Abstract
Simple SummarySome sea slugs have evolved highly specialized feeding habits and solely prey upon a reduced number of species. This is the case of Berghia stephanieae, a sea slug that feeds exclusively on glass anemones, such as Exaiptasia diaphana. Glass anemones host photosynthetic microalgae that B. stephanieae ingest when preying upon E. diaphana. The association between these photosynthetic microalgae and sea slugs appears to be limited in time, particularly if B. stephanieae is deprived of prey hosting these microalgae. In the present study, we validate the use of a non-invasive and non-destructive approach that allows monitoring the persistence of this association in live sea slugs by measuring chlorophyll fluorescence. A complete loss of photosynthetic microalgae was observed within 8 days when animals were deprived of food or fed glass anemones with no microalgae (bleached anemones). As such, the association between B. stephanieae and photosynthetic microalgae acquired when preying glass anemones is not a true symbiosis. Future studies may use the technique here described to monitor the prevalence of the association between sea slugs and photosynthetic microalgae, particularly under bleaching events that will impair sea slugs to acquire microalgae by preying upon their invertebrate hosts.Berghia stephanieae is a stenophagous sea slug that preys upon glass anemones, such as Exaiptasia diaphana. Glass anemones host photosynthetic dinoflagellate endosymbionts that sea slugs ingest when consuming E. diaphana. However, the prevalence of these photosynthetic dinoflagellate endosymbionts in sea slugs appears to be short-lived, particularly if B. stephanieae is deprived of prey that host these microalgae (e.g., during bleaching events impacting glass anemones). In the present study, we investigated this scenario, along with food deprivation, and validated the use of a non-invasive and non-destructive approach employing chlorophyll fluorescence as a proxy to monitor the persistence of the association between sea slugs and endosymbiotic photosynthetic dinoflagellates acquired through the consumption of glass anemones. Berghia stephanieae deprived of a trophic source hosting photosynthetic dinoflagellate endosymbionts (e.g., through food deprivation or by feeding on bleached E. diaphana) showed a rapid decrease in minimum fluorescence (Fo) and photosynthetic efficiency (Fv/Fm) when compared to sea slugs fed with symbiotic anemones. A complete loss of endosymbionts was observed within 8 days, confirming that no true symbiotic association was established. The present work opens a new window of opportunity to rapidly monitor in vivo and over time the prevalence of associations between sea slugs and photosynthetic dinoflagellate endosymbionts, particularly during bleaching events that prevent sea slugs from incorporating new microalgae through trophic interactions.
Highlights
Mutualistic symbioses are characterized by specialization of each of the species taking part in these remarkable associations, as each one of them specializes in absorbing different nutrients, producing different metabolites, or providing an array of services that complement each other [1]
Our study supports the finding of Monteiro et al [9] that no true symbiotic association exists between B. stephanieae and the photosynthetic dinoflagellate endosymbionts that it acquires through the ingestion of E. diaphana
The use of chlorophyll fluorescence was successfully validated as a non-destructive approach that allows to rapidly monitor, in real time and in vivo, the persistence of photosynthetic dinoflagellate endosymbionts in sea slugs that predate marine invertebrates hosting these microalgae
Summary
Mutualistic symbioses are characterized by specialization of each of the species taking part in these remarkable associations, as each one of them specializes in absorbing different nutrients, producing different metabolites, or providing an array of services that complement each other [1] These associations commonly occur in the marine environment between different marine invertebrate taxa and photosynthetic dinoflagellate endosymbionts [2]. One of the potential benefits suggested for this association is crypsis, the ability of a given animal to be less conspicuous in its natural environment, avoiding being detected by predators [5,10,11] Another suggested benefit is the ability of sea slugs to endure periods of food shortage, being able to search the environment for suitable food sources [5,12]
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