Intraspecific competition disadvantages inbred natterjack toad (Bufo calamita) genotypes over outbred ones in a shared pond environment

1 We carried out a replicated pond experiment to compare the viabilities of natterjack toad Bufo calamita embryos and larvae from inbred and outbred populations. Surviving genotypes were identified at the end of the experiment using fixed diagnostic alleles at a microsatellite locus. 2 Inbred larvae grew more slowly than outbred larvae and in mixed populations the survival of outbred larvae was three- to 10-fold higher than that of inbred larvae. 3 Larval mortality correlated with the abundance of dytiscid water beetles, and was therefore probably caused mainly by predation. The relatively higher rate of mortality of inbred larvae was in turn due probably to lower growth rates delaying achievement of a size refuge. 4 Intraspecific competition may help to purge inbred individuals in populations with mixed levels of inbreeding. The significance of inbreeding with relatively cryptic effects, such as reduction in amphibian larval growth rate, is discussed with respect to population viability.