Multiple paternity in a viviparous toad with internal fertilisation

Anurans are renowned for a high diversity of reproductive modes, but less than 1 % of species exhibit internal fertilisation followed by viviparity. In the live-bearing West African Nimba toad (Nimbaphrynoides occidentalis), females produce yolk-poor eggs and internally nourish their young after fertilisation. Birth of fully developed juveniles takes place after 9 months. In the present study, we used genetic markers (eight microsatellite loci) to assign the paternity of litters of 12 females comprising on average 9.7 juveniles. In 9 out of 12 families (75 %), a single sire was sufficient; in three families (25 %), more than one sire was necessary to explain the observed genotypes in each family. These findings are backed up with field observations of male resource defence (underground cavities in which mating takes place) as well as coercive mating attempts, suggesting that the observed moderate level of multiple paternity in a species without distinct sperm storage organs is governed by a balance of female mate choice and male reproductive strategies.