Male-biased Secondary Sex Ratio Research Articles

The association between the 2D:4D ratio and offspring sex at birth: A cross‐sectional study in Ghana

The 2D:4D ratio is the putative marker of prenatal androgen exposure. Low maternal 2D:4D ratio has been associated with high or male-biased secondary sex ratio. Hitherto, there has not been any study in Ghana regarding the maternal 2D:4D ratio and sex ratio at birth. This study sought to investigate this observation in a Ghanaian population. The study was cross-sectional from December 2020 to April 2021 involving 272 first-time mothers. The mean ± SD age of the mothers was 23.9 ± 3.67 years. The right (2D:4DR), the left (2D:4DL), the mean (M2D:4D) digit ratios and the right-left difference (Dr-l) of the mothers were measured using computer-assisted analysis. The mothers were stratified by their digit ratios, and the cohort sex ratio (CSR) for each stratum was then calculated as the proportion of sons. The mean ± SD of the 2D:4DR of mothers-with-daughters and mothers-with-sons were 0.941 ± 0.032 and 0.933 ± 0.037, respectively. The mean ± SD of the 2D:4DL of mothers-with-daughters was 0.934 ± 0.034, while that of mothers-with-sons was 0.931 ± 0.039. The offspring sex at birth and the CSR was not associated with either the mother's right, left, mean 2D:4D ratio or their difference (Dr-l). However, mothers-with-daughters showed rightward asymmetry in their 2D:4D ratios as the Dr-l significantly and positively deviated from zero (p < .010). The maternal 2D:4D ratio may not be associated with their offspring sex at birth among first-time mothers. This study adds to the limited data on studies regarding offspring sex at birth and the 2D:4D ratio in Ghana and Sub-Saharan Africa.

Reproductive potential and seed fate of Sclerocarya birrea subsp. caffra (marula) in the low altitude savannas of South Africa

Even though Sclerocarya birrea subsp. caffra (marula) is a well-studied, keystone tree species with high ecological, commercial and cultural value, significant gaps in our understanding of its reproductive biology exist, particularly the factors limiting fruit and seed production, seed fate and the persistence of the seed bank. Therefore, a detailed quantitative assessment of these factors was conducted at five sites in the low altitude savannas of South Africa. Sites varied with respect to fire regime, large mammals, geology and rainfall. Most sites showed male-biased secondary sex ratios and the minimum fruiting stem diameter ranged between 7.1 and 15.7 cm across sites. Sites with higher levels of disturbance (fire and large browsers) had trees producing fruit at larger minimum stem diameters than sites with lower levels of disturbance. Fruit production was highly variable between individuals, within and between sites, and from year to year. Variability in fruit production across years at one site was greater than the variability across sites in one year, indicating that drivers such as weather, insect herbivory, fire and predator numbers, which vary annually, play a greater role than more constant drivers such as mammalian herbivory, soil types or long-term rainfall. No significant relationship was found between environmental variables (rainfall and temperature) and annual fruit production, indicating a trade-off between vegetative growth and reproduction between years. Since marula fruits are large and heavy, the species relies primarily on mammalian dispersal agents such as the African elephant, which have also been shown to increase the germination rate. However, rodents also appear to play a significant role in seed dispersal. Seed predation rates tend to be highest in areas of low disturbance (no fire and no large browsers). While marula has a small persistent seed bank, recruitment appears to be reliant on the current season's fruit crop. This study provides a detailed quantitative assessment of important reproductive and seed fate vital rates for future population modelling.

Sex-ratio distortion driven by migration loads

The significance of migration load in driving the evolution of recipient populations has long been documented in population genetics, but its effects have not been linked to the formation of biased sex ratios in natural populations. In this study, we develop a single-locus model to demonstrate how the migration load can shape the primary and secondary sex ratios in dioecious plants where sexual dimorphism is determined by the sex chromosomes (the XX–XY or similar systems). Our results show that migration load can generate an array of sex ratios (from the female- to male-biased primary/secondary sex ratios), depending on the selection systems at the gametophyte and sporophyte stages and on the sex ratio in the migrating seeds. Ovule abortion and the purging of maladaptive genes from the immigrating pollen at the gametophyte stage can alter the primary sex ratio and indirectly alter the secondary sex ratio. The presence of maladaptive sex-linked genes from the migrating pollen and seeds of males facilitates the outcome of the female-biased secondary sex ratios, while the presence of maladaptive sex-linked genes from the migrating seeds of females can lead to the male-biased secondary sex ratios. The detrimental effects of the Y-chromosome from the migrating pollen and seeds can enhance the formation of female-biased primary and secondary sex ratios. These theoretical predictions highlight an alternative approach to the existing sex-ratio theories for interpreting the formation of biased sex ratios in the populations that are subject to the impacts of maladaptive genes from immigrants.

Classification and Differential Diagnosis of Malignant Lymphomas, Abstract 126–130, Symposium

The significance of migration load in driving the evolution of recipient populations has long been documented in population genetics, but its effects have not been linked to the formation of biased sex ratios in natural populations. In this study, we develop a single-locus model to demonstrate how the migration load can shape the primary and secondary sex ratios in dioecious plants where sexual dimorphism is determined by the sex chromosomes (the XX–XY or similar systems). Our results show that migration load can generate an array of sex ratios (from the female- to male-biased primary/secondary sex ratios), depending on the selection systems at the gametophyte and sporophyte stages and on the sex ratio in the migrating seeds. Ovule abortion and the purging of maladaptive genes from the immigrating pollen at the gametophyte stage can alter the primary sex ratio and indirectly alter the secondary sex ratio. The presence of maladaptive sex-linked genes from the migrating pollen and seeds of males facilitates the outcome of the female-biased secondary sex ratios, while the presence of maladaptive sex-linked genes from the migrating seeds of females can lead to the male-biased secondary sex ratios. The detrimental effects of the Y-chromosome from the migrating pollen and seeds can enhance the formation of female-biased primary and secondary sex ratios. These theoretical predictions highlight an alternative approach to the existing sex-ratio theories for interpreting the formation of biased sex ratios in the populations that are subject to the impacts of maladaptive genes from immigrants.

Primary and secondary sex ratios in monogyne colonies of the fire ant

Patterns of sex ratios and sex investment ratios play an instrumental role in theoretical and empirical considerations of the evolution and maintenance of insect sociality. An assumption of sex-ratio studies in the eusocial Hymenoptera is that workers, who reproduce indirectly by rearing the queen's offspring, have the ability to distinguish the sex of larvae and direct preferential treatment towards developing females. To determine if workers of the monogyne (single queen per colony) form of the fire ant, Solenopsis invicta, have this ability and the extent to which they might use it to influence the sex ratio of the colony's reproductives, the primary sex ratio (ratio of male/female-determined eggs produced by the queen) and the secondary sex ratio (ratio of male/female reproductive adults or pupae) were compared, in mature colonies producing sexuals of almost exclusively one sex or the other, a common condition in monogyne colonies of this and other ant species. Queens of male-producing colonies laid about 19% haploid (male) eggs, whereas queens of female-producing colonies laid about 11% haploid eggs. In both cases, the proportion of haploid eggs laid was far higher than the proportion of adult males reared by the workers. These results suggest that workers strongly influence the colony's secondary sex ratio by selective elimination of male larvae, but the magnitude of this influence depends upon the primary sex ratio produced by the queen. Highly male-biased secondary sex ratios produced by workers in relation to more male-biased primary sex ratios may be caused by ergonomic constraints that could limit the ability of workers to skew the sex-investment ratio.

Gender Dimorphism in Growth and Mass Partitioning by Box-Elder (Acer negundo L.)

Sex ratio, growth rate, aboveground biomass allocation and phenology of the genders of Acer negundo were investigated. Male biased secondary sex ratios were consistent throughout 11 populations examined indicating that male bias is a real population phenomenon despite nonsignificance within most populations. Nonsignificant 'differences between genders in within-year growth (basal diameter) were found but significantly greater female growth occurred over the 1st 15 years of an individual's life span. Regressions of harvest data showed males to have significantly more foliage mass (P <0.001), more inflorescences (P <0.001) and a greater mass in flowers (P <0. 001). Females have greater total reproductive mass expenditure (P <0.001) and exceeded males in estimated seasonal wood production. Although male and female phenology differ significantly, it does not account for the observed differences in growth. Gender specific response to increased density is discussed using these and previously published results, suggesting that density is positively correlated with the degree of gender dimorphism. Our results contradict the idea that cost to a female's growth and/or maintenance result from a relatively greater reproductive effort and indicate that greater consideration of demographic and ecological variables is required.

Sex Ratio and Local Resource Competition in a Prosimian Primate

Competition between female kin for local limiting resources may explain a male-biased secondary sex ratio in the prosimian Galago crassicaudatus. Data demonstrating the skewed sex ratio, a brief summary of field observations on the species, and a simple mathematical statement of the hypothesis are presented. Local resource competition may influence sex ratio in other mammals.