Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 118, Issue 8, Pages -Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.2005063118
Keywords
siphonophores; nematocysts; predation; specialization; character evolution
Categories
Funding
- Society of Systematic Biologists Graduate Student Award
- Yale Institute of Biospheric Studies Doctoral Pilot grant
- National Science Foundation [NSF-OCE 1829835, OCE-1829805, OCE-1829812]
- Fulbright Spain Graduate Studies Scholarship
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Specialization in siphonophores is not an evolutionary dead end as previously thought, with specialists able to evolve into generalists and transition between different prey types. Morphological changes in tentacle structures are strongly associated with prey type and play a key role in the evolution and diversification of predatory niches.
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: a) Measured 29 morphological characters of tentacles from 45 siphonophore species, b) mapped these data to a phylogenetic tree, and c) 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 evolutionary 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.
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