The first known monogamous amphibian species, based on genetic data, is Dendrobates imitator (Brown et al. 2010) as reported in a paper in the April issue of American Naturalist.
Ecological factors appear to have driven the evolution of monogamy; this species breeds in tiny pools that lack food resources for tadpoles, necessitating parental care. A closely related species (D. variabilis) that breeds in larger pools is not monogamous and mothers of that species do not feed unfertilized eggs to tadpoles.
Previously, pair bonding had been reported in a different species, Dendrobates vanzolinii, by Janalee Caldwell in Nature, based on behavioral observations.