Mitochondrial and nuclear markers reveal a lack of genetic structure in the entocommensal nemertean Malacobdella arrokeana in the Patagonian gulfs

Abstract Malacobdella arrokeana is an entocommensal nemertean exclusively found in the bivalve geoduck Panopea abbreviata, and it is the only representative of the genus in the southern hemisphere. To characterize its genetic diversity, population structure and recent demographic history, we conducted the first genetic survey on this species, using sequence data for the cytochrome oxidase I gene (COI), 16S rRNA (16S) and the internal transcribed spacer (ITS2). Only four different ITS2 genotypes were found in the whole sample, and the two main haplotypes identified in the mitochondrial dataset were present among all localities with a diversity ranging from 0.583 to 0.939. Nucleotide diversity was low (p = 0.001?0.002). No significant genetic structure was detected between populations, and mismatch distribution patterns and neutrality tests results are consistent with a population in expansion or under selection. Analysis of molecular variance (AMOVA) revealed that the largest level of variance observed was due to intrapopulation variation (100, 100 and 94.39 % for 16S, COI and ITS2, respectively). Fst values were also non-significant. The observed lack of population structure is likely due to high levels of genetic connectivity in combination with the lack or permeability of biogeographic barriers and episodes of habitat modification.Fil: Fernandez Alfaya, Jose Elias. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Bigatti, Gregorio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Machordom, Annie. Consejo Superior de Investigaciones Cientificas. Museo Nacional de Cs. Naturales; Españ

Caracterización molecular, genética poblacional y relación biológica del nemertino Malacobdella arrokeana endocomensal de la almeja gigante Panopea abbreviata

[ES] Malacobdella arrokeana Ivanov et al., 2002 es un nemertino que vive en la cavidad del manto de la almeja gigante Panopea abbreviata, ambas especies endemicas del Mar Argentino. Mediante la secuenciación y análisis del gen mitocondrial citocromo oxidasa I (COI), se corroboró que M arrokeana diverge genéticamente de M. grossa en un 11,6%, y 10,4% con respecto a M. japonica. Tanto M. arrokeana como P. abbreviata comparten el mismo nivel trófico y los mismos ítems alimentarios, compuestos en su mayoría por microalgas, diatomeas y pequeños crustáceos. Se registró la posición de M. arrokeana dentro de la cavidad del manto de P. abbreviata y la morfología de las estructuras utilizadas en la alimentación (probóscide y faringe). Ambas estructuras están compuestas de papilas que recubren toda su extensión. Por un lado la probóscide está compuesta por papilas con dos tipos de células glandulares diferentes, uno en la porción basal y otro tipo en la porción distal, en forma de “cepillo”, posiblemente con capacidad de secreción, mientras que las papilas de la faringe son evaginaciones del tegumento recubiertas de cilias. A partir de estos resultados se proponen dos mecanismos complementarios de alimentación en M. arrokeana ,1) de sucesivas contracciones musculares de la faringe que provocan una corriente incurrente hacia el esofago donde las partículas pequeñas son retenidas por las acción de las papilas de ambas estructuras (faringe y probóscide) y otro para la captura de partículas de mayor tamaño directamente con la probóscide. Se confirma que M. arrokeana no se alimenta del tejido de P. abbreviata. La población de M. arrokeana del golfo San José posee un ciclo reproductivo con desoves parciales a lo largo del año y un pico marcado durante el mes de septiembre. Este ciclo está dividido en dos etapas una de desarrollo gonadal y crecimiento del individuo (aumento de talla media, Lt), que dura 4 meses durante la época otoño - inverno, y una fase de reproducción que corresponde a la primavera acompañada de un descenso en la Lt de los individuos. Este descenso y el posterior aumento del Lt, durante los siguientes cuatro meses primaverales, podrían indicar una estrategia semélpara de reproducción. Se logró obtener en condiciones de laboratorio larvas de M. arrokeana de 4 semanas de edad; esta larva es planuliforme, planctónica y no se alimenta, al igual que las larvas de otros hoplonemertinos conocidos. Se propone que el asentamiento de las larvas dentro de P. abbreviata podría ser a través de dos mecanismos complementarios, 1) por una retención larvaria dentro de los láminas branquiales de P. abbreviata, y 2) de re-infección por parte de larvas exógenas. El análisis de 4 poblaciones de M. arrokeana que habitan los golfos norpatagónicos (San Matías, San José y Nuevo), mostraron una escasa variabilidad en su estructura genética (Fst = 0) comparando porciones de los genes COI, ARNr 16S, y el marcador molecular ITS2. La escasa variabilidad podría ser causada por una falta de barreras naturales al flujo génico, la vida planctónica de las larvas (30 días) y un posible proceso de selección sobre los haplotipos comunes en las poblaciones. Con toda la información obtenida en esta tesis se propone que M. arrokeana presenta una asociación de tipo comensal, donde la especie encuentra en el hospedador, refugio y alimento, sin provocarle daños a P. abbreviata.[EN] Malacobdella arrokeana Ivanov et al., 2002 is a nemertean living in the mantle cavity of the giant clam Panopea abbreviata, both endemic of the Argentine Sea. Using a portion of the mitochondrial gene Cytochrome Oxidase I (COI), M. arrokeana showed a genetic divergence of 11.6% compared to M. japonica and 10.4% with respect to M.grossa. M. arrokeana and P. abbreviata share the same trophic level and the same food items, consisting mostly of algae, diatoms and small crustaceans. Through live observation of the position of M. arrokeana within the mantle cavity of P. abbreviata and the morphology of the structures used in feeding (proboscis and pharynx), it was observed that both structures are covered by papillae. Papillae´s proboscis are composed of two different cellular types, one situated in the basal portion and the other cells from the distal portion with "brush" form, with possible secretion capacity. Meanwhile papillae´s pharynx are evaginations of the tegument covered by cilia. Two complementary feeding behavior are proposed, 1) by successive muscle pharynx contractions that cause a water inward current into the pharynx, and small particles are retained by the action of papillae of both structures (pharynx and proboscis) and 2) using the proboscis to capture bigger particles stucked on the gill surface ("gill brushing"). The results obtained confirm, that M. arrokeana do not feeds on P. abbreviata tissues. M. arrokeana has a reproductive cycle with partial spawning events along the year and a marked peak spawning during September. The seasonal cycle of M. arrokeana can be roughly divided into two phases: the individual growth, followed by gonad development and the reproductive phase. The first one begins with an increase in average length size (Lt) and gonad maturing, during fall autumn and winter (four months), and the other phase corresponding to the spawning that begins in September and continues during spring and early summer. The decline and subsequent rise of mean population Lt, and the increase in the percentages of multiinfections during the next four spring months, might be indicating a semelparous reproductive strategy. Larval development was described for the first time for M. arrokeana. A four weeks planuliform, planktonic and not feeding larvae was obtained in laboratory conditions. Two complementary larval settlement mechanisms are proposed 1) by a larval retention in the host lamellae gills, and 2) re-infection by the exogenous larvae (formed outside the host), probably mediated by a host signal cue. The analysis of the four populations of M. arrokeana living the north Patagonian gulfs (San Mafias, San José and Nuevo), showed no genetic difference among populations (Fst = 0) comparing portions of genes COI, 16S rRNA, and ITS2. The low variability registered may be explainded by the lack of natural barriers to gene flow, long planktonic larval life (four weeks) and a possible selection process on common haplotypes in populations.Based on the results obtained, M. arrokeana presents a commensal association. M. arrokeana living into the host, obtain shelter and secure food source and not causing severel damage to the host.Peer reviewe

Malacobdella arrokeana: Parasite or commensal of the giant clam Panopea abbreviata?

We examined trophic relationship between the nemertean Malacobdella arrokeana and its host, the edible geoduck Panopea abbreviata by studying the diets of both species by direct (stomach contents) and indirect methods (stable-isotope analysis of C and N). In addition to these methods, the feeding behavior of M. arrokeana within the host and the morphology of its feeding organs were examined. The feeding behavior of M. arrokeana did not exhibit parasitic characteristics, and the proboscis morphology indicates it is unable to injure host tissues. Analysis of stomach contents revealed a diet consisting mainly of microalgae and diatoms. Panopea abbreviata and M. arrokeana shared similar trophic levels, presenting no differences in the spread of the isotopic niches and high overlap (SEAB overlapped 63%). Consistent with this, our results showed no differences in δN or δC values between the two species. The combination of direct and indirect approaches revealed that M. arrokeana has a diet similar to that of its host, confirming a commensal relationship.Peer Reviewe

Reproductive cycle and gonad development of the Northern Argentinean Mesodesma mactroides (Bivalvia: Mesodesmatidae)

The reproductive cycle and gonad development of the yellow clam Mesodesma mactroides was studied over a period of 24 months (January 2005December 2006) at the Argentinean sandy beach Santa Teresita. Histological examination of gonadal tissue revealed that sex ratios did not significantly deviate from the proportion of 1:1 and no case of hermaphroditism was found. The reproductive cycle of M. mactroides followed an annual cyclicality, which was significantly correlated to monthly mean sea surface temperatures (SST). Oocytes showed highest abundance in winter, indicating a process of gonadal development and sexual maturation. The mean oocyte size decreased significantly during spring. Modal oocyte sizes decreased significantly during winter and late spring of each year, suggesting spawning events. The condition index was not useful in describing the annual reproductive cycle of M. mactroides. Ash-free, shell-free dry mass was chosen to detect the condition of the specimens, and this significantly correlated with monthly mean SST and the gametogenic cycle. Annual recruitment patterns during summerautumn indicated a 3-month-long planktonic phase of M. mactroides. The reproduction cycle and gonad development of M. mactroides showed only weak differences between data from the present study and those collected 40 years ago

Population structure, growth and production of the yellow clam Mesodesma mactroides (Bivalvia: Mesodesmatidae) from a high-energy, temperate beach in northern Argentina

The yellow clam Mesodesma mactroides (Bivalvia: Mesodesmatidae) was once the most abundant intertidal species on the Atlantic coast of northern Argentina and an important commercial resource in South America. This study of a population inhabiting the intertidal zone of the sheltered-dissipative sandy beach Santa Teresita documents the species' population biology, including demographic structure, growth and production during December 2004 and December 2006, and adumbrates the critical state of M. mactroides at present. A total of 3,015 M. mactroides were collected and measured, whereas individuals were found with an anterior-posterior shell length between 2 and 64 mm. A von Bertalanffy growth function with an asymptotic length (L∞) of 85 mm and a growth constant (K) of 0.47 year-1 was established from length-frequency distributions. The longevity of the species is estimated at approximately 6 years, and instantaneous mortality rate was about three times higher than 40 years ago. Besides, this study confirmed that the overall growth performance index (OGP) is habitat-specific and can be used to group M. mactroides and M. donacium from different areas into temperate and upwelling species. Furthermore, OGP is inversely correlated with the latitudinal distribution of Mesodesma populations. The intertidal biomass ranged between 0.06 and 0.07 g AFDM m-2 year-1. Individual production was observed to be highest at 47 mm length (0.35 g AFDM m-2 year-1), and annual production ranged between 0.12 and 0.19 g AFDM m-2 year-1, resulting in productivity values (P/B) between 1.84 and 2.93. The comparison of the results of the present study with those of growth studies conducted on M. mactroides 40 years ago revealed the following considerable differences in the population structure of M. mactroides, indicating the conservation status of this intertidal bivalve as endangered: (1) present growth rates are faster, but that the maximum length attained has decreased, (2) the numbers of individuals per square metre were many times higher in the past than in the present, (3) bivalves from the present work never reached the 'commercial size' of 60 mm and (4) 40 years ago, the population of M. mactroides was composed of up to three cohorts, whereas in this study, there was only one single cohort visible.Fil: Herrmann, Marko. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina. Johann Heinrich von Thünen Institute; AlemaniaFil: Fernandez Alfaya, Jose Elias. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; ArgentinaFil: Lepore, Mauro L.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; ArgentinaFil: Penchaszadeh, Pablo Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; ArgentinaFil: Arntz, Wolf E.. Institute for Polar and Marine Research; Alemani

Panopea abbreviata (Bivalvia: Hitellidae) in the southwestern Atlantic ocean, taxonomic revision and anatomy

The taxonomy and anatomy of the southwestern Atlantic geoduck, Panopea abbreviata Valenciennes, 1839, are revised. Materials from several institutions, as well as new living specimens collected from the coast of Argentina were studied. Type materials of all related nominal species are illustrated. The shell morphology, shell ultrastructure, hinge, ligamentand mantle cavity organs are described. The symbiotic relationship with the nemertean Malacobdella arrokeana, attached to host mantle tissues, is mentioned. Panopea abbreviata is abundant in the gulfs of northern Patagonia. It occurs in the subtidal zone from 8 to 25 meters deep, deeply buried in the sediment. It has a large thick shell, shortener at the posterior end, with exposed siphons covered by a dark brownish periostracum; a hinge plate characterized by a single cardinal tooth in each valve; and shell ultrastructure with three layers: an outerlayer of nearly vertical and composite prisms, a middle, true homogeneous layer, and an inner layer of alternating sublayers of fine complex crossed lamellar and irregular simple prisms. The fused mantle is only interrupted in the pedal gape. Ctenidia and labial palps associationbelongs to the Category III and ctenidia type C(1). Panopea antarctica is its only synonym. The fossil taxa Panopea truncata, P. inferior, P. hauthali, P. coquimbensis and P. guayacanensis are excluded from the synonymy.Fil: Signorelli, Javier Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; ArgentinaFil: Alfaya, José E. F.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentin

Permanent genetic resources note. Permanent Genetic Resources added to Molecular Ecology Resources Database 1 August 2012-30 September 2012

This article documents the addition of 83 microsatellite marker loci and 96 pairs of single-nucleotide polymorphism (NSP) sequencing primers to the Molecular Ecology Resources Database. Loci were developed for the following species: Bembidion lampros, Inimicus japonicus, Lymnaea stagnalis, Panopea abbreviata, Pentadesma butyracea, Sycoscapte rhirticola and Thanatephorus cucumeris (anamorph: Rhizoctonia solani). These loci were cross-tested on the following species: Pentadesma grandiofolia and Pentadesma reyndersii. This article also documents the addition of 96 sequencing primer pairs and 88 allele-specific primers or probes for Plutella zylostella