title: Extraordinary sex ratios: cultural effects on ecological consequences.
abstract: We model sex-structured population dynamics to analyze pairwise competition between groups differing both genetically and culturally. A sex-ratio allele is expressed in the heterogametic sex only, so that assumptions of Fisher's analysis do not apply. Sex-ratio evolution drives cultural evolution of a group-associated trait governing mortality in the homogametic sex. The two-sex dynamics under resource limitation induces a strong Allee effect that depends on both sex ratio and cultural trait values. We describe the resulting threshold, separating extinction from positive growth, as a function of female and male densities. When initial conditions avoid extinction due to the Allee effect, different sex ratios cannot coexist; in our model, greater female allocation always invades and excludes a lesser allocation. But the culturally transmitted trait interacts with the sex ratio to determine the ecological consequences of successful invasion. The invading female allocation may permit population persistence at self-regulated equilibrium. For this case, the resident culture may be excluded, or may coexist with the invader culture. That is, a single sex-ratio allele in females and a cultural dimorphism in male mortality can persist; a low-mortality resident trait is maintained by father-to-son cultural transmission. Otherwise, the successfully invading female allocation excludes the resident allele and culture and then drives the population to extinction via a shortage of males. Finally, we show that the results obtained under homogeneous mixing hold, with caveats, in a spatially explicit model with local mating and diffusive dispersal in both sexes.
authors.affiliation: Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York, United States of America.
authors.forename: Ferenc
authors.initials: F
authors.lastname: Molnár
authors.forename: Thomas
authors.initials: T
authors.lastname: Caraco
authors.forename: Gyorgy
authors.initials: G
authors.lastname: Korniss
mesh_terms: D000465:Algorithms; D000483:Alleles; D000818:Animals; D005075:Biological Evolution; D001717:Birds; D002080:Butterflies; D003466:Cultural Characteristics; D004463:Ecology; D005260:Female; D008040:Genetic Linkage; D005828:Genetics, Population; D006801:Humans; D008297:Male; D008954:Models, Biological; D015233:Models, Statistical; D008962:Models, Theoretical; D011157:Population Dynamics; D012727:Sex Characteristics; D012744:Sex Ratio