Coevolution between Lamellodiscus (Monogenea: Diplectanidae) and Sparidae (Teleostei): the study of a complex host-parasite system

Abstract.— Host-parasite coevolution was studied between Sparidae (Teleostei) fishes and their parasites of the genus Lamellodiscus (Monogenea, Diplectanidae) in the northwestern Mediterranean Sea. Molecular phylogenies were reconstructed for both groups. The phylogenetic tree of the Sparidae was obtained from previously published 16S mitochondrial DNA (mtDNA) sequences associated with new cytochrome-b mtDNA sequences via a "total evidence" procedure. The phylogeny of Lamellodiscus species was reconstructed from 18S rDNA sequences that we obtained. Host-parasite coevolution was studied through different methods: TreeFitter, TreeMap, and a new method, ParaFit. If the cost of a host switch is not assumed to be high for parasites, all methods agree on the absence of widespread cospeciation processes in this host-parasite system. Host-parasite associations were interpreted to be due more to ecological factors than to coevolutionary processes. Host specificity appeared not to be related to host-parasite cospeciation.     

Sexual size dimorphism in parasitic oxyurid nematodes

As in many invertebrates, female oxyurids are larger than male. Sexual size dimorphism (SSD) of oxyurid nematodes (the hosts of which are both invertebrate and vertebrate), is investigated regarding body size of both host and parasite. SSD of parasites appeared to be weakly, but not significandy, correlated with invertebrate and vertebrate host body size. However, this study reveals a different pattern for SSD with respect to either type of host. SSD does not increase in tandem with body size in vertebrate parasites either at the level of species or genus. SSD is much more pronounced in Syphaciidae than in Heteroxynematidae, two families of vertebrate parasites exhibiting different modes of transmission (members of the Syphaciidae are transmitted through perianal contamination). SSD is investigated in one monophyletic group of parasites of primates, for which a phylogeny is known. Independent comparisons method is used and we find that the body size of female parasite is strongly correlated with that of the male. The hypoallometry (slope<1) of the relationship suggests that the SSD is not linked to an increase of parasite body size. Moreover, there is no influence of host body size on parasite SSD. The pattern in parasites of invertebrates is different. First, SSD has been found to increase with parasite body size in two groups of invertebrate parasites: the oxyurids of Dictyoptera and Coleoptera. Second, female body size of invertebrate parasites is not correlated with male body size either at genus or species level. Finally, the evolution of SSD is discussed in relation to the demographic patterns of invertebrate parasites and the haplodiploid mode of reproduction of these parasitic nematodes.     

Stabilisation of ‘Green tides’ Ulva by a method of composting with a view to pollution limitation

85 000 m³ of Ulva sp. is harvested each year in Brittany (France) during a 3–4-month season. Spreading is often impossible and the alga does not keep for more than a few days. Storage results in objectionable odours and release of a liquified fraction. Such pollution can be suppressed by composting the alga with the lowest possible quantity of ligno-cellulosic substrates. This results in the stabilisation of the seaweed, and its use can thereby be delayed. This system of processing the seaweed decreases the cost of treatment by composting and the product can be used either as a substrate for later composting or as an organic enhancing and fertilising agent. (*author for correspondence)     

Complementation pattern of lexB and recA mutations in Escherichia coli K12; mapping of tif-1, lexB and recA mutations

Summary Three lexB mutations, whose phenotypes have been previously characterized, are studied here in relation to a few recA mutations as to their complementation pattern and relative location.The restoration of resistance to UV-light and to X-rays in the hetero-allelic diploid bacteria was used as a test for dominance and complementation. The wild type allele was always dominant over the mutant allele. Only partial complementation was found between lexB and two recA alleles. There was no complementation between the recA alleles. All the data taken together strongly suggest that the complementations found are intragenic: lexB and recA mutations are in one gene.Mapping of lexB, recA and tif-1 mutations in relation to srl-1 and cysC by phage P1 transduction shows that lexB and the tif-1 mutations form a cluster proximal to srl-1 whereas recA mutations are located at the other extremity of the gene. Variability with temperature of cotransduction frequencies as well as their extended range of values prevent a meaningful calculation of the length of the recA gene.Our hypothesis is that the recA protein has two functional regions called A and B respectively defined at the genetical level by recA and lexB mutations and that it is, in vivo, an oligomeric protein forming a complex with the lexA protein. This complex is postulated to be multifunctional: recombination and control of exonuclease V are effected by the A region while the B region and lexA protein effect induced DNA repair and lysogenic induction.     

Regional immunotherapy in resectable squamous cell lung carcinoma

Summary Patients with resectable squamous cell carcinoma were randomly allocated after surgery to receive either no further treatment (57 patients) or a single intrapleural injection of BCG (61 patients). No significant improvement in survival was observed in patients treated with BCG, even when their disease was staged as N₀. These was a slight trend for the recurrence rate to be lower in patients classed as N₀, but this was not significant.     

Parasite body size and interspecific variation in levels of aggregation among nematodes

The aggregation of parasites among individual hosts is one of the best documented features of parasite populations; we still do not know, however, why certain parasite species are more highly aggregated than other, related species. Here we search for a general explanation of interspecific variation in aggregation levels, based on the relationship between parasite body size and fecundity, transmission success, and intensity-dependent population regulation. We test the prediction that larger-bodied parasite species are more weakly aggregated than smaller-bodied related species, in a comparative analysis across parasitic nematode species. Across species, the variance-to-mean abundance ratio correlated negatively and significantly with nematode body sizes, as predicted. All other tests, however, including the more robust analyses controlling for phylogenetic influences, failed to support this result. This is mainly because the variance in infection levels is almost completely explained by mean parasite abundance. For this reason, it may prove difficult to identify a general biological explanation for interspecific variability in aggregation levels among parasites.     

Host death: a necessary condition for the transmission of Aphalloides coelomicola Dollfus, Chabaud, and Golvan, 1957 (Digenea, Cryptogonimidae)?

Eggs of the trematode Aphalloides coelomicola were observed free in the abdominal cavity of Pomatoschistus microps from March 1993 to October 1995 (Pisces, Gobiidae) in the Vaccares lagoon (delta du Rhone, France). The eggs were contained in a fine membrane of parasitic origin as no immunological reaction of the fish was noted. The alternatively high prevalence of adults and low prevalence of free eggs, and vice versa, suggest that P. microps is both the second intermediate and final hosts of the trematode Aphalloides coelomicola and that the mechanism of transfer to the first intermediate host is through death of the definitive host.