Award: OCE-1829835

This project addressed several fundamental questions about ocean ecosystems. What is the structure of ocean food webs? What determines which prey a predator eats, and therefore what the links in the food web are? We focused on siphonophores, a group of about 200 species of large, abundant, and beautiful predators. Siphonophores are gelatinous animals, related to other animals with medusae jellyfish, that capture prey with elaborate tentacles that can be very different from species to species. Because the tentacles plays a major role in determining what a siphonophore can eat, and serves no other function than capturing prey, siphonophores are very well suited to studying the mechanism, ecological impact, and evolution of prey selection. This was a large, interdisciplinary project that succeeded through the close collaboration of three teams. We started by describing what prey siphonophores eat, which was unknown for many species. We used several methods for this. First, we described the prey seen captured in siphonophore tentacles in deep sea video collected by remotely operated underwater vehicles. Second, we used stable isotopes of siphonophores to get a longer term understanding of where in the foodweb their prey are. Third, we sequenced DNA from the siphonophores and the prey in their stomach to identify with high precision which prey species they had recently eaten. This required the development of a variety of genomic resources for siphonophores and their prey. Some siphonophores specialized in eating fish, some in eating specific crustaceans, and others are generalists that eat a variety of animals. Next we described the structure and function of siphonophore tentacles. This allowed us to identify which siphonophore tentacle features are associated with the capture of specific prey, and why. We then integrated these results in an evolutionary context to identify evolutionary shifts in tentacle features and in prey selection. We found the surprising result that the prey generalist siphonophores evolved multiple times from prey specialist siphonophores, which contradicts the common expectation that predators tend to become more specialized in the course of evolution. Last Modified: 01/17/2024 Submitted by: CaseyWDunn