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Leung, Siu Lun. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 153-190). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese.

No description available.

The thesis is mainly focused on the analysis and evaluation of the effects influencing the sex ratio of live births. After studying of the foreign language literature, main factors influencing the sex ratio are defined. Data used in the thesis (births by the sex) are retrieved from The Human Mortality Database, database of United Nations Statistics Division and from particular statistical offices. Based on the results of the exploratory data analysis, countries with unreliable data (data skewed due to the manipulation or due to the not appropriate standard of the registration of born) are specified. Subsequently, the countries with abnormal values of the sex ratio at birth resulting from the cultural traditions or technological development are defined. For countries with not evident influence of the factors mentioned the analysis of the relations and dependencies between sex ratio at birth and variables chosen (groups of the geographical, socioeconomics and demographical impacts). On the basis of this analysis it has been proved that the sex ratio at birth depends primarily, but not exclusively, on the total fertility rate and life expectancy.

Aedes aegypti is one of the most important mosquito vectors of human disease, transmitting dengue, Chikungunya and yellow fever viruses. New control methods are much needed for this species and an ability to skew sex ratios toward males would be very useful for a number of strategies. In this study, male-specific chromosomal regions were searched for in Ae. aegypti using novel approaches such as microdissection of chromosomes. The sex determination pathway of Ae. aegypti was also explored, using Drosophila melanogaster as a model, to find candidate genes that could be used to induce male biased sex ratios. The transformer-2 (tra-2) gene is necessary for sexual differentiation of females in D. melanogaster, but its role remains unknown in mosquitoes. A homolog of tra-2 was identified in Ae. aegypti. Rapid Amplification of cDNA ends (RACE) experiments were conducted to characterize this gene in Ae. aegypti. The Ae. aegypti tra-2 gene, as for D. melanogaster, was highly variable in transcription due to alternative splicing and alternative polyadenylation, with 9 different variants identified. RNA interference (RNAi) was then used to determine if knockdown of all variants of Ae. aegypti tra-2 can be achieved and if it would cause gender switching in individuals, initially by means of direct injection of double stranded RNA, and then progressing to germline transformation. A construct designed to produce tra-2 dsRNA was injected into Ae. aegypti embryos and integrated into the Ae. aegypti genome. The transgenic population showed up to 100% male bias in single pair crosses. The male bias effect could still be seen in the heterozygous population. The results suggest that knockdown of tra-2 could provide a useful tool for sex ratio distortion as part of the development of novel control methods for Ae. aegypti.

Sex ratio theory is a focus in evolutionary biology that explores how natural selection shapes investment in males and females. It has provided some of the best quantitative evidence of evolution and could find utility in public health efforts through its application to malaria parasites. These parasites have distinct male and female forms that are produced following massive asexual replication, and they mate within the blood-feeding insects that transmit them between vertebrate hosts. A very similar population structure is assumed by local mate competition (LMC), a model from sex ratio theory that predicts female-biased sex ratios dependent on the degree of selfing within a mating patch. In this dissertation, I test a series of predictions from LMC for the lizard malaria parasite Plasmodium mexicanum. These include: (i) sex ratios have heritable variation that is not constrained by other life history traits; (ii) single-genotype infections have female-biased sex ratios that are determined by male fecundity; (iii) multiple-genotype infections have less biased sex ratios than single genotype infections; (iv) if males are limiting, sex ratios may be less biased when there are fewer parasites present (an extension of LMC called fertility insurance); and (v) less biased sex ratios may also be favored if increased female production yields diminishing returns on transmission to a new vertebrate host. To test these predictions, I combined the study of natural and experimental infections, microscopy (parasite density and sex ratio), molecular genetics (infection genetic diversity), and mathematical modeling (of how transmission patterns might affect sex ratio evolution). Overall, the results were qualitatively consistent with both LMC and my new model predictions. Sex ratios showed evidence of heritable variation that was unlinked to other life history traits measured. Sex ratios in single-genotype infections were female biased and consistent with the male fecundity observed, and were lower than sex ratios in experimental multiple-genotype infections, as predicted. Sex ratios were not less biased with lower sexual cell density, suggesting that males were not limiting. In fact, the opposite trend was sometimes observed: sex ratios were less biased with more sexual cells. This pattern has been observed previously in this and other species, and the only model that currently predicts such a trend is the new transmission model I outline. This dissertation contributes to our understanding of sex ratio evolution for malaria parasites in a number of ways. First, it adds evidence to the idea that the selective forces implicated in LMC are at work in malaria parasites and that malaria parasites are able to detect and respond to relevant cues. Second, it helps account for discrepancies in existing data, which have often reached conflicting conclusions. Third, it offers one of the first detailed studies of malaria parasite male fecundity, an essential piece of the sex ratio puzzle. Finally, it outlines a new theoretical extension of LMC that provides novel predictions and highlights areas of study that may be fruitful for future work on malaria parasites and other organisms.

This study investigated the reproduction and survival of Formosan macaques (Macaca cyclopis). Data on birth and death of Formosan macaques at Mt. Longevity were collected from 1996 till 2006. The birth of Formosan macaques peaked from April to June (94.4%). The sex ratio of 604 infants at birth was 1:1.2 (female to male), which was not significantly different from 1:1. The death of less than one-month-old infants accounted for 22.2% of all infant death. Infant mortality (less than 1 years old) was very high (35.2%) and no sexual difference was found (p > 0.05). Mortality of males equal or older than 6 years old (16.8-33.3%) were higher than those of females (p < 0.05). In primiparous females, most females (57.6%) gave birth at four years old. The average interbirth intervals of females after infant death within the first 3 months was 0.96 years (¡Ó 0.07, n = 23) which was significantly shorter than that after the successful rearing infants (1.02 years ¡Ó 0.09, n = 185, p < 0.05). Maternal ranks, age, infant sex ratio and troop size had no significant effect on the interbirth intervals (p > 0.05). The average interbirth intervals of high-ranking females (1.03 years) were similar to those from middle- (1.10 years) and low-ranking females (1.01 years). The average interbirth intervals after daughters were slightly longer than those after sons (1.02 and 1.01 years, prospectively). Interbirth intervals among small-sized troops (0.97 years) was slightly shorter than those from large- (1.02 years) and middle-sized troops (1.00 years). The birth rates of high- and middle-ranking females (66.3% and 68.0%, prospectively) were significantly higher than that of low-ranking females (45.6%, p < 0.05). Maternal rank and age had no significant effect on male infant ratio (p > 0.05). However, male infant ratio of high-ranking and young-aged females (76.2%) was 1.3-1.6 times of high-ranking, middle- and old-aged females, 1.5-1.7 times of middle-, low-ranking and young-aged females. Male infant ratio of middle troop size and high-ranking females (66.7%) was 1.2-1.4 times of large- and small-sized troops; 1.4-1.5 times of middle troop size and middle- and low-ranking females.

Sexual conflict occurs when individuals of one sex express traits that reduce the fitness of their mates. Males of many species harass females to gain copulations, which benefits males by increasing the number of offspring they sire but imposes energetic and opportunity costs on the females they harass. This thesis examined the fitness costs of sexual harassment to females, the energetic costs of mating to males, and the factors influencing the intensity of male competition for mates in the western mosquitofish Gambusia affinis. I quantified male and female behavior, four female fitness components (number of offspring per female, embryo number, growth, and survival), and an index of male body condition in response to changes in operational sex ratio (experiment 1) and male and female density (experiment 2). I found that a strong, negative effect of female density on female fitness overwhelmed any potential costs of male harassment, suggesting that ecological interactions between females may play a larger role in determining female fitness than conflict between the sexes. Agonistic chases and displays between males increased as the operational sex ratio increased (became male-biased), while the number of copulations males attempted decreased. This inverse relationship suggests a tradeoff between interfering with other males and attempting additional copulations with females. Increases in chases between males were largely due to changes in female density, but not male density, suggesting that the availability of females determines whether males escalate contests with other males. In contrast, the number of displays between males depended varied with male density but did not female density. This difference between chases and displays is likely due to their difference in function; chases are performed to prevent other males from mating while displays are used to assess male competitors. I did not detect any energetic cost of mating to males.

The Silver Gull is a small gull (265 - 450g), which exhibits sexual dimorphism, with males larger than females. It has a protracted laying period of about 8 months over the winter on Penguin Island in Western Australia. The Silver Gull was studied on Penguin Island from 2000 to 2002. Completed clutches were removed from breeding pairs to induce repeat laying in order to determine the effect of increased reproductive effort on maternal body condition, egg production ability, offspring sex ratio and chick rearing capacity. Increased egg production had no significant effect on maternal body condition as measured by condition index, derived from mass divided by a measure of skeletal size. The seasonal period, divided into thirty-day intervals, had a significant impact on female condition index, with a decline in condition toward the end of the breeding season. While male condition also appeared to decline at the end of the season, this pattern was not significant. The initiation of laying varied between the three years of the study. The earliest occurred in 2000, which also experienced earlier rainfall than the later two years. Egg size and mass decreased throughout the breeding season although the number of eggs in a clutch did not decline. The size and mass of the eggs was significantly affected by the laying history of the parents, although this effect was dependent on the year in which the eggs were produced. The minimum interval required by Silver Gulls to replace a lost clutch is about 14 days. This interval increased from the start of the breeding season, but then declined toward the end, as summer was approaching. Laying interval increased significantly as the number of clutches produced by the parents also increased, up to 4 clutches in total. As more clutches were produced past this point, the laying interval became shorter. The probability of a replacement clutch being produced after clutch removal, declined as the clutch number increased and as the season progressed. Individuals that laid clutches with a larger mean mass were more likely to lay a replacement clutch. Increasing reproductive output caused a decline in the proportion of clutches that were replaced after clutch removal. The proportion of clutches that were replaced also varied between the years with the highest rates of replacement seen in 2000 which was also the year that experienced the earliest start in laying. The size of the original clutch in terms of its mean mass and volume was related to the size of the replacement clutch, but this relationship varied according to the timing of laying. During 2000 and 2001 male offspring predominated in the first two clutches produced by Silver Gulls. Further clutches that were produced demonstrated a sex ratio skewed toward females, the smaller sex in this species. Offspring sex ratio was close to equality in 2002 with very little effect caused by increased egg production. There was no effect of year, season or the laying history of the parents on hatching success. Growth rate in chicks was influenced by the year in which the chick hatched, the period during the season in which the chicks hatched, its sex and the laying history of the parents. The relationship between chick growth and the laying history, however, was complex with no consistent pattern emerging in terms of the performance of chicks from each treatment group. While the chicks from control groups generally grew faster than the chicks from manipulated parents, those individuals that were laid or raised by manipulated parents that had laid at least three clutches in total also performed well. Using the two main measures of reproductive success in the current study, egg production and chick rearing, those birds that were induced to lay multiple replacement clutches, were able to maintain a high level of condition and reproductive success. It is proposed that in the Silver Gull, only those individuals with a high level of condition continue to lay replacement clutches. If the female is unable to produce well provisioned eggs with a high chance of success, the breeding attempt is abandoned. Despite no loss of condition detected in female Silver Gulls with increasing clutch number, there was a significant shift in the offspring sex ratio toward females, indicating that strategies were in place to cope with the increased reproductive effort incurred as a consequence of repeat laying. Protracted laying in this species allows replacement of lost clutches only after maternal condition has been regained after laying.

Thesis(M.S.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references.