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2002 The Society for the Study of Evolution. All rights reserved. Evolution, 56(5), 2002, pp. 10451058
 

Summary: 1045
2002 The Society for the Study of Evolution. All rights reserved.
Evolution, 56(5), 2002, pp. 10451058
DWARFISM IN INSULAR SLOTHS: BIOGEOGRAPHY, SELECTION, AND
EVOLUTIONARY RATE
ROBERT P. ANDERSON1,2,3 AND CHARLES O. HANDLEY, JR.4,5
1Division of Vertebrate Zoology (Mammalogy), American Museum of Natural History, Central Park West at 79th Street,
New York, New York 10024
2E-mail: rpa@amnh.org
3Natural History Museum and Department of Ecology & Evolutionary Biology, University of Kansas, Lawrence, Kansas 66045
4Division of Mammals, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560
Abstract. The islands of Bocas del Toro, Panama, were sequentially separated from the adjacent mainland by rising
sea levels during the past 10,000 years. Three-toed sloths (Bradypus) from five islands are smaller than their mainland
counterparts, and the insular populations themselves vary in mean body size. We first examine relationships between
body size and physical characteristics of the islands, testing hypotheses regarding optimal body size, evolutionary
equilibria, and the presence of dispersal in this system. To do so, we conduct linear regressions of body size onto
island area, distance from the mainland, and island age. Second, we retroactively calculate two measures of the
evolutionary rate of change in body size (haldanes and darwins) and the standardized linear selection differential, or
selection intensity (i). We also test the observed morphological changes against models of evolution by genetic drift.
The results indicate that mean body size decreases linearly with island age, explaining up to 97% of the variation

  

Source: Anderson, Robert P. - Department of Biology, City College, City University of New York

 

Collections: Environmental Sciences and Ecology