A fundamental goal in biological research is to gain an understanding of the evolutionary processes and genetic elements that drive speciation. Genes responsible for reproductive isolation in young divergent lineages are particularly poorly known. In this thesis, the speciation genetics of carrion (Corvus (corone) corone) and hooded (C. (corone) cornix) crows were studied. These taxa differ strikingly in colouration and meet in a narrow hybrid zone in Europe, yet appear to be very similar genetically. A major component of reproductive isolation is social selection on colour differences. First, we investigated the genetic basis of plumage divergence between carrion and hooded crows using a candidate gene approach. Nucleotide divergence was confirmed to be low, while there was no evidence for any of the sequenced genes to be associated with colour differences. Second, we performed a simulation study to assess the performance of RNA-seq, a relatively novel approach that we later employed ourselves. We asked how variation in transcriptome complexity and bioinformatic workflow affected the accuracy of gene expression profiling. We generally found reassuring robustness and made a number of specific recommendations. Third, we compared the corticosterone stress response of carrion and hooded crows. In accordance with the hypothesis that the degree of melanization and physiological traits are correlated due to pleiotropy, we found a higher stress response in hooded crows, and detected possibly associated gene expression in pituitary. Fourth, we investigated genomic divergence by assembling a hooded crow reference genome followed by whole-genome resequencing of four European population samples. Northern European carrion crows were more similar to hooded crows than to Spanish carrion crows, pointing towards rampant introgression far beyond the hybrid zone. Nevertheless, several narrow genomic regions harboured high between-taxon divergence and were potentially associated with phenotypic traits. Fifth, we compared whole-transcriptome gene expression profiles between crows, focusing on skin with developing feathers. We used a design that allowed to differentiate between taxon-specific, colour-specific and body patterning effects. Widespread underexpression of genes in the melanogenesis pathway was associated with grey colour, and we detected several genes that may contribute to colour divergence in this system.

Si la sélection sexuelle proposée par Darwin fournit un cadre théorique satisfaisant pour expliquer l'évolution et le maintien des ornements sexuellement dimorphiques, le cas de l'ornementation mutuelle requiert l'emploi du cadre plus large offert par la sélection sociale. Dans de nombreux cas en effet, l'explication du maintien de l'ornementation mutuelle nécessite de considérer non seulement la compétition pour l'accès au partenaire de reproduction, mais également la compétition pour l'accès à d'autres types de ressources telles que la nourriture ou les emplacements pour nicher. Cependant, le maintien de l'ornementation mutuelle n'est encore que partiellement compris chez les oiseaux marins. Les travaux réalisés au cours de cette thèse s'inscrivent dans la continuité des recherches initiées depuis quelques années dans le but de comprendre le maintien de l'ornementation mutuelle chez le manchot royal, un oiseau exprimant un patch orange présentant un pic de réflectance ultraviolet de chaque côté de la mandibule, des patches auriculaires jaunes de chaque côté de la tête et un patch formant un dégradé allant du marron au jaune pâle sur le poitrail. Les travaux présentés dans ce manuscrit de thèse portent (i) sur les combats entre individus du même sexe pour accéder à un partenaire de reproduction, (ii) sur le rôle des ornements colorés dans le processus d'appariement, (iii) sur l'association entre le degré de développement des ornements et la position du territoire occupé au sein de la colonie, et enfin (iv) sur l'existence de variations interannuelles concernant le degré de coloration des ornements et le processus de choix de partenaire. Les résultats révèlent que : (i) les affrontements pour l'accès au partenaire sont beaucoup plus fréquents chez les mâles que chez les femelles ; (ii) l'ornementation mutuelle du bec pourrait être maintenu pas le processus de choix mutuel ; (iii) les individus occupant les territoires les plus centraux de la colonie expriment des patches auriculaires plus large et un patch de poitrine plus coloré ; (iv) les ornements présentent des variations notables entre deux années, tout comme le processus de choix de partenaire. Pris dans leur ensemble, ces résultats révèlent que le maintien de l'ornementation mutuelle du manchot royal est multifactoriel, et des pistes de recherches sont proposées pour affiner notre compréhension de ce phénomène complexe. / Darwin devised sexual selection theory in order to explain the evolution and maintenance of secondary sexual traits. In mutually ornamented species, however, the broader theoretical framework of social selection is needed. In many cases indeed, understanding the maintenance of mutual ornamentation requires to take into account competition for both sexual (i.e. mates) and non-sexual resources (e.g. food, nest sites). How mutual ornaments maintain and evolve is actually not well understood in seabirds species. The aim of the research program within which this Ph.D. thesis took place was to understand the maintenance of mutual ornamentation in king penguin, a bird exhibiting a ultraviolet and orange beak spot on each side of the mandible, two yellow auricular patches, and a patch on the breast that grade from brown to bright yellow. We studied (i) same-sex fight over mates; (ii) mate choice for color ornaments; (iii) the relationships between conspicuousness of ornaments and position of the territory within the colony; and finally (iv) the existence of inter-annual variations in color ornaments expression and mate choice process. Our results show that: (i) same-sex fights over mates are highly male-biased; (ii) color of the beak spots may be involved in mutual mate choice; (iii) central individuals exhibit larger auricular patches and more colorful breast patch; (iv) ornament conspicuousness as well as mate choice show inter-annual changes. Taken together, these results reveal that maintenance of king penguin mutual ornaments is multifactorial, and some research avenues are suggested for future researches.

Social behaviour is shaped by complex relationships between evolutionary and ecological processes interacting at different scales. Benefits gained from social associations can range from predator dilution to collective sensing, but little is known about how these can be influenced by social structure and phenotypic composition. In this thesis, I investigated how individual decision-making affects phenotypic social structure, and how this mediates social behaviour through emergent properties of collective group behaviour. First, using mixed-species flocks as a model system, I showed individual tits (Paridae, chapter 2) and thornbills (Acanthizae, chapter 3) varied significantly in their social positions. Within-species variation in network position was as large as between-species variation, sug- gesting that prescribing functional roles at the species level may not sufficiently account for potential differences in fitness operating at the individual level. Rather, this suggested that structure may be driven by phenotypic traits, underpinning network structure (chapter 4). Next, I used an extensive data set of foraging records to explore factors determining the composition, of flocks of great tits (Parus major, chapter 5). For example, assortment by dispersal phenotype (immigration status) was the result of spatial disaggregation, and I showed that this may facilitate social selection for breeding territories (chapter 6). Finally, I investigated how decision-making shaped mixed-species social structure. I found that tits used a common strategy for managing pressures of predation and starvation by shifting from exploration to exploitation at different times of the day (chapter 7). I then found that a very simple interaction rule successfully replicated mixed-species group structure (chapter 8). Strikingly, the same rule was applied to both conspecifics and het- erospecifics, potentially playing an important role in the maintenance of flock structure. Through experimental manipulation of ecological conditions, I found that heightened per- ceived predation resulted in stronger social attraction overall, whereas increased competition led to a reduction in attraction to conspecifics (chapter 9). Simulations suggested this could be one potential mechanism underpinning fission-fusion dynamics in these species. Together, the results in this thesis form a framework linking social behaviour to individ- ual fitness where natural selection is shaped by the social environment. This approach may prove useful for testing whether following common social rules reduces variance in benefits accrued by individuals, and how within-species variation in social behaviour can impact emergent properties of groups.

Depuis 157 ans et la publication originelle de la théorie de l’évolution par sélection naturelle de Charles Darwin, ce concept n’a cessé d’évoluer. Un principe fondamental suggère que des traits handicapants aient évolués dans la mesure où ils informent de manière honnête les congénères sur la qualité intrinsèque du porteur. Le manchot royal est un modèle exceptionnel permettant de tester la valeur sélective de ce signal dans un contexte sexuel et social (non-reproductif). Mes résultats suggèrent que l’apparition et le maintien de certains de ces traits au cours de l’évolution se sont opérés sous l’influence de la sélection sexuelle et d’un choix mutuel du partenaire, tandis que d’autre, non contraint par la condition fluctuante de l’individu, aurait évolué sous l’influence de la sélection sociale. Ce travail de recherche participe à la compréhension des mécanismes impliqués dans l’évolution de signaux coûteux, et à la nature des bénéfices ultimes que ces traits procurent. / Darwin’s seminal theory of evolution by means of natural selection, first published 157 years ago, has been in constant refinement ever since. The production and maintenance of extravagant ornaments is widely suggested to evolve by conspecific preference providing information on individual intrinsic quality in sexual contexts or on individual social quality in non-reproductive contexts. The king penguin is a monomorphic bird species and an outstanding model to study ornament evolution. My results show that those ornaments are partly condition-dependent, and reliable traits that may be used to assess the quality of a potential sexual partner, implying that their evolution and maintenance is partly determined by sexual selection. On the other hand, some traits remained condition-independent in their production, suggesting that the cost associated with their expression was deferred over time and the evolution of those ornaments likely shaped by non-sexual social selection.

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Problématique : L’exposition à l’adversité socioéconomique pendant les premières années de vie peut avoir des conséquences à long terme sur la santé physique et mentale de l’enfant. La fréquentation des services d’éducation préscolaire (SEP) a été proposée comme un moyen de promouvoir le développement des enfants de familles plus défavorisées permettant ainsi de contrecarrer les conséquences négatives associées aux contextes de vie adverses auxquels ils sont exposés. Les SEP sont désormais accessibles à la population et largement utilisés par les parents pour leurs enfants d’âge préscolaire. Cependant, des processus de sélection sociale font en sorte que les enfants plus défavorisés sont moins nombreux à fréquenter les SEP. De plus, bien que les SEP soient généralement des milieux de vie cognitivement et socialement stimulants, il existe des variations importantes dans la qualité de ces services. De surcroît, ces milieux sont propices à des situations pouvant susciter du stress et l’expression de comportements perturbateurs. Objectifs : L’objectif principal de cette thèse est d’examiner les associations entre l’adversité socioéconomique, la fréquentation des SEP et le développement de l’enfant selon une approche des parcours de vie, en prêtant une attention particulière aux effets de sélection sociale connus pour être présents dans les SEP. Quatre articles composent cette thèse. Les deux premiers articles examinent l’effet d’un programme d’entraînement aux habiletés sociales implanté dans des SEP de quartiers défavorisés sur la fréquence des comportements perturbateurs et les indicateurs neurophysiologiques du stress vécu par les enfants. De plus, nous avons investigué si l’adversité socioéconomique de la famille modifiait la magnitude des impacts attendus du programme. Dans le troisième article, nous examinons le rôle de la fréquentation des SEP dans la relation entre l’exposition à l’adversité au début de la vie, les habiletés cognitives de l’enfant et l’expression de comportements perturbateurs à l’adolescence. Avec le quatrième article de la thèse, nous étudions l’association entre la fréquentation des SEP et le taux de diplomation de l’école secondaire, et nous examinons si cette association est magnifiée auprès des enfants issus de mères avec un plus faible niveau d’éducation. Nous réalisons également une analyse bénéfice-coût afin d’évaluer si la subvention publique des SEP est une solution économiquement rentable. Méthodes : Les données utilisées pour les deux premiers articles proviennent d’un essai randomisé en grappes où 19 SEP (n = 362 enfants) de quartiers économiquement défavorisés ont été randomisés à la condition expérimentale : recevoir un programme d’entraînement aux habiletés sociales, ou à la condition contrôle de type liste d’attente. Dans le projet « Brindami », les comportements perturbateurs ont été mesurés par le biais de questionnaires répondus par les éducatrices alors que le stress a été quantifié par la sécrétion cortisolaire diurne mesurée dans la salive. Ces mesures ont été effectuées à deux reprises, avant et après l’intervention. Afin d’étudier l’impact du programme, des analyses multiniveaux et à mesures répétées ont été utilisées. Les effets de sélection sociale ont été considérés par l’application de critères de sélection stricts en regard de la défavorisation des SEP. Les données des troisième et quatrième articles proviennent de l’Avon Longitudinal Study of Parents and Children (ALSPAC), où 14 451 familles ont été suivis de 1991-2020. La fréquentation des SEP et l’exposition à l’adversité socioéconomique ont été mesurées par questionnaire au cours des quatre premières années de vie de l’enfant. Les habiletés cognitives de l’enfant ont été mesurées lors d’une visite en laboratoire lorsque l’enfant était âgé de huit ans. Les comportements perturbateurs de l’enfant ont été évalués par la mère à trois reprises au cours de l’adolescence à l’aide d’un questionnaire validé. Les informations sur la diplomation de l’école obligatoire ont été obtenues grâce à l’établissement d’un lien entre la base administrative du National Pupil Database du Royaume-Uni et de l’étude ALSPAC. Des analyses de médiation modérées et des analyses de régression multinomiale ont été utilisées. Les effets de sélection ont été estimés et minimisés par le biais de l’utilisation de coefficients de propension. Résultats : Dans les deux premiers articles, nous avons montré que l’implantation d’un programme d’entraînement aux habiletés sociales était associée à 1) une diminution des comportements perturbateurs, mais seulement chez les filles, et 2) à des patrons de sécrétion cortisolaire diurnes plus normatifs, et ce, particulièrement chez les enfants de familles plus économiquement défavorisés. Les résultats issus du troisième article suggèrent que, pour les enfants exposés à de l’adversité socioéconomique, la fréquentation des SEP est associée à une diminution des comportements perturbateurs à l’adolescence via l’augmentation des habiletés cognitives de ces derniers à l’enfance. Enfin, le quatrième article présente une association entre la fréquentation des SEP et la diplomation scolaire pour les enfants de mères ayant un plus faible niveau d’éducation, et suggère que les politiques publiques visant à subventionner la fréquentation des SEP pour ces enfants sont des stratégies économiquement rentables. Implications : Cette thèse souligne l’importance de la fréquentation des SEP pour les enfants exposés à de l’adversité socioéconomique. Afin que les SEP deviennent une stratégie de réduction des iniquités de santé pour un plus grand nombre d’enfants, les futures initiatives de santé publique devront chercher à minimiser les effets de sélection sociale dans l’élaboration de leur politique. / Background: Early life adversity is associated with life-long consequences on children's physical and mental health. Early childhood education and care (ECEC) attendance has been proposed as a solution to promote the development of children from vulnerable families and thus diminishing the negative consequences associated with their early exposure to adversity. ECEC is widely available to the general population and used by working parents for their preschool children. However, because of social selection processes, vulnerable children are less likely to attend ECEC than their more advantaged counterparts. In addition, although ECEC is generally a cognitively and socially stimulating environment, there are significant variations in the quality of these services. Moreover, ECEC are conducive to situations that can be a stressful and associated with the expression of disruptive behaviors. Objectives: The main objective of this thesis is to examine the associations between exposure to socioeconomic adversity, ECEC attendance, and children development while using a life-course approach and paying particular attention to social selection processes into ECEC. This thesis is divided into four papers. The first two articles examine the impact of a social skills training program implemented in ECEC facilities of low-income neighborhoods on children's levels of disruptive behaviour and stress. In addition, these papers investigate the moderating role of family socioeconomic adversity on the impact of the program. The third paper examines the moderating effect of ECEC attendance on the association between exposure to early life adversity and disruptive behaviours during adolescence via children's cognitive abilities. The fourth paper investigates whether ECEC attendance is associated with higher rates of compulsory school graduation, and whether this association is stronger among children of mothers with lower levels of education. Finally, this paper provides a benefit-cost ratio analysis to assess whether subsidising ECEC is an economically viable option. Methods: The first two papers used data from the Brindami cluster randomized trial in which 19 ECEC facilities (n = 362 children) from low-income neighborhoods were randomized to the experimental condition: receiving a social skills training program, or to the waiting list control condition. Levels of disruptive behaviours and stress levels assess with salivary cortisol were measured at pre- and post-intervention. Multi-level analysis with repeated measures were used to study the impact of the program. Social selection effects were considered through the application of strict ECEC selection criteria. For the third and fourth thesis paper, data were drawn from the Avon Longitudinal Study of Parents and Children (ALSPAC) where 14,451 families were followed from 1991-2020. ECEC attendance and exposure to early life adversity were measured by questionnaires during the child's first four years of life. Children’s cognitive abilities were measured during a laboratory visit when the child was eight years old. Children’s disruptive behaviours were assessed by the mother on three occasions during adolescence using a validated questionnaire. Information on compulsory school graduation was obtained via a linkage between the United Kingdom National Pupil Database and the children from the ALSPAC study. Moderated mediation and multinomial regression analyses were used. Social selection effects were controlled through the use of propensity scores. Results: The first two papers showed that the implementation of a social skills training program was associated with 1) a decrease in disruptive behaviours, but only among girls, and 2) with more normative diurnal cortisol secretion patterns, particularly for children of economically disadvantaged families. The third paper suggests that for children exposed to early life adversity, ECEC attendance is associated with a decrease in disruptive behaviours during adolescence via an increase in children’s cognitive abilities. Finally, the fourth paper presents a significant association between ECEC attendance and school graduation for children of mothers with lower levels of education and suggests that subsidising ECEC for these children is a cost-effective measure. Implications: This thesis highlights the importance of ECEC attendance for children exposed to socioeconomic adversity. To achieve ECEC social equalizing effect, stakeholders need to consider social selection processes into ECEC in the elaboration of their policy.

This dissertation interrogates the deficit assumptions about English proficiency of skilled immigrants who were recruited by Canadian governments between the late 1990s and early 2000s. Through the lens of literacy as social practice, the eighteen-month ethnographic qualitative research explores the sequential experiences of settlement and economic integration of seven well-educated Chinese immigrant professionals. The analytical framework is built on sociocultural approaches to literacy and learning, as well as the theories of discourses and language reproduction. Using multiple data sources (observations, conversational interviews, journal and diary entries, photographs, documents, and artifacts collected in everyday lives), I document many different ways that well-educated Chinese immigrants take advantage of their language and literacy skills in English across several social domains of home, school, job market, and workplace. Examining the trans-contextual patterning of the participants’ language and literacy activities reveals that immigrant professionals use literacy as assistance in seeking, negotiating, and taking hold of resources and opportunities within certain social settings. However, my data show that their language and literacy engagements might not always generate positive consequences for social networks, job opportunities, and upward economic mobility. Close analyses of processes and outcomes of the participants’ engagements across these discursive discourses make it very clear that the monolithic assumptions of the dominant language shape and reinforce structural barriers by constraining their social participation, decision making, and learning practice, and thereby make literacy’s consequences unpredictable. The deficit model of language proficiency serves the grounds for linguistic stereotypes and economic marginalization, which produces profoundly consequential effects on immigrants’ pathways as they strive for having access to resources and opportunities in the new society. My analyses illuminate the ways that language and literacy create the complex web of discursive spaces wherein institutional agendas and personal desires are intertwined and collide in complex ways that constitute conditions and processes of social and economic mobility of immigrant populations. Based on these analyses, I argue that immigrants’ successful integration into a host country is not about the mastery of the technical skills in the dominant language. Rather, it is largely about the recognition and acceptance of the value of their language use and literacy practice as they attempt to partake in the globalized new economy.

This dissertation interrogates the deficit assumptions about English proficiency of skilled immigrants who were recruited by Canadian governments between the late 1990s and early 2000s. Through the lens of literacy as social practice, the eighteen-month ethnographic qualitative research explores the sequential experiences of settlement and economic integration of seven well-educated Chinese immigrant professionals. The analytical framework is built on sociocultural approaches to literacy and learning, as well as the theories of discourses and language reproduction. Using multiple data sources (observations, conversational interviews, journal and diary entries, photographs, documents, and artifacts collected in everyday lives), I document many different ways that well-educated Chinese immigrants take advantage of their language and literacy skills in English across several social domains of home, school, job market, and workplace. Examining the trans-contextual patterning of the participants’ language and literacy activities reveals that immigrant professionals use literacy as assistance in seeking, negotiating, and taking hold of resources and opportunities within certain social settings. However, my data show that their language and literacy engagements might not always generate positive consequences for social networks, job opportunities, and upward economic mobility. Close analyses of processes and outcomes of the participants’ engagements across these discursive discourses make it very clear that the monolithic assumptions of the dominant language shape and reinforce structural barriers by constraining their social participation, decision making, and learning practice, and thereby make literacy’s consequences unpredictable. The deficit model of language proficiency serves the grounds for linguistic stereotypes and economic marginalization, which produces profoundly consequential effects on immigrants’ pathways as they strive for having access to resources and opportunities in the new society. My analyses illuminate the ways that language and literacy create the complex web of discursive spaces wherein institutional agendas and personal desires are intertwined and collide in complex ways that constitute conditions and processes of social and economic mobility of immigrant populations. Based on these analyses, I argue that immigrants’ successful integration into a host country is not about the mastery of the technical skills in the dominant language. Rather, it is largely about the recognition and acceptance of the value of their language use and literacy practice as they attempt to partake in the globalized new economy.