Interspecific barriers between salmonids when hybridisation is due to sneak mating.

Male sneaking behaviour can lead to interspecific hybridisation if sneakers attempt to fertilise ova in heterospecific mating, contributing to break down of interspecific barriers. In south European rivers, sneaking Atlantic salmon males fertilise an important proportion of ova from adult females in heterospecific crosses, up to 65%. In a south French flow-controlled stream, we found that they were able to naturally fertilise brown trout ova in absence of brown trout males. Aggressiveness of brown trout males towards sneaking salmon males and low survival of hybrids issued from salmon sneakers are found to be interspecific barriers.

Análisis de las técnicas continuas de sustitución renal en pacientes críticos con insuficiencia renal aguda / Continuous renal replacement therapies in critically-ill patients with acute renal failure

Fundamento. El fallo renal agudo (FRA) se asocia frecuentemente al síndrome de disfunción multiorgánica (SDMO) en los pacientes críticos. El uso de técnicas continuas de sustitución renal (TCSR) fue descrito por primera vez hace unos 20 años. Analizamos aquí nuestra experiencia valorando los factores pronósticos y la evolución clínica de los pacientes. Pacientes y métodos. Se realizó un estudio descriptivo, observacional y retrospectivo de todos los pacientes críticos con FRA tratados con TCSR, durante el período comprendido entre enero de 1996 y diciembre de 2000. Se recogieron datos demográficos y clínicos, y se realizó un análisis estadístico descriptivo, comparativo y de regresión logística para el estudio de los factores de riesgo relacionados con la mortalidad. Resultados. Fueron evaluados 73 pacientes. La media de edad fue 61 años (intervalo, 17-79), el 62 per cent eran varones, el APACHE II medio fue de 24 (8) y el SAPS II medio fue de 65 (16). La mortalidad global alcanzó el 86,3 per cent. Mediante regresión logística el riesgo de muerte fue más alto en los pacientes con complicaciones relacionadas con la técnica (OR = 2,00; IC del 95 per cent, 1,763-250,0; p = 0,016) y más bajo en pacientes con diuresis residual mayor (OR = 0,995; IC del 95 per cent, 0,990-0,999; p = 0,028). Conclusiones. La mortalidad del FRA que acompaña al SDMO sigue siendo elevada. Las TCSR pueden ser útiles en estos pacientes. En nuestra unidad la ausencia de complicaciones relacionadas con la técnica y la mayor diuresis residual se relacionan con una menor mortalidad. (AU)

[Comparison of the in vitro and in vivo effects of meropenem and ciprofloxacin on the morphology of Escherichia coli and Staphylococcus aureus]. / Comparación del efecto in vitro e in vivo de meropenem y ciprofloxacino sobre la morfología de Escherichia coli y Staphylococcus aureus.

In the treatment of infections, subinhibitory concentrations are commonly present and induce a wide range of effects. Some of these effects have been reported to improve the efficacy of these compounds. One of these effects, the change of the bacterial morphology, was assayed in this study both in vitro and in vivo, and their results were compared. Two antimicrobial agents (meropenem and ciprofloxacin) and two standard Gram-positive and Gram-negative strains (S. aureus y E. coli) were used. The methods employed included the in vitro exposure of microorganisms on Mueller-Hinton agar plates, and the in vivo intraperitoneal infection model in mice. With all the sub-MICs tested, the in vitro results showed that meropenem induced the formation of round cells (spheroplasts) on E. coli, while ciprofloxacin produced filaments. With S. aureus, the two antimicrobial agents induced the formation of cellular aggregates (clusters) with a diameter greater than 1 mm. The in vivo results confirmed those observed in vitro, but to a lesser extent. These results agree with those expected in relation with the mechanisms of action of each drug, and could be important in order to prevent a lost in efficacy when the levels of the drug are below the MIC.

Brown trout as biomonitor of heavy metal pollution: effect of age on the reliability of the assessment.

Brown trout (Salmo trutta L.) is a native fish of the rivers of northern Spain. It is the dominant fish species in these rivers, and it is widespread over all the range of freshwater ecosystems in the area, including ecosystems potentially polluted with heavy metals. In this study, the potential of brown trout as biomonitor of heavy metal pollution and the effect of fish age on the reliability of the assessment are analyzed. Copper, lead, and cadmium concentrations of both abiotic compartments (water and sediments) and brown trout (S. trutta) from three northern Spanish rivers were analyzed. Significant correlations were found between sediment lead content and lead concentration in trout liver. One-year-old juvenile trouts were demonstrated to be useful as a biomonitor of copper and lead pollution, revealing between-location differences. Older trouts do not seem adequate to properly monitor heavy metal pollution. The effect of aging on the reliability of this species as biomonitor is discussed.

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.

Bidirectional selection for female receptivity in Drosophila melanogaster.

A wild population of Drosophila 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 with D. simulans males, emphasizing the role of female receptivity in maintaining isolation with its sibling species D. simulans.

Response to selection for increased hybridization between Drosophila melanogaster females and D. simulans males.

Females of Drosophila melanogaster and males of D. simulans hybridizing in a nonchoice condition were artificially selected for 12 generations. The frequency of hybridization increased from 10% to 79%. Response to selection occurred in both species, particularly in D. melanogaster. Female receptivity was the primary sexual trait that accounted for breaking up sexual isolation in these species, but it remained unclear which elements of the D. simulans male courtship were involved.

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

Atlantic 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.

Correlated variation of chromosomal inversion (3R)C and extra bristles in Drosophila melanogaster.

Chromosomal inversion In(3R)C and extra dorsocentral and scutellar macrochaetae are correlated in Asturian natural populations of Drosophila melanogaster in that selection for extra bristles produced an increase in In(3R)C frequency. In the present work two populations with significantly different frequencies of the In(3R)C inversion were created and a significant positive correlation between In(3R)C frequency and frequency of individuals carrying extra bristles was found. This result confirms the correlation between bristles and In(3R)C. In addition, the correlation between the two characters is also demonstrated at the individual level.

Allozyme polymorphism at the alpha Gpdh and Adh loci and fitness in Drosophila melanogaster.

We have studied in Drosophila melanogaster the effects of allozyme variation at the alpha Gpdh and Adh loci on the following fitness components: female fecundity, egg hatchability, egg-to-adult survival under near-optimal and competitive conditions, rate of development under near-optimal and competitive conditions, and mating capacity of males. Significant effects of the alpha Gpdh locus on rate of development under competitive conditions (SS greater than FS greater than SS), and of the Adh locus on egg hatchability (FF = SS greater than FS) and egg-to-adult survival under competitive conditions (FF greater than SS = FS) were revealed. Possible natural selection mechanisms involved in the maintenance of allozyme polymorphisms at the alpha Gpdh and Adh loci are described. These mechanisms and the fitness of In(2L)t may account for the persistence and clinal distribution of the two allozyme polymorphisms in nature.

Environmental sensitivity and heterosis for egg laying in Drosophila melanogaster.

Genotype × temperature interactions for egg laying were studied in Drosophila melanogaster using two sets of half diallel crosses: one between inbred lines of the same geographic origin, and the other between established laboratory, newly derived inbred lines from different geographic origins. The sensitivity of most genotypes to changes in temperature was adequately described as a linear regression of mean in temperature. The regression coefficients (linear sensitivities) were heterogeneous between genotypes. Hybrids were more affected by temperature variation than were inbreds. All the heterogeneity of linear sensitivities was accounted for by a linear function of the genotypic means, which strongly suggests that a scale effect is responsible for the differences in sensitivity to temperature. In contrast, no general relationship was found between standard error deviation (sensitivity to small environmental changes) and mean performance between genotypes, although hybrids tended to be less variable than inbreds. This shows that the sensitivity to environmental variation depends not only on the genotype, but also on the nature of the environmental variation. The variability within temperatures may be affected by the general homeostasis of individual genotypes, while the variability between temperatures could be the result of genes directly affecting the trait and their multiplicative interaction with the environment.