Geographical variability in size and shape skulls of the arctic fox Alopex lagopus, comparison with the red fox Vulpes vulpes variability Olga G. Nanova Zoological Museum, Moscow Lomonosov State University Two subspecies of arctic fox Alopex lagopus from the Commander Islands have being been isolated for an evolutionarily significant time. Now island populations are different by a number of characteristic traits differentiating them from mainland ones, which is termed the «island syndrome» (Goltsman et al., 2005). The aim of the present study was to determine to what extent cranial morphology of arctic fox has been modified under the insular isolation. We have studied skull morphology variation in the arctic fox from the Commander Islands and from mainland territory of the Russian North. The red fox Vulpes vulpes was used as an “outgroup” for comparison of magnitude of intra- and interspecific variation. A sample of 390 skulls of the arctic fox from Mednyi Island, Bering Island and three locality from mainland and 382 skulls of the red fox from five locality of Eurasia was examined. Variability of size and shape of skull and dentition was studied by means of standard and geometric morphometry. Arctic foxes from Commander Islands are drastically different from mainland arctic foxes in their skull size and shape. The population from Mednyi Island is the most specific one in respect to both cranial and dental traits. Morphological differentiation between island and mainland arctic foxes is comparable to differences between arctic foxes and red foxes. The difference between island and mainland arctic foxes can not be explained by a shift along the age-related allometric vector, but is rather caused a by more complicated transformations of growth pattern. As it follows from the analysis of the age corrected data (Burnaby method), age-unrelated shape changes between Arctic fox from Commander Islands and mainland arctic fox are highly significant (Fig. 2, Mahalanobis distances are 29.8–58.2, mean = 44.6). Differentiation of Mednyi arctic fox from mainland arctic fox ( ) is higher than differentiation of the latter from the Bering arctic fox ( ). There is no difference in age-corrected shape between the three populations of mainland arctic fox (6.3–16.4, 7.9). However, the two island populations are significantly different (24.1). Results Materials and methods 32 skull measurements were taken by electronic calipers, while analysis of upper toothrow shape was based on landmark data obtained from digitized images. The sample includes: for the arctic foxes 76 skulls (and 25 images) from Arkhangelsk region, 80 skulls from Dikson Peninsula, 78 skulls (23 images ) from Chukot, 80 skulls from Bering Island (22), 76 skulls from Mednyi Island (15); for the red fox 71 skulls from Turkmenistan (16), 80 skulls from Chukot (20), 80 skulls Moscow region (28), 71 skulls from North Kazakhstan (15), 80 skulls from the Primorye (17). Specimens were classified as either subadults (10-12 month old) or adults (>1 year old). Numbers of specimens in each sex- and age-specific subsamples are approximately equal. Age-related allometric pattern was removed from skulls dimensions data by Burnaby’s method for size adjusment. The data were projected onto the hyperplane orthogonal to the specified age eigenvectors. To check the hypothesis that the difference between island and mainland arctic foxes can be explained by a shift along the age-related allometric vector we have calculated the angle between specific age eigenvector and specific geography eigenvector. Fig. 1 CBL variability as an indicator of overall skull size variability Arctic fox from Commander Islands are significantly larger (Fig. 1) then mainland arctic fox (t-test, p 0.7). The differentiation between Bering arctic fox and Mednyi arctic fox is not significant as well (p=0.88). Fig. 2 Skull shape intra- and interspecific differentiation. PC analysis of age–corrected data Fig. 3 Direction of age vector and geographical variability in arctic fox The difference between island and mainland arctic foxes can not be explained by a shift along the age- related allometric vector (Fig. 3). The angle between geographical vector and common age vector is large. Therefore, the main trends of age and geographic variation are not collinear, as they involve different traits and are influenced by fundamentally different factors. The angle between age vectors of mainland and island arctic fox is relatively small. Conclusion 1. Isolation of the arctic fox on a small territory in non- typical environment over a long period of time has strongly influenced cranial morphology of Commander Island fox, especially of Mednyi arctic fox. Morphological intraspecific differentiation between Mednyi and mainland arctic foxes is comparable to interspecific differences between the mainland arctic fox and red fox. 2. The difference between the island and mainland arctic foxes can not be explained by a simple age-related allometric vector only, but is rather caused by more complicated transformations of growth pattern. Shape differences of the upper toothrow are independent from size change. The continuation of the above study includes the following questions: a) What is the place of unique Commander arctic foxes in the morphological diversity of the arctic fox over its entire range (including other islands populations from the Pacific Ocean and the Arctic Ocean)? b) If the difference between mainland and Commander arctic foxes is not accounted for by changes on late ontogenetic stages, then, at what developmental stage do these changes begin to appear? Fig. 4 Geometric morphometric analysis. Distribution of the toothrow consensus configurations for males and females from each populations arctic and red fox in the shape spaces of 1st and 2d relative warps Fig. 5 Geometric morphometric analysis: a) Landmarks used in the analysis, b) Vectors showing shape transformations in Mednyi arctic fox against mainland arctic fox (vectors indicate direction and magnitude of variability) Geographical variability of toothrow shape (Fig. 4) is smallest for mainland arctic fox (Procrustes distances are , mean =0.014). Arctic fox from Commander Islands are significantly different from mainland arctic fox in toothrow shape ( ). Mednyi arctic is much more specific ( , 0.050) than Bering arctic fox ( , 0.27). Difference between Mednyi and Bering arctic foxes in toothrow shape is also high ( , 0.039). Most of differentiation between island and mainland arctic foxes is associated with the position of the 3rd and 4th premolars (Fig. 5b). Correlation between shape and size variability is insignificant both in the arctic fox (R=0.23, F=4.49, p=0.04) and in the red fox (R=0.21, F=4.38, p=0.04). I am grateful to my scientific adviser Prof. Pavlinov I.Ya. and research fellow Dr. Lebedev V.S. I am indebted to Prof. Anders Angerbjörn for financial support my being at the conference