Spawning Behavior in a Non-Teleost Actinopterygian: Genetic Evidence for Both Monogamy and Polygamy in Amia

The bowfins, Amia, have been regarded as regarded as promiscuous or polygynous spawners, although this has not been directly observed. Species of Amia spawn largely at night in male-constructed and male-guarded nests, making it difficult to view spawning behavior. Furthermore, in many species, field observations of spawning behavior do not always match genetic observations. To investigate the mating system of Amia, we collected fin tissue from guarding males and a sample of associated eggs or fry from 15 broods to assess the number of parents involved in each brood. Using these tissues, we genotyped individuals at 11 microsatellite DNA loci. The genotype of the male was known; we inferred the genotype of the primary female by subtraction, using the most abundant fry genotypes and the known male genotype. We inferred polygamy (presence of multiple fathers or multiple mothers) in cases where there was more than a single fry at a single locus for which the genotype could not be explained by primary parental genotypes. Among sampled broods, seven contained offspring of a single male-female pair. Fry from eight broods show evidence of polygamy: in one brood, there was evidence of an extra-pair male; in five broods, there was evidence of at least one additional female, and in two of these five broods, there was also involvement by at least one additional male; in two broods, it could not be determined whether the additional parent was male or female. Thus, nearly half of our sampled broods were both behaviorally and genetically monogamous, while other broods were genetically polygamous. It has been suggested previously that female bowfin may spawn with more than one male, but there are no behavioral observations to support this claim and our genetic data cannot discern whether females are spawning in more than one nest. We conclude that Amia is behaviorally monogamous and weakly genetically polygynous. With respect to the evolution of mating systems of fishes, it is interesting that Amia, representing a member of the Holostei or the sister group to teleosts, is behaviorally monogamous, albeit with opportunistic participation in spawning by either extra males or extra females or both. A review of the literature on spawning behavior of non-teleostean ray-finned fishes suggests that additional behavioral and genetic studies of these fascinating taxa are warranted.