1,721,059 research outputs found
MOLECULAR SYSTEMATICS, PHYLOGENY AND ECOLOGY OF THE ANISAKID NEMATODES OF GENUS ANISAKIS DUJARDIN, 1845: AN UPDATE
No full textAdvances in the taxonomy and ecological aspects concerning geographical distribution and hosts of the so far genetically recognised nine taxa of the nematodes belonging to genus Anisakis (i.e. A. pegreffii, A. simplex s.s., A. simplex C, A. typica, A. ziphidarum, Anisakis sp., A. physeteris, A. brevispiculata and A. paggiae) are here summarized. Genetic differentiation and phylogenetic relationships inferred from allozyme (20 enzyme-loci) and mitochondrial (sequences of cox-2 gene) markers, are revised and compared. The two genetic analyses are congruent in depicting their phylogenetic relationships. Two main clusters are showed to exist in the obtained trees, one encompassing the species A. pegreffii, A. simplex s.s., A. simplex C, A. typica, A. ziphidarum and Anisakis sp.; while, the second including A. physeteris, A. brevispiculata and A. paggiae. The existence of two clades is also supported by their morphological differentiation in adult and larval morphology. Comparison of phylogenetic relationships among Anisakis spp. with those currently available for their cetacean definitive hosts suggests parallelism between host and parasite phylogenetic tree topologies. Preliminary data for reconstruction of a possible co-evolutionary scenario between cetacean hosts and their Anisakis endoparasites suggests that cospeciation and host-switching events may have accompanied the evolution of this group of parasites. Finally, genetic/molecular markers for the identification of the so far genetically recognized taxa of Anisakis at any life-stage and both sexes were given also in relation to human anisakiosis is discussed
Speciation by interspecific hybridization in animals
No full textSpeciation by hybridization occurs when new species arise from crosses between parental ones. Hybrid speciation has traditionally been considered prominent in plants, while rare in animals. This view has been changing in the last few decades, mainly due to the increased availability of various genetic markers. The number of animal hybrid species is steadily increasing and now includes lizards, geckos, frogs, salamanders, fishes, beetles, moths, grasshoppers, stick-insects, copepods, snails, turbellarians, nematodes, corals, etc. Several well documented cases will be examined, and a number of points will be considered, such as: (i) the modes of reproduction of animal hybrid species, such as thelytokous parthenogenesis, gynogenesis, hybridogenesis, selfing, fragmentation, bisexuality; (ii) the role of polyploidy; (iii) the short- and long-term evolutionary success of animal hybrid species. These species generally combine a heterotic advantage (from the coexistence of two or more parental genomes), with a demographic advantage (from the switch from sexuality to clonal or emiclonal reproduction). This explains the frequent successful spread and competitive dominance of hybrid species over their parental ones. Recently proposed cases of homoploid sexual hybrid species (e.g. in fishes, butterflies and flies) will be discussed, with particular regard to their recombinant genomes, ecological characteristics, and mating behaviour
Hybrid zones between two genetically differentiated forms of the pond frog Rana lessonae in southern Italy
No full textTwo distinct population groups of the pond frog Rana lessonae were detected in peninsular Italy and Sicily by multilocus electrophoresis: one group inhabits the peninsula down to northern Calabria, the second occurs in southern Calabria and on Sicily. Fixed alternative alleles distinguish the two groups at 5 of the 25 loci examined; marked allele frequency differences were observed at two additional loci. On average, the two groups differ by a Nei's standard genetic distance of 0.4. A wide hybrid zone (about 120 km) occurs between the two groups, with high genotypic diversity and absence of pure parental genotypes in central Calabria. Patterns of allozyme variation suggest that at least two distinct contact and hybridization events occurred, one in the Catanzaro, the other in the Crati-Sibari plains, about 70 km to the north. Geological evidence indicates that these areas correspond to two main marine-flooded grabens that would have repeatedly interrupted or reduced genetic exchange during Plio-Pleistocene times. The finding of a fixed difference at the Mdhp-1 locus between Sicilian and Calabrian R. lessonae witnesses their continuing differentiation following their last separation by definitive opening of the Strait of Messina, about 50 000 years ago. The wide hybrid zone, the diversity of genotypes and the agreement with Hardy-Weinberg expectations suggest complete hybrid fertility. Different patterns of introgression were observed at the various loci. The pattern of allelic variation at loci in R. lessonae is paralleled by the pattern of variation in lessonae genomes of the sympatric hemiclonal hybrid Rana esculenta, into which lessonae genomes are introduced each generation as a result of hybridogenesis
Speciation by hybridization in stick insects and Bulinus snails: ecological and evolutionary aspects.
No full textAdvances and Trends in the Molecular Systematics of Anisakid Nematodes, with Implications for their Evolutionary Ecology and Host-Parasites Co-evolutionary Processes
No full textThe application of molecular systematics to the anisakid nematodes of the genera Anisakis, Pseudoterranova and Contracaecum, parasites of aquatic organisms, over the last two decades, has advanced the understanding of their systematics, taxonomy, ecology and phylogeny substantially. Here the results of this effort on this group of species from the early genetic works to the current status of their revised taxonomy, ecology and evolutionary aspects are reviewed for each of three parasitic groups. It has been shown that many anisakid morphospecies of Anisakis, Contracaecum and Pseudoterranova include a certain number of sibling species. Molecular genetic markers provided a rapid, precise means to screen and identify several species that serve as definitive and intermediate and or/paratenic hosts of the so far genetically characterized species. Patterns of differential distribution of anisakid nematodes in various definitive and intermediate hosts are presented. Differences in the life-history of related species can be due both to differential host-parasite coadaptation and coevolution, and/or to interspecific competition, that can reduce the range of potential hosts in sympatric conditions. Phylogenetic hypotheses attempted for anisakid nematodes and the possible evolutionary scenarios that have been proposed inferred from molecular data, also with respect to the phylogeny of their hosts are presented for the parasite-host associations Anisakis-cetaceans and Contracaecum-pinnipeds, showing that codivergence and host-switching events could have accompanied the evolution of these groups of parasites. Finally, examples in which anisakid nematodes recognized genetically at the species level in definitive and intermediate/paratenic hosts from various geographical areas of the Boreal and Austral regions and their infection levels, have been used as biological indicators of fish stocks and food-web integrity in areas at high versus low levels of habitat disturbance (pollution, overfishing, by-catch) are presented
Contracaecum gibsoni n. sp. and C. overstreeti n. sp. (Nematoda: Anisakidae) from the Dalmatian pelican Pelicanus crispus (L.) in Greek waters: morphological and genetic evidence
No full textTwo new species of Contracaecum Railliet & Henry, 1912, previously referred to as C. multipapillatum sp. A and C. multipapillatum sp. B by Nascetti et al. (1990) from the Dalmatian pelican Pelecanus crispus (L.) in the Ambracian Gulf off Greece, are described as C. gibsoni n. sp. and C. overstreeti n. sp., respectively. Morphological analysis and the differential diagnosis of genetically recognised male specimens of C. gibsoni and C. overstreeti with respect to C. multipapillatum (von Drasche, 1882) (sensu lato) from Egretta alba (L.) in northern Colombia and other morphologically related Contracaecum spp. enabled the detection of differences between the two species in a number of characters, including spicule length and the shape of its tip, and the arrangement of the proximal and distal papillae on the male tail. Accordingly, formal descriptions are presented for C. gibsoni n. sp. and C. overstreeti n. sp. from P. crispus. The genetic characterisation of the two taxa is based on 20 allozyme loci and sequence analyses (519 bp) of the mtDNA cox2 gene. Reproductive isolation was demonstrated between these two taxa, which sympatrically infect the same definitive host, and fixed allele differences between the two species were found at some (Aat-2, PepC-1, PepC-2 and Pgm-1) of the 20 allozyme loci analysed. Their genetic divergence, estimated at the allozyme level, was D (Nei) = 0.31. The genetic relationships of C. gibsoni and C. overstreeti with respect to C. multipapillatum (s. l.) collected from E. alba in Colombia, as well as with other congeners from fish-eating birds which had previously been genetically characterised using the same genetic markers, i.e. C. rudolphii A and C. rudolphii B of Bullini et al. (1986), C. septentrionale Kreis, 1955, C. microcephalum (Rudolphi, 1809), C. bioccai Mattiucci et al., 2008, C. pelagicum Johnston & Mawson, 1942 and C. micropapillatum (Stossich, 1890), were inferred from mtDNA cox2 sequence analysis. The MP, NJ and BI trees obtained were congruent in depicting C. gibsoni and C. overstreeti as closely related species but quite distinct from each other and forming a subclade with specimens of C. multipapilllatum (s. l.) from E. alba (L.) in Colombia. This subclade was also found to be distinct from the remainder of the taxa considered
Genetic structure and conservation biology of freshwater crayfish (Austropotamobius pallipes) in Italy.
No full textMolecular taxonomy of European Plethodontid salamanders (genus Hydromantes).
No full textGenetic variation of 33 enzyme loci was analysed electrophoretically in 32 populations of the plethodontid genus Hydromantes from southern France, northern and central Italy, and Sardinia. Eight taxa were recognized, included in three groups: from the mainland, eastern Sardinia, and south-western Sardinia, respectively. In the mainland area, two semispecies were detected: H. italicus and H. ambrosii (sensu stricto), as well as a third species: H. strinatii (combinatio nova), previously included within H. ambrosii. Eastern Sardinian populations correspond genetically to three species: H. flavus, H. supramontis, and H. imperialis. In south-western Sardinia, two genetically differentiated but morphologically very similar groups were found within H. genei, whose specific status remains doubtful. The distinctness of a number of subspecific taxa (H. italicus gormani, H. i. ligusticus, H. i. argentatus, H. i. bonzanoi, H. genei funereus), is not supported by genetic evidence. Data from two contact zones in Italy indicate that taxa showing comparable levels of genetic differentiation (i.e., H. italicus-H. ambrosii s. s. and H. ambrosii s. s.-H. strinatii, both pairs with Nei's D about 0.4) have not reached the same level of reproductive isolation. On the basis of available data, attempts are made: (1) to interpret the present pattern of geographic distribution of European Hydromantes studied; (2) to explain their genetic relationship
Ecological parapatry and competition in two sibling species of European plethodontid salamanders.
No full textThe analysis of a zone of parapatric contact between the European plethodontid salamanders Speleomantes ambrosii and Speleomantes strinatii in northwestern Italy (Liguria) has shown that no syntopic populations exist in the area. The spatial distributions of both species and their relationships with the main environmental parameters has been investigated at two different scales.
At a larger scale, a vegetation survey has revealed that two main vegetation types exist in the contact zone, representing different sets of environmental conditions. The two species are distributed according to the observed vegetationalclimatic patches, with S. strinatii in the more mesic environment and S. ambrosii in the more xeric, and hence less suitable, patches. At a smaller scale, a field experiment artificially created a syntopy, putting together specimens of both species in the same micro-environment. This allowed the study of the spatial distribution of the two species within the environmental micro-patches observed in the caves that Speleomantes use as retreats. S. ambrosii was again found mainly in the micro-patches that were less effective as refuges, while S. strinatii occupied the patches with steady favourable environmental conditions and abundant prey. The comparison of the two sets of results obtained suggests that the two species compete for cover (i.e., a micro-habitat providing high humidity, low temperature and prey availability even during the dry and hot Mediterranean summer). S. strinatii would be the superior competitor, able to confine S. ambrosii in the less suitable environment at both scales
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