Morphometric Variation Between 
Bufo woodhousii fowler i Hinckley (Anura: Bufonidae) 
on Assateague Island, Virginia and 
the Adjacent Mainland 
John M. Hranitz 1 , Thomas S. Klinger, Frederick C. Hill, 
Robert G. Sagar, Thomas Mencken, and John Carr 
Department of Biological and Allied Health Sciences, 
Bloomsburg University of Pennsylvania, Bloomsburg, Pennsylvania 17815 
ABSTRACT — Mark and recapture studies of Bufo woodhousii 
fowled in 1988 and 1989 on Assateague Island, Virginia, and the 
adjacent mainland showed that adult toads were significantly 
(P 0.05) more abundant on the island than the mainland in both 
years. The masses and snout-vent lengths (SVL) of toads were sig- 
nificantly greater on the mainland than on the island in both years, 
and adults were significantly larger at each location in 1989 than 
in 1988. Sex ratios were close to 1:1 or 1:2 on the island and the 
mainland in both years. Male and female toads were not sexually 
dimorphic in size at either location in 1988 or 1989. The smaller 
of two adult size classes on the island in 1988 was not present on 
the island in 1989; there were three size classes on the mainland 
in both years. Electrophoretic analysis revealed the low genetic 
diversity of the two populations. There were no noteworthy differ- 
ences in allele frequencies or polymorphism (P = 0.142) and mean 
A A 
heterozygosity (H = 0.01 island; H = 0.03 mainland) between the 
two populations. 
This study documents morphometric differences that often exist 
between island and mainland populations. Factors that could affect 
the inverse relationship between toad abundance and size include 
low genetic diversity at loci controlling body size, the age structure 
of each deme, and instraspecific competition or physiological 
stress on the island. These explanations for small body size of 
island toads are consistent with the existing hypotheses of small 
immigrant size, small food particle or food supply, and age struc- 
ture of populations that are presented to account for the smaller 
size of island versus mainland conspecifics. 
Differences in size between island and mainland conspecifics 
include gigantism and dwarfism, but explanations and correlations 
for differences in size structure of such populations are difficult to 
determine (Carlquist 1974). On Atlantic coast barrier islands, slider 
turtles ( Chrysemys scripta) are larger on Kiawah and Caper’s is- 
1 Present address: Department of Biological Sciences, Drawer GY, Mississippi State 
University, Mississippi State, MS 39762. 
Brimleyana 19:65-75, December 1993 
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