nucleares publicadas de otros gĂ©neros de Corallimorpharia (Actinodiscus, Amplexidiscus, Corynactis y Rhodactis) y cada linaje formĂ³ un grupo monofilĂ©tico altamente apoyado. Al igual que para R. florida, los anĂ¡lisis filogenĂ©ticos del 16S de Mithraculus sculptus, revelaron dos linajes distribuidos a travĂ©s de la regiĂ³n muestreada. Los anĂ¡lisis de varianza molecular y la filogeografia de las poblaciones muestreadas de M. sculptus reflejaron que la mayor parte de los especĂ­menes, dentro de cada linage, fueron colectados de poblaciones demogrĂ¡ficamente abiertas dentro del Caribe occidental. En general, las tres especies estudiadas son consistentes con la predicciĂ³n de que si los Ă­ndices de dispersiĂ³n son altos disminuyen la divergencia y los estimados de diversidad de nucleĂ³tidos. Como en estudios previos, la ausencia de la diferenciaciĂ³n genĂ©tica entre poblaciones geogrĂ¡ficamente distantes de estas especies sugiere una alta conectividad entre las Ă¡reas muestreadas. En adiciĂ³n, la presencia de linajes crĂ­pticos confirma la preocupaciĂ³n de que la biodiversidad estĂ¡ sub-estimada en los ambientes marinos.
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Date
2009-12
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Research Projects
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Keywords
Marine invertebrate populations - Phylogeography, Marine invertebrate populations - Genetic sequencing, Corallimorpharian Ricordea florida - Genetic population structure, Emerald crab Mithraculus sculptus - Genetic population structure
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