The Trivers-Willard hypothesis (TWH) states that parents in good conditions will bias the sex ratio toward sons and parents in poor conditions will bias the sex ratio toward daughters. The present study contributes to literature in several ways: a large, general, country population data set (N= 1 401 851) from modern contemporary society; first study in the Czech Republic; an inclusion of air pollution into the TWH estimation; and a more detailed focus on stillbirths. With the natality microdata from the Czech Statistical Office and data concerning the level of air pollution in the Czech Republic from the Czech Hydrometeorological Institute, I analyze if the biological and socio-economics status of mothers and the characteristics of our surroundings (air pollution) affect the sex of children. The results are insignificant or not robust across specifications. I identified three hypotheses which are most likely the reason for the insignificant results: a non-inclusion of the biological and socio-economical status of a father, insufficient diversity or evolutionarily novel environment in the Czech Republic. As a conclusion, the presented evidence suggests that stillbirths are random in the Czech Republic and that the sex ratio is not affected by the socio-economics status of mothers or the characteristics of our surroundings (pollution).

No description available.

This dissertation consists of four chapters on the economics of marriage and divorce in Iran. The first chapter outlines major forces driving the recent transitions in Iran's marriage market. Age structure of the population, the rise of women's education, marriage and divorce laws, and fertility decline are the four main forces influencing marriage transitions, that is, the age of marriage, couple's age and education gaps, quality of marriage (stability, education status of children), and women's power within marriage. Chapter two looks at the change in age structure that influences the sex ratio. I consider the influence of the sex ratio on couples' age and education gaps using data from multiple national surveys from 1984-2007. The findings of this chapter show that a lower sex ratio, i.e. a greater supply of marriage-age women, increases the bargaining power of men at the time of marriage and thereby increases their ability to marry younger and more educated women. In chapter three, I evaluate the effects of demographic change, the sex ratio, and policy change, particularly the provision of family planning programs through health clinics on delayed marriage in rural Iran. I use data from Iran's 2000 Demographic and Health Survey to estimate a hazard model of timing of marriage. The results show that a lower sex ratio decreases the chances of a woman finding a man five years older, and easier access to family planning decreases her probability of marriage. In chapter four, I provide a legal history of Iran's marriage and divorce laws and then discuss how changes in the legal structure of marriage and divorce alter the terms of marital bargaining and force women to circumvent inequitable Iranian laws to improve their position. Then, I present a model of how Mahrieh could improve a woman's position within the household in light of the unequal divorce rights favoring men. As women cannot exit their marriage, they request a conditional and legally enforceable bond known as Mahrieh from their husbands to secure themselves against the risks of divorce or maltreatment within marriage. / Ph. D.

Sex ratio is very important for the evolution of dioecious plants. It can influence the reproductive success of plants. Sex ratio bias is common among reproductive individuals. Studying the reproductive traits can help to understand possible mechanisms that could influence the generation and maintenance of sex ratio bias. However, few studies have reported the relationship between reproductive traits and sex ratio bias. We investigated 29 full-sib families of the dwarf willow Salix herbacea L. S.herbacea exhibits an overall female sex ratio bias but also strong variation in sex ratio among families. We used variance component analysis to investigate from which morphological level the variation of reproductive traits (cumulative catkin number over four growth periods, annual catkin number in the fourth growth period, flower number, ovule number) came from. And we used mixed models to test the influence of family, sex and the sex by family interaction on reproductive traits. Besides that, we also tested the correlation between sex ratio and reproductive traits. Our results suggest that genetic factors can influence the degree of sexual dimorphism of S. herbacea in the different families Flowers from families with higher sex ratios had more ovules, sex ratio and the ovule number co-varied across families.

California red scale (CRS), Aonidiella aurantii (Maskell) (Hemiptera: Diaspididae), one of the most important pests of citrus worldwide, began to cause damages in eastern Spain in 1986. The main biological control agents of A. aurantii in this zone are the native parasitoid A. chrysomphali (Mercet) and the introduced A. melinus DeBach (both Hymenoptera: Aphelinidae). Nevertheless, the control they exert is insufficient. In order to improve the biological control of A. aurantii we studied several biotic factors that may affect the efficiency of A. chrysomphali and A. melinus in the field. More concretely, we studied the spatial and temporal variation in the scale size, the host sizes used by A. chrysomphali and A. melinus as well as the influence of host size on various parasitoid traits. Moreover, we studied the foraging ecology and the effect of the ants native to the Mediterranean on the populations of the scale and, finally, the nutritional state and food sources used by adult A. melinus in the field. In the field, the body size of A. aurantii varied with plant substrate, locality, time of the year, and probably, with the nutritional state of the host plant. Plant substrate was found to substantially influence the body size of A. aurantii with scales being significantly larger on fruits that on leaves or twigs. Another important source of variation for A. aurantii size was geographic location since significant differences were found among orchards. Moreover, significant seasonal variation in the body size of A. aurantii was observed; body sizes were smaller during summer and autumn, apparently due to the effect of temperature. Finally, a positive relationship between the content of potassium in leaves and scale size was observed. From all the above factors, temperature related seasonal variation had the most profound effect on A. aurantii size. Aphytis chrysomphali and A. melinus used different sizes of A. aurantii in the field. / Pekas, A. (2011). Factors affecting the biological control of California red scale Aonidiella aurantii (Hemiptera: Diaspididae) by Aphytis (Hymenoptera: Aphelinidae) in eastern Spain citrus: host size, ant activity, and adult parasitoid food sources [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/10293

Thesis (MSc)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: This thesis investigates the population structure of a number of ungulate species occurring within Rooipoort private reserve. Specifically the study serves to make estimates of the ratio of males to females and calves to cows within each species population under observation, based on the data collected. Data were also analysed to ascertain the distribution patterns of the species in question, in relation to vegetation type and habitat. Distribution data were additionally compared to distribution data collected at an earlier period on Rooipoort, to determine whether any change has occurred in distribution patterns of the ungulates concerned. Through analysis of both sex/age data and distributional data, one of the main objectives of the study was to determine the most appropriate time of the year, length of time and managment costs involved to undertake sex/age counts on Rooipoort. Results of the study were also compared to existing population models of ungulates on the reserve. Results obtained from data concluded that a single monthly sex/age count or, in some cases, even three consecutive monthly counts, to determine age ratios, would be insufficient to deliver a reliable estimate of population structure. A number of counts would have to be carried out throughout the year in order to make reliable estimates. Distribution data revealed that all habitat/vegetation types on Rooipoort would have to be covered in order to effectively sample all of the species in question. / AFRIKAANSE OPSOMMING: Gegewens is ook ontleed om die verspreidingspatrone van hoefdiersoorte te bepaal met betrekking tot plantegroeitipe en habitat. Die verspreidingsdata is ook vergelyk met vorige ..studies wat op Rooipoort gedoen is om te. bepaal. of enige. veranderings in die verpreidingspatrone van die hoefdiere onder bespreking plaasgevind het. Een van die hoof doelwitte van die studie was om.. deur ontleding. van beide die geslags/ouderdom data en die verspreidingsdata, die mees geskikte tye van die jaar, die tydsduur en bestuurskoste te bepaal, om geslags/ouderdomstellings op Rooipoort uit te voer. Resultate van die studie is ook met vertroude populasiemodelle op die reservaat vergelyk. Die dataontledings het aangeduidat 'n enkele maandlikse geslags/ouderdoms telling, of, In sekere gevalle, selfs drie agtereenvolgende maandlikse tellings, om ouderdomsverhoudings te bepaal, nie voldoende sal wees om 'n vertroubare beraming van die bevolkings struktuur te maak. n' Aantal tellings moet gedurende die yaar uitgevoer word om vertroubare beramings te kan doen. Verspreidingsdata het bevestig dat alle habitate en plantegroeitipes op Rooipoort bemonster moet word om alle spesie effektief te bemonster.

Background: The human secondary sex ratio has been the subject of long-standing medical, environmental and social scientific curiosity and research. A decline in male birth proportion in some industrialised countries is linked to endocrine disruption and is validated by some empirical studies. Increasing parental age and population stress and associated decreases in sex ratio have also been demonstrated. A thorough literature review of 123 relevant and diverse studies provides context for these assessments. Methods: A spatial-temporal investigation of birth sex ratio in Scotland and potential determinants of endocrine disruptor pollution, socio-economic factors including neighbourhood stress, deprivation, smoking, and maternal age, was conducted. This involved review of national and regional sex ratio time trends, and stratified/spatial analysis of such factors, including the use of GIS tools. Secondary data were sourced from Scottish Government web portals including Scottish Neighbourhood Statistics and the Scottish Environmental Protection Agency. Results: Regional differences in sex ratio between 1973 and 2010 are observed which likely lever the national male birth proportion downwards, with the region of poorest air quality from industrial emissions, the Forth Valley, displaying the greatest sex ratio reduction. Further analysis shows significant upwards skewing in sex ratio for the population cohort experiencing the least and 2nd most deprivation. Localised reductions in sex ratio for areas of high modelled endocrine disruptor pollution within the Central Region in Scotland are also displayed. Discussion: Limitations of the analyses include the danger of ecological fallacy in interpreting from area-based measurement and the simplified pollution modelling adopted. Despite this, and given elevated incidence of testicular cancer in Scottish regions mirrors the study’s results, tentative confirmation of the endocrine disruptor hypothesis can be substantiated. Further, elucidation on advanced parental age as a contributory factor to secondary sex ratio change is also given. Recommendations are made with respect to environmental monitoring and health protection, and preventative health strategies in Scotland.

Chameleons are an understudied taxon facing many threats, including collection for the international pet trade and habitat loss and fragmentation. A recent field study reports a highly female-biased sex ratio in the Eastern Arc Endemic Usambara three horned chameleon, Trioceros deremensis, a large, sexually dimorphic species. This species is collected for the pet trade, and local collectors report males bring a higher price because only this sex has horns. Thus, sex ratios may vary due to differential rates of survival or harvesting. Alternatively, they may simply appear to be skewed if differences in habitat use biases detection of the sexes. Another threat facing chameleons is that of habitat loss and fragmentation. Despite enormous amounts of research, the factors of fragmentation that different species respond to is still under debate. Understanding these responses is important for current mitigation efforts as well as predicting how species will respond to future habitat alteration and climate change. My study suggests that differences in survival and detection may explain much of the observed seasonal sex skew in adult T. deremensis. Within fragmented habitat chameleons consistently responded more to edge effects and vegetative characteristics associated with fragmentation than to area or isolation effects. This may bode poorly for chameleon populations in the coming decades as climate change further alters vegetative communities and exacerbates edge effects.

De l'Albanie à la Chine, différents pays dans le monde sont affectés par des déséquilibres du rapport de masculinité à la naissance. Le Viêt Nam est de ceux parmi lesquels le phénomène est le plus récent, mais la hausse mesurée depuis 2006 est extrêmement rapide : il s'établit aujourd'hui à 112 naissances de garçons pour 100 naissances de filles au niveau national, et excède 120 dans plusieurs provinces. Au Viêt Nam, cette hausse est exclusivement liée à la sélection sexuelle prénatale, qui résulte de la combinaison de trois facteurs (Guilmoto, 2009), que cette recherche se propose de comprendre. Les couples qui ont recours aux avortements sexo-sélectifs sont disposés à le faire (facteur de demande), parce qu'ils ont une préférence pour les garçons liée à différents arguments sociaux, culturels et économiques. Ils en ont également la possibilité (facteur d'offre), grâce à la légalité du recours à l'avortement provoqué et à l'accès aux échographies qui s'est généralisé au cours de la dernière décennie, dans la majorité des zones urbaines et rurales. Enfin, il y a un facteur de pression, exercée par le faible niveau de fécondité - allant de 1,7 à 2,6 enfants par femme selon les régions en 2009 -, qui accroît le risque de ne pas avoir de fils. S'il existe de fortes disparités régionales dans les statistiques de la masculinité des naissances, partiellement liées à des différences de fécondité et de prospérité, ce sont les variations dans l'intensité de la préférence pour les garçons qui expliquent en premier lieu cette diversité. Le Delta du Fleuve Rouge, dans le Nord, est marqué par un système de parenté patriarcal et patrilinéaire, dans lequel avoir un fils apparaît indispensable pour légitimer le statut des femmes au sein de leur famille et de la société. La situation au sud du Viêt Nam apparaît plus complexe : la mixité de la descendance est privilégiée, en raison notamment du brassage culturel des Khmer bilatéraux et des Cham matrilinéaires, avec les Kinh traditionnellement patrilinéaires, qui s'est développé à travers les siècles. En outre, le Doi Moi à la fin des années 80 et la libéralisation du marché économique ont entraîné un désengagement de l'État de nombreuses structures sociales collectives et engendré une résurgence des traditions rituelles et familiales, qui ont renforcé la dimension patriarcale de la société; c'est cependant moins marqué dans le Sud, en raison de la fracture qui s'est établie durant plusieurs décennies du XXe siècle entre les deux parties du pays. Ce travail de thèse associe une analyse statistique approfondie des données du recensement de 2009 et de l'enquête intercensitaire 2014, et une étude sociologique des différents rôles de genre au sein du couple et de la famille, notamment grâce à la conduite de trois enquêtes qualitatives au Nord et au Sud du Viêt Nam. Il décrit les variations régionales de la préférence de genre, et compare les effets distincts de plusieurs caractéristiques (notamment zone urbaine ou rurale, niveau d'éducation, statut socio-économique, origine ethnique, composition sexuelle de la descendance) sur les comportements de fécondité. / From Albania to China, several countries in the world experience unbalanced Sex Ratio at Birth. In Vietnam, the phenomenon is very recent (2006), but rapidly increasing. Currently, the national sex ratio at birth is 112 boys for 100 girls, and exceeds 120 in several provinces. The rising proportion of male births is directly linked to prenatal sex selection, that is abortion of female fetuses. It results from the combination of three factors (Guilmoto, 2009): expanding access to ultrasonography and abortion in both urban and rural areas (supply factor), low fertility level increasing the risk of remaining « sonless » (squeeze factor) and preference for sons (demand factor). However, important regional disparities exist, partly associated with differences in fertility and prosperity levels. But discrepancies in son preference appear to be the main factor. Northern Vietnam presents a very strong preference for sons, linked to a patriarchal descent system, where the birth of a son legitimizes women's status within their family and the society. However, mixed offspring is privileged in the South, since cultural mixing of bilateral Khmer and matrilineal Cham people, with Kinh population traditionally patrilineal, developed through centuries. Moreover, the Doi Moi economic reforms in the 80's lead the State to withdraw from collective social structures and yielded a resurgence of ritual and familial traditions, which reinforced the patriarcal aspect of society; however the split of the country for several decades during the 20th century makes it less noticeable in the South. This thesis combines statistical analysis of the 2009 census data and the 2014 intercensal survey, and a sociological study of different gender roles within couples and families, based on three qualitatives surveys conducted in Northern and Southern Vietnam. It describes regional variations of gender preference, and compares the distinct effects of several characteristics (including rural/urban areas, level of education, socio-economic status, ethnicity, sex composition of offspring) on fertility behaviors.

La plupart des études sur l’influence de la température sur la production des spermatozoïdes portent en grande partie sur les vertébrés. Néanmoins, les invertébrés constituent la majorité de la biodiversité terrestre animale, sont également plus sensibles à ces variations de température. Les travaux réalisés au cours de cette thèse ont porté sur la compréhension des capacités de reproduction, et sur l’influence d’une augmentation de température sur les fonctions mâles chez Nasonia vitripennis, un hyménoptère parasitoïde. Ce travail de thèse m’a permis de confirmer que chez cette espèce, la spermatogenèse était synchronisée et de décrire pour la première fois, un système de stockage intermédiaire des spermatozoïdes entre les testicules et les vésicules séminales. De plus, j’ai pu mettre en évidence que la spermatogénèse était sensible à une augmentation de température pendant le développement, altérant le sexe ratio de la descendance par des modifications d’allocations des sexes par les femelles. Ces résultats apportent de nouvelles connaissances sur la fertilité mâle chez cette espèce et démontrent la sensibilité de la spermatogenèse à la température. / Many studies on the impact of the temperature on spermatogenesis have largely focused on vertebrates. Nevertheless, invertebrates constitute the vast majority of terrestrial biodiversity, and are especially vulnerable to variations of temperatures. The studies realized during my thesis are focused on understanding male reproductive capacities and effects of heat stress on male fertility in a parasitic wasp Nasonia vitripennis. This work allowed to confirm that spermatogenesis was synchronized, and to describe for the first time a system of spermatozoa regulation between testis and seminal vesicles. Moreover, I was able to demonstrate that spermatogenesis was sensible to temperature variation during male development, and the offspring sex ratio was altered by modifications of sex allocation. These findings open the way to the description of male fertility in this species, and show the sensitivity of spermatogenesis to temperature variation.