Immuno-modulation of settlement cues in the barnacle, Amphibalanus amphitrite: significance of circulating haemocytes
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Gregarious settlement in barnacles has been attributed to chemical cues originating from the associated microorganisms, lectins, and settlement-inducing protein complex from arthropodin, a glycoprotein present in their conspecifics/adults. In this study, we explored the influence of haemolymph haemocytes on the metamorphosis of barnacle, Amphibalanus amphitrite cyprids. The barnacle haemocytes were also characterized for the first time using flow cytometry. Cyprid metamorphosis was significantly higher in the presence of surface-bound haemocytes compared to water-borne cues from haemolymph or adult glycoprotein, a known settlement inducer. The flow cytometry-assisted haemocyte characterization, sorting and their subsequent microscopic evaluation indicated the presence of hyalinocytes and granulocytes. Tagging of these haemocytes with lectins revealed that a significant number of haemocytes had d-glucose/d-mannose and N-acetyl-d-galactosamine, which are important settlement cues. These glycoconjugates were also detected in the cyprid larva pointing out the origin of conspecific cues. The retention of these glycoconjugates in the adult haemocytes and their occurrence in adult leachants indicate pelago-benthic coupling in sessile barnacles wherein these glycoconjugates play a significant role in their gregarious settlement. Characterization of such a coupling process in other sessile benthic invertebrates will pave the way to the understanding of complexities in their population dynamics.
KeywordsAmphibalanus amphitrite Glycoconjugates Haemocytes Immuno-modulation Flow cytometry Lectins Settlement cues
We thank the Director of CSIR-National Institute of Oceanography for providing the facilities and support. This work was supported by the Council of Scientific and Industrial Research (CSIR)-funded Ocean Finder Program (PSC0105). This is NIO contribution 6332.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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