scholarly journals An experimental demonstration of the impact of predation on sexual segregation and primary sex ratios among ungulates

2016 ◽  
Vol 42 (4) ◽  
pp. 414-421
Author(s):  
Christopher A. J. O'Kane ◽  
David W. Macdonald
Keyword(s):  
Sex Ratios ◽  
Sexual Segregation ◽  
Experimental Demonstration ◽  
The Impact

scholarly journals Sex Chromosome Meiotic Drive in Stalk-Eyed Flies

Genetics ◽  
1997 ◽  
Vol 147 (3) ◽  
pp. 1169-1180 ◽  
Author(s):  
Daven C Presgraves ◽  
Emily Severance ◽  
Gerald S Willrinson
Keyword(s):  
Sex Ratio ◽  
Sex Chromosome ◽  
Sex Ratios ◽  
Natural Populations ◽  
Meiotic Drive ◽  
Operational Sex Ratio ◽  
Genetic Modifiers ◽  
Ratio Distortion ◽  
The Impact ◽  
Sex Ratio Distortion

Meiotically driven sex chromosomes can quickly spread to fixation and cause population extinction unless balanced by selection or suppressed by genetic modifiers. We report results of genetic analyses that demonstrate that extreme female-biased sex ratios in two sister species of stalk-eyed flies, Cyrtodiopsis dalmanni and C. whitei, are due to a meiotic drive element on the X chromosome (Xd). Relatively high frequencies of Xd in C. dalmanni and C. whitei (13–17% and 29%, respectively) cause female-biased sex ratios in natural populations of both species. Sex ratio distortion is associated with spermatid degeneration in male carriers of Xd. Variation in sex ratios is caused by Y-linked and autosomal factors that decrease the intensity of meiotic drive. Y-linked polymorphism for resistance to drive exists in C. dalmanni in which a resistant Y chromosome reduces the intensity and reverses the direction of meiotic drive. When paired with Xd, modifying Y chromosomes (Ym) cause the transmission of predominantly Y-bearing sperm, and on average, production of 63% male progeny. The absence of sex ratio distortion in closely related monomorphic outgroup species suggests that this meiotic drive system may predate the origin of C. whitei and C. dalmanni. We discuss factors likely to be involved in the persistence of these sex-linked polymorphisms and consider the impact of Xd on the operational sex ratio and the intensity of sexual selection in these extremely sexually dimorphic flies.

Bionomics of Anopheles Arabiensis from Mamfene in KwaZulu-Natal (South Africa): An Area of High Malaria Transmission in the Province

2020 ◽  
Author(s):  
Rajendra Maharaj ◽  
Vishan Lakan ◽  
Kiash Maharaj
Keyword(s):  
South Africa ◽  
Vector Control ◽  
Anopheles Arabiensis ◽  
Mosquito Control ◽  
Sex Ratios ◽  
Adult Mosquito ◽  
Mosquito Vector ◽  
Larval Control ◽  
Kwazulu Natal ◽  
The Impact

Abstract Background: Although great strides have been made in controlling malaria, the disease is of significant public health importance. Historically, efforts to control the vector has concentrated on adult vector control targeting the female Anopheles mosquitoes. As there is now a focus on eliminating residual malaria from KwaZulu-Natal, new strategies are being investigated to increase the impact of malaria elimination strategies. Greater attention is now being given to larval control, as a complementary measure to indoor residual spraying. However, there is a large gap in knowledge of the bionomics of the larval stages of this mosquito vector of malaria in South Africa. In order to focus on both larval and adult mosquito control methods, larval development and the reproductive stages of the vector were investigated since these variables influences our ability to impact mosquito populations through larval control. This study was therefore conducted to determine the peak eruption times and the emergent sex ratios, as well as the peak egg oviposition time in order to attack the mosquito when it is at its most vulnerable and when control interventions will have the most impact.Results: Oviposition studies showed two peaks corresponding with late evening and again just before dawn. Most eggs were also laid in the first half of the night (18h00 – midnight). Most mosquitoes erupted just after sunset and the sex ratios showed that twice as many females as males emerged. Females readily took a bloodmeal after oviposition or just after erupting. Hatch rate to viable first instar larvae was 74.5%.Conclusions: The results of this study have provided information as to when interventions would be most effective in controlling mosquito populations and have provided information that highlights the value of larval control as a complementary measure to adult mosquito control. The most vulnerable stages of the female Anopheles arabiensis are when they have just emerged or when they have just oviposited. Vector control strategies should be designed to target these vulnerable stages at the breeding sites in order to have maximum impact.

scholarly journals Marriage and Marriage Markets

2017 ◽  
pp. 54-74
Author(s):  
Shoshana Grossbard
Keyword(s):  
Labor Market ◽  
Sex Ratio ◽  
Labor Supply ◽  
Empirical Evidence ◽  
Sex Ratios ◽  
Economic Models ◽  
Marriage Markets ◽  
Gary Becker ◽  
Marriage Formation ◽  
The Impact

This chapter reviews models of marriage, with special emphasis on how the sex ratio can help explain outcomes such as marriage formation, the intramarriage distribution of consumption goods, labor supply, savings, type of relationship, divorce, and intermarriage. Economic models of marriage pioneered by Gary Becker are reviewed in the first section and then extended in the next section to incorporate the labor market for the work-in-household approach of Grossbard. The following section discusses challenges in identifying exogenous variation in sex ratios and presents empirical evidence on the impact of sex ratios on labor supply, consumption, savings, and several other outcomes.

scholarly journals Frail Males on the American Frontier: The Role of Environmental Harshness on Sex Ratios at Birth Across a Period of Rapid Industrialization

2021 ◽  
Author(s):  
Ryan Schacht ◽  
Mike Hollingshaus ◽  
Heidi Hanson ◽  
Tim Bruckner ◽  
Shane J Macfarlan ◽  
...  
Keyword(s):  
Sex Ratios ◽  
Early 20Th Century ◽  
Social Variables ◽  
American Frontier ◽  
Rapid Industrialization ◽  
Post Industrial ◽  
The Impact ◽  
Industrial Societies ◽  
Shed Light

While sex ratios at birth (SRB) have been shown to vary within and across populations, after over a century of research, explanations have remained elusive. A variety of ecological, demographic, economic, and social variables have been evaluated, yet their association with SRB has been equivocal. Here, in an attempt to shed light on this unresolved topic within the literature, we approach the question of what drives variation in SRB using detailed longitudinal data spanning the frontier-era to the early 20th century in a US population. Using several measures of environmental harshness, we find that fewer boys are born during challenging times. However, these results hold only for the frontier-era and not into a period of rapid industrialization. We argue that the mixed state of the literature may result from the impact and frequency of exogenous stressors being dampened in post-industrial societies.

scholarly journals Frail Males on the American Frontier: The Role of Environmental Harshness on Sex Ratios at Birth across a Period of Rapid Industrialization

2021 ◽  
Vol 10 (9) ◽  
pp. 319
Author(s):  
Ryan Schacht ◽  
Mike Hollingshaus ◽  
Heidi Hanson ◽  
Shane J. Macfarlan ◽  
Douglas Tharp ◽  
...  
Keyword(s):  
Sex Ratios ◽  
Early 20Th Century ◽  
Infrastructure Development ◽  
Social Variables ◽  
American Frontier ◽  
The Us ◽  
Rapid Industrialization ◽  
The Impact ◽  
Shed Light

While sex ratios at birth (SRB) have been shown to vary within and across populations, after over a century of research, explanations have remained elusive. A variety of ecological, demographic, economic, and social variables have been evaluated, yet their association with SRB has been equivocal. Here, in an attempt to shed light on this unresolved topic within the literature, we approach the question of what drives variation in SRB using detailed longitudinal data spanning the frontier-era to the early 20th century in a population from the US state of Utah. Using several measures of environmental harshness, we find that fewer boys are born during challenging times. However, these results hold only for the frontier-era and not into a period of rapid economic and infrastructure development. We argue that the mixed state of the literature may result from the impact and frequency of exogenous stressors being dampened due to industrialization.

Changing Age and Sex Structures and Their Consequences

2018 ◽  
Author(s):  
Michael Anderson ◽  
Corinne Roughley
Keyword(s):  
Western Europe ◽  
Sex Ratios ◽  
Age Groups ◽  
World War ◽  
Gender Differentials ◽  
And Migration ◽  
The Impact ◽  
First World ◽  
North Western ◽  
Age And Sex

Scotland’s age and sex profiles have changed markedly over time, reflecting changing numbers of births, and the age and sex profiles of mortality and migration. For much of the period, large gender-differentials in emigration gave Scotland the most skewed sex ratios in north-western Europe. The impact on sex ratios in the most marrying age groups of Scottish First World War deaths (whose numbers have often been much exaggerated) was much less than in England. There were major differences in both sex ratios and age profiles between different parts of the country. Its impact on local cultures and the position of women is explored. Crude birth and death rates, while important for some policy purposes where numbers matter, are misleading as guides to the relative impacts on people and families in any area.

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