Polecats M. putorius were sampled between 1996 and 1999 from eight populations in France, Brittany (mean temperature of July: 17.5 °C, mean temperature of January: 5.8 °C, annual precipitation 880 mm), Brière (18.5 °C, 5.0 °C, 850 mm), Anjou (20 °C, 5 °C, 650 mm), Sologne (19.4 °C, 0.4 °C, 600 mm), Morvan (21 °C, 0.0 °C, 1050 mm), Vendée (18.2 °C, 6.0 °C, 750 mm), Limousin (20.1 °C, 1.3 °C, 900 mm), and Aquitaine (22.0 °C, 6.6 °C, 850 mm) (Fig. 1). Polecats are mainly found in wetlands, ponds and streams, but also in oligotrophic forest brooks in Brittany, Morvan and less frequently in Limousin. Habitats in Brière, Anjou, and Vendée are mostly eutrophic marsh ditches, ponds or slow streams. Polecats are regarded as pests and extensively trapped. I obtained muscle tissue samples from trapped or road-killed animals from trappers, taxidermists and naturalist associations (DPN authorization no. 98/717/AUT).
Figure . 1. Location of polecat M. putorius samples in eight populations from France (dots are individuals sampled).
Download figure to PowerPoint
Only clearly localized adult animals which were successfully investigated by starch gel electrophoresis have been retained (n=114). Each polecat was weighed and sexed and detailed habitat features were described in an area of 1 km2 around the point of discovery (radius = 564 m). A surface of 1 km2 corresponds to the mean home range size recorded in western France from radiotracked polecats (Lodé, 1994) while daily movements reached 600 m on average (Blandford, 1987; Lodé, 1993). Measurements were taken on variables related to vegetation structure. The cover rate of each vegetation type was used as six descriptive habitats:
1 deciduous woods, percentage of surface covered by woods mainly composed of Oaks Quercus sp., Ashes Fraxinus excelsior and elms Ulmus minor;
2 coniferous or mixed forest;
3 willow groves composed of Salix sp. and Populus nigra and marshes, including peat-bogs and reed-beds;
4 natural meadows, with herbaceous cover often hedged by oaks and ashes;
6 urban and peri-urban zones. Variables were measured on 1 : 25000 topographic maps.
Habitat diversity was calculated from habitat frequencies using Levin’s index (1968) B=1/∑Pi2 where Pi is the cover rate of each habitat type. Statistical tests (one-way ANOVA or Kruskal–Wallis) and correlation were performed using Pcsm program considering:
1 variations among populations (pooling data from individuals for each population); and
2 differences among genotypes (pooling all data).
Tissue samples removed from each individual were immediately frozen and stored until electrophoresis was performed. Crude protein extracts from this tissue, macerated in equal volume of distilled water were centrifuged at 10 000 g for 15 min at 4°. Electrophoresis of soluble proteins was carried out in starch gel (Sigma) using three buffer systems, Tris-citrate pH 6, Tris-citrate pH 8 and Tris-Edta-borate pH 8 (see Lodé, 1998). Slices were stained for 27 enzymes encoded by 40 gene structure loci following Pasteur et al. (1987), Murphy et al. (1990) and Rothe (1994) procedures. Loci successfully resolved were AAT-1 and AAT-2 (EC 184.108.40.206), ACO-1 and ACO-2 (EC 220.127.116.11), ADA (EC 18.104.22.168), AK (EC 22.214.171.124), CK-1 and CK-2 (EC 126.96.36.199), DDH-1 and DDH-2 (EC 188.8.131.52), EST-1 and EST-2 (EC 184.108.40.206), FUMH (EC 220.127.116.11), GLY2DH (EC 18.104.22.168), G6PDH (EC 22.214.171.124), GPI (EC 126.96.36.199), HK-1, HK-2 and HK-3 (EC 188.8.131.52), IDH-1 and IDH-2 (EC 184.108.40.206), LDH-1 and LDH-2 (EC 220.127.116.11), MDH-1 and MDH-2 (EC 18.104.22.168), ME-1 and ME-2 (EC 22.214.171.124), MPI (EC 126.96.36.199), PEP-1 and PEP-2 (EC 188.8.131.52), PGDH (EC 184.108.40.206), PGM-2 (EC 220.127.116.11), PNP (EC 18.104.22.168), SDH (EC 22.214.171.124), SOD (EC 126.96.36.199), TPI (EC 188.8.131.52), TYR1 and TYR2 (EC 184.108.40.206) and two nonspecific proteins. Allozymes were scored alphabetically according to the mobility of their products.
Tyrosinase converts Tyrosine to Dopachrome which leads to dark eumelanin but the pigmentation pattern is also under the control of several other loci such as TRP1, TRP2, or MC1-R (Searle, 1968; Willis, 1989). Although fur pattern in polecat varied from a clear coat in winter to a darker one in summer, the polymorphism in the Tyrosinase locus resulted in three identified coat colour phenotypes in the wild, the ‘typical’ one with a distinct bandit mask, a ‘dark’ phenotype with no mask apparent and dark fur and one intermediate (heterozygote) with only two light spots above eyes. Another recessive allele determined albinistic phenotype or Tyrosinase positive albinos mainly found in the domestic ferret. Further, some erythristic polecats in which dark guard hairs were replaced by red ones were found in Britain (Blandford, 1987; Birks & Kitchener, 1999), a phenotype probably derived from another allelic variant of Tyrosinase producing phaeomelanin.
Genotypic frequencies at each locus were tested for fit to Hardy–Weinberg equilibrium and F-statistics were calculated using Genetix (Belkhir, K., Borsa, P., Goudet, J., Chikhi, L. & Bonhomme, F. 1996–98, Genetix version 3.3, Laboratoire Génome & Populations, CNRS UPR 9060, Montpellier, France) and Popgen32 software (Yeh, F., Yang, R.C., Boyle, B.J., Ye, Z.H. & Mao, J.X. 1997, Pop Gen 3.2. Mol Biol Biotech Centre, Univ Alberta). The effective number of alleles was assessed as in Kimura & Crow (1964) revised by Nei (1987). Observed (Ho) and expected (HE) average heterozygosities (Nei, 1978) were estimated and heterozygote deficiency was based on the FIS index as in Wright (1978).