The buff-breasted rat (Rattus flavipectus) is a major agricultural pest across China. Warfarin-resistant animals have been found in several major provinces in China, and are hampering effective control. Molecular mechanisms underlying resistance to anticoagulant rodenticides have been determined for other species, but genetic information regarding resistance in R. flavipectus remains unknown. The vitamin K 2,3-epoxide reductase complex subunit 1 (VKORC1) encoded by VKORC1 gene is the molecular target of coumarin anticoagulants, and amino acid substitutions in VKORC1 coding-regions have been reported as one of the supposed mechanisms of warfarin resistance. Here, lethal feeding test in R. flavipectus (n = 36) was conducted in Zhanjiang, China. Four animals (11%) survived the test period of 25 days and were identified as warfarin resistance. Polymorphism across the whole genome DNA sequence of the VKORC1 gene was screened out and compared with resistant and non-resistant rats. A total of nine single nucleotide polymorphisms (SNPs) were identified including seven SNPs in introns and two SNPs in exons, and the SNP (2317A [ G) located in exon 3 led to the amino acid substitution (Tyr139Cys) in VKORC1 protein. Based on the characteristics of Tyr139Cys mutation of VKORC1 in humans or rats and its relationship with warfarin-resistance, Tyr139Cys mutation may be one mutation responsible for anticoagulant resistance in R. flavipectus. Given the low numbers of resistant rats in our feeding test, wider surveillance, tests of resistance development in a larger wild population and further researches on the genetic mechanisms of anticoagulant resistance in R. flavipectus are necessary.
Highly polymorphic microsatellite markers are the most powerful tools to infer kinship relations. In this study, a library enriched for (AC)(n) (AG)(n) and (AGAT)(n) was constructed for screening microsatellite markers in Brandt's vole (Lasiopodomys brandtii), and nine novel polymorphic microsatellite markers were developed and characterized. The number of alleles ranged from 4 to 11 per locus and the mean polymorphism information content was 0.7535. The observed and the expected heterozygosity values averaged 0.760 (0.554-0.908) and 0.7914 (0.718-0.845), respectively. Average nonexclusion probability for one candidate parent varied from 0.485 to 0.716. These nine novel markers are highly polymorphic and powerful enough for our future kinship analysis.
The brown rat (Rattus norvegicus) originated in north-eastern China, Siberia and Japan and subsequently spread worldwide. However, despite its importance to agriculture, public health and scientific and medical research, surprisingly few studies have focused on wild brown rat populations. There are four subspecies in China, but little is known about their original distributions. In the present study, we investigated the seasonal biological and ecological characteristics of brown rats in their native range in Harbin, north-eastern China. Trapping campaigns were conducted in June and November 2006 at a farm site and a rice site, and seasonal variation was analysed. The sex ratio was male biased at the farm site and female biased at the rice site in both seasons. Although juvenile, sub-adult and young-adult rats comprised over 80% of the population in both seasons, the age composition displayed seasonal differences, with higher proportions of juvenile rats in the summer and sub-adults in the winter. There were no significant morphological differences between different sexes or seasons, or between sites. Heavy, female and pregnant rats were captured first and heavier male rats maintained relatively higher reproductive activities than lighter ones, reflecting the link between social dominance and feeding priority. Rats had heavier reproductive organs in summer than in winter. The relative masses of the spleen and adrenal glands also showed seasonal and gender differences. This study demonstrates that brown rats in their native region have similar seasonal biological and ecological characteristics to American and European populations. This information on brown rat in north-east China will contribute to the development of management strategies for controlling this agricultural pest.
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