title: 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.
authors.affiliation: Institute of Wildlife Veterinary Research, KVAFSU,Doddaluvara,Kodagu 571232,India.
authors.forename: Madhukar S
authors.initials: MS
authors.lastname: Dama
authors.affiliation: Department of Anthropology,Faculty of Humanities,Charles University,Prague 158 00,Czech Republic.
authors.forename: Lenka
authors.initials: L
authors.lastname: Martinec Nováková
authors.affiliation: Department of Biology,Faculty of Science,Charles University,Prague 128 44,Czech Republic.
authors.forename: Jaroslav
authors.initials: J
authors.lastname: Flegr
mesh_terms: D002980:Climate; D015986:Confounding Factors, Epidemiologic; D002149:Energy Intake; D005260:Female; D005298:Fertility; D014943:Global Health; D006304:Health Status; D006801:Humans; D007182:Income; D008297:Male; D008393:Marriage / Q000706:statistics & numerical data; D015995:Prevalence; D012044:Regression Analysis; D012744:Sex Ratio; D012959:Socioeconomic Factors; D014123:Toxoplasmosis / Q000453:epidemiology* / Q000503:physiopathology; D055815:Young Adult
keywords: Toxoplasmosis; Trivers Willard effect; ecological regression; manipulation hypothesis; secondary sex ratio