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- Age and growth of megrim, Lepidorhombus boscii, Risso of the portuguese continental coastPublication . Castilho, Rita; Dinis, Maria Teresa; Erzini, KarimThe first study of age and growth of four-spotted scaldfish, more commonly known as megrim (Lepidorhombus boscii, Risso), an important (by catch ) species of the Portuguese trawl fishery from the Atlantic coast is presented. The analysis was based on data obtained from a total of 609 specimens sampled between 1985 and 1986. Otoliths were used for age determination. The Von Bertalanf~, growth parameters were estimated using the non-linear fitting method: Lt (females)=440[ 1 -e -°-14(t+ 1.32) ] and Lt= 375 [ 1 -e -°~4(t+ 1.93) ] for males. L~ and to values are significantly different. The megrim grows allometrically (slope of length-weight regressions > 3 ). Females live longer and gain weight at a faster rate than males. Differences in growth between sexes become more apparent from the second year onwards.
- Genetic diversity and historical demography of Atlantic bigeye tuna (Thunnus obesus)Publication . Martinez, P.; Gonzalez, Elena G.; Castilho, Rita; Zardoya, R.Bigeye (Thunnus obesus) is a large, pelagic, and migratory species of tuna that inhabits tropical and temperate marine waters worldwide. Previous studies based on mitochondrial RFLP data have shown that bigeye tunas from the Atlantic Ocean are the most interesting from a genetic point of view. Two highly divergent mitochondrial haplotype clades (I and II) coexist in the Atlantic Ocean. One is almost exclusive of the Atlantic Ocean whereas the other is also found in the Indo-PaciWc Ocean. Bigeye tuna from the Atlantic Ocean is currently managed as a single stock, although this assumption remains untested at the genetic level. Therefore, genetic diversity was determined at the mitochondrial control region to test the null hypothesis of no population structure in bigeye tuna from the Atlantic Ocean. A total of 331 specimens were sampled from four locations in the Atlantic Ocean (Canada, Azores, Canary Islands, and Gulf of Guinea), and one in the Indian and PaciWc Oceans, respectively. The reconstructed neighbor-joining phylogeny conWrmed the presence of Clades I and II throughout the Atlantic Ocean. No apparent latitudinal gradient of the proportions of both clades in the diVerent collection sites was observed. Hierarchical AMOVA tests and pairwise ST comparisons involving Atlantic Ocean Clades I and II were consistent with a single stock of bigeye tuna in the Atlantic Ocean. Population genetic analyses considering phylogroups independently supported gene Xow within Clade II throughout the Atlantic Ocean, and within Clade I between Atlantic and Indo-PaciWc Oceans. The latter result suggests present uni-directional gene Xow from the Indo-PaciWc into the Atlantic Ocean. Moreover, mismatch analyses dated divergence of Clades I and II during the Pleistocene, as previously proposed. In addition, migration rates were estimated using coalescent methods, and showed a net migration from Atlantic Ocean feeding grounds towards the Gulf of Guinea, the best-known spawning ground of Atlantic bigeye tuna.
- Congruence between starch gel and polyacrylamide gel electrophoresis in detecting allozyme variation in pulmonate land slugsPublication . Geenen, S.; Jordaens, Kurt; Castilho, Rita; Backeljau, T.The predominantly selfing slug species Arion (Carinarion) fasciatus, A. (C.) silvaticus and A. (C.) circumscriptus are native in Europe and have been introduced into North America, where each species consists of a single, homozygous multilocus genotype (strain), as defined by starch gel electrophoresis (SGE) of allozymes. In Europe, the “one strain per species” hypothesis does not hold since polyacrylamide gel electrophoresis (PAGE) of allozymes uncovered 46 strains divided over the three species. However, electrophoretic techniques may differ in their ability to detect allozyme variation. Therefore, several Carinarion populations from both continents were screened by applying the two techniques simultaneously on the same individual slugs and enzyme loci. SGE and PAGE yielded exactly the same results, so that the different degree of variation in North American and European populations cannot be attributed to differences in resolving power between SGE and PAGE. We found four A. (C.) silvaticus strains in North America indicating that in this region the “one strain per species” hypothesis also cannot be maintained. Hence, the discrepancies between previous electrophoretic studies on Carinarion are most likely due to sampling artefacts and possible founder effects.
- Pillars of Hercules: is the Atlantic-Mediterranean transition a phylogeographical break?Publication . Patarnello, T.; Volckaert, F.; Castilho, RitaThe geological history of the Mediterranean Sea, its hydrography and connection with the Atlantic Ocean have been well documented. Despite a wealth of historical and oceanographic data, the Atlantic–Mediterranean transition remains controversial at the biological level as there are discordant results regarding the biogeographical separation between the Atlantic and Mediterranean biota. The opening of the Strait of Gibraltar at the end of the Messinian Salinity Crisis (some 5.33 million years ago), removed the land barrier that impeded the marine biota allowing it to disperse freely into the Mediterranean Sea. However, present day genetic patterns suggest a limitation to gene flow for some marine species, preventing population admixture. In the last few years, a large number of studies have challenged the hypothesis of the Strait of Gibraltar representing a phylogeographical break. A review of more than 70 papers reveals no obvious relationship between either dispersal ability or life history, and observed patterns of partial or complete genetic isolation between Atlantic and Mediterranean populations. We re-analysed a selection of this large body of data (20 studies in total) in order to provide a homogeneous and coherent view on the generality of the phylogeographical patterns and the presence of a phylogeographical barrier. This offered the opportunity to summarize the state of the art on this matter and reach some general conclusions on the evolutionary history across the Atlantic–Mediterranean range. Geographically, some species in the transition zone showed step changes of allele frequencies associated with the Almeria-Oran Front rather than with the Strait of Gibraltar itself. A major part of the data describe evolutionary events well within the time frame of the Quaternary age as very few taxa pre-date closure of the Tethys Sea. Results point to a combined signature of vicariance, palaeoclimate fluctuation and life-history traits on the Atlantic–Mediterranean phylogeographical patterns. Principal component analysis failed to show any particular association between biological traits and genetic variables. It would argue that organismal determinism may play a far less significant role than marine biogeographers have generally believed.
- Genetic differentiation between close eastern Mediterranean Dicentrarchus labrax (L.) populationsPublication . Castilho, Rita; Ciftci, Y.Differentiation at nine microsatellite loci revealed that a Levantine Basin sea bass Dicentrarchus labrax population probably represents a further subdivision of this species in the eastern Mediterranean.
- Population structure of seabass in Portugal: evidence from allozymesPublication . Castilho, Rita; McAndrew, B. J.Starch-gel electrophoresis was used to assess the level and distribution of genetic variation in juvenile European seabass sampled from five different nursery grounds along the coast of Portugal between November 1992 and February 1994. Thirty-eight loci were examined, of which six (AAT-3*, ADA*, GPI-1*, GPI-2*, G3PDH-2*, SOD*) were polymorphic at the 99% level and were used in population surveys. Low but statistically significant multilocus FST values suggest that population structuring exists along the Portuguese coast. There is some restriction in gene flow between the population at Faro and all other sites to the north.
- Has time come for the genetic management of sea bass?Publication . Volckaert, F.; Alvarez, M. C.; Argenton, F.; Bonhomme, F.; Chatain, B.; Colombo, L.; Castilho, Rita; Chevassus, B.; Gorshkova, G.; Kohler, M.; Magoulas, A.; Martinez, G.; McAndrew, B. J.; Piferrer, F.; Vandeputte, M.; Zanuy, S.Since 1980 the industrial production of European sea bass has risen considerably up to at least 18,000 MT in 1996 ( see also Josupeit, Aquaculture Europe 20(2):-12, 1995). This growth is remarkable since few were able to culture the species in the seventies. Several "classical" stages of development can be observed; they are typical of a rapidly expanding bioindustry.