Objective
The research project plans to analyse the relationship between the genetic diversity of hake populations from different geographic areas of Mediterranean Sea and North-East Atlantic waters and the levels of parasitic infections. The aim is to ascertain if a genetic erosion process is acting on exploited populations of hake and if a loss of genetic variation in depleted populations could affect their capability to respond efficaciously to parasitic infection outbreaks. In order to achieve these objectives, a multidisciplinary approach will be used that is expected to provide innovative tools to define the state of hake samples and will contribute to a better knowledge of the correlation between fishing activities and its effects on biodiversity.
The maintenance of a stable equilibrium between conservation and exploitation of marine resources is recognised as a crucial goal for the survival of the whole fishery sector. In this perspective new tools allowing a reliable state assessment of marine resources and a quick address of their management are needed.
Data drawn from ecology and population dynamics have been the main ground of fishery management, because the abundance and size of fish available for harvesting were considered as the most relevant information to address exploitation (A11endorf et al., 1987). In the last years, however, methods of population genetics have been fruitfully used to produce a bulk of data frequently allowing the estimation of parameters having management imprecations (Avise, 1996) such as stock identification, evaluation of degrees of genetic variability, investigations on the relationship occurring between over-exploitation and genetic erosion. At the same time it has been assessed that genetic diversity plays an important role in natural populations to respond to environmental changes: its maintenance is therefore a main goal for conservation in fishery management (Avise, 1996; Frankham, 1995). Genetic diversity can be strongly depleted by overexploitation, that can cause genetic erosion phenomena either by genetic drifi and/or selective removal of genotypes. This process can be very rapid and accomplished in a few years (Gharrett and Thomason, 1987; Nielsen et al., 1997; Smith et al., 1991; Vuorinen et al., 1991). As a consequence, the investigation of the genetic variation levels through time and of their relationships with the exploitation pressure can provide a quick and reliable method to monitor the status of fish populations. The study of the genetic structure of natural populations have also suggested that the existence of high levels of polymorphism seems to be necessary in recognition and resistance to parasitic diseases (Gray and Gill, 1993).Consequently, the genetic erosion of the host gene pool could lower its capability to respond to parasitic infections.
The study of the genetic diversity of Mediterranean and North-East Atlantic populations of the European hake (Merluccius merluccius) together with the prevalence and intensity of parasitic infections and the biodiversity of their parasitic communities will allow the evaluation of the state of this resource and supply indications for its sustainable exploitation. The research therefore plans to analyse the relationships between the degree of genetic diversity and fish exploitation and to investigate the relationship between genetic variability in host populations and levels of parasitic infections.
ACTIVITIES
This research project integrates biological, genetic and parasitological approaches. Sampling Hake samples will be taken from 11 selected areas of Mediterranean and North-East Atlantic Ocean characterized by different levels of fishing pressure (Fig. 1): oveffished (samples 2, 3, 5, 6, 7, 8, 9, 10), fished (1, 4), moderately fished (11, where fishing activity is carried out by artisanal trawlers only).
Biological data
Morphometric and biological data will be collected and processed to draw information on the state and the dynamics of the studied hake populations. The evaluations obtained with this traditional approach will be compared with the data reached by means of both genetic and parasitological approaches.
Genetic diversity estimation
The estimation of intra- and interpopulational genetic diversity in hake samples from the selected areas will be carried out by means of different molecular genetic approaches. The multilocus electrophoresis (MAE), will permit to obtain genetic markers at 40-50 allozyme loci and will provide basic data to evaluate, by a number of different parameters, intra- and interpopulation genetic diversity of hake samples as weE as the genetic structure of populations. The Restriction Fragment Length Polymorphisms analysis of mtliNA (mtRFLPs), will analyse the genetic variation in sampled hake populations from Mediterranean Sea and the North-East Atlantic Ocean. the use of highly polymorphic microsatellites DNA markers (msDNA), will permit to detect intra- and interpopulational genetic variability at a fine scale and will clarit the pattern of genetic material exchanges between different areas.
Each one of these techniques will allow: i) the access to different molecular markers, each characterized by typical rates of evolution, inheritance modalities, etc.; ii) the creation of multiple data sets that will validate each other results; iii) the comparison of the cost-benefit ratio for different techniques in order to identify an economic and reliable tool to assess exploited fish state.
Parasitological survey
The parasitological survey will be carned out on all the hake samples from the 11 selected areas of the Mediterranean Sea and the North-East Atlantic Ocean. It will comprise the evaluation of parasitic infection levels in different hake sarnples and the study of biodiversity of parasitic communities. The results obtained will permit: i) the identification, at specific level, of all ecto- and endometazoan parasites recovered from the collected specimens; ii) the evaluation of prevalence and intensity of the infections of each parasite species in the different hake samples; iii) the study of biodiversity of hake parasitic communities.
EXPECTED OUTCOME
The planned research will produce basic data describing: i) the degree of genetic variability; ii) the levels of parasitic infections; iii) the morphometric and biological parameters of hake from Mediterranean and North-East Atlantic waters.
Hake covers a major role in the economy of fisheries in the Mediterranean and North-East Atlantic waters, and has consequently experienced strong fishing pressures in the greater part of its range. It is therefore impossible to witness the process of genetic erosion, as in the case of newly exploited species (for example, the orange roughly in New Zealand; Smith et al., 1991). However, evidences about the relationship of over fishing with the levels of genetic variability and parasitic infections can be drawn from the comparison between samples from areas where high fishing pressure has caused a strong biomass dechne, with samples from areas characterised by a moderate exploitation. The conclusions on the hake state obtained by means of this new approach will be compared with the results provided by the traditional biometrical analyses. This comparison will allow to test the sensitiveness of these alternative methodologies that could constitute a quick and rehable tool in the assessment of exploited fish populations state using limited data sets.
OUTCOME
The objectives planned were pursued by the study of 11 hake samples from selected areas of the Mediterranean and North-eastern Atlantic Ocean. On these samples different genetic markers were used to estimate their intra- and inter-population genetic diversity: multilocus allozyme electrophoresis (MAE), RFLPs ofmtDNA, microsatellite DNA (msDNA). The analysis of morphometric and biological parameters was also applied to evaluate populations state. A parasitological survey was carried out, aimed at the evaluation of the prevalence and intensity of the infections by different parasite species in all the hake populations genetically characterised.
According to the objectives, the research activities of the Participants, during the first year of the Project, were carried out and structured following the planned workplan and forecasted timetable. This allowed to attain the following objectives. Hake samples were collected from 10 out of the 11 selected localities, comprising all the Mediterranean sites and two from NE Atlantic. Specimens were scored morphometrically, genetically analysed by all the genetic markers and parasitologically surveyed. The genetic study carried out by means of multilocus allozyme electrophoresis (MAE) analysed 28 enzymatic loci on all the specimens collected from all the selected sites. It revealed a substantial subdivision, at genetic level, between the populations from the Mediterranean basin and those from the Atlantic Ocean. A geographic cline E/W oriented was observed at the allele frequencies of locus Gapdh, from the eastern Mediterranean populations to the Atlantic ones, while at other loci (Pep B-3, Gpi-1 and Gpi-3) differences in allele frequencies were reported. Clustering analysis confirmed these findings: an UPGMA dendrogram built on genetic distances grouped Mediterranean and Atlantic populations in two differentiated clusters. The partitioning of genetic diversity as well as gene flow estimation support the existence of two geographically distinct populations of hake: Mediterranean and Atlantic. As to the genetic analysis of mtDNA, DNA was extracted from 184 hakes from 7 localities. Two different regions of the mitochondrial molecule, the Cytochrome b gene (344bp) and the D-loop control region (216bp), were studied. A complete, double strand sequence of the fragments was carried out as preliminary step. The Cyt-b fragment did not provide evidence of variation in the samples from Mediterranean Sea and Northern Atlantic area. The D-loop fragment showed six variable nucleotide sites, corresponding to four different haplotypes. This fragment could be informative and suitable for investigating geographic population structure of hake. Microsatellite DNA analysis of hake samples was carried out on four selected loci: Mm4A, Mm6, Mm13B, Mm14, scored on 640 hake specimens from 9 selected localities. Preliminary data analysis provided evidence of little differentiation between the samples studied. Indeed, there is no apparent shift in allele size ranges or frequencies.
As to the statistical analysis of morphometric and biological data, length-weight relationship was calculated for all the samples; allometry approach was applied in the morphometric and meristic analysis. Regression analysis was performed on samples from Gulf of Biscay and Morocco samples. These studies evidenced slight differences among Balearic Islands and the Atlantic populations.
Parasitological analysis was performed on 358 hake specimens captured from all the 10 selected sites. A minimum of 30 specimens from each locality was surveyed. All the parasites were identified at their specific level. Genetic markers obtained from multilocus allozyme electrophoresis (MAE) were used to identify at the specific level a sample of Anisakis larvae from all the selected areas, whose identification is not possible by morphological analysis. The genetic markers have permitted to reveal the existence of five distinct biological species of Anisakis (A.simplex s.s. A.pegreffii A.ziphidarum A.physeteris and A.brevispiculata) whose relative presence in hake populations in the Mediterranean Sea and in the North-eastern Atlantic Ocean was significantly different, suggesting their possible use as "biological tags" for hake populations' discrimination.
REFERENCES
Allendorf F. W., Ryman N., Utter F. M. (1987). Genetics and Fishery Management. In: Ryman N., Utter F.M. (eds.). Population genetics and f shery. University of Washington Press, Seattle. pp. 1-20.
Avise J.C. (1996). The scope of Conservation Genetics. In: Avise J.C. Hamrich J.L. (eds.) Conservation Genetics. Case histories from nature, Chapman & Hal1, New York, pp. 1-9.
Frankham R (1995). Conservation genetics. Annual Review of Genetics, 29: 305-327.
Gharrett A. J., Thomason M. A., 1987. Genetic changes in pink sahnon (Oncorhynchus gorbuscha) following their introduction nato the Great Lakes. Canadian Journal of Fisheries aquatic Science, 48: 722-731.
Gray G. D., Gill H. S. (1993). Host genes, parasites and parasitic infections. International JournalforParasitology, 23: 485-494.
Nielsen E. E., Hansen M. M., Loeschoke V. (1997). Analysis of microsatellite DNA from old scale samples of Atlantic sahnon Salmo salar a comparison of genetic composition over 60 years. Molecular Ecology, 6: 487-492.
Smith P.J. Francis RI., McVeagh M. (1991). Loss of genetic diversity due to fishing pressulre. Fishery Research, 10: 309-316
Vuorinen J., Aaesie T.F. Sandlund O.T. (1991). Genetic changes in a vendance Coregonus albula (L.) population, 92 years after introduction. Journal of Fish Biology, 39: 193-201.
Fields of science (EuroSciVoc)
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: The European Science Vocabulary.
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: The European Science Vocabulary.
- natural sciences computer and information sciences data science
- natural sciences biological sciences genetics DNA
- natural sciences biological sciences ecology
- natural sciences biological sciences genetics nucleotides
- natural sciences chemical sciences electrochemistry electrophoresis
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