Yamamori L and Kato M (2020), Shift of Feeding Mode in an Epizoic Stalked Bar...

ECB-ART-48553

iScience 2020 Mar 27;233:100885. doi: 10.1016/j.isci.2020.100885.

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Shift of Feeding Mode in an Epizoic Stalked Barnacle Inducing Gall Formation of Host Sea Urchin.

Yamamori L , Kato M .

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Among diverse stalked barnacles, Rugilepas pearsei (Thoracica: Cirripedia: Arthropoda) is a rare unique species that is associated with echinoids and has highly atrophied cirri. We rediscovered the barnacle for the first time from description and verified that the barnacles live obligately in half-open galls formed on the test of the sea urchin Echinothrix diadema (Diadematidae: Echinodermata). A molecular phylogenetic analysis demonstrated that the obligate association with echinoids derived from epizoic life on crustaceans. A stable isotope analysis suggests that the barnacle feeds on particulate organic matter (POM) without parasitizing the host echinoids. These findings suggest that the host shift caused losses of plates and feather-like cirri, changes in the attachment device from cementation to anchoring, and a shift in feeding mode from filter feeding to POM collection. The barnacle''s epizoic, superficially sub-endozoic, communal life in stout but narrow galls causes repetitive reproduction at the cost of reduced growth.

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Genes referenced: LOC100887844

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	Figure 1. Habit, Morphology, and Phylogeny of Rugilepas pearsei(A) A living individual of Echinothrix diadema inhabiting crevice of coral reef.(B) Two living barnacles (arrowheads) attached to the base of a semi-open gall formed on the test of the host sea urchin Echinothrix diadema.(C) Computed tomography (CT) image of a gall inhabited by two barnacle individuals (arrowheads).(D) Undersurface of a bleached test of a galled sea urchin.(E) Lateral view of a detached individual with extended cirri.(F) Lateral view of a brooding individual after carapace removal. Scale bars: 10 cm in (A), 1.0 cm in (B)–(D), and 1.0 mm in (E) and (F).See also Figure S1 and Table S1.
	Figure 2. δ13C and δ15N Values of Rugilepas pearsei and Its Host Sea Urchin, Echinotrhrix diadema, Collected off Manzamo, Okinawa Island (This Study), and of Diverse Organisms and Organic Materials Collected in the Ishigaki and Palau Coral Reef Ecosystems.Producers are colored green, zooplankton blue, corals orange, benthic consumers red, and particulate organic matter (POM) gray. Superimposition of the data suggests that Echinothrix diadema feeds on corals and Rugilepas pearsei on POM.
	Figure 3. Bayesian Tree of Lepadomorpha and Heteralepadomorpha Species Based on the 18S rRNA, 28S rRNA, CO1, and H3 Gene SequencesThe numbers at the nodes are (1) Bayesian posterior probability values and (2) maximum likelihood bootstrap support values. Illustration of the ecological habitus (plates are shaded) and the following six morphological/ecological properties of the barnacle species shown adjacent to the species binomials: (1) the dominant attachment host/substratum (a, Anthozoa; c, crustacean; d, driftage matter; e, echinoid; s, abiotic hard substratum; m, Mollusca; h, Hydrozoa; v, vertebrate); (2) attachment site (e, exoskeleton; g, gill; i, inside of host body; m, molluscan shell; o, outside surface; s, spine); (3) habit (g, sub-endozoic in a gall; p, parasitic; s, sessile on abiotic substratum, z, epizoic); (4) number of plates; (5) attachment device (a, anchoring; c, cementing); and (6) morphology of cirri. (a, atrophied; f, feather-like). See also Table S2.

References [+] :

Herrera, Evolutionary and biogeographical patterns of barnacles from deep-sea hydrothermal vents. 2015, Pubmed