Non-random pairing with respect to past breeding experience in the common toad (Bufo bufo)



A 20-year study of a common toad Bufo bufo population in south Dorset, U.K. was carried out between 1980 and 1999. On average, c. 33% of all experienced males and females arriving each year did so during the first quarter of each breeding season with only 18% arriving during the last quarter. Conversely, a slightly higher proportion (27%) of all inexperienced (first-time breeders) males and females arrived during the last quarter season than during the first quarter (22%). In 18 of the 20 years, the proportion of inexperienced females found paired with inexperienced males was significantly higher than could be expected from the proportion of inexperienced males in the pond, suggesting that selective pairing was occurring. One potential effect of pairings between inexperienced male and female toads, coupled with the sex difference in the age of attaining sexual maturity, might be a reduction in the incidence of sibling matings (inbreeding) in the common toad. This is particularly relevant in a species that is both highly philopatric and which congregates in large numbers every spring to breed in very localized areas.