Symbiotic Life of Echinoderm Larvae

Abstract

Echinoderm larvae have served as a fundamental system for understanding development and life history evolution over much of the last century. In the last few decades, our understanding of echinoderm larvae has expanded to the microbiota that they associate with. These symbionts and the communities that they form in relation to echinoderm larval host are the focus of this review. Our synthesis of the literature suggests three primary themes. First, larval echinoderms associate with "subcuticle bacteria" that appear to colonize select tissue types. Second, the bacterial communities associated with larval echinoderms exhibit compositional shifts that are correlated with several fundamental properties of larval biology (e.g., development and morphological plasticity) and ecology (e.g., feeding environment). Third, echinoderm larvae exhibit specific responses to pathogenic bacteria that may aid in maintaining the symbiont community and avoid dysbiosis. To our knowledge, no studies have focused on whether climate-related stressors impact the composition of these symbiont communities or how changes in bacteria may modulate response by larvae to these environmental stressors. Lastly, we conclude by outlining techniques that need to be established in echinoderm larvae to transition from correlations between larvae and their associated microbiota to the function of these symbionts.

Microbiome reduction and endosymbiont gain from a switch in sea urchin life history

“…We qualitatively and quantitatively compared the microbiome of both Heliocidaris sister species to test whether lecithotrophic developers associate with a bacterial community that is less diverse and less abundant than planktotrophic developers. Consistent with other echinoderm larvae (16,23), the bacterial communities of H. tuberculata and H. erythrogramma are species-specific and are distinct from the seawater microbiome throughout development (permutational multivariate analysis of variance [PERMANOVA], unweighted and weighted UniFrac, P < 0.001; SI Appendix, Fig. S1 and Table S1).…”

“…The planktotrophic larvae of several echinoderm species associate with bacterial communities that are taxonomically and compositionally specific to food availability (16,23). When diet restriction is prolonged and morphological plasticity is expressed, planktotrophic larvae exhibit shifts in their bacterial community that precede and then correlate with the expression of morphological plasticity (16,17).…”

Gut Microbial Composition and Diversity in Four Ophiuroid Species: Divergence Between Suspension Feeder and Scavenger and Their Symbiotic Microbes

“…Symbiotic bacteria widely identified in the gut microflora from varied marine invertebrates ( Carrier and Reitzel, 2020 ) Ca. Hepatoplasma, as a symbiotic bacterium, are comparatively stable intestinal members, which are reported in a variety of the isopod species ( Sebastian and Zimmer, 2008 ; Cheng et al, 2019 ), sea urchin ( Li et al, 2018 ), and shrimps ( Dong et al, 2019 ).…”

Composition and geographic variation of the bacterial microbiota associated with the coelomic fluid of the sea urchin Paracentrotus lividus

“…The observed effects could depend on the bacterial doses used in our assay, which are presumably much higher than those encountered in the ocean by free-living echinoderm embryos. In support of this hypothesis, previous reports showed that many bacterial strains normally associate with healthy sea urchin larvae, where they behave as commensal or mutualistic microorganisms (reviewed in 69 ). However, under dysbiosis conditions an excessive bacterial load can overwhelm larval defenses, thereby affecting larval welfare and physiology 66 , 70 .…”