title: Caught in the act: phenotypic consequences of a recent shift in feeding strategy of the shark barnacleAnelasma squalicola(Lovén, 1844).
abstract: Anelasma squalicolais a barnacle found attached to deep-water lantern sharks of the family Etmopteridae and is the only known cirriped on fish hosts. WhileA. squalicolais equipped with mouth and thoracic appendages (cirri), which are used for suspension feeding in conventional barnacles, its attachment device (peduncle) appears to have evolved into a feeding device, embedded into the tissue of its host. Here we demonstrate, through comparisons of the feeding apparatuses betweenA. squalicolaand conventional suspension-feeding barnacles, that mouthparts and cirri ofA. squalicolaare highly reduced, and incapable of suspension-feeding activities. We show that in conventional suspension-feeding barnacles strong symmetries exist within these vital trophic structures. InA. squalicolastrong asymmetries are widespread, indicating that those structures have been uncoupled from natural selection. The digestive tract is consistently empty, suggesting that feeding via cirri does not occur inA. squalicola. In addition, comparisons of stable isotope ratios (δ13C and δ15N) betweenA. squalicola, its shark host, and a conventional suspending feeding barnacle indicate thatA. squalicolais taking nutrition directly from its host shark and not from the surrounding water. Our results strongly indicate that this barnacle has abandoned suspension feeding and now solely relies on obtaining nutrition from its host by a de novo evolved feeding mechanism.
authors.affiliation: Department of Biology, University of Bergen, Bergen, Norway.
authors.forename: Anders
authors.initials: A
authors.lastname: Ommundsen
authors.affiliation: Department of Biology, University of Bergen, Bergen, Norway.
authors.forename: Christoph
authors.initials: C
authors.lastname: Noever
authors.affiliation: Department of Biology, University of Bergen, Bergen, Norway ; CMEC, Natural History Museum, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Henrik
authors.initials: H
authors.lastname: Glenner
keywords: Evolutionary transition; Feeding strategy; Macro-evolution; Parasitism; Selection