Generation of sex ratio biases in the red-tailed phascogale (Phascogale calura)

2008 ◽  
Vol 20 (2) ◽  
pp. 275 ◽  
Author(s):  
W. K. Foster ◽  
D. A. Taggart
Keyword(s):  
Sex Ratio ◽  
Mating System ◽  
Meta Analysis ◽  
Sex Ratios ◽  
Corpora Lutea ◽  
Sex Ratio At Birth ◽  
Maternal Weight ◽  
Female Age ◽  
Male Bias ◽  
Sex Biases

Male semelparous dasyurid species are annual breeders that use a promiscuous mating system. These species have shown biases in litter sex ratios and, with females producing more young than they have available teats, this provides an opportunity for the manipulation of the sex ratio at birth. The sex ratio of embryos and pouch young, and the degree of embryonic overproduction, in red-tailed phascogales (Phascogale calura) was investigated to gain an understanding of the mechanism by which sex biases may be generated. The sex ratio of embryos did not differ from parity, but a male bias was observed in young attaching to teats. Females produced an average of 15.1 ± 1.9 corpora lutea and 10.5 ± 3.5 viable embryos, with no difference in fecundity observed with female age or weight. Because females only have eight teats, the overproduction of young, and male-biased attachment, was sufficient to explain the observed male bias in pouch young. No relationship was observed between maternal weight and sex ratio, but heavier females did tend to produce more ova. Meta-analysis of studies providing information on litter sex ratios in male semelparous dasyurid species did not show any consistent trend.

Biased sex ratios and parasite mating probabilities

Parasitology ◽  
1993 ◽  
Vol 107 (3) ◽  
pp. 287-295 ◽  
Author(s):  
R. M. May ◽  
M. E. J. Woolhouse
Keyword(s):  
Population Dynamics ◽  
Sex Ratio ◽  
Mating System ◽  
Sex Ratios ◽  
Theoretical Framework ◽  
Main Body ◽  
Female Mating ◽  
The Mean ◽  
Mated Female

SummaryAn earlier paper (May, 1977) developed a theoretical framework for exploring the consequences of dioecy for the population dynamics of schistosomes, assuming an unbiased sex ratio. This paper extends the analysis to biased sex ratios, as have been reported in practice. We consider the relationships of the mean number and distribution of worms among hosts, the sex ratio, and the mating system (monogamous or polygamous) to: (i) the female mating probability, Φ the prevalence of mated female worms. Ω: and (iii) the mean number of mated female worms per host, ξ. Among other results, we show how high values of Φ are associated with male-biased sex ratios and polygamous mating; that Ω is independent of the mating system and is relatively unaffected by the sex ratio; and that ξ is maximal for unbiased sex ratios given monogamous mating, and for female-biased sex ratios if mating is polygamous. These results, together with the confounding effects of the mean number and distribution of worms, are described in detail in the main body of the paper.

Sex-Ratios and Related Characteristics in Spinifex sericeus (Poaceae)

1990 ◽  
Vol 38 (2) ◽  
pp. 153 ◽  
Author(s):  
KM Maze ◽  
RDB Whalley
Keyword(s):  
Sex Ratio ◽  
New Caledonia ◽  
New South ◽  
Sand Dunes ◽  
Sex Ratios ◽  
Experimental Period ◽  
North Coast ◽  
Male Bias ◽  
South Wales ◽  
Males And Females

Spinifex sericeus R.Br. is a dioecious, stoloniferous grass which occurs on sand dunes around much of the south-eastern coastline of Australia, New Zealand and New Caledonia. Sex ratios of ramets of S. sericeus and some associated characteristics were studied on the mid-north coast of New South Wales. Generally there was a male bias in the observed ramet sex ratio, although the extent of this bias varied with the beach investigated, the position in the dunes and the time of sampling. Male inflorescences matured and died more rapidly than females, and hence the observed male bias was greatest at the beginning of the flowering period. Male ramets were found to have more sexual tillers per clump than female ramets. The genet sex ratio was estimated from plants grown from seed and separated from each other throughout the experimental period. Males and females were found to be equal in number, although this equality may not be a true reflection of the genet sex ratio in the field.

scholarly journals Sex-selective Abortion Bans are Not Associated with Changes in Sex Ratios at Birth in Illinois and Pennsylvania

2017 ◽  
Author(s):  
Sital Kalantry
Keyword(s):  
Sex Ratio ◽  
Census Data ◽  
Sex Ratios ◽  
State Legislatures ◽  
The United States ◽  
Sex Selection ◽  
Sex Ratio At Birth ◽  
Selective Abortion ◽  
Sex Selective Abortion ◽  
Newborn Children

Legal prohibitions on sex-selective abortions are proliferating in the United States. Eight state legislatures have banned abortions sought on the basis of the sex of the fetus, 21 states have considered such laws since 2009, and a similar bill is pending in U.S. Congress. These laws have been introduced and enacted without any empirical data about their impact or effectiveness. Prior studies of U.S. Census data found sex ratios among foreign-born Chinese, Korean and Indian immigrants were skewed in favor of boys, but only in families where there were already one or two girls. Using the variation in the timing of bans in Illinois and Pennsylvania as natural experiments, we compare the pre-ban and post-ban sex ratios of certain Asian newborn children in these states over 12-year periods. We then compare these ratios with the sex ratios of Asian newborn children in neighboring states during the same period. We find that the bans in Illinois and Pennsylvania are not associated with any changes in sex ratios at birth among Asians. In Illinois and its neighboring states, the sex ratio at birth of Asian children was not male-biased during our study period. On the other hand, the sex ratio at birth among Asians in Pennsylvania and its neighboring states was skewed slightly in favor of boys, but the enactment of the ban did not normalize the sex ratio. This strongly suggests that sex-selective abortion bans have had no impact on the practice of sex selection, to the extent that it occurs, in these states. This finding is highly relevant to legislative and policy debates in the U.S. Congress and state legislatures where sex-selective abortion laws are being considered.Published: Sex-selective Abortion Bans are Not Associated with Changes in Sex Ratios at Birth in Illinois and Pennsylvania (with Arindam Nandi and Brian Citro), Forum on Health and Economic Policy, December 2014 (peer-reviewed journal).

SEX RATIO AT BIRTH AND FAMILY COMPOSITION IN SUB-SAHARAN AFRICA: INTER-COUPLE VARIATIONS

2009 ◽  
Vol 41 (3) ◽  
pp. 399-407 ◽  
Author(s):  
MICHEL GARENNE
Keyword(s):  
Sex Ratio ◽  
Sex Ratios ◽  
The United States ◽  
Sub Saharan Africa ◽  
Family Composition ◽  
Sex Ratio At Birth ◽  
First Birth ◽  
Wide Range ◽  
Sub Saharan ◽  
Linear Logistic Model

SummaryIn this study, sex ratios at birth (male/female births) were found to vary according to family composition. Using Demographic and Health Survey (DHS) maternity histories from sub-Saharan Africa, the study shows that the sex ratio at birth increases with the number of previous male births and decreases with the number of previous female births. For families with only males, the sex ratio increases from 1·046 for the first birth to 1·083 for the 8th birth. For families with only females, the sex ratio decreases from 1·046 for the first birth to 0·942 for the 8th birth. The differences were highly significant when tested with a linear logistic model (p=0·018 for males; p=1·85✕10−11 for females). The effect was not symmetrical, and was found to be significantly stronger for females. These effects could be reproduced assuming a strong heterogeneity between couples. The distribution of sex ratios was fitted with an asymmetrical log-gamma function, which revealed a wide range of variation in the sex ratio between 0·50 and 1·30, and a peak around 1·14. The results and their implications are discussed in the light of former findings in France and in the United States of America.

THE HIGH SEX RATIO IN CHINA: WHAT DO THE CHINESE THINK?

2011 ◽  
Vol 44 (1) ◽  
pp. 121-125 ◽  
Author(s):  
C. ZHOU ◽  
X. L. WANG ◽  
W. J. ZHENG ◽  
X. D. ZHOU ◽  
L. LI ◽  
...  
Keyword(s):  
Sex Ratio ◽  
Sex Ratios ◽  
Sex Ratio At Birth ◽  
Asian Countries ◽  
Negative Impacts

SummaryHigh sex ratios are well documented in many Asian countries, including China. This study was conducted in three Chinese provinces to explore awareness of the high sex ratios and its effects. Questionnaires were completed by 7435 respondents; 46% were urban and 53% were female. Sixty-four per cent were aware of the high sex ratio, and the majority were able to identify a range of consequences both for society and for unmarried men. These high levels of awareness of the negative impacts of high sex ratios should ultimately help to reduce the sex ratio at birth.

Experimental observations on the sex ratio of adult Schistosoma mansoni, with comments on the natural male bias

Parasitology ◽  
2000 ◽  
Vol 121 (4) ◽  
pp. 379-383 ◽  
Author(s):  
J. BOISSIER ◽  
H. MONÉ
Keyword(s):  
Sex Ratio ◽  
Schistosoma Mansoni ◽  
Sex Ratios ◽  
Vertebrate Host ◽  
Natural Conditions ◽  
Male And Female ◽  
Male Bias ◽  
Biased Sex Ratio ◽  
And Bisexual

The sex ratio of adult worms has been observed biased towards males in Schistosoma mansoni under natural conditions. The origin of this bias is unknown. This paper determines whether males are more infective than females under controlled experimental bisexual conditions, and hence if the sex ratio is male-biased as a consequence of this. The male and female cercarial infectivities in uni- and bisexual vertebrate host infections using a range of controlled cercarial sex ratios were studied. The results showed that, in experimental unisexual infections, male cercariae were more infective than females, and that in experimental bisexual infections, male cercarial infectivity was similar to that of female, irrespective of cercarial sex ratio. Furthermore, cumulative male and female cercarial infectivity was maximal when sex ratio was equilibrated. The unbiased sex ratios obtained in our experimental bisexual infections are discussed in terms of behavioural and/or biochemical male–female interaction. Alternative explanations of the natural biased sex ratio are proposed.

scholarly journals Age-Dependent Constraints of Sex Allocation in a Parasitoid Wasp

2014 ◽  
Vol 2014 ◽  
pp. 1-4 ◽  
Author(s):  
Takatoshi Ueno
Keyword(s):  
Sex Ratio ◽  
Sex Ratios ◽  
Parasitoid Wasp ◽  
Maternal Control ◽  
Offspring Sex Ratio ◽  
Female Age ◽  
Physiological Constraints ◽  
Offspring Sex ◽  
Age Dependent ◽  
Control Failure

The offspring sex ratios of parasitoid wasps often depend on the age of ovipositing females. Physiological constraints such as sperm depletion and senescence are a likely cause. Also, maternal control in response to female age may be an alternative explanation. Here valvifer or abdominal tip movements were used to assess whether age-dependent sex ratio was due to physiological constraints or maternal control with an ichneumonid wasp,Pimpla nipponica; the offspring sex ratio at the time of wasp emergence was compared with the sex ratio predicted from abdominal tip movements. When the female was relatively young, there was little difference between the sex ratios examined. However, as the age of the females increased, the realized offspring sex ratio at wasp emergence was more male-biased than the sex ratio predicted at the time of oviposition. Thus, there was an inconsistency between the sex ratios. Curiously, the predictions of continuous movements for male egg deposition were always perfect, regardless of maternal age; fertilization control failure was detected when the females had decided to lay female eggs. Thus, physiological constraints are a likely explanation for the inconsistency in relation to female age forP. nipponica.

scholarly journals Sex biases in bird and mammal natural history collections

2019 ◽  
Vol 286 (1913) ◽  
pp. 20192025 ◽  
Author(s):  
Natalie Cooper ◽  
Alexander L. Bond ◽  
Joshua L. Davis ◽  
Roberto Portela Miguez ◽  
Louise Tomsett ◽  
...  
Keyword(s):  
Body Size ◽  
Natural History ◽  
Evolutionary Biology ◽  
Large Scale ◽  
Sex Ratios ◽  
Museum Specimens ◽  
Male Bias ◽  
Biological Sex ◽  
Natural History Collections ◽  
Sex Biases

Natural history specimens are widely used across ecology, evolutionary biology and conservation. Although biological sex may influence all of these areas, it is often overlooked in large-scale studies using museum specimens. If collections are biased towards one sex, studies may not be representative of the species. Here, we investigate sex ratios in over two million bird and mammal specimen records from five large international museums. We found a slight bias towards males in birds (40% females) and mammals (48% females), but this varied among orders. The proportion of female specimens has not significantly changed in 130 years, but has decreased in species with showy male traits like colourful plumage and horns. Body size had little effect. Male bias was strongest in name-bearing types; only 27% of bird and 39% of mammal types were female. These results imply that previous studies may be impacted by undetected male bias, and vigilance is required when using specimen data, collecting new specimens and designating types.

scholarly journals Sex-selective Abortion Bans are Not Associated with Changes in Sex Ratios at Birth among Asian Populations in Illinois and Pennsylvania

2015 ◽  
Vol 18 (1) ◽  
pp. 41-64
Author(s):  
Arindam Nandi ◽  
Sital Kalantry ◽  
Brian Citro
Keyword(s):  
Sex Ratio ◽  
Census Data ◽  
Sex Ratios ◽  
State Legislatures ◽  
The United States ◽  
Sex Selection ◽  
Sex Ratio At Birth ◽  
Selective Abortion ◽  
Sex Selective Abortion ◽  
Newborn Children

Abstract Legal prohibitions on sex-selective abortions are proliferating in the United States. Eight state legislatures have banned abortions sought on the basis of the sex of the fetus, 21 states have considered such laws since 2009, and a similar bill is pending in U.S. Congress. These laws have been introduced and enacted without any empirical data about their impact or effectiveness. Prior studies of U.S. Census data found sex ratios among foreign-born Chinese, Korean and Indian immigrants were skewed in favor of boys, but only in families where there were already one or two girls. Using the variation in the timing of bans in Illinois and Pennsylvania as natural experiments, we compare the pre-ban and post-ban sex ratios of certain Asian newborn children in these states over 12-year periods. We then compare these ratios with the sex ratios of Asian newborn children in neighboring states during the same period. We find that the bans in Illinois and Pennsylvania are not associated with any changes in sex ratios at birth among Asians. In Illinois and its neighboring states, the sex ratio at birth of Asian children was not male-biased during our study period. On the other hand, the sex ratio at birth among Asians in Pennsylvania and its neighboring states was skewed slightly in favor of boys, but the enactment of the ban did not normalize the sex ratio. This strongly suggests that sex-selective abortion bans have had no impact on the practice of sex selection, to the extent that it occurs, in these states. This finding is highly relevant to legislative and policy debates in the U.S. Congress and state legislatures where sex-selective abortion laws are being considered.

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