Mating structure & multiple paternity in house mice with implications for management

Invasive house mice (Mus musculus) can spread disease and frequently damage agriculture, infrastructure, and biodiversity. Genetic engineering and, specifically, gene drives are being explored as new methods to effectively suppress rodent pests. Prior to trialing a genetically engineered mouse in the wild, quantitative models and free-ranging lab/pen trials are the best methods for understanding gene drive effectiveness and risks to the environment. Current gene drive models lack predictive power due to gaps in basic understanding of mouse breeding ecology, particularly with respect to rates of multiple paternity and female breeding structure under natural conditions. Our study aimed to better understand characteristics critical for predicting gene drive spread in wild mouse populations, including breeding structure, mate competition, multiple paternity, and gene flow levels. Known numbers of wild-caught mice were placed in an indoor pen at USDA and monitored for several months. Genotyping all trialed mice (n = 29) and offspring (n = 53) allowed us to reconstruct parentage of every individual born during the trial period. The process entailed analysis of 10 microsatellite loci per individual, and then matching each offspring’s genotype to potential dams and sires using program CERVUS 3.0.7. Of the 11 dams with known litters, nine were sired by a single male and two had multiple sires (one litter with five successful fathers and one with two fathers). Of the 15 males that were trialed in the arena, just seven (47%) sired offspring. Female mate competition also appears frequent as just eight of the 14 females (57%) produced offspring. These findings are critical for models attempting to predict gene flow, including gene drive spread, as it appears that less than half of the available males and just over half of the available females in a free-ranging population contribute genes to subsequent generations.