Mercè Durfort

Cellular defence mechanism of the clam Tapes semidecussatus against infection by the protozoan Perkinsus sp.

The cellular defence mechanism of the clam Tapes semidecussatus (Mollusca, Bivalvia) against infection by the parasite protozoan Perkinsus sp. (Apicomplexa, Perkinsea) was studied in the gill filaments. The parasites, localized in the connective tissue, induced a cellular reaction involving infiltrated granulocytes. These showed a secretory aspect, with the cytoplasm being filled by membrane-bound granules with internal membranes. The holocrine secretion, which was proteic and slightly glycosylated, by the granulocytes gave rise to the encapsulation of the parasites. After incubation with lectins from Canavalia ensiformis, Triticum vulgaris, Helix pomatia, Glycine max, Arachis hypogaea, Ricinus communis (agglutinin), Ulex europeus I and Limax flavus, a lack of specific and/or main sugars was observed in the plasma membrane of parasite and granulocyte, and in the wall of the former. Furthermore, GalNacα1,3GalNac and β-d-gal residues were only detected in association with the internal membranes and dense regions of both granules and capsule, respectively. Blood granulocytes were observed at the periphery of the cellular reaction, close to blood vessels, and these appeared to re-differentiate to give the granulocytes of the cellular reaction. The data reported here suggest that this parasite induces the infiltration and re-differentiation of specialized cells in the host mollusc. In addition, a polarized secretion of a specific defence product is described for the first time.

Dynamics of gametogenesis, embryogenesis, and larval release in a Mediterranean homosclerophorid demosponge

We investigated the cycle of sexual reproduction in a Mediterranean population of Corticium candelabrum by light and electron microscopy, using non-destructive tissue sampling. Most individuals of this hermaphroditic species engaged in reproduction. The relationship between seawater temperature and gametogenesis was not straightforward. Oogenesis, characterised by a long phase of oocyte growth, was continuous, with new oocytes appearing every single month of the year. Nevertheless, maximum oocyte production coincided with declining temperatures. Likewise, spermatogenesis started in the coldest month of the year. In contrast, embryonic development and larval release were limited to a few weeks during the seasonal rise of temperature and the warmest months, respectively. Female and male gametes were located in close proximity in the mesohyl. Monociliated spermatogonia putatively derived from choanocytes, and oogonia from archaeocytes. Spermatogenesis, which strongly resembled that in higher animals, produced round spermatozoa that were provided with acrosome and anchoring system for the cilium. Mature oocytes became surrounded by a bacterial layer. Many symbiotic bacteria served for oocyte nourishment, but others were transferred to the larva. As a whole, the reproductive cycle, which also exhibited quite successful fertilisation and low mortality during embryonic development, appears finely tuned to improve the competitive ability of this sponge.

Perkinsus sp. (Phylum Apicomplexa) in Mediterranean clam Ruditapes semidecussatus: ultrastructural observations of the cellular response of the host

Abstract An infection caused by a Perkinsus sp. was observed in Ruditapes semidecussatus collected on the western Mediterranean coast (Tarragona, Spain). The trophozoites were generally grouped and surrounded by amorphous material that constituted a nodule. These nodule reactions with trophozoites were located in connective tissue of the gut, hepatopancreas, kidney, gonads, mantle, and gill. Ultrastructural features of the host reaction due to the presence of Perkinsus sp. are described. A large number of hemocytes was present in infested clams. These hemocytes present numerous eosinophilic and metachromatic granules of varying size, some coalescing into megagranules which contain Thiery-positive membrane remains in the interior. Single trophozoites are sometimes located in these cells. Ultrastructural data show that the lysis of the hemocytes and the coalescence of the granules result in the nodule that encapsulates various trophozoites.

Histopathology related to cadmium and lead bioaccumulation in chronically exposed wood mice, Apodemus sylvaticus, around a former smelter

The ceasing of industrial activities often reduces the emission of pollutants but also often leaves disturbed areas without remediation and with persistent pollutants that can still be transferred along the food chain. This study examines the potential relationships between non-essential trace metals and histopathology in target tissues of wood mice (Apodemus sylvaticus) collected along a gradient of contamination around the former smelter, Metaleurop Nord (northern France). Cadmium and lead concentrations were measured, and histological alterations attributable to chronic trace metal exposure were assessed in the liver and the kidneys of 78 individuals. Metal concentrations quantified in the present study were among the highest observed for this species. Some histological alterations significantly increased with Cd or Pb concentrations in the soil and in the organs. Sixteen mice from polluted sites were considered at risk for metal-induced stress because their Cd and/or Pb tissue concentrations exceeded the LOAELs for single exposure to these elements. These mice also exhibited a higher severity of histological alterations in their organs than individuals with lower metal burdens. These results indicate that the Metaleurop smelter, despite its closure in 2003, still represents a threat to the local ecosystem because of the high levels and high bioavailability of Cd and Pb in the soil. However, among the mice not considered at risk for metal-induced stress based on the metal levels in their tissues, a large percentage of individuals still exhibited histological alterations. Thus, the present study suggests that the evaluation of toxic effects based only on the LOAELs for single metal exposure may result in the underestimation of the real risks when specimens are exposed to multiple stressors.

Ultrastructural damage of Loligo vulgaris and Illex coindetii statocysts after low frequency sound exposure.

There is a considerable lack of information concerning marine invertebrate sensitivity to sound exposure. However, recent findings on cuttlefish and octopi showed that exposure to artificial noise had a direct consequence on the functionality and physiology of the statocysts, sensory organs, which are responsible for their equilibrium and movements in the water column. Owing to a lack of available data on deep diving cephalopod species, we conducted a noise exposure comparative experiment on one Mediterranean squid, Illex coindetii, and on the European squid Loligo vulgaris. Scanning electron microscopy (SEM) revealed similar injuries in the inner structure of the statocysts, as those found in cuttlefish and octopi. In addition to the ultrastructural description of the lesions, we publish here the first images of the crista-cupula system and inner statocyst cavity of I. coindetii.

Elemental and biochemical composition of Nephrops norvegicus (Linnaeus 1758) larvae from the Mediterranean and Irish Seas

The Norway lobster, Nephrops norvegicus, is a commercially exploited decapod which is widely distributed throughout the north-eastern Atlantic and the Mediterranean Sea. Ovigerous females originating from the Mediterranean and the Irish Seas were held in the laboratory until larvae hatched. Biomass and biochemical composition, as well as digestive gland structure, were examined in newly hatched larvae from these two regions. In addition, previously published data from a North Sea population were included in our comparison. Elemental analyses showed that the absolute quantities of dry mass (DM), carbon (C), nitrogen (N) and hydrogen (H) (collectively referred to as CHN) per individual, and the C:N mass ratios, were significantly lower, while the relative CHN, protein and lipid values (in % of DM) were higher in samples from the Irish Sea compared to larvae originating from either the Mediterranean or the North Sea. As in CHN, the absolute level of protein per individual was higher in larvae from the Mediterranean, while no significant differences were observed in the individual lipid contents. Likewise, the digestive gland structure at hatching did not show any differences between study areas. Intraspecific variability in biomass and chemical composition of newly hatched larvae from different regions may be related to differential patterns of reproduction in regions with different climatic conditions. Lobster larvae hatch in the Mediterranean Sea predominantly in winter when both water temperature and planktonic food availability are at a minimum, while hatching in the Irish Sea occurs under more favourable conditions in spring. Hence, significantly higher wet mass, dry mass and protein values in Mediterranean larvae may represent adaptive traits allowing for early posthatching survival and development under food-limited conditions in an oligotrophic environment.

Characterization and localization of an Mr 225 kDa polypeptide specifically involved in the defence mechanisms of the clam Tapes semidecussatus

Parasitosis by the trophozoite protozoan Perkinsus sp. (Apicomplexa, Perkinsea) induces in the gill filaments of the clam Tapes semidecussatus (Mollusca, Bivalvia) a cellular reaction, which is constituted by infiltrated granulocytes. This cellular reaction has characteristics of those of a holocrine gland, since the parasites are encapsulated by the secretion product of the granulocytes after cell death. An enriched fraction of prezoosporangia and their associated capsule was obtained after culture of the parasitized gills in fluid thioglycollate medium. Specific polypeptides from this fraction were separated by SDS-PAGE and isolated for rabbit immunizations. The serum obtained against an Mr 225 kDa polypeptide, revealed its exclusive localization in the capsule and in the granules of the infiltrated granulocytes, thus indicating that this polypeptide is synthesized by these cells and secreted, in a polarized way, around the trophozoites resulting in their encapsulation. Selective deglycosylation of the polypeptide, by Endo H and alkaline β-elimination, did not show an effect on its molecular weight or antibody recognition. Furthermore, the absence of the 225 kDa band in the Western-blots of non-parasitized gills indicated the specific association of this polypeptide with the parasitosis. Finally, this is the first tissue-specific factor described in molluscs in relation to defence mechanisms.

Ultrastructural study of hemocytes and phagocytes associated with hemolymphatic vessels in the hepatopancreas of Palaemonetes zariquieyi (Crustacea, Decapoda)

Ultrastructural and cytochemical studies of the hepatopancreatic hemal space of Palaemonetes zariquieyi revealed the presence of three cell types: 1) hemocytes containing spherical and elongated granules, also localized in heart and the branchial hemal space; 2) cells containing lipidic inclusions and sub‐polyhedric granules with a paracrystalline component; and 3) phagocytic cells surrounding hemal vessels, exhibiting positive acid phosphatase reactivity in the Golgi complex and lysosomes. Possible functions of these cell types are discussed.

Internal anatomy and ultrastructure of the male reproductive system of the Norway lobster Nephrops norvegicus (Decapoda: Astacidea)

The Norway lobster (Nephrops norvegicus) is economically important in Europe. However, apart from the female reproductive system, very little is known about its internal anatomy. This article focuses on studying the internal anatomy and ultrastructure of the male reproductive system. This system follows the general pattern found among decapod crustaceans, with several peculiarities. Testes are composed of lobular sperm ducts in which the spermatozoa are fully constituted. The spermatozoa present three lateral arms and a long acrosome, which gives a false appearance of flagellated spermatozoa. The two testes form a double H under the heart, and the vas deferens (VD) arise from each side at the posterior edge of the double H. The main characteristic of the VD is the presence of a sphincter in the enlarged area of the distal end of the middle VD. The MVD here shows an increase in musculature of the wall as compared to the VD, which regulates the passage of the sperm cord to the distal VD (DVD) and thence to the thelycum of the female. The wall of the spermatophore is formed in the distal part of the proximal VD, which surrounds the unique sperm cord present in the VD. Isolated spermatophores are not observed in the VD. The sperm cord is pinched off during copulation by the musculature of the DVD. Then, a portion of the sperm cord is transferred from each VD to form the isolated spermatophores. The wall of the spematophores and the spermatozoa that are observed inside the thelycum have the same morphology as those observed in the VD. J. Morphol., 2012.

Ultrastructure of the sperm of the deep-sea decapod Aristeus antennatus

The sperm of Aristeus antennatus presents notable differences in relation to the two basic models of decapod crustaceans considered to date. Basically, it does not present a single appendage, or spike, characteristic of the so‐called unistellate sperm of the suborder Dendrobranchiata and the infraorder Caridea of the suborder Pleocyemata. Nor does it have arms or spikes characteristic of the multistellate sperm that all belong to the Pleocyemata group. The spermatozoa of A. antennatus are composed of a nucleus and an electron‐dense acrosome, which have the polarity of multistellate sperm. A number of mitochondria and vesicles are present in the cytoplasm, located between the acrosome and the nucleus. In accordance with the fine structural details, the morphology of the sperm has been described at two different levels of the male gonad, the vas deferens and terminal ampulla, and in the spermatophore placed in the thelycum of the female. Three ultrastructural changes in the acrosome (unorganized structures, tubular organization, disintegration process) and the nucleus (uncondensed, condensed, and compact) are present along the male reproductive apparatus. They first appear in a non‐organized manner at the level of the vas deferens, subsequently undergo a process of structural configuration in the ampulla, and finally show disorganized structures in the spermatophore. J. Morphol. 234:79–87, 1997.