Abstract
Barnacle settlement involves sensing of a variety of exogenous cues. A pair of antennules is the main sensory organ that the cyprid larva uses to explore the surface. Antennules are equipped with a number of setae that have both chemo- and mechanosensing function. The current study explores the repertoire of sensory receptors in Balanus improvisus cyprid antennules with the goal to better understand sensory systems involved in the settling behavior of this species. We carried out transcriptome sequencing of dissected B. improvisus cyprid antennules. The generated transcriptome assembly was used to search for sensory receptors using HMM models. Among potential chemosensory genes, we identified the ionotropic receptors IR25a, IR8a and IR93a, and several divergent IR candidates to be expressed in the cyprid antennules. We found one gustatory-like receptor but no odorant receptors, chemosensory or odorant-binding proteins. Apart from chemosensory receptors, we also identified 13 potential mechanosensory genes represented by several transient receptor potential channels (TRP) subfamilies. Furthermore, we analyzed changes in expression profiles of IRs and TRPs during the B. improvisus settling process. Several of the sensory genes were differentially expressed during the course of larval settlement. This study gives expanded knowledge about the sensory systems present in barnacles, a taxonomic group for which only limited information about receptors is currently available. It furthermore serves as a starting point for more in depth studies of how sensory signaling affects settling behavior in barnacles with implications for preventing biofouling.
Highlights
The barnacle Balanus improvisus Darwin 1854 (= Amphibalanus improvisus) is a common fouling species in temperate waters that, together with Balanus amphitrite (= Amphibalanus amphitrite), has become a model organism for developing and testing antifouling coatings [1]
Sequencing of the obtained RNA generated more than 260 million good quality read pairs
In the present study we identified three types of sensory receptors in the barnacle B. improvisus, olfactory ionotropic receptors, gustatory-like receptors and mechanosensory transient receptor potential channels, present in the cyprid antennules that most likely are involved in the sensing of settlement cues
Summary
The barnacle Balanus improvisus Darwin 1854 (= Amphibalanus improvisus) is a common fouling species in temperate waters that, together with Balanus amphitrite (= Amphibalanus amphitrite), has become a model organism for developing and testing antifouling coatings [1]. The barnacle life cycle involves sessile adults and planktonic larvae, including six naupliar larval stages followed by a cyprid larva that settles and metamorphoses into the sessile stage. Settling cyprids show a complex searching behavior that includes several distinct stages; e.g. free. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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