Constraints on paternal care capacity favor a monogamous mating system in the group-living gobiid fish Trimma marinae

We examined why the group-living gobiid fish Trimma marinae is monogamous despite a high potential for polygamy. Our observations revealed that in 75.5% of spawning events within established pairs, females spawned before the previous clutch hatched, forcing males to care for two clutches simultaneously. Previous findings showed males can care for up to three clutches, while mating with a second female would likely require them to care for four. Our results indicate that female mate guarding is a strategy to monopolize a male’s limited paternal capacity by preventing her partner from mating with additional females.