Genetic evidence for inter-population male – Biased dispersal of lesser rice field rat (Rattus losea) in Zhoushan Archipelago, China

Dispersal is a fundamental life history trait that has profound effect on both the genetics and evolution of species, and sex-biased dispersal is pervasive in vertebrates. Lesser rice field rat ( Rattus losea ) belongs to the family Muridae and is one of the dominant rodents in Zhoushan archipelago, China. In this study, we genotyped 168 samples including 74 males and 94 females R. losea , live-captured from five neighboring islands during breeding seasons. Based on eight highly polymorphic autosomal microsatellite markers analyzed, we found that the island populations of R. losea maintained a large amount of genetic diversity, along with low to moderate levels of genetic variation, extensive gene flow and declining inbreeding. The Bayesian clustering divided the populations into three distinct genetic clusters. Analyses of sex-biased dispersal conducted over the total R. losea individuals presented that Fst , Fis , mAIc and r in females were higher than those in males, and conversely vAIc in females was lower than males, which all suggested a male-biased dispersal pattern in R. losea populations. This pattern of dispersal may be influenced by factors such as reducing mate competition and preventing inbreeding. In general, the study provides strong genetic evidence for male-biased dispersal of R. losea in Zhoushan archipelago, which has practical implications for understanding behavioral strategies for the adaptive evolution of island species in fine-scale populations and developing control methods for rodents in island ecosystems. • Genetic diversity : Analysis of eight microsatellite loci in 168 samples of Rattus losea revealed high genetic diversity in each island population. The average number of alleles was 8.325, the average observed heterozygosity was 0.954, and the average expected heterozygosity was 0.802. There were also many rare alleles, which might be attributed to their swimming and diving abilities as well as gene exchanges facilitated by human activities. • Genetic variation and structure : The genetic variation coefficient (Fst) indicated a low to moderate level of genetic differentiation (0.018 - 0.059) among populations, with extensive gene flow (Nm ranging from 4.018 to 13.957). There was a significant positive correlation between geographic and genetic distances. Bayesian clustering analysis supported the presence of three genetic clusters, consistent with the geographical distribution, suggesting that both historical gene flow and current dispersal have influenced the genetic structure of the populations. • Inter-population dispersal : Genetic assignment methods detected that 20.24% of individuals had dispersed between populations, and the dispersal rate was significantly negatively correlated with geographic distance. The swimming ability, reproductive characteristics of Rattus losea, and geographical features such as "marine erosion terraces" between islands jointly contributed to their dispersal among islands. • Male-biased dispersal pattern : Multiple genetic indicators (Fst, Fis, mAIc, vAIc, and r) suggested a male-biased dispersal pattern in Rattus losea, which might be related to reducing mate competition and avoiding inbreeding. This is consistent with the results of studies on other mammalian species.