Data and code for: The evolution of siphonophore tentilla for specialized prey capture in the open ocean

Predator specialization has often been considered an evolutionary
‘dead-end’ due to the constraints associated with the evolution of
morphological and functional optimizations throughout the organism.
However, in some predators, these changes are localized in separate
structures dedicated to prey capture. One of the most extreme cases of
this modularity can be observed in siphonophores, a clade of pelagic
colonial cnidarians that use tentilla (tentacle side branches armed with
nematocysts) exclusively for prey capture. Here we study how siphonophore
specialists and generalists evolve, and what morphological changes are
associated with these transitions. To answer these questions, we: (1)
measured 29 morphological characters of tentacles from 45 siphonophore
species, (2) mapped these data to a phylogenetic tree, and (3) analyzed
the evolutionary associations between morphological characters and prey
type data from the literature. Instead of a dead-end, we found that
siphonophore specialists can evolve into generalists, and that specialists
on one prey type have directly evolved into specialists on other prey
types. Our results show that siphonophore tentillum morphology has strong
evolutionary associations with prey type, and suggest that shifts between
prey types are linked to shifts in the morphology, mode of evolution, and
genetic correlations of tentilla and their nematocysts. The evolutionary
history of siphonophore specialization helps build a broader perspective
on predatory niche diversification via morphological innovation and
evolution. These findings contribute to understanding how specialization
and morphological evolution have shaped present-day food webs.