Intra- and intersexual selection and their potential consequences on fitness-relevant traits in several fish species

Résumé : Les mécanismes de sélection sexuelle, en particulier la compétition entre mâles (sélection inter-sexuelle) et le choix des femelles (sélection intra-sexuelle), peuvent fortement influencer le succès reproducteur d'un individu, c'est-à-dire son nombre de descendants. On observe ainsi que les mâles dominants et les mâles élaborant des caractères sexuels secondaires marqués ont un succès reproducteur élevé. Toutefois, le succès reproducteur ne suffit pas pour garantir une contribution génétique élevée, parce que la fitness dépend également de la performance des descendants (c'est-à-dire de leur survie et de leur propre succès reproducteur). Si cette performance dépend en partie des gènes paternels, les males ont un avantage certain à signaler leur qualité aux femelles afin d'atteindre des taux de reproduction élevé. Ce mécanisme de signalisation est connu sous le nom de 'good genes hypothesis', toutefois très peu d'études ont clairement démontré le lien entre la qualité génétique des individus et la signalisation. De plus, la performance des descendants peut aussi dépendre des effets génétiques de compatibilité entre mâles et femelles ('compatible genes'). C'est-à-dire que certains allèles paternels n'apporteraient un avantage aux descendants qu'en combinaison avec certains allèles maternels. Nous avons déterminé, durant la période de reproduction, le statut de dominance des mâles pour deux espèces de poissons d'eau douce : la truite (Salmo trotta) et le vairon (Phoxinus phoxinus), puis nous avons évalué la relation entre le succès reproducteur et le statut de dominance et/ou la quantité de signalisation des caractères sexuels secondaires. Nous avons également fécondés artificiellement des oeufs de truites et de corégones (Coregonus palaea), en croisant chaque mâle avec chaque femelle (full-factorial breeding design). Ce type de design autorise la quantification précise des effets génétiques et permet de séparer les effets de 'good genes' et de 'compatible genes'. Cela a été fait sous différentes intensités de stress bactérien, ainsi que dans des conditions naturelles, et nous avons pu ainsi tester si certains indicateurs de qualité génétique des mâles ('good genes') étaient liés a) à la dominance et/ou b) à l'expression des caractères sexuels secondaires des mâles comme l'intensité mélanique ou la taille des tubercules sexuels. En outre, nous cherchons à savoir si la survie des descendants est liée à certaines combinaison des gènes du complexe d'histocompatibilité majeur (MHC) et/ou à la parenté génétique des parents, les deux traits étant soupçonnés d'avoir des influences génétique de compatibilité (`compatible genes') à la performance des descendants. Nous avons constaté que la dominance des mâles est directement liée à la taille et au poids des mâles (truites, vairons), mais également aux caractères sexuels secondaires (tubercules). De plus, les mâles vairons dominant ont eu un succès de fécondation plus élevés que les mâles subordonnés. Nous montrons que les truites et corégones mâles diffèrent dans leur qualité génétique, qui a été mesurée avéc la survie embryonnaire, le temps avant l'éclosion et enfin la croissance juvénile. Contrairement aux prédictions, la dominance (ou les traits indicatifs de dominance) n'était liée à la qualité génétique, dans aucun des traitements, et ne fonctionne donc pas comme indicateur de qualité. Par contre, la qualité génétique était liée aux caractères sexuels secondaires, particulièrement par la teinte mélanique chez les truites. Les embryons de truites issus de pères sombres survivaient mieux que ceux issus de pères clairs dans des environnements difficiles, de plus leur croissance était plus élevée lors de leur première année dans des conditions naturelles. La taille des juvéniles lors de leur première année est un trait important lié au succès dans la compétition pour des ressources telles qu'abri ou nourriture. De plus, les femelles truites peuvent augmenter la survie de leurs descendants en choisissant des mâles selon leur type de MHC ou selon leur degré de parenté. En outre, chez les corégones, la morphologie des tubercules sexuels ne semble pas signaler la qualité génétique. Nous avons également remarqué que l'exposition à des pathogènes non-létaux pouvait influencer la performance des alevins à court et long terme, probablement en affaiblissant leur système immunitaire. Cette thèse montre que les mâles diffèrent dans leur qualité génétique et que différents mécanismes de sélection inter- ou intra-sexuelle (par exemple la préférence pour des mâles sombres, pour des génotypes MHC ou pour des couples avec degré de parenté basse) pouvait avoir un effet positif sur la qualité des descendants, bien que cet effet génétique pouvait changer au cours du temps et entre différents environnements. Contrairement à nos attentes, le résultat de la compétition intra-sexuelle (la hiérarchie de dominance entre mâles) n'était pas lié à la qualité génétique individuelle ('good genes'). Dans ce sens, ce travail permet également de contribuer à l'explication du fait que la sélection sexuelle, de par sa forte sélection directionnelle, ne conduit pas à la diminution de la variance génétique, mais plutôt à la maintenance du polymorphisme génétique. Summary : Sexual selection mechanisms, especially male-male competition (inteasexual selection) and female mate choice (inteasexual selection), can strongly influence individual mating success, often resulting in dominant males and males with elaborate secondary sexual characters having higher fertilisation success. However, siring a high number of offspring alone does not guarantee high individual fitness, as fitness does also strongly depend on offspring performance (i.e. survival, fecundity). If this superiority in offspring performance depends on paternally inherited genes, the fathers are expected to signal this potential indirect benefit to females in order to attain high mating rates. This mechanism is also known as the 'good genes' hypothesis of sexual selection but until now most studies failed to conclusively show the relation of an individual genetic quality and its potential signalling traits. Further, offspring performance could also depend on compatible gene effects. These are alleles that increase offspring performance only in combination with other specific alleles. We first determined male dominance status from intrasexual competition during mating season for brown trout (Salmo trutta) and European minnows (Phoxinus phoxinus). For minnows we additionally checked if dominance and/or secondary sexual traits were linked to fertilisation success. Further, we artificially fertilised brown trout and alpine whitefish (Coregonus palaea) eggs, following full factorial breeding designs, enabling to properly measure `good gene' and `compatible gene' effects on offspring performance. This was done under different intensities of natural stressors, as well as under natural conditions. This procedure allowed us to test if the obtained male genetic quality measures (good genes effects) were indicated by a) dominance or lay traits linked to dominance and/or by b) secondary sexual characteristics such as melanin-based male skin darkness or breeding tubercles. Further, we investigated if offspring survival was linked to the MHC (major histocompatibility complex) gene combinations and/or to the parental genetic relatedness, as both traits were shown to have 'compatible gene' effects that may influence offspring performance. We found that male dominance in intrasexual competition was positively linked to body size, body weight (brown trout, minnows) but also to elaborate secondary sexual characteristics (breeding tubercles in minnows). Further, dominant minnow males did have an increased fertilisation success compared to subordinate ones. We show that brown trout and whitefish males do usually differ in their genetic quality, which was measured as embryo survival, hatching timing and finally as juvenile growth. Contrary to prediction male dominance or dominance indicating traits do not function as a quality signal as they were not linked to genetic quality. This result was constant when measuring genetic quality under different levels of natural stressors and under natural conditions (brown trout). On the other hand genetic quality seemed to be indicated by secondary sexual characteristics, specifically by melanin-based skin darkness in brown trout as brown trout embryos sired by darker fathers had increased survival rates when raised under harsh conditions and. they grew larger as juveniles after one year of growth in a natural stream, which is an important trait influencing success of juveniles in competition for hidings, food and other resources. Furthermore, brown trout females may increase the survival of their embryos when choosing males according to their MHC genotypes or to the general genetic relatedness between themselves and their potential mates. In whitefish on the other hand breeding tubercle morphology did not seem to signal genetic quality. Eventually, we saw that anon-lethal exposure to pathogens might influence short term and long term offspring performance probably by weakening an exposed individual's immune system. This thesis shows that males usually differ in their genetic quality and that different inter- or intrasexual selection mechanisms (e.g. mate selection favouring dark males, preference for MHC genotype combinations or for unrelated mates) may have strong positive effects on genetically dependent offspring performance but that such genetìc effects can change over time and environments. In contrast to our a priori expectations, the outcome of intrasexual selection, namely male dominance hierarchies, with dominant males often having high fertilisation success, was not linked to individual genetic quality (`good genes'). In this sense the present thesis may also be a helpful contribution to understand why sexual selection does not lead to rapid loss of genetic variation by strong directional selection but could even lead to the maintenance of genetic variation in natural populations.

Effects of a lifestyle intervention on adiposity and fitness in overweight or low fit preschoolers (Ballabeina).

OBJECTIVE: Overweight (OW) and low fit children represent cardiovascular high-risk groups. A multidimensional school-based lifestyle intervention performed in 652 preschoolers reduced skinfold thickness and waist circumference, and improved fitness, but did not affect BMI. The objective of this study is to examine whether the intervention was equally effective in OW (≥90th national percentile) and/or low fit (lowest sex- and age-adjusted quartile of aerobic fitness) children compared to their normal weight and normal fit counterparts. DESIGN AND METHODS: Cluster randomized controlled single blinded trial, conducted in 2008/09 in 40 randomly selected preschool classes in Switzerland. The intervention included a playful physical activity program and lessons on nutrition, media use and sleeps. Primary outcomes were BMI and aerobic fitness; secondary outcomes included sum of four skinfolds, waist circumference and motor agility. Modification of intervention effects by BMI-group and fitness-group was tested by interaction terms. RESULTS: Compared to their counterparts, OW children (n = 130) had more beneficial effects on waist circumference (p for interaction = 0.001) and low fit children (n = 154) more beneficial effects on all adiposity outcomes (p for interaction ≤0.03). The intervention effects on both fitness outcomes were not modified by BMI- or fitness-group (all p for interaction ≥0.2). Average intervention effect sizes for BMI were -0.12, -0.05, -0.26 and -0.02 kg/m(2) and for aerobic fitness were 0.40, 0.30, 0.12 and 0.36 stages for OW, normal weight, low fit and normal fit children, respectively. Conclusions: This multidimensional intervention was equally and for some adiposity measures even more effective in high-risk preschoolers and represents a promising option for these children.

A new neuropsychological instrument measuring effects of age and drugs on fitness to drive: development, reliability, and validity of MedDrive

Background: Current guidelines underline the limitations of existing instruments to assess fitness to drive and the poor adaptability of batteries of neuropsychological tests in primary care settings. Aims: To provide a free, reliable, transparent computer based instrument capable of detecting effects of age or drugs on visual processing and cognitive functions. Methods: Relying on systematic reviews of neuropsychological tests and driving performances, we conceived four new computed tasks measuring: visual processing (Task1), movement attention shift (Task2), executive response, alerting and orientation gain (Task3), and spatial memory (Task4). We then planned five studies to test MedDrive's reliability and validity. Study-1 defined instructions and learning functions collecting data from 105 senior drivers attending an automobile club course. Study-2 assessed concurrent validity for detecting minor cognitive impairment (MCI) against useful field of view (UFOV) on 120 new senior drivers. Study-3 collected data from 200 healthy drivers aged 20-90 to model age related normal cognitive decline. Study-4 measured MedDrive's reliability having 21 healthy volunteers repeat tests five times. Study-5 tested MedDrive's responsiveness to alcohol in a randomised, double-blinded, placebo, crossover, dose-response validation trial including 20 young healthy volunteers. Results: Instructions were well understood and accepted by all senior drivers. Measures of visual processing (Task1) showed better performances than the UFOV in detecting MCI (ROC 0.770 vs. 0.620; p=0.048). MedDrive was capable of explaining 43.4% of changes occurring with natural cognitive decline. In young healthy drivers, learning effects became negligible from the third session onwards for all tasks except for dual tasking (ICC=0.769). All measures except alerting and orientation gain were affected by blood alcohol concentrations. Finally, MedDrive was able to explain 29.3% of potential causes of swerving on the driving simulator. Discussion and conclusions: MedDrive reveals improved performances compared to existing computed neuropsychological tasks. It shows promising results both for clinical and research purposes.

Suitability, success and sinks: how do predictions of nesting distributions relate to fitness parameters in high arctic waders?

AimAlthough habitat suitability maps derived from species distribution models (SDMs) are often assumed to highlight locations that can sustain healthy populations over time, the relationship between suitability scores and fitness parameters has rarely been tested thoroughly. LocationZackenberg Valley, north-east Greenland. MethodsUsing 14years of data (1997-2010) representing three wader species (dunlin Calidris alpina, sanderling Calidris alba and ruddy turnstone Arenaria interpres), we tested the relationships between modelled suitability and fitness parameters at nesting locations. ResultsAmong the three species examined, only the ruddy turnstone exhibited significant relationships between suitability and nest success, but over time rather than space. During years with extensive snow cover in the landscape, the nesting sites of ruddy turnstone occurred in different habitats than were typically used across years. Moreover, in years with extensive snow cover, the ruddy turnstone initiated nests later and suffered from higher egg predation rates. Main conclusionOur results suggest that SDMs derived from species occurrences that include years of low reproductive success may over-estimate the potential suitable habitat in the landscape. Whenever possible, variation in reproductive success should be considered when building models to inform species' response to environmental change. species' response to environmental change.

Fitness, sport et pression artérielle [Fitness, sports and blood pressure].

Blood pressure is lowered for a few hours after aerobic exercise, but also after resistance exercise, although for a shorter period of time. An exercise program can significantly lower resting and ambulatory BP measurements. Multiple mechanisms interact for the BP lowering effect, such as decreased total peripheral resistance, enhanced endothelial function, diminished sympathetic or rennin plasmatic activity, structural vascular modifications and baroreceptor reflex modulation. New exercises like eccentric or isometric (handgrip) contractions are promising. Resistance activities have long been considered dangerous for blood vessels because of increased arterial stiffness, but if the intensity remains moderate and aerobic exercises are integrated, then the effects are altogether beneficial.

Effects of alpha-phosphoglucomutase deficiency on cell wall properties and fitness in Streptococcus gordonii.

Streptococcus gordonii alpha-phosphoglucomutase, which converts glucose 6-phosphate to glucose 1-phosphate, is encoded by pgm. The pgm transcript is monocistronic and is initiated from a sigma(A)-like promoter. Mutants with a gene disruption in pgm exhibited an altered cell wall muropeptide pattern and a lower teichoic acid content, and had reduced fitness both in vitro and in vivo. In vitro, the reduced fitness included reduced growth, reduced viability in the stationary phase and increased autolytic activity. In vivo, the pgm-deficient strain had a lower virulence in a rat model of experimental endocarditis.

Heterozygosity-fitness correlations among wild populations of European tree frogs (Hyla arborea) detect fixation load.

Quantifying the impacts of inbreeding and genetic drift on fitness traits in fragmented populations is becoming a major goal in conservation biology. Such impacts occur at different levels and involve different sets of loci. Genetic drift randomly fixes slightly deleterious alleles leading to different fixation load among populations. By contrast, inbreeding depression arises from highly deleterious alleles in segregation within a population and creates variation among individuals. A popular approach is to measure correlations between molecular variation and phenotypic performances. This approach has been mainly used at the individual level to detect inbreeding depression within populations and sometimes at the population level but without consideration about the genetic processes measured. For the first time, we used in this study a molecular approach considering both the interpopulation and intrapopulation level to discriminate the relative importance of inbreeding depression vs. fixation load in isolated and non-fragmented populations of European tree frog (Hyla arborea), complemented with interpopulational crosses. We demonstrated that the positive correlations observed between genetic heterozygosity and larval performances on merged data were mainly caused by co-variations in genetic diversity and fixation load among populations rather than by inbreeding depression and segregating deleterious alleles within populations. Such a method is highly relevant in a conservation perspective because, depending on how populations lose fitness (inbreeding vs. fixation load), specific management actions may be designed to improve the persistence of populations.

Age-specific fitness components and their temporal variation in the barn owl.

Theory predicts that temporal variability plays an important role in the evolution of life histories, but empirical studies evaluating this prediction are rare. In constant environments, fitness can be measured by the population growth rate lambda, and the sensitivity of lambda to changes in fitness components estimates selection on these traits. In variable environments, fitness is measured by the stochastic growth rate lambda(S), and stochastic sensitivities estimate selection pressure. Here we examine age-specific schedules for reproduction and survival in a barn owl population (Tyto alba). We estimated how temporal variability affected fitness and selection, accounting for sampling variance. Despite large sample sizes of old individuals, we found no strong evidence for senescence. The most variable fitness components were associated with reproduction. Survival was less variable. Stochastic simulations showed that the observed variation decreased fitness by about 30%, but the sensitivities of lambda and lambda(S) to changes in all fitness components were almost equal, suggesting that temporal variation had negligible effects on selection. We obtained these results despite high observed variability in the fitness components and relatively short generation time of the study organism, a situation in which temporal variability should be particularly important for natural selection and early senescence is expected.