Kin Recognition and Incest Avoidance in Toads

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Abstract
Toads, like many amphibians, display breeding site fidelity. Individuals that return to natal ponds to breed are likely to encounter siblings as potential mates. We examined the genetic structure of Bufo americanus breeding populations at five localities within a 1 km radius. Mitochondrial DNA (mtDNA) haplotypes significantly differed among the breeding populations, but haplotype distributions did not differ from year to year within breeding sites. Natal philopatry may account for these results. Although incest is thus possible, siblings rarely mate. Comparing haplotypes of toads captured while mating, we found only 2 of 86 pairs that could possibly be siblings. We suggest that toads might recognize and actively avoid close kin as mates. Advertisement vocalizations given by males serve as potential cues by which females might recognize their kin. We recorded calls of males, in the field, and later obtained rank estimates of their relationships to one another by DNA fingerprinting of the nuclear genome. The resemblance of males' calls was positively correlated with the similarity of their fingerprints. Significant differences in call characteristics were also found among breeding populations. Temporal parameters, rather than frequency components, encode kinship information. Recently developed techniques in molecular genetics facilitate studies of the heritability of behavioral traits in natural populations.

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