RESUMO

The nemertean Malacobdella arrokeana is a commensal of the edible giant bivalve Panopea abbreviata; 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 M. arrokeana 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 M. arrokeana 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.

Assuntos

Distribuição Animal , Invertebrados/genética , Animais , Oceano Atlântico , Bivalves/fisiologia , Invertebrados/classificação , Invertebrados/fisiologia , Larva/genética , Filogeografia , Simbiose

RESUMO

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.

Assuntos

Comportamento Alimentar , Invertebrados/classificação , Invertebrados/fisiologia , Simbiose , Animais , Invertebrados/ultraestrutura , Especificidade da Espécie

RESUMO

BACKGROUND: Nemerteans of the genus Malacobdella live inside of the mantle cavity of marine bivalves. The genus currently contains only six species, five of which are host-specific and usually found in a single host species, while the sixth species, M. grossa, has a wide host range and has been found in 27 different bivalve species to date. The main challenge of Malacobdella species identification resides in the similarity of the external morphology between species (terminal sucker, gut undulations number, anus position and gonad colouration), and thus, the illustrations provided in the original descriptions do not allow reliable identification. In this article, we analyse the relationships amongthree species of Malacobdella:M.arrokeana,M.japonica andM.grossa,adding new data for the M.grossa and reporting the first for M. japonica, analysing 658 base pairs of the mitochondrial cytochrome c oxidase subunit I gene(COI).Based on these analyses, we present and discuss the potential of DNA barcoding for Malacobdellaspecies identification. RESULTS: Sixty-four DNA barcoding fragments of the mitochondrial COI gene from three different Malacobdella species (M. arrokeana, M. japonica and M. grossa) are analysed (24 of them newly sequenced for this study, along with four outgroup specimens) and used to delineate species. Divergences, measured as uncorrected differences, between the three species were M.arrokeana-M. grossa11.73%,M.arrokeana-M.japonica 10.62%and M.grossa-M. japonica 10.97%. The mean intraspecific divergence within the ingroup species showed a patent gap with respect to the interspecific ones: 0.18% for M.arrokeana,0.13% for M.grossa and0.02% for M.japonica (rangesfrom 0 to 0.91%). CONCLUSIONS: We conclude that there is a clear correspondence between the molecular data and distinguishing morphological characters. Our results thus indicate that some morphological characters are useful for species identification and support the potential of DNA barcoding for species identification in a taxonomic group with subtle morphological external differences.