title: Male pygmy hippopotamus influence offspring sex ratio.
abstract: Pre-determining fetal sex is against the random and equal opportunity that both conceptus sexes have by nature. Yet, under a wide variety of circumstances, populations shift their birth sex ratio from the expected unity. Here we show, using fluorescence in situ hybridization, that in a population of pygmy hippopotamus (Choeropsis liberiensis) with 42.5% male offspring, males bias the ratio of X- and Y-chromosome-bearing spermatozoa in their ejaculates, resulting in a 0.4337±0.0094 (mean±s.d.) proportion of Y-chromosome-bearing spermatozoa. Three alternative hypotheses for the shifted population sex ratio were compared: female counteract male, female indifferent, or male and female in agreement. We conclude that there appears little or no antagonistic sexual conflict, unexpected by prevailing theories. Our results indicate that males possess a mechanism to adjust the ratio of X- and Y-chromosome-bearing spermatozoa in the ejaculate, thereby substantially expanding currently known male options in sexual conflict.
authors.affiliation: Research Group Reproductive Management, Leibniz Institute for Zoo and Wildlife Research, Alfred-Kowalke strasse 17, Berlin, Germany. Saragusty@izw-berlin.de
authors.forename: Joseph
authors.initials: J
authors.lastname: Saragusty
authors.forename: Robert
authors.initials: R
authors.lastname: Hermes
authors.forename: Heribert
authors.initials: H
authors.lastname: Hofer
authors.forename: Tim
authors.initials: T
authors.lastname: Bouts
authors.forename: Frank
authors.initials: F
authors.lastname: Göritz
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Hildebrandt
mesh_terms: D000818:Animals; D005260:Female; D017404:In Situ Hybridization, Fluorescence; D008297:Male; D008322:Mammals / Q000502:physiology*; D011157:Population Dynamics; D019849:Sex Determination Processes; D012737:Sex Factors; D012744:Sex Ratio; D013094:Spermatozoa / Q000502:physiology*; D014960:X Chromosome; D014998:Y Chromosome