Behavioral differences among mutualist species in a shrimp–goby association

Alpheid shrimps and gobiid fishes engage in a mutualism in which shrimp construct burrows that are co-habited with gobies and used as refuge from predators by both. Gobies act as sentinels for shrimp. In the western Atlantic, different goby species have been hypothesized to have a facultative (Ctenogobius saepepallens) and obligate (Nes longus) association with the shrimp Alpheus floridanus. I compared various behaviors among these 2 gobies and another goby that occasionally associates with shrimp (Coryphopterus glaucofraenum). The putatively obligate goby had the greatest preference for shrimp burrows versus other shelters, had the greatest partner fidelity, and facilitated more emergence by shrimp by remaining for longer periods at shrimp burrow entrances. These findings provide evidence that in shrimp–goby mutualism, the more specialized and dependent mutualist gobies provide greater services to their shrimp partners.