Bufo woodhousii fowleri 
71 
hognose snake ( Heterondon platyrhinos Latreille) is a major preda- 
tor of toads and is abundant on the island (Scott 1986), we found 
only one hognose snake while trapping on the island. In the ab- 
sence of any predator-prey data, it is not possible to assess whether 
predator pressures on toad body size exist. We suggest other expla- 
nations for the smaller body size and greater abundance of island 
than mainland toads. Two of these are consistent with the hypoth- 
eses of Carlquist (1974), whereas a third hypothesis is consistent 
with the discussion of age structure of King (1989). 
The island and mainland toad populations have very similar 
genetic composition with respect to each other and low genetic di- 
versity compared to other populations of this species (Green 1984, 
Breden 1988). The considerable genetic similarity of the two popu- 
lations is not entirely surprising. First, Assateague Island likely was 
colonized from the north as sand from currents was deposited on 
remnants of Pleistocene barriers (Leatherman 1979). Second, gene 
flow likely occurred between the two populations for the 200 or 
more years that existed between the time that Assateague Island 
assumed its current formation during colonial times and 1933, when 
a hurricane produced the inlet that exists today between Assateague 
Island and the part of the peninsula known as Fenwick Island 
(Leatherman 1979, Amos 1980). The low genetic variation exhibited 
in these two populations of toads could be attributed to a combina- 
tion of biological (e.g., inbreeding, fidelity to breeding sites) and 
historical factors (e.g., founder’s effects, post-Pleistocene changes in 
sea level which restricted gene flow to the narrow window of land 
at the northern end of the peninsula). Although no genetic variation 
was detected at each of seven loci studied in the island and main- 
land populations of Virginia, except Mdh- 1, considerable genetic variation 
is present at five of these seven loci in toads from east-central 
Mississippi (J. M. Hranitz and W. J. Diehl, Mississippi State Uni- 
versity, personal observation). Therefore, from the preliminary ge- 
netic analysis we present, further study of the genetic composition 
of the island and Delmarva toad populations and toad populations 
on the mainland proper, using a larger sample of individuals as 
well as enzyme loci, is warranted. 
If body size is a quantitative genetic character, then the low 
genetic diversity of a population restricts the body size of in- 
dividuals in the deme to only a small proportion of the total 
distribution of body size in the species. If the seven loci studied 
serve as genetic markers for the loci controlling body size, then the 
small body size of toads on Assateague Island might result from 
low genetic diversity at loci controlling body size. Low genetic 
