Rafaela Amaro

Life Span Variation of the Freshwater Pearl Shell: A Model Species for Testing Longevity Mechanisms in Animals

Abstract Only about a dozen species of animals are known to achieve maximum ages (Amax) exceeding 100 yrs, including the freshwater pearl shell (Margaritifera margaritifera). This species has a life-span of between 100–200 years depending on latitude and environmental conditions. The difference in Amax is 3–7 times when southern populations, with Amax of 28–40 yrs, are compared to northern Arctic populations, with Amax of 114–190 yrs. Evolutionary and ecological explanations for longevity in the Arctic pearl shell include adaptations to the severe, unstable climatic and hydrological conditions in rivers. Extreme longevity seems to be related not only to the low metabolic rate in the cold climate, but the species can reduce energy expenditure for growth, and can rapidly increase metabolic rate up to 130x the normal level, to regenerate damaged shell or tissue. The physiology of this species may provide valuable clues to understanding the mechanisms that sustain longevity and retard senescence.

Threatened freshwater pearl mussel Margaritifera margaritifera L. in NW Spain: low and very structured genetic variation in southern peripheral populations assessed using microsatellite markers

A genetic analysis of freshwater pearl mussel Margaritifera margaritifera populations from NW Spain, a peripheral area of its European distribution, was carried out using microsatellite markers. These populations were formerly reported as genetically differentiated on the basis of growth and longevity studies. Ten loci previously characterized in populations from central Europe were used to comparatively analyze the genetic variability at the southern edge of the species’ range. Iberian pearl mussel populations showed very low genetic variability and significant high genetic differentiation. Half of the total genetic diversity observed appeared to be distributed between populations, which suggested a highly structured adaptive potential in pearl mussel at the southern peripheral distribution of the species. Population distinctiveness was evidenced by assignment tests, which revealed a high accuracy of individual assignments to their population of origin. All data suggested low effective population size and major effects of genetic drift on population genetic structure. In order to avoid further loss of genetic variation in biologically distinctive populations from NW Spain, prioritization of genetic resources of this species is required for conservation and management.

Cytogenetic characterization of the AS cell line derived from the Atlantic salmon (Salmo salar L.)

The chromosome complement of the fish cell line AS, derived from the Atlantic salmon (Salmo salar L., 2N = 58), was investigated by C-, Ag-NOR, restriction endonuclease, and BrdU-replication banding. The cell line has a modal chromosome number of 52 with a fixed number of chromosomal rearrangements. The variety of banding patterns obtained allowed us to identify three chromosome markers in the cell line. The identification of their possible origin and significance in karyotype evolution are discussed.

Morphometric and meristic variation in Galician threespine stickleback populations, northwest Spain

SynopsisWe evaluated morphological differentiation among populations of threespine stickleback, Gasterosteus aculeatus, from the Limia and Miño basins (Galicia, NW Spain), the river Karup (Denmark) and Aiguamolls de l’Empordà (Girona, northeast Spain), using multivariate analysis of morphometric and meristic characters. Multivariate discriminant analysis and hierarchical cluster analysis uncovered significant differences among the four main groups, between the two groups from Galicia and among populations within the Miño basin. The stickleback from Galicia differed from the Danish group in head and body armour characters. Between the Miño and Limia groups, we found differences in both head and body proportions as well as in number of gill rakers. Within the Miño basin populations varied with respect to head and body armour traits and the number of lower gill rakers. Clustering analysis divided these populations into two groups based on the latter trait: fish from the upper section of river Miño and tributaries (a lower number of lower gill rakers) and fish from the central and lower reaches of the river. Overall, morphometric traits were more useful than meristic ones; however, the two types of data provided congruent information about the morphological differentiation of stickleback populations.

Lateral plate variation in Galician stickleback populations in the rivers Miño and Limia, NW Spain

We examined lateral plate variation in populations of stickleback, Gasterosteus aculeatus, from the rivers Mino and Limia in Galicia (Northwest Spain), by analysing morphs, number of lateral plates, and position of the plates. In order to test for sexual dimorphism, the means and variances of plates were compared in males and females of some populations. No significant differences were found between sexes, therefore all remaining populations were analysed without controlling for sex. As stickleback populations in Galicia have an annual life span, the populations from the river Mino were divided in two age groups to compare lateral plate number. Analysis of each group revealed significant differences among populations, in accordance with the large amount of variation found in populations from other regions. Analysis of samples collected from the same place and at the same time of year, but in different years, indicated that there was little year to year variation. This suggests that populations are well adapted to their habitat, or that environmental conditions did not change significantly during the period of sampling. Finally, we propose a new method for the evaluation of scute variation analysis of the position of lateral plates. Cluster analysis of our data clearly differentiated populations from the rivers Mino and Limia.

Synaptonemal complex analysis in oocytes and spermatocytes of threespine stickleback Gasterosteus aculeatus (Teleostei, Gasterosteidae)

A surface-spreading synaptonemal complex (SC) technique was employed to analyze spermatocytes and oocytes of stickleback, Gasterosteus aculeatus, in order to visualize the process of chromosome synapsis. The mean SC length was 150 ± 18 μm in three males and 143 ± 12 μm in one female analyzed. A representative SC karyotype with 21bivalents was also presented. Each SC had lateral elements of equal length. No bivalent displaying the atypical synaptic behaviour which is often associated with heteromorphic sex chromosomes was observed neither in males nor in the female analyzed.

Chromosomal evolution in salmonids: a comparison of Atlantic salmon, brown trout, and rainbow trout R-band chromosomes

Replication banding technique was applied to the chromosomes of Salmo salar, Salmo trutta, and Oncorhynchus mykiss. The in vitro technique has proved more advantageous than the in vivo technique due to a higher number of bands obtained. The comparison of these replication banding patterns has revealed that some chromosomes of Salmo trutta karyotype appeared associated with Salmo salar and Oncorhynchus mykiss karyotypes by single chromosomal rearrangements.

Phylogeography and Conservation Genetics of the Ibero-Balearic Three-Spined Stickleback (Gasterosteus aculeatus)

Genetic isolation and drift may imperil peripheral populations of wide-ranging species more than central ones. Therefore, information about species genetic variability and population structure is invaluable for conservation managers. The Iberian populations of three-spined stickleback lie at the southwestern periphery of the European distribution of Gasterosteus aculeatus. This teleost is a protected species in Portugal and Spain and local extinctions have been reported in both countries during the last decades. Our objectives were (i) to determine whether the Iberian populations of G. aculeatus are unique or composed of any of the major evolutionary lineages previously identified and (ii) to assess the evolutionary potential of these peripheral populations. We genotyped 478 individuals from 17 sites at 10 polymorphic microsatellite loci to evaluate the genetic variability and differentiation of the Ibero-Balearic populations. We also sequenced 1,165 bp of the mitochondrial genome in 331 of those individuals in order to complement the estimates of genetic diversity in the Ibero-Balearic region. We predicted the evolutionary potential of the different sites analysed based on the contribution of each of them to total allelic/mitochondrial diversity. An intraspecific phylogeny at European level was reconstructed using our data from the mitochondrial cytochrome b gene (755 bp) and published sequences. The so-called Transatlantic, European and Mediterranean mitochondrial lineages were found to be present in the Ibero-Balearic region. Their phylogeography suggests a history of multiple colonisations. The nuclear results show, however, a strong correlation between population structure and drainage system. The following basins should be prioritised by conservation policies in order to preserve those populations with the highest evolutionary potential: the Portuguese Vouga and Tagus as well as the Spanish Majorca and Limia. Maintenance of their connectivity, control of exotic species and monitoring of habitat properties are strongly recommended in those areas. Genetic variation alone cannot, however, ensure the persistence of these peripheral southern populations of G. aculeatus. On the one hand, the analysis of a historical sample from Eastern Spain (Penyscola) revealed no genetic erosion, which suggests a fairly sudden extinction of that population. On the other hand, the reintroduction program implemented in the Valencian Community has mostly failed despite our finding of similar level of genetic diversity between the wild source and the captive-bred released individuals.

Phylogeography and Conservation Genetics of the Iberian Three-spined Stickleback (Gasterosteus aculeatus)

Genetic isolation and drift may imperil peripheral populations of wide-ranging species more than central ones. Therefore, information about species genetic variability and population structure is invaluable for conservation managers. The Iberian populations of three-spined stickleback lie at the southwestern periphery of the European distribution of Gasterosteus aculeatus. This teleost is a protected species in Portugal and Spain and local extinctions have been reported in both countries during the last decades. Our objectives were (i) to determine whether the Iberian populations of G. aculeatus are unique or composed of any of the major evolutionary lineages previously identified and (ii) to assess the evolutionary potential of these peripheral populations. We genotyped 478 individuals from 17 sites at 10 polymorphic microsatellite loci to evaluate the genetic variability and differentiation of the Ibero-Balearic populations. We also sequenced 1,165 bp of the mitochondrial genome in 331 of those individuals in order to complement the estimates of genetic diversity in the Ibero-Balearic region. We predicted the evolutionary potential of the different sites analysed based on the contribution of each of them to total allelic/mitochondrial diversity. An intraspecific phylogeny at European level was reconstructed using our data from the mitochondrial cytochrome b gene (755 bp) and published sequences. The so-called Transatlantic, European and Mediterranean mitochondrial lineages were found to be present in the Ibero-Balearic region. Their phylogeography suggests a history of multiple colonisations. The nuclear results show, however, a strong correlation between population structure and drainage system. The following basins should be prioritised by conservation policies in order to preserve those populations with the highest evolutionary potential: the Portuguese Vouga and Tagus as well as the Spanish Majorca and Limia. Maintenance of their connectivity, control of exotic species and monitoring of habitat properties are strongly recommended in those areas. Genetic variation alone cannot, however, ensure the persistence of these peripheral southern populations of G. aculeatus. On the one hand, the analysis of a historical sample from Eastern Spain (Penyscola) revealed no genetic erosion, which suggests a fairly sudden extinction of that population. On the other hand, the reintroduction program implemented in the Valencian Community has mostly failed despite our finding of similar level of genetic diversity between the wild source and the captive-bred released individuals.