Estimation of multiple male mating frequency using paternity skew: An example from a grey-sided vole (Myodes...

Multiple male mating (MMM) causes sperm competition, which may play an important role in the evolution of reproductive traits. The frequency of multiple paternity (MP), where multiple males sire offspring within a single litter, has been used as an index of MMM frequency. However, MP frequency is necessarily lower than MMM frequency. The magnitude of the difference between MMM and MP frequency depends on litter size (LS) and fertilization probability skew (FPS), and this difference may be meaningfully large in animals with small LSs. In this study, we propose a method to estimate MMM frequency using an individual-based model with three variables (MP frequency, LS and FPS). We incorporated observed paternity skew data to infer a possible range of FPS that cannot be measured in free-living populations and tested the validity of our method using a data set from a grey-sided vole (Myodes rufocanus) population and from hypothetical populations. MP was found in 50 out of 215 litters (23.3%) in the grey-sided vole population, while MMM frequency was estimated in 67 of 215 litters (31.2%), with a certainty range of 59-88 (27.4%-40.9%). The point estimation of MMM frequency was realized, and the certainty range was limited within the practical range. The use of observed paternity skew was very effective at narrowing the certainty range of the estimate. Our method could contribute to a deeper understanding of the ecology of MMM in free-living populations.