MORPHOMETRIC VARIATION BETWEEN BUFO-WOODHOUSII-FOWLERI HINCKLEY (ANURA, BUFONIDAE) ON ASSATEAGUE ISLAND, VIRGINIA AND THE ADJACENT MAINLAND

Mark and recapture studies of Bufo woodhousii fowleri in 1988 and 1989 on Assateague Island, Virginia, and the adjacent mainland showed that adult toads were significantly (P less-than-or-equal-to 0.05) more ab undant on the island than the mainland in both years. The masses and s nout-vent lengths (SVL) of toads were significantly greater on the mai nland 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 fem ale toads were not sexually dimorphic in size at either location in 19 88 or 1989. Te 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 l ow genetic diversity of the two populations. There were no noteworthy differences in allele frequencies or polymorphism (P = 0.142) and mean heterozygosity (H = 0.01 island; H = 0.03 mainland) between the two p opulations. This study documents morphometric differences that often e xist between island and mainland populations. Factors that could affec t 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, smal l food particle or food supply, and age structure of populations that are presented to account for the smaller size of island versus mainlan d conspecifics.