Jorge I. Izquierdo

Micronuclei and fluctuating asymmetry in brown trout (Salmo trutta): complementary methods to biomonitor freshwater ecosystems

In this work we measured both micronuclei number in kidney erythrocytes and fluctuating asymmetry in wild brown trout (Salmo trutta), caught in different fluvial ecosystems of Asturias (northern Spain) characterized by different levels of anthropic influence. Brown trout samples from rivers with high anthropic influence possessed significantly higher averages of both micronuclei and fluctuating asymmetry than brown trout samples from less anthropic-influenced rivers. These findings demonstrated the sensitivity of the micronucleus test in kidney erythrocytes to biomonitor freshwater ecosystems. The positive association found between micronuclei average and fluctuating asymmetry at the populational level suggests that fluctuating asymmetry tests could be potential indicators of environmental threat. Variation of fish asymmetry with ageing indicates that fluctuating asymmetry surveys of wild populations should be carried out in trouts of the same age class.

Assessing pollution in coastal ecosystems: a preliminary survey using the micronucleus test in the mussel Mytilus edulis

Mussels Mytilus edulis were sampled at increasing distances from urban effluents in two very different locations, Gijon (northern Spain, Europe, 43 degrees N) and Puerto Madryn (Argentina, South America, 43 degrees S), and from an industry effluent in Puerto Madryn. The micronucleus test was performed on branchial cells. For the three situations, a statistically significant negative association was found between the distance of sampling site from the effluent and the mean number of micronuclei per 1000 cell counts, in a range of distances as short as 300m. The micronucleus test in Mytilidae, here revealed to be sensitive enough to monitor urban pollution, is proposed for routine surveys of pollution as a bioindicator of choice for coastal ecosystems.

Bidirectional selection for female receptivity in Drosophila melanogaster

A wild population ofDrosophila melanogaster was subjected to selection for high and low female receptivity. Selection was only applied in females on the basis of the mating times observed in a 30-min period. We applied a selection paradigm that allowed us to conclude that females unmated after 30 min correspond to the truncated upper tail of the distribution underlying mating times. Selection was successful, with mean mating times of about 5 min for the high lines, 35 min for the low lines, and 12 min for the control. Receptivity of the selection lines remained steady after 42 generations of relaxed selection, suggesting a lack of natural selection on receptivity in laboratory conditions. We also found a clear relationship between high or low receptivity and high or low frequency of hybridization withD. simulans males, emphasizing the role of female receptivity in maintaining isolation with its sibling speciesD. simulans.

Receptivity and sexual maturation of Drosophila melanogaster females in relation to hybridization with D. simulans males: a populational analysis

Abstract Females from a wild population of Drosophila melanogaster were examined for the their frequency of hybridization with D. simulans males using no-choice tests, and for receptivity and sexual maturation speed using conspecific males. Genetic variability within the population was revealed for the three traits, and significant positive correlations between them were found. Females that matured earlier had greater receptivity indicating a common physiological basis for both characteristics. Notably, high female receptivity was correlated with high tendency to hybridize with D. simulans males. The involvement of female receptivity in both sexual isolation and sexual selection processes are discussed.

Fluctuating Asymmetry and Isozyme Variation in Atlantic Salmon: Relation to Age of Wild and Hatchery Fish

Abstract Isozyme variation and fluctuating asymmetry at different ages of Atlantic salmon Salmo salar were analyzed for hatchery and wild stocks. Significant age-related decrease of fluctuating asymmetry was detected in wild stocks but not in hatchery stocks. Natural selection may act against phenotype asymmetry, or some trait associated with asymmetry, in wild but not in hatchery populations. Heterozygosity did not vary significantly with fish age in most cases, suggesting the lack of association between heterozygosity and asymmetry.

Status of Genetic Conservation in Salmonid Populations from Asturian Rivers (North of Spain)

Salmo salar L. and S. trutta L. (migratory and not migratory) are the two native species of salmonids from Asturias, north of Spain. S. trutta is the dominant species in Asturian rivers, without apparent recession. However, S. salar populations are changing in two ways: catches have decreased significantly from 1953 to 1989 in three rivers, Navia, Sella, and Cares-Deva, and the proportion of grilse (one-sea-winter salmon) increased in all rivers with the increases being significant in two rivers, Narcea and Cares-Deva (Garcia de Leaniz and Martinez, 1988; Nicieza et al., 1990). S. salar populations show signs of being disturbed.

Studies in individual spawnings of Salmo salar: a model to explain chromosome polymorphism patterns.

SummaryAtlantic salmon fry from nine offspring belonging to individual spawnings were karyotyped. Different patterns of Robertsonian chromosome polymorphism were obtained. A theoretical model is developed to explain the different chromosome polymorphism patterns in Salmo salar offspring in terms of the chromosome numbers of the parents.

Evolution of chromosome polymorphic patterns in salmonids: Within-generation variation with ageing

Abstract Robertsonian polymorphism has been analysed in samples of successive ages of Atlantic salmon ( Salmo salar L.) and brown trout ( Salmo trutta L.). Polymorphism changed significantly with ageing, the standard 2n class increasing for each species (2n = 58 for Atlantic salmon and 2n = 80 for brown trout). No significant within-population changes were found among same-aged samples from different generations. The results support the notion that selection favours a standard karyotype. On the other hand, permanence of polymorphic patterns within age groups in successive generations also was demonstrated.

Cytological and Population Genetic Changes in Northwestern Iberian Mussels After the Prestige Oil Spill

The ecological catastrophe produced by the Prestige oil spill (November 2002) caused severe damage in both North Spanish and French coastal communities. Wild mussel populations of Mytilus galloprovincialis in a zone with marginal introgression of Mytilus edulis were affected at all levels, from high DNA damage to increased polycyclic aromatic hydrocarbon content in tissues. In this article, we describe cytological and population genetic changes of wild mussel populations from the northwestern Iberian coast following the catastrophe. The micronucleus test was employed as an indicator of cytological damage, and the Barcoding mitochondrial cytochrome oxidase I (COI) and the nuclear Glu-5′ genes were analyzed for determining the species and assessing population genetic diversity. Immediate increase of micronuclei counts after the oil spill was found, with a further decrease in consecutive months although the counts did not recover pre-Prestige levels. Reduced variation at mitochondrial sequences in the most exposed areas and reduction of M. edulis traces in the regional genetic pool also suggest long-term impact that may result in evolutionary changes. These results highlight the need of adopting more strict measures in order to prevent this type of accidents and avoid long-term effects on wild populations.

Effect of Parental Numbers on Chromosome Patterns Found in Artificially Produced Atlantic Salmon Stocks

Abstract The number of wild Atlantic salmon Salmo salar that return to Spanish rivers has steadily decreased because of environmental degradation and overfishing. To alleviate this decline, juvenile salmon obtained from adults returning to Asturian rivers are used in a supplementation program. Gametes from no more than 35 adults are used to create groups of juveniles that are released back into the wild. We examined the effect of parental numbers on the chromosomal patterns found in juveniles produced by this protocol. When less than 20 parental fish were used, the chromosomal patterns found in their offspring were significantly different (P < 0.001) from those found in naturally produced fish. Consequently, in supplementation endeavors, at least 20 parents should be used to create groups of juveniles.