Biología y genética poblacional de Arvicola scherman cantabriae (Rodentia, Arvicolinae)

Résumé

The montane water vole Arvicola scherman occurs in mountainous areas of Europe, living in underground burrow systems located in grasslands and fruit orchards. This species feeds on the root system of plants, including fruit trees. Specifically, the subspecies A. scherman cantabriae is nowadays one of the main causes of economical loss in apple orchards of Asturias (northwestern Spain). An official control program in Spain considers all sustainable phytosanitary measures that can reduce population growth of this species. Since the pest condition of A. scherman depends on its biology and ecology, a deep knowledge of these aspects is needed to set up specific and suitable control strategies. Thus, the aim of this research is to obtain essential information on the reproductive biology and population genetics of this species in the agricultural landscape of Asturias. More than 800 individuals of A. scherman cantabriae were gathered in apple orchards located at low altitude in Villaviciosa and Nava municipalities during two annual cycles (from February 2011 to January 2013). Sexual characteristics, body measurements and relative age class of each specimen were recorded. Body condition of females, which indicates energy provision, and the number of embryos of each one were also wrote down. Skeletal muscle samples of 137 specimens from ten demes were used to conduct a microsatellite-based analysis (12 microsatellite loci). These orchards are placed in a landscape conformed by a mosaic of small and different land-use plots, which was assessed in a vector based geographic information system and it was focused on soil-occupancy categories. Pregnant females and young specimens were detected over the whole year, which mean that A. scherman cantabriae showed a continuous breeding pattern during the study period. Intra-annual changes in body mass and size of sexual organs of males did not affect significantly reproduction at a population scale. Thus, primary demands of these voles seem to be properly fulfilled during the whole year and hence energy budgets can be destined to cop continuous reproduction. To our knowledge, no other A. scherman population shows regularly this reproductive pattern. Females were able to produce a high number of litters per year (7.30) although litter size was relatively moderate (embryos/female: first year: 3.87; second year: 3.63). Each female was able to produce 28.25 pups per year. The reproductive potential showed by Cantabrian voles is, to our knowledge, the highest one reported to date for this species; probably because the breeding season does not entail a critical factor in this area. A positive correlation between litter size and the body condition of the mother was observed. Therefore, the body condition of females seems to be one of the main factors involved in the variation of the reproductive potential in A. scherman cantabriae. These studied demes showed relatively low level of genetic diversity (HE = 0.621; HO = 0.601; AR = 4.42) probably due to both the inbreeding and genetic drift effects. Significant genetic differentiation appeared among demes, which revealed a strong pattern of significant isolation-by-distance both for Euclidean distances (r = 0.790) and effective distances (r = 0.780). The spatial autocorrelation analysis detected four genetic clusters or populations in this study area (120 km2). Thus, this mosaic of different land-use plots decreases connectivity among suitable habitats even at local scale, in which A. scherman populations mainly depend on birth and death rates. An estuary and a four-lane road did not suppose a barrier for gene flow of this species. Less seasonal environment and highly patched landscape would suggest that this species does not show well marked multiannual fluctuations of density at large scale in this area. Control strategies for A. scherman cantabriae at a regional scale can be discarded. The monitoring of each population, or management unit, will be essential to know the population dynamic and to establish coordinated control strategies. Preserving and promoting this patchy landscape would favour the presence of predators and hamper dispersion of this species. A continuous population control throughout the year would be advisable, using sustainable methods, such as traps, the installation of barriers and/or coordinated manipulation of habitat.