Mr. Mom: Nocomis Embryo‐Burying Effectively Increases Embryo Survival Amidst Predation by All Mutualism Participants

Nest association is a putatively mutualistic mode of reproduction utilized by many fishes of the North American freshwater family Leuciscidae. It is defined by the interaction between one ‘host’ species that builds and maintains a nest, and multiple other species of ‘nest associates’ that spawn upon it. We studied the aggregations of spawning Nocomis leptocephalus in order to identify potential embryo predation behaviors of the host or associates. We investigated the effectiveness of host parental care by comparing predation upon buried and unburied embryos. The main observed parental care behavior of the host—embryo burying—increased embryo survival by 26.8 (±5.6%) on average, indicating that it is an effective method of improving reproductive success. We hypothesized that both host and associates are responsible in part for embryo predation, and that nest associate abundance increased the risk of embryo predation. DNA metabarcoding of gut contents revealed that indeed both host and associates consumed heterospecific embryonic material, whereas model‐based evidence suggested that associate abundance only weakly affected embryo predation rate. This work furthers and supports previous research recognizing the nuance in identifying nest association as a mutualism, and work which has suggested the host benefits from nest associates beyond the predation‐dilution effect on its embryos. Here we identify an additional benefit to hosts and associates—the direct consumption of each other's embryos—making this the first study to directly investigate and demonstrate predation upon embryos by nesting fishes in this system.