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

Luna Yamamori,Makoto Kato

doi:10.1016/j.isci.2020.100885

Abstract

SummaryAmong 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.

Highlights

Most stalked barnacles (Thoracica: Cirripedia) are sessile suspension feeders that live attached to hard substrata or the exoskeletons/epithelia of diverse marine animals (Darwin, 1851), but some of these cirripedes parasitize their host animals such as annelids (Day, 1939) and sharks (Johnstone and Frost, 1927; Rees et al, 2014) by embedding a root-like organ into the host body
Because R. pearsei has not been recorded since its original description, rediscovery of the barnacle has been kept waiting to answer the questions: how the association with echinoids derived, which prey/substance the barnacle feeds on, and how shift of feeding mode has occurred in a lineage of epizoic suspension feeders
By conducting extensive search for the barnacle, morphological and ecological observations, a molecular phylogenetic analysis, and a stable isotope analysis, we explored the evolutionary trajectory of the echinoid-symbiotic barnacle

Summary

Introduction

Most stalked barnacles (Thoracica: Cirripedia) are sessile suspension feeders that live attached to hard substrata or the exoskeletons/epithelia of diverse marine animals (Darwin, 1851), but some of these cirripedes parasitize their host animals such as annelids (Day, 1939) and sharks (Johnstone and Frost, 1927; Rees et al, 2014) by embedding a root-like organ into the host body. Other epizoic barnacles living on jellyfish (Pages, 2000) and sea anemones (Yusa et al, 2001) have different parasitic feeding modes that are facilitated by shifting their attachment and feeding devices. Rugilepas pearsei (Microlepadidae: Lepadiformes) is a rare naked stalked barnacle with atrophied cirri, and it lives in a symbiotic relationship with echinoids (Grygier, 1991), but its feeding habit is poorly understood. Because R. pearsei has not been recorded since its original description, rediscovery of the barnacle has been kept waiting to answer the questions: how the association with echinoids derived, which prey/substance the barnacle feeds on, and how shift of feeding mode has occurred in a lineage of epizoic suspension feeders. By conducting extensive search for the barnacle, morphological and ecological observations, a molecular phylogenetic analysis, and a stable isotope analysis, we explored the evolutionary trajectory of the echinoid-symbiotic barnacle

Methods

Results

Conclusion