The nemertean
is a commensal of the edible giant bivalve
; both species have a restricted geographic distribution, high specificity and populations settled along distinct biogeographic provinces. ...This supposes a high genetic structuring among populations and low intra-populational variability; nevertheless, a lack of genetic structure was detected previously between
populations from the Atlantic Northern Patagonia Gulfs System (NPGS) by means of mitochondrial and nuclear markers. Here, we present a model that explains this lack of genetic structure, integrating larval development and behavior, as well as bio-oceanographical model simulations. We observed in cultured larvae a maximum 30 days of planktonic life before settlement. Planuliform larval morphology and behavior of
suggested that the dispersion is more influenced by passive transport rather than active swimming. Modeling larvae as particles indicated that the limit of biogeographical provinces along the NPGS is not a barrier for dispersal, corroborating that larval dispersion is strictly related to season and to hydrodynamic diffusion patterns present in the area. These results explain the lack of genetic population structure recorded before in the NPGS. Our results provide novel baseline data regarding larval connectivity and oceanographic circulation patterns on the southwestern Atlantic. This information can be used as a reference for the implementation of management plans of invertebrate species with pelagic larvae to ensure the long-term viability of fishery resources shared by different government districts.
The implementation of molecular data for the analysis of nemertean diversity has unraveled the taxonomic status of several species and many higher taxa within the group. Nowadays, a large proportion ...of novel putative species are being discovered and it is necessary to add molecular data to the morphological description to obtain a correct identification. In this study, we used mitochondrial cytochrome oxidase I gene (COI) as molecular marker to investigate the diversity of nemerteans from a marine Sub-Antarctic environment. We used Automatic Barcode Gap Discovery (ABGD), Poisson Tree Processes (PTP) and Bayesian implementation of the PTP model (bPTP) as well as reciprocal monophyly on neighbor-joining (NJ) and maximum likelihood (ML) trees for species delimitation. ABGD showed a clear barcoding gap (6 to 10%) and the presence of 15 different putative nemertean species in the dataset of 54 COI sequences from the marine protected area “Namuncurá–Burdwood Bank” (MPA-BB), expanding the known biodiversity for the Sub-Antarctic region. Ten monostiliferan and five heteronemertean species were found. Our results also confirm the presence of two
Parborlasia corrugatus
cryptic species in the Antarctic and Sub-Antarctic region. This work highlights the importance of the MPA-BB as a biodiversity hotspot and provide molecular data for the Phylum Nemertea in the Southwestern Atlantic Ocean.
Heteronemerteans, such as Lineus ruber, L. viridis, Ramphogordius sanguineus, R. lacteus, Riseriellus occultus, and Micrura varicolor, share many similar external characters. Although several ...internal characters useful for distinguishing these nemertean species have been documented, their identification is based mostly on coloration, the shape of the head, and how they contract, which may not be always reliable. We sequenced the mitochondrial COI gene for 160 specimens recently collected from 27 locations around the world (provisionally identified as the above species, according to external characters and contraction patterns, with most of them as R. sanguineus). Based on these specimens, together with sequences of 16 specimens from GenBank, we conducted a DNA-based species delimitation/identification by means of statistical parsimony and phylogenetic analyses. Our results show that the analyzed specimens may contain nine species, which can be separated by large genetic gaps; heteronemerteans with an external appearance similar to R. sanguineus/Lineus ruber/L. viridis have high species diversity in European waters from where eight species can be discriminated. Our 42 individuals from Vancouver Island (Canada) are revealed to be R. sanguineus, which supports an earlier argument that nemerteans reported as L. ruber or L. viridis from the Pacific Northwest may refer to this species. We report R. sanguineus from Chile, southern China, and the species is also distributed on the Atlantic coast of South America (Argentina). In addition, present analyses reveal the occurrence of L. viridis in Qingdao, which is the first record of the species from Chinese waters.
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.
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 δ(15)N or δ(13)C 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.
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 (π = 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). F ₛₜ 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.
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, ligament and 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 outer layer 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 association belongs 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.
The reproductive cycle and gonad development of the yellow clam Mesodesma mactroides was studied over a period of 24 months (January 2005–December 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 summer–autumn 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.
This article documents the addition of 83 microsatellite marker loci and 96 pairs of single‐nucleotide polymorphism (SNP) 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, Sycoscapter hirticola and Thanatephorus cucumeris (anamorph: Rhizoctonia solani). These loci were cross‐tested on the following species: Pentadesma grandifolia and Pentadesma reyndersii. This article also documents the addition of 96 sequencing primer pairs and 88 allele‐specific primers or probes for Plutella xylostella.
Climate change has consequences over marine organisms and their behavior. Echinoderms have been found to be negatively affected on righting time, survival, feeding rate or growth by high ...temperatures, low salinity or their interaction. We analyzed the effects of temperature and salinity fluctuation under a climate change scenario on feeding rate, righting time and heat shock proteins (Hsp70) expression in the sea star Anasterias minuta. Our results showed negative effects of increased temperature in the feeding rate of A. minuta. In addition, Hsp70 expression in gonads showed an upregulation after water temperature increase in normal salinity conditions. Regarding the righting activity, we detected a variable pattern among treatments with significant statistical differences in the interaction of temperature and salinity, and in time intervals measured. Variations in sea stars feeding ecology could produce direct and cascading effects driving ecological shifts as changes in species composition of the coastal Patagonian ecosystems. Investigating the effect of sea stars on intertidal and subtidal assemblages in a climate change scenario is of great importance to provide valuable information for an adequate management of intertidal habitats, which have been little studied in Atlantic Patagonia.
•Increasing temperature decreases the feeding rate of the sea star Anasterias minuta.•Righting activity of A. minuta showed statistical differences among treatments.•Interaction of temperature and salinity triggers an increased in Hsp70 expression.•Climate change will drive to direct and cascading effects on Patagonian coasts.
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