Natural selection and quantitative genetics of life-history traits in Western women: A twin study

Whether contemporary human populations are still evolving as a result of natural selection has been hotly debated. For natural selection to cause evolutionary change in a trait, variation in the trait must be correlated with fitness and be genetically heritable and there must be no genetic constraints to evolution. These conditions have rarely been tested in human populations. In this study, data from a large twin cohort were used to assess whether selection Will cause a change among women in contemporary Western population for three life-history traits: age at menarche, age at first reproduction, and age at menopause. We control for temporal variation in fecundity (the baby boom phenomenon) and differences between women in educational background and religious affiliation. University-educated women have 35% lower fitness than those with less than seven years education, and Roman Catholic women have about 20% higher fitness than those of other religions. Although these differences were significant, education and religion only accounted for 2% and 1% of variance in fitness, respectively. Using structural equation modeling, we reveal significant genetic influences for all three life-history traits, with heritability estimates of 0.50, 0.23, and 0.45, respectively. However, strong genetic covariation with reproductive fitness could only be demonstrated for age at first reproduction, with much weaker covariation for age at menopause and no significant covariation for age at menarche. Selection may, therefore, lead to the evolution of earlier age at first reproduction in this population. We also estimate substantial heritable variation in fitness itself, with approximately 39% of the variance attributable to additive genetic effects, the remainder consisting of unique environmental effects and small effects from education and religion. We discuss mechanisms that could be maintaining such a high heritability for fitness. Most likely is that selection is now acting on different traits from which it did in pre-industrial human populations.

Ultraviolet reflectance in a melanin-based plumage trait is heritable

Question: Is ultraviolet (UV) reflectance of melanin-based plumage ornaments heritable? Data studied: We considered the barn owl (Two alba), a species that varies continuously from white to reddish-brown, a pheomelanin-based trait. Methods: To perform a partial cross-fostering experiment. we exchanged one to three hatchlings between 16 pairs of nests with a similar hatching date. This experiment allocated hatchlings randomly among rearing environments. Forty-nine days later, we collected three feathers per individual to measure UV reflectance. Conclusions: The cross-fostering experiment showed that. independently of human-visible coloration, variation in UV reflectance is significantly sensitive to origin-related factors.

Strength and cost of an induced immune response are associated with a heritable melanin-based colour trait in female tawny owls.

1. Melanin pigments provide the most widespread source of coloration in vertebrates, but the adaptive function of such traits remains poorly known. 2. In a wild population of tawny owls (Strix aluco), we investigated the relationships between plumage coloration, which varies continuously from dark to pale reddish, and the strength and cost of an induced immune response. 3. The degree of reddishness in tawny owl feather colour was positively correlated with the concentration of phaeomelanin and eumelanin pigments, and plumage coloration was highly heritable (h(2) = 0.93). No carotenoids were detected in the feathers. 4. In mothers, the degree of melanin-based coloration was associated with antibody production against a vaccine, with dark reddish females maintaining a stronger level of antibody for a longer period of time compared to pale reddish females, but at a cost in terms of greater loss of body mass. 5. A cross-fostering experiment showed that, independent of maternal coloration, foster chicks reared by vaccinated mothers were lighter than those reared by nonvaccinated mothers. Hence, even though dark reddish mothers suffered a stronger immune cost than pale reddish mothers, this asymmetric cost was not translated to offspring growth. 6. Our study suggests that different heritable melanin-based colorations are associated with alternative strategies to resist parasite attacks, with dark reddish individuals investing more resources towards the humoral immune response than lightly reddish conspecifics.

Phenotypic plasticity in salmonid embryos : characterizing pathogen-induced stress effects on heritable variation in traits and reaction norms

Les pressions ��cologiques peuvent varier tant en nature qu'en intensit�� dans le temps et l'espace. C'est pourquoi, un ph��notype unique ne peut pas forc��ment conf��rer la meilleure valeur s��lective. La plasticit�� ph��notypique peut ��tre un moyen de s'accommoder de cette situation, en augmentant globalement la tol��rance aux changements environnementaux. Comme pour tout trait de caract��re, une variation g��n��tique doit persister pour qu'��voluent les traits plastiques dans une population donn��e. Cependant, les pressions ext��rieures peuvent affecter l'h��ritabilit��, et la direction de ces changements peut d��pendre du caract��re en question, de l'esp��ce mais aussi du type de stress. Dans la pr��sente th��se, nous avons cherch�� �� ��lucider les effets des pressions pathog��niques sur les ph��notypes et la g��n��tique quantitative de plusieurs traits plastiques chez les embryons de deux salmonid��s, la pal��e (Coregonus palaea), et la truite de rivi��re (Salmo trutta). Les salmonid��s se pr��tent �� de telles ��tudes du fait de leur extraordinaire variabilit�� morphologique, comportementale et des traits d'histoire de vie. Par ailleurs, avec le d��clin des salmonid��s dans le monde, il est important de savoir combien la variabilit�� g��n��tique persiste dans les normes de r��action afin d'aider �� pr��dire leur capacit�� �� r��pondre aux changements de leur milieu. Nous avons observ�� qu'une augmentation de la croissance des communaut��s microbiennes symbiotiques entra��nait une mortalit�� accrue et une ��closion pr��coce chez la pal��e, et d��voilait la variance g��n��tique additive pour ces deux caract��res (Chapitres 1-2). Bien qu'aucune variation g��n��tique n'ait ��t�� trouv��e pour les normes de r��action, nous avons observ�� une variabilit�� de la plasticit�� d'��closion. N��anmoins, on a trouv�� que les temps d'��closion ��taient corr��l��s entre les environnements, ce qui pourrait limiter l'��volution de la norme de r��action. Le temps d'��closion des embryons est li�� �� la taille des g��niteurs m��les, ce qui indique des effets pl��iotropiques. Dans le Chapitre 3, nous avons montr�� qu'une interaction triple entre la souche bact��rienne {Pseudomonas fluorescens}, l'��tat de d��velopement de l'h��te ainsi que ses g��nes ont une influence sur la mortalit��, le temps d'��closion et la taille des alevins de la pal��e. Nous avons d��montr�� qu'une variation g��n��tique subsistait g��n��ralement dans les normes de r��action des temps d'��closion, mais rarement pour la taille des alevins, et jamais pour la mortalit��. Dans le m��me temps, nous avons exhib�� que des corr��lations entre environnements d��pendaient des caract��res ph��notypiques, mais contrairement au Chapitre 2, nous n'avons pas trouv�� de preuve de corr��lations transg��n��rationnelles. Le Chapitre 4 compl��te le chapitre pr��c��dent, en se pla��ant du point de vue mol��culaire, et d��crit comment le traitement d'embryons avec P. fluorescens s'est traduit par une r��gulation n��gative d'expression du CMH-I ind��pendemment de la souche bact��rienne. Nous avons non seulement trouv�� une variation g��n��tique des caract��res ph��notypiques moyens, mais aussi de la plasticit��. Les deux derniers chapitres traitent de l'investigation, chez la truite de rivi��re, des diff��rences sp��cifiques entre populations pour des normes de r��action induites par les pathog��nes. Dans le Chapitre 5, nous avons illustr�� que le m��tissage entre des populations g��n��tiquement distinctes n'affectait en rien la hauteur ou la forme des normes de r��action d'un trait pr��coce d'histoire de vie suite au traitement pathog��nique. De surcro��t, en d��pit de l'��closion tardive et de la r��duction de la taille des alevins, le traitement n'a pas modifi�� la variation h��ritable des traits de caract��re. D'autre part, dans le Chapitre 6, nous avons d��montr�� que le traitement d'embryons avec des stimuli contenus dans l'eau de consp��cifiques infect��s a entra��n�� des r��ponses propre �� chaque population en terme de temps d'��closion ; n��anmoins, nous avons observ�� peu de variabilit�� g��n��tique des normes de r��action pour ce temps d'��closion au sein des populations. - Ecological stressors can vary in type and intensity over space and time, and as such, a single phenotype may not confer the highest fitness. Phenotypic plasticity can act as a means to accommodate this situation, increasing overall tolerance to environmental change. As with any trait, for plastic traits to evolve in a population, genetic variation must persist. However, environmental stress can alter trait heritability, and the direction of this shift can be trait, species, and stressor-dependent. In this thesis, we sought to understand the effects of pathogen stressors on the phenotypes and genetic architecture of several plastic traits in the embryos of two salmonids, the whitefish (Coregonus palaea), and the brown trout (Salmo trutta). Salmonids lend themselves to such studies because their extraordinary variability in morphological, behavioral, and life-history traits. Also, with declines in salmonids worldwide, knowing how much genetic variability persists in reaction norms may help predict their ability to respond to environmental change. We found that increasing growth of symbiotic microbial communities increased mortality and induced hatching in whitefish, and released additive genetic variance for both traits (Chapters 1-2). While no genetic variation was found for survival reaction norms, we did find variability in hatching plasticity. Nevertheless, hatching time was correlated across environments, which could constrain evolution of the reaction norm. Hatching time in the induced environment was also correlated to sire size, indicating pleiotropic effects. In Chapter 3 we report that a three-way interaction between bacterial strain (Pseudomonas fluorescens), host developmental stage, and host genetics impacted mortality, hatching time, and hatchling size in whitefish. We also showed that genetic variation generally persisted in hatching age reaction norms, but rarely for hatchling length, and never for mortality. At the same time, we demonstrated that cross-environmental correlations were trait-dependent, and unlike Chapter 2, we found no evidence of cross-generational correlations. Chapter 4 expands on the previous chapter, moving to the molecular level, and describes how treatment of embryos with P. fluorescens resulted in strain-independent downregulation of MHC class I. Genetic variation was evident not only in trait means, but also in plasticity. In the last two chapters, we investigated population level differences in pathogen- induced reaction norms in brown trout. In Chapter 5, we found that interbreeding between genetically distinct populations did not affect the elevation or shapes of the reaction norms of early life-history traits after pathogen challenge. Moreover, despite delaying hatching and reducing larval length, treatment produced no discernable shifts in heritable variation in traits. On the other hand, in Chapter 6, we found that treatment of embryos with water-borne cues from infected conspecifics elicited population-specific responses in terms of hatching time; however, we found little evidence of genetic variability in hatching reaction norms within populations. We have made considerable progress in understanding how pathogen stressors affect various early life-history traits in salmonid embryos. We have demonstrated that the effect of a particular stressor on heritable variation in these traits can vary according to the trait and species under consideration, in addition to the developmental stage of the host. Moreover, we found evidence of genetic variability in some, but not all reaction norms in whitefish and brown trout.

Trait�� d'analyse chimique quantitative ... /

��ndice.

Trait�� d'analyse chimique quantitative ou trait�� du dosage et de la s��paration des corps simples et compos��s les plus usit��s en pharmacie, dans les arts et en agriculture /

��ndice.

Power of the joint segregation analysis method for testing mixed major-gene and polygene inheritance models of quantitative traits

Understanding the genetic architecture of quantitative traits can greatly assist the design of strategies for their manipulation in plant-breeding programs. For a number of traits, genetic variation can be the result of segregation of a few major genes and many polygenes (minor genes). The joint segregation analysis (JSA) is a maximum-likelihood approach for fitting segregation models through the simultaneous use of phenotypic information from multiple generations. Our objective in this paper was to use computer simulation to quantify the power of the JSA method for testing the mixed-inheritance model for quantitative traits when it was applied to the six basic generations: both parents (P-1 and P-2), F-1, F-2, and both backcross generations (B-1 and B-2) derived from crossing the F-1 to each parent. A total of 1968 genetic model-experiment scenarios were considered in the simulation study to quantify the power of the method. Factors that interacted to influence the power of the JSA method to correctly detect genetic models were: (1) whether there were one or two major genes in combination with polygenes, (2) the heritability of the major genes and polygenes, (3) the level of dispersion of the major genes and polygenes between the two parents, and (4) the number of individuals examined in each generation (population size). The greatest levels of power were observed for the genetic models defined with simple inheritance; e.g., the power was greater than 90% for the one major gene model, regardless of the population size and major-gene heritability. Lower levels of power were observed for the genetic models with complex inheritance (major genes and polygenes), low heritability, small population sizes and a large dispersion of favourable genes among the two parents; e.g., the power was less than 5% for the two major-gene model with a heritability value of 0.3 and population sizes of 100 individuals. The JSA methodology was then applied to a previously studied sorghum data-set to investigate the genetic control of the putative drought resistance-trait osmotic adjustment in three crosses. The previous study concluded that there were two major genes segregating for osmotic adjustment in the three crosses. Application of the JSA method resulted in a change in the proposed genetic model. The presence of the two major genes was confirmed with the addition of an unspecified number of polygenes.

Signal trait sexual dimorphism and mutual sexual selection in Drosophila serrata

The evolution of sexual dimorphism may occur when natural and sexual selection result in different optimum trait values for males and females. Perhaps the most prominent examples of sexual dimorphism occur in sexually selected traits, for which males usually display exaggerated trait levels, while females may show reduced expression of the trait. In some species, females also exhibit secondary sexual traits that may either be a consequence of a correlated response to sexual selection on males or direct sexual selection for female secondary sexual traits. In this experiment, we simultaneously measure the intersex genetic correlations and the relative strength of sexual selection on males and females for a set of cuticular hydrocarbons in Drosophila serrata. There was significant directional sexual selection on both male and female cuticular hydrocarbons: the strength of sexual selection did not differ among the sexes but males and females preferred different cuticular hydrocarbons. In contrast with many previous studies of sexual dimorphism, intersex genetic correlations were low. The evolution of sexual dimorphism in D. serrata appears to have been achieved by sex-limited expression of traits controlled by genes on the X chromosome and is likely to be in its final stages.

Quantitative genetic modeling and inference in the presence of nonignorable missing data.

Natural selection is typically exerted at some specific life stages. If natural selection takes place before a trait can be measured, using conventional models can cause wrong inference about population parameters. When the missing data process relates to the trait of interest, a valid inference requires explicit modeling of the missing process. We propose a joint modeling approach, a shared parameter model, to account for nonrandom missing data. It consists of an animal model for the phenotypic data and a logistic model for the missing process, linked by the additive genetic effects. A Bayesian approach is taken and inference is made using integrated nested Laplace approximations. From a simulation study we find that wrongly assuming that missing data are missing at random can result in severely biased estimates of additive genetic variance. Using real data from a wild population of Swiss barn owls Tyto alba, our model indicates that the missing individuals would display large black spots; and we conclude that genes affecting this trait are already under selection before it is expressed. Our model is a tool to correctly estimate the magnitude of both natural selection and additive genetic variance.

Population differentiation and its consequences in the white campion "Silene latifolia" (Caryophyllaceae): a functional analysis

Summary In his theory On the Origin of Species by Means of Natural Selection (1859), Darwin describes evolution as a gradual change in population over time and that natural selection is a process that caused evolution. Because quantitative variation in species is partly influenced by several genes and thus heritable, association between levels of genetic variation at neutral markers and at quantitative traits and their partitioning within and among populations are important to study mechanisms that drive evolution in populations. Most studies addressing quantitative variation in plants focused on morphological and life history traits but not in traits affecting reproductive success. The aim of this thesis is to better understand how patterns of variation for neutral molecular markers and phenotypic traits drive the evolution of reproduction and defensive mechanisms in six European populations of Silene latifolia, a dioecious plant species. We found evidence for extremely high within and between population variation at six microsatellite loci and at most quantitative traits studied in plants grown under standardized conditions (morphology, life history and reproductive traits). Interestingly, there was clinal variation between age at first flowering and latitude. This pattern is likely due to natural selection since differentiation of this trait was high, heritable and probably higher than differentiation at neutral markers. Our study focused on sex specific selective pressures: mechanisms of intersexual coadaptation and defence mechanism against the seed predator Hadena bicruris. To address divergence at reproductive traits, we studied male and female population of origin effects and in particular pollen competitive ability on male post-pollination success in the study populations with within and between populations crosses. We crossed the same female plant with pollen from a male within the same population of origin and pollen from two males from two distinct populations, using a fixed tester male as a competitor. Additionally, we conducted control crosses with pollen from each male as a single donor. We analysed paternity success of each competitor with two microsatellite loci, seed set and offspring fitness. Male population of origin showed significant among-population variation for siring success at pollen competition. In vitro pollen germination rate showed heritable variation among populations and was positively correlated to siring success. Local or foreign pollen did not have a consistent advantage. Furthermore, female population of origin affected the outcome of pollen competition in some populations. There was no difference of seed set or offspring fitness in within/ between population crosses. This suggests that reproductive divergence may occur via pollen competition in Silene latifolia. The specialist seed predator Hadena bicruris may also induce divergence between populations. We tested potential constitutive and induced defence mechanisms against the specialist predator Hadena bicruris. Because fruit wall thickness is smaller in the invasive range (Northern America) were the moth is absent, this suggests that a thicker fruit wall is a potentially defensive trait against larval attack, and that relaxed selection in the absence of the seed predator has resulted in an evolutionary loss of this defence in the invasive range. Fruit wall thickness was different among three populations. Experimental exposure to moth eggs increased fruit abortion. Fruits built after attack on exposed plants did not have thicker fruit walls compared to fruits on non-exposed plants. Furthermore, fruits with thicker fruit walls were not less profitable, nor did they require longer handling time when exposed to larvae, suggesting no defensive role of fruit wall thickness. Our results show that there is high molecular and phenotypic variation in Silene latifolia and that traits potentially involved in reproductive success both for intra-specific (between sexes) and inter-specific interactions are heritable. Different selective forces may thus interact and cause differential evolution of geographically separated Silene latifolia populations in Europe, leading to the observed differentiation. R��sum�� Dans sa th��orie de l'��volution, L'origine des esp��ces, ch. 4 (1859), Darwin d��crit l'��volution comme un processus continu au cours du temps �� l'int��rieur de populations et que la s��lection naturelle en est le moteur. La variation quantitative est en partie d��termin��e par plusieurs g��nes, donc transmissible �� la descendance. Associer le niveau de variation g��n��tique �� des marqueurs neutres au niveau de la variation �� des traits quantitatifs, ainsi que la r��partition �� l'int��rieur et entre les populations d'une esp��ce donn��e de cette variation, sont importants dans la compr��hension des forces ��volutives. La plupart des ��tudes scientifiques sur la variation quantitative chez les plantes se sont int��ress��es �� la morphologie et �� la ph��nologie mais pas aux caract��res impliqu��s dans le succ��s reproducteur. L'objectif de cette th��se est de mieux comprendre comment la r��partition de la variation �� des marqueurs neutres et des caract��res quantitatifs influence l'��volution de la reproduction et des m��canismes de d��fense dans six populations Europ��ennes de l'esp��ce dio��que Silene latifolia. Nous avons mis en ��vidence une grande diversit�� intra et inter-population �� six loci microsatellites ainsi qu'�� la plupart des caract��res quantitatifs mesur��s (morphologie, ph��nologie et traits reproducteurs) sur des plantes cultiv��es dans des conditions standardis��es. Un r��sultat int��ressant est la pr��sence d'un cline latitudinal pour l'��ge �� la floraison. Ceci est probablement une cons��quence de la s��lection naturelle, puisque ce caract��re est diff��renci�� entre les populations ��tudi��es, h��ritable et que la diff��renciation de ce trait est sup��rieure �� la diff��renciation des marqueurs neutres ��tudi��s. Notre ��tude a ensuite port�� plus pr��cis��ment sur les pressions de s��lection sp��cifiques aux sexes : la coadaptation entre les sexes et les m��canismes de d��fense contre l'insecte granivore Hadena bicruris. Afin d'��valuer la divergence sur les traits reproducteurs, nous avons ��tudi�� les effets des populations d'origine des m��les et des femelles et en particulier le succ��s reproducteur des m��les apr��s pollinisation �� l'aide de croisements inter et intra-population. Nous avons pollinis�� la m��me femelle avec du pollen provenant d'un m��le de la m��me population ainsi qu'avec le pollen de deux m��les provenant de deux autres populations en situation de comp��tition avec un pollen provenant d'une population test. Des croisements contr��le ont ��t�� r��alis��s avec les m��mes m��les en pollinisation pure. Nous avons ��valu�� le succ��s reproducteur de chaque m��le �� l'aide d'analyses de paternit�� ainsi que la production de graines et la fitness de la descendance. L'origine du m��le avait un effet sur la paternit��. Le taux de croissance in vitro du pollen est un caract��re h��ritable et a eu un effet positif sur le succ��s reproducteur. De plus, l'origine de la femelle avait un effet sur le succ��s des m��les en comp��tition dans certaines populations. Nos r��sultats sugg��rent qu'une divergence reproductive chez Silene latifolia pourrait appara��tre suite �� la comp��tition pollinique. Nous avons ensuite test�� des m��canismes potentiels de d��fense constitutive et induite contre l'herbivore sp��cialiste Hadena bicruris, un papillon nocturne qui pourrait aussi jouer un r��le dans la diff��renciation des populations. L'��paisseur des fruits ��tant plus faible dans les r��gions o�� la plante est invasive (Am��rique du Nord) et o�� l'insecte est absent, ce trait pourrait jouer un r��le d��fensif. Une pression de s��lection plus faible caus��e par l'absence de l'herbivore aurait abouti �� une perte de cette d��fense dans ces r��gions. Nous avons montr�� que l'��paisseur du fruit est variable selon les populations. L'infestation artificielle de fruit par l'insecte induit l'abscission s��lective des fruits. Les fruits produits apr��s une infestation n'��taient pas plus ��pais que les fruits issus de plantes non infest��es. De plus, les fruits ��pais n'��taient pas moins nutritifs et ne causaient pas de perte de temps pour la pr��dation pour les larves, ce qui sugg��re que l'��paisseur des fruits ne joue pas un r��le d��fensif. Nos r��sultats montrent que plusieurs pressions de s��lection interviennent et interagissent dans l'��volution de populations distantes, provoquant la divergence des populations Europ��ennes de l'esp��ce Silene latifolia.

Temperature-dependent turnovers in sex-determination mechanisms: a quantitative model.

Sex determination is often seen as a dichotomous process: individual sex is assumed to be determined either by genetic (genotypic sex determination, GSD) or by environmental factors (environmental sex determination, ESD), most often temperature (temperature sex determination, TSD). We endorse an alternative view, which sees GSD and TSD as the ends of a continuum. Both effects interact a priori, because temperature can affect gene expression at any step along the sex-determination cascade. We propose to define sex-determination systems at the population- (rather than individual) level, via the proportion of variance in phenotypic sex stemming from genetic versus environmental factors, and we formalize this concept in a quantitative-genetics framework. Sex is seen as a threshold trait underlain by a liability factor, and reaction norms allow modeling interactions between genotypic and temperature effects (seen as the necessary consequences of thermodynamic constraints on the underlying physiological processes). As this formalization shows, temperature changes (due to e.g., climatic changes or range expansions) are expected to provoke turnovers in sex-determination mechanisms, by inducing large-scale sex reversal and thereby sex-ratio selection for alternative sex-determining genes. The frequency of turnovers and prevalence of homomorphic sex chromosomes in cold-blooded vertebrates might thus directly relate to the temperature dependence in sex-determination mechanisms.

Quantitative genetics of learning ability and resistance to stress in Drosophila melanogaster.

Even though laboratory evolution experiments have demonstrated genetic variation for learning ability, we know little about the underlying genetic architecture and genetic relationships with other ecologically relevant traits. With a full diallel cross among twelve inbred lines of Drosophila melanogaster originating from a natural population (0.75��< F��<��0.93), we investigated the genetic architecture of olfactory learning ability and compared it to that for another behavioral trait (unconditional preference for odors), as well as three traits quantifying the ability to deal with environmental challenges: egg-to-adult survival and developmental rate on a low-quality food, and resistance to a bacterial pathogen. Substantial additive genetic variation was detected for each trait, highlighting their potential to evolve. Genetic effects contributed more than nongenetic parental effects to variation in traits measured at the adult stage: learning, odorant perception, and resistance to infection. In contrast, the two traits quantifying larval tolerance to low-quality food were more strongly affected by parental effects. We found no evidence for genetic correlations between traits, suggesting that these traits could evolve at least to some degree independently of one another. Finally, inbreeding adversely affected all traits.

Aspects de la syntaxe, de la semantique et de la morphologie des verbes a trait de /complexite/

Cette dissertation porte sur l���analyse syntactico-s��mantique des verbes �� trait de complexit��. Le trait de complexit�� (Blanche-Benveniste et al. 1984) r��unit une classe de verbes connue comme verbes ���sym��triques���, ���r��ciproques��� ou ���collectifs��� sans toutefois se limiter �� ces ensembles (cf. grouiller, collectionner, amonceler, scinder, etc.). Ce trait induit une lecture ���plurielle��� �� l���entit�� form��e du lex��me verbal et de ses arguments et qui se traduit, sur le plan morphosyntaxique, par deux propri��t��s: s��lection obligatoire d���une position syntaxique (sujet ou objet) au pluriel; en absence de ce pluriel morphologique, le trait de complexit�� se r��alise par la s��lection d���un compl��ment pr��positionnel correli�� �� une position syntaxique (sujet ou objet) et l���interpr��tation de ���pluriel��� des deux ��l��ments correli��s. L���hypoth��se g��n��rale, et point de d��part de cette dissertation, consiste �� pr��ciser l���interpr��tation de ���pluralit�� inh��rente��� des verbes �� trait de complexit�� comme ��tant de type ���collectif���, d��fini comme d��signant du ���plus d���un en un��� (Jespersen, 1971). La notion de ���collectif��� est �� distinguer de la notion de ���pluriel��� (Gillon, 1992) et permet d���expliquer le lien entre les deux propri��t��s morphosyntaxiques pr��sent��es. Cette hypoth��se g��n��rale s���appuie sur la s��lection d���un ensemble d���outils d���analyse. Un premier outil vise �� rendre compte, du point de vue formel, des r��seaux syntactico-s��mantiques, par une repr��sentation abstraite de la syntaxe verbale, con��ue comme une ���syntaxe de position��� et o�� sont d��limit��es, autour du noyau verbal, deux zones syntaxiques (zone SUJET et zone OBJET) constitu��es de points d���ancrage du trait de complexit��. En tenant compte de la sp��cificit�� du ���collectif��� par rapport �� la ���pluralit�����, le recours au concept d���op��rateurs de complexit��, entendus comme des op��rateurs du trait [+discret] (Doetjes, 1999), permet de mieux d��finir la notion du ���collectif��� appliqu��e au domaine verbal. Les diff��rents op��rateurs ��� affixes d��rivationnels, constructions pr��positionnelles, constructions en SE - se situent �� diff��rents niveaux de structuration. L���analyse par ���op��rateurs de complexit����� ([+discret]) pr��suppose ��galement la prise en compte de la fonction quantitative. Dans cette perspective, ces op��rateurs induisent diff��rents degr��s de l���individuation��� des constituants du ���collectif��� d��not�� par la s��mantique des verbes �� trait de complexit��. Les ��chelles de gradation de [+discret] rendent compte de cette propri��t��. Les valeurs de ���plus d���un��� et ���en un��� d��not��es par les expressions verbales �� trait de complexit�� sont interpr��t��es comme faisant partie d���une structure conceptuelle de type ���tout-int��gr����� d���apr��s l���approche lexicale et multidimensionnelle de la s��mantique conceptuelle des relations parties/tout de Moltmann (1997).

Quantitative genetic study of age at subsequent rebreeding in Nellore cattle by using survival analysis

The continuous trait age at subsequent rebreeding (ASR) was evaluated using survival analysis in Nellore breed cows that conceived for the first time at approximately 14 months of age. This methodology was chosen because the restricted breeding season produces censored data. The dataset contained 2885 records of ASR (in days). Records of females that did not produce calves in the following year after being exposed to a sire were considered censored (48.3% of the total). The statistical model used was a Weibull mixed survival model, which included fixed effects of contemporary groups (CG) and period and a random effect of individual animal. The effect of contemporary groups on ASR was significant (P < 0.01). Heritabilities obtained for ASR were 0.03 and 0.04 in logarithmic and original scales, respectively. These results indicate that the genetic selection response for subsequent reproduction of 2-year-old Nellore breed females is not expected to be effective based on survival analysis. Furthermore, these results suggest that environmental improvement is fundamental to this important trait. It should be highlighted that an increase in the average date of birth can produce an adverse effect in the future, since this cannot be compensated by genetic improvement.