title: Sex allocation conflict between queens and workers in Formica pratensis wood ants predicts seasonal sex ratio variation.
abstract: Sex allocation theory predicts parents should adjust their investment in male and female offspring in a way that increases parental fitness. This has been shown in several species and selective contexts. Yet, seasonal sex ratio variation within species and its underlying causes are poorly understood. Here, we study sex allocation variation in the wood ant Formica pratensis. This species displays conflict over colony sex ratio as workers and queens prefer different investment in male and female offspring, owing to haplodiploidy and relatedness asymmetries. It is unique among Formica ants because it produces two separate sexual offspring cohorts per season. We predict sex ratios to be closer to queen optimum in the early cohort but more female-biased and closer to worker optimum in the later one. This is because the power of workers to manipulate colony sex ratio varies seasonally with the availability of diploid eggs. Consistently, more female-biased sex ratios in the later offspring cohort over a three-year sampling period from 93 colonies clearly support our prediction. The resulting seasonal alternation of sex ratios between queen and worker optima is a novel demonstration how understanding constraints of sex ratio adjustment increases our ability to predict sex ratio variation.
authors.affiliation: Centre of Excellence in Biological Interactions, Department of Biosciences, University of Helsinki, POB 65, FI-00014, Helsinki, Finland. heikki.helantera@helsinki.fi.|Tvärminne Zoological Station, University of Helsinki, J.A. Palménin tie 260, FI-10900, Hanko, Finland. heikki.helantera@helsinki.fi.
authors.forename: Heikki
authors.initials: H
authors.lastname: Helanterä
authors.affiliation: Centre of Excellence in Biological Interactions, Department of Biosciences, University of Helsinki, POB 65, FI-00014, Helsinki, Finland.|Tvärminne Zoological Station, University of Helsinki, J.A. Palménin tie 260, FI-10900, Hanko, Finland.|Current Address: Department of Animal and Plant Sciences, Alfred Denny Building, University of Sheffield, Western Bank, S10 2TN, Sheffield, United Kingdom.|Department of Biology and Biocenter Oulu, University of Oulu, FI-90014, Oulu, Finland.
authors.forename: Jonna
authors.initials: J
authors.lastname: Kulmuni
authors.affiliation: Centre of Excellence in Biological Interactions, Department of Biosciences, University of Helsinki, POB 65, FI-00014, Helsinki, Finland.|Tvärminne Zoological Station, University of Helsinki, J.A. Palménin tie 260, FI-10900, Hanko, Finland.
authors.forename: Pekka
authors.initials: P
authors.lastname: Pamilo
mesh_terms: D000818:Animals; D001000:Ants / Q000235:genetics* / Q000502:physiology; D005260:Female; D006238:Haploidy; D008297:Male; D012621:Seasons; D012744:Sex Ratio
keywords: Fitness; inclusive; kin conflict; kin selection; sex ratio conflict; social evolution