Do differences in Toxoplasma prevalence influence global variation in secondary sex ratio? Preliminary ecological regression study

Abstract

Sex of the fetus is genetically determined such that an equal number of sons and daughters are born in large populations. However, the ratio of female to male births across human populations varies significantly. Many factors have been implicated in this. The theory that natural selection should favour female offspring under suboptimal environmental conditions implies that pathogens may affect secondary sex ratio (ratio of male to female births). Using regression models containing 13 potential confounding factors, we have found that variation of the secondary sex ratio can be predicted by seroprevalence of Toxoplasma across 94 populations distributed across African, American, Asian and European continents. Toxoplasma seroprevalence was the third strongest predictor of secondary sex ratio, β = −0·097, P < 0·01, after son preference, β = 0·261, P < 0·05, and fertility, β = −0·145, P < 0·001. Our preliminary results suggest that Toxoplasma gondii infection could be one of the most important environmental factors influencing the global variation of offspring sex ratio in humans. The effect of latent toxoplasmosis on public health could be much more serious than it is usually supposed to be.

The Role of Hormones and Toxoplasma gondii Infection to Change the Secondary Sex Ratio

“…In a systematic review of several toxoplasmosis infection and male birth is negative. They found that low concentrations of parasite antibodies stimulate more male birth [30]. These results are consistent with the findings of our current study, which can explain this result to the effect of sex hormones, including testosterone, as females with low testosterone concentration have an increased chance of giving birth to females [31].…”

Association between latent toxoplasmosis and fertility parameters of men

“…On the other hand, latent toxoplasmosis affects about one third of the world's population. Therefore, its effects on human reproduction, although sometimes small on the level of individuals, could be important on the level of the large populations 62 . The results of our observational study suggest that more attention should be paid to the study of the effects of latent toxoplasmosis on male reproductive functions in the future.…”

Do Toxoplasma-Infected Subjects Have Better Leadership Skills? Comment on Paper “Puppet Master: Possible Influence of the Parasite Toxoplasma gondii on Managers and Employees”

“…Women infected with Toxoplasma for less than two years give birth to 2.5 more sons than daughters, while the women infected for a longer time give birth to significantly more daughters than sons. The long term negative effect of toxoplasmosis on offspring sex ratio is more important than the transient positive effect of toxoplasmosis on the offspring sex ratio, as the secondary sex ratio (fraction of newborn males) correlates negatively with prevalence of toxoplasmosis in particular countries (Dama, Novakova, & Flegr, 2016). Despite the fact that our data brought no formal proof for this, Houdek could be right when saying: "Toxoplasmapositive people can achieve high positions, but their performance may decline due to a decrease in conscientiousness, increased neuroticism, and possible health risks."…”