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Miguel
Christian Pinto
Research Training Program, 2004
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Introduction In 1986 a giant bear was killed by a hunter in Alaska, and the skull was sent to the National Museum of Natural History to confirm his identity because if it was a true black bear it would be the largest black bear ever recorded. However, this bear shows characteristics of brown and black bears. It presents the size of a large brown bear, and dental characteristics of black bears. The bear is also black, but could represent a melanistic brown bear. In order to identify this unusual bear skull, we analyzed the shape of the last upper molar, one of the most important taxonomic structures in bears (Gordon, 1977; Rausch, 1961).
We compare the unidentified black bear with series of Alaskan black and brown bears from the National Museum of Natural History (USNM). Data recording: We took digital photos of the last left upper molar, and nine landmarks were digitalized in each photo using TPSdigit program (Rohlf, 2004).
Data analysis:
A typical bear skull (middle) in relation with an adult black bear (left) and an adult female brown bear (right). Relative Warp Plot (differences in shape) of the last upper molar in black and brown bears. X axis Relative Warp 1, Y axis Relative Warp 2, amount of explained variation 48,79 %. Arrows show thin spline deformation together with photos of a typical black bear tooth (above), an overlap shape (middle), and a typical brown bear tooth (below). Multivariate linear regression of shape against size. Highly significant (P<0.001). Multivariate regression of shape against size and color. Highly significant (P<0.001).
These results suggest that the unknown specimen is a probable hybrid between Ursus arctos and Ursus americanus. If our assumption is correct, it is the first known natural hybrid between black and brown bears. Our analysis indicates that the giant black shares characteristics of both parental species. The size and the vigor of this specimen shows it was viable, we do not know if it was fertile or sterile. Ursus arctos x U. americanus hybrids have been recorded previously in captivity (Gray, 1971), and hybrids between U. arctos and U. maritimus are well known. However, the usual interaction reported in the wild between these two species is predation of black bears by brown bears (Gunther, et al., 2002). The following questions remain unanswered: What is the significance of hybrids on natural populations? What is the evolutionary effect of bear hybrids for the parental species? Evolutionary death? Speciation? Where are the limits for species?
We would like to thank to all the people who provided us advise in geometric morphometric approaches and statistical methods: Andrea Cardini, Ralph Chapman, Heidi Schultz, and Richard Thorington. The collection manager staff: Robert Fischer, Jeremy Jacobs, and Suzanne Peurach provided valuable help during this research. This research was supported by a grant to the NMNH Research Training Program from the Smithsonian Latino Initiatives Fund.
Cardini, A., Tongiorgi, P. 2003. Yellow-bellied marmots (Marmota flaviventris) ‘in the shape space’ (Rodentia: Sciuridae): Sexual dimorphism, growth and allometry of the mandible. Zoomorphology 122: 11-23. Gordon, K.R. 1977. Molar measurements as a taxonomic tool in Ursus. Journal of Mammalogy 58(2): 247-248. Gray, A.P. 1971. Mammalian hybrids: a check-list with bibliography. Second ed. Commonwealth Agriculture Bureux, Farnham Royal, Slough, UK. Gunther, K.A., Biel, M.J., Anderson, N., Waits, L. 2002. Probable grizzly bear predation on an American black bear in Yellowstone National Park. Ursus 13: 372-374. Rausch, R. 1961. Notes on the black bear Ursus americanus Pallas in Alaska, with particular reference to dentition and growth. Z. Saugetierk, 26: 77-107. Rohlf, F.J. 2004. TPS series. Department of Ecology and Evolution. State University of New York, Stoony Brook, New York. http://life.bio.sunysb.edu/morph/ Slice, D.E., Bookstein, F.L., Marcus, L.F., Rohlf, F.J. 1996. A glossary for Geometric Morphometrics. pp. 531-551 in Marcus, L.F., Corti, M., Loy, A., Naylor, G.J.P., Slice, D.E. (Eds.) Advances in Morphometrics. Plenum Press, New York. SPSS, 2001. SPSS Inc. Standard Version, 10.0.7, SPSS, Chicago.
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