Sp. Hitchings et Tjc. Beebee, LOSS OF GENETIC DIVERSITY AND FITNESS IN COMMON TOAD (BUFO-BUFO) POPULATIONS ISOLATED BY INIMICAL HABITAT, Journal of evolutionary biology, 11(3), 1998, pp. 269-283
Measures of genetic diversity (including heterozygosity), survival and
developmental homeostasis were found to be significantly lower in sma
ll, urban populations of the Common Toad (Bufo bufo) than in larger, r
ural populations of the same region. The autecology and genetic analys
is of this relatively sedentary species suggested that the causal mech
anism was genetic drift, arising from barriers to migration created by
urban development. The pre-metamorphic survival of larvae cultured in
identical conditions increased positively with the mean number of all
eles at a locus and the percentage of polymorphic loci. Observed heter
ozygosity in urban garden and rural populations was correlated inverse
ly with the number of observed physical abnormalities (used as st meas
ure of developmental homeostasis) in the developing tadpoles. Genetic
distances between town sites of mean 2.2 km separation were significan
tly higher than those between rural sites of mean 37 km separation. Ge
netic data were based on allozyme analysis of 27 loci in 8 urban and 4
rural populations. A subset of these sites (3 urban, 2 rural) were al
so assessed at 3 minisatellite loci and a positive correlation found b
etween the average number of alleles per locus detected by the two met
hods. Estimates of Nei's 1972 genetic distance, derived separately fro
m the DNA and protein data, were not, however, correlated. The reducti
on in genetic diversity and fitness observed in these urban toads prov
ides an example of the effect on population persistence that longer te
rm depletion in numbers and habitat fragmentation can have in the wide
r environment.