Genetic monogamy and biparental care in an externally fertilizing fish, the largemouth bass (Micropterus salmoides)

Breeding, male North American sunfish (Centrarchidae), are often brightly c oloured and promiscuous. However, the largemouth bass (Micropterus salmoide s) is sexually monomorphic in appearance and socially monogamous. Unlike so me other nest-tending centrarchids in the genus Lepomis, largemouth bass ha ve also been reported to provide biparental care to eggs and fry. Here we u se microsatellite markers in order to test whether social monogamy predicts genetic monogamy in the largemouth bass. Offspring were collected from 26 nests each usually guarded by a pair of adults, many of which were also cap tured. Twenty-three of these progeny cohorts (88%) proved to be composed al most exclusively of full-sibs and were thus the product of monogamous matin gs. Cuckoldry by males was rare. The genetic data also revealed that some n ests contain juveniles that were not the progeny of the guardian female, a finding that can be thought of as low-level 'female cuckoldry'. Overall, ho wever, the data provide what may be the first genetic documentation of near -monogamy and biparental care in a vertebrate with external fertilization.