VARIABILITY IN THE DISTRIBUTION AND COMPOSITION OF ADIPOSE-TISSUE IN WILD ARCTIC FOXES (ALOPEX-LAGOPUS) ON SVALBARD

Adipose tissue was dissected completely from 35 adult and subadult arc tic foxes collected between November 1991 and March 1992 in four diffe rent areas of Svalbard (latitude 78 degrees 5' to 79 degrees 50' N). T he gross mass,lipid, protein and collagen content and mean adipocyte v olume were measured in adipose tissue from six superficial, four intra -abdominal, three intermuscular and two cardiac depots homologous to t hose of other terrestrial mammals. The total adipocyte complement was calculated from the mass of each depot and its site-specific adipocyte volume. The mean fatness was 14.81 +/- 1.3% and sex differences were not significant. All depots except the epicardial enlarged with increa sing fatness, but the superficial depots expanded more than the intern al depots. The average partitioning of adipose tissue between intra-ab dominal and superficial depots was consistent with predictions from al lometric equations fitted to data from other Carnivora, but there was much unexplainable variation between individuals. The relative masses of the four intra-abdominal depots were also variable. The mean adipoc yte complement was low compared to other continually or seasonally obe se arctic mammals, only slightly larger than that predicted from allom etric equations relating adipocyte complement to body mass in other ca rnivorous mammals, but there were large differences between specimens, with some having more than four times the expected number and others only half the expected number. The size of the adipocyte complement wa s unrelated to age, sex or fatness. Because of such variation in numbe r and size of adipocytes, measurements of adipocyte volume from biopsi es of adipose tissue would not provide an accurate estimate of fatness . Almost all the adipose depots found in other terrestrial mammals wer e present. Site-specific differences in adipocyte volume and the lipid and protein content of adipose tissue were similar to those of other wild mammals and did not change with fatness. The collagen content was highest in superficial and lowest in intra-abdominal adipose depots. The differences of up to 60% in the collagen content of homologous dep ots of different foxes could not be explained by age or cytologically visible blood vessels and fascia but correlated with adipocyte complem ent.