High Fat Diet Prevents Over-Crowding Induced Decrease of Sex Ratio in Mice

Adaptive theory predicts that mothers would be advantaged by adjusting the sex ratio of their offspring in relation to their offspring's future reproductive success. In the present study, we tested the effect of housing mice under crowded condition on the sex ratio and whether the fat content of the diet has any influence on the outcome of pregnancies. Three-week-old mice were placed on the control diet (NFD) for 3 weeks. Thereafter the mice were allotted randomly to two groups of 7 cages each with 4, 6, 8, 10, 12, 14, and 16 mice in every cage to create increasing crowding gradient and fed either NFD or high fat diet (HFD). After 4 weeks, dams were bred and outcomes of pregnancy were analyzed. The average dam body weight (DBW) at conception, litter size (LS) and SR were significantly higher in HFD fed dams. Further, male biased litters declined with increasing crowding in NFD group but not in HFD. The LS and SR in NFD declined significantly with increasing crowding, whereas only LS was reduced in HFD group. We conclude that female mice housed under overcrowding conditions shift offspring SR in favor of daughters in consistent with the TW hypothesis and high fat diet reduces this influence of overcrowding

Sex Ratio at Birth and Mortality Rates Are Negatively Related in Humans

Evolutionary theory posits that resource availability and parental investment ability could signal offspring sex selection, in order to maximize reproductive returns. Non-human studies have provided evidence for this phenomenon, and maternal condition around the time of conception has been identified as most important factor that influence offspring sex selection. However, studies on humans have reported inconsistent results, mostly due to use of disparate measures as indicators of maternal condition. In the present study, the cross-cultural differences in human natal sex ratio were analyzed with respect to indirect measures of condition namely, life expectancy and mortality rate. Multiple regression modeling suggested that mortality rates have distinct predictive power independent of cross-cultural differences in fertility, wealth and latitude that were earlier shown to predict sex ratio at birth. These findings suggest that sex ratio variation in humans may relate to differences in parental and environmental conditions

Predicted sex ratio at birth as a function of parasite stress across 226 countries.

<p>Solid line represents the fitted linear trend and dotted lines its 95% confidence intervals.</p

Independent samples t test for estimated data against missing data.

<p>Independent samples t test for estimated data against missing data.</p

Parasite Stress Predicts Offspring Sex Ratio

<div><p>In this study, I predict that the global variation of offspring sex ratio might be influenced in part by the level of parasite stress. From an energetic standpoint, higher gestational costs of producing a male offspring could decrease male births in a population with limited resources. This implies that, any factor that limits the parental resources could be expected to favor female offspring production. Human sex ratio at birth (SRB) is believed to be influenced by numerous socioeconomic, biological, and environmental factors. Here, I test a prediction that parasite stress, by virtue of its effects on the general health condition, may limit the parental investment ability and therefore could influence the SRB at the population level. The statistical analysis supports this prediction, and show that the level of parasite stress has a significant inverse relation with population SRB across the world. Further, this relation is many-folds stronger than the association of SRB with other factors, like; polygyny, fertility, latitude, and son-preference. Hence, I propose that condition affecting ability of parasites (but not adaptive significance) could be a likely causal basis for the striking variation of SRB across populations.</p> </div

Correlations between individual parasite stress, latitude and sex ratio at birth in temperate and tropical countries.

<p>N = 182, 102 and 80 countries respectively for total, tropical zone and temperate zone.</p

Ridge regression summary for predicting offspring sex ratio using test variables.

<p>Whole model: n = 226 countries, R² = .32391749, F_(11,214) = 9.3209, p<0.00000.</p

The best-fit models among the ten variables, based on AIC-based model selection.

<p>The best-fit models among the ten variables, based on AIC-based model selection.</p

Dam body weight at conception and outcomes of pregnancy in NFD and HFD groups.

<p>a) Dam body weight (b = 0.03 vs. 0.02, both <i>P</i><0.05), b) Litter size (b = −0.30 vs. −0.26, both <i>P</i><0.01), c) Percent male biased litters (b = −4.29, <i>P</i><0.01vs. −0.36, <i>P</i>>0.05) and d) Sex ratio (<i>b</i> = −0.02, <i>P</i><0.01 vs. 0.00, <i>P</i>>0.05). Squares represent NFD, crosses represent HFD, broken and solid lines are linear trends through NFD and HFD datasets, respectively.</p