Abstract

Despite deleterious effects on individuals, the t haplotype is a selfish genetic element present in many house mouse populations. By distorting the transmission ratio, +/t males transmit the t haplotype to up to 90% of their offspring. However, t/t individuals perish in utero. Theoretical models based on these properties predict a much higher t frequency than observed, leading to the t paradox. Here, we use empirical field data and theoretical approaches to investigate whether polyandry is a female counterstrategy against the negative fitness consequences of such distorters. We found a significant decrease of the t frequency over a period of 5.5 years that cannot be explained by the effect of transmission ratio distortion and recessive lethals, despite significantly higher life expectancy of +/t females compared to +/+ females. We quantified life-history data and homozygous and heterozygous fitness effects. Population subdivision and inbreeding were excluded as evolutionary forces influencing the t system. The possible influence of polyandry on the t system was then investigated by applying a stochastic model to this situation. Simulations show that polyandry can explain the observed t dynamics, making it a biologically plausible explanation for low t frequencies in natural populations in general.

Highlights

  • We found a significant decrease of the t frequency over a period of 5.5 years that cannot be explained by the effect of transmission ratio distortion and recessive lethals, despite significantly higher life expectancy of +/t females compared to +/+ females

  • The present study focuses on both empirical and theoretical approaches to understanding the dynamics of the t haplotype on a specific wild house mouse population

  • PREDICTIONS BASED ON DETERMINISTIC MODEL To investigate the potential impact of polyandry on the t frequency pt, the life cycle described by equations (1–4) was repeated for 1000 generations

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Summary

THE MODEL

A classical Fisher–Wright population with infinite population size and no mutation is assumed. The sex-independent t allele frequency pt can be expressed as pt = f 1 pt(1) + f 2 pt(2), where f 1 and f 2 are relative frequencies of females and males in the population ( f 1 + f 2 = 1). The frequency of single matings between a female of genotype a and a male of genotype b can be expressed as. If a female mates with more than one male, both “quantity” and “quality” of the sperm are assumed to determine the fertilization success of the involved males (gamete fitness). The zygote frequencies of the total population Paz(i) of the genotypes a ∈ {+ + , + t , tt } are given by the sum of the outcomes of each individual mating cross Paz weighed by the frequency of the respective mating cross derived in equations (1) and (2).

Zygote frequencies per mating cross
THE STUDY POPULATION
Results
Ne Effective population size τ
Supporting Information
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