Opportunity for natural selection in human populations has so far mainly been studied on anthropological data for tribal populations or on census data for nations. The present study is mainly based on data on individual lifehistories but also, for part of the longitudinal study, on census data. Six of the populations, Nedertorneå, Tuna, Svinnegarn, Trosa, Locknevi and Fleninge are parishes. These sets of data covers the period 1800-1850 as defined by the birthyears of the women. The data for the longitudinal study are derived from two sour­ces, a biography over all clergymen in the diocese of Linköping, cove­ring the period 1600-1845, and material published by the National Swe­dish Central Bureau of Statistics (SCB) that covers the period 1750-1980. For each subpopulation data on childhood mortality and female fertility has been collected and from these data Crow's index of opportunity for natural selection has been calculated. The original index has also been modified in order to estimate the importance of childlessness in relation to the total index. The study shows that for the periods and the populations studied, there is a considerable opportunity for natural selection both through mortality and through differential fertility and that, during our cen­tury, differential fertility has become the main asset for natural se­lection, as mortality has been reduced to very low levels. It is also obvious that childlessness is an important factor as regards natural selection in human populations. The cross-sectional study shows signi­ficant differences between the populations for all components of the index. The longitudinal study covers when, the two sets of data are combined, a period of over 350 years, 1600-1980. Over this period changes in index of opportunity for natural selection have occured but these changes are not very drastic as compared to other longitudinal studies. However, within a separate region there can be drastic chang­es in index between decades and there are large differences between regions. Mortality and fertility patterns have been studied from different angles. With the exception for the census data, each woman in the stu­dy has be followed from 16 to 40 years of age and each of her children (if any) has be followed from birth to 16 years of age or death, if prior. Therefore it was possible to obtain distributions for age at first childbirth, sibship size, succesful sibship size, childhood mor­tality by age at death, female mortality, and childlessness, total and marital. In some cases a study of sex ratio at birth and at 16 years of age, and birth intervals, have been made. Statistical analysis of the results shows significant differences between populations for all tests that have been applied. The Linköping data was analysed for dif­ferences between periods. Significant differences were found for all of the parameters with the exception of female mortality. / <p>Härtill 5 uppsatser</p>

In this dissertation, I report new information that is necessary for future mating system studies in a little studied species, the marbled salamander (Ambystoma opacum). I studied female mating behavior, sexual selection, and the consequences of polyandry for individual females and salamander populations. I also compared the performance of several statistical approaches for analyzing genetic mating system data. The first chapter summarizes the characteristics of several novel microsatellite DNA loci as well as cross-amplified loci for marbled salamanders and mole salamanders that may be used for future studies. In the second chapter, I report estimates of sire number for 13 marbled salamander clutches based on microsatellite data from 32 hatchlings per clutch. Females mated with as many as three different males as indicated by conservative techniques. Less than half of females mated with multiple males. Based on comparative analyses, I recommend the parental reconstruction approach with the computer program GERUD for assessing multiple paternity. The third chapter describes an experiment designed to study sexual selection. As expected, in breeding mesocosms, the potential for sexual selection was much higher for males than for females. Size was unrelated to variance in male reproductive fitness. Only opportunity for selection and Morisita’s index conformed to theoretical expectations of the relationship between operational sex ratio and the potential for sexual selection among males. Because opportunity for selection has intuitive links to formal sexual selection theory, I recommend its continued use. In the fourth chapter, I compared polyandrous and monandrous females to explore the potential fitness consequences of multimale mating. No fitness measure at the egg or hatchling stage (clutch size, hatching success, hatchling size, etc.) differed between the two types of clutches. Size of metamorphs was not different, but polyandrous clutches had significantly higher survival to metamorphosis. In the fifth chapter, I analyzed effects of increased polyandry and male availability on genetic diversity, effective population size (Ne), and fitness of experimental populations. Although no analyses were significant, some effects were moderate to high in size. Ne was higher when estimated from hatchlings than with metamorphs.

Environmental factors can have profound effects on the strength and direction of selection and recent studies suggest that such environment-dependent selection can be sex-specific. Sexual selection theory predicts that male fitness is more condition dependent compared to female fitness, suggesting that male fitness is more sensitive to environmental stress. However, our knowledge about the effect of environmental factors on sex-specific reproductive performance and on sex differences in the opportunity for selection is still very limited. In the present study, we investigated the sex-specific effects of diet quality (yeast deprivation and flour type) in the red flour beetle Tribolium castaneum. Specifically, we manipulated yeast supplementation in wheat and whole-wheat flour in competition assays allowing us to test for sex-specific effects of food quality (i) on reproductive success and (ii) on the opportunity for selection. Our data show that yeast deprivation in wheat flour had significantly negative effects on body mass and reproductive success of both sexes, while high-quality flour (whole-wheat flour) was able to buffer the negative impact to a large extent. Importantly, our data suggest no sex-specific effect of dietary stress on reproductive success because the magnitude of the negative effect of yeast deprivation was similar for males and females. Moreover, our study demonstrates that low food quality inflated the opportunity for selection and did not differ between sexes neither under benign nor stressful dietary conditions. We discuss the implications of our findings for the adaptation to stressful environments.