Aiptasia sp. larvae as a model to reveal mechanisms of symbiont selection in cnidarians

Abstract

Symbiosis, defined as the persistent association between two distinct species, is an evolutionary and ecologically critical phenomenon facilitating survival of both partners in diverse habitats. The biodiversity of coral reef ecosystems depends on a functional symbiosis with photosynthetic dinoflagellates of the highly diverse genus Symbiodinium, which reside in coral host cells and continuously support their nutrition. The mechanisms underlying symbiont selection to establish a stable endosymbiosis in non-symbiotic juvenile corals are unclear. Here we show for the first time that symbiont selection patterns for larvae of two Acropora coral species and the model anemone Aiptasia are similar under controlled conditions. We find that Aiptasia larvae distinguish between compatible and incompatible symbionts during uptake into the gastric cavity and phagocytosis. Using RNA-Seq, we identify a set of candidate genes potentially involved in symbiosis establishment. Together, our data complement existing molecular resources to mechanistically dissect symbiont phagocytosis in cnidarians under controlled conditions, thereby strengthening the role of Aiptasia larvae as a powerful model for cnidarian endosymbiosis establishment.

Marine Invertebrate Larvae Associated with Symbiodinium: A Mutualism from the Start?

“…In the case of cnidarians, while broad knowledge on their association with Symbiodinium is available, there are still relatively few studies on the larva-Symbiodinium association (Rodriguez-Lanetty et al, 2006;Voolstra et al, 2009b;Schnitzler and Weis, 2010;Wolfowicz et al, 2016). Approximately 80-90% of reef-building coral species (Scleractinia) are broadcast spawners and acquire symbionts horizontally (Harrison and Wallace, 1990;Baird et al, 2009;Harrison, 2011).…”

“…Only recently, a study by Mohamed et al (2016) detected a transient period of differential expression involving a limited number of genes (3% of assayed transcriptome) 4 h after the exposure of Acropora digitifera planula larvae to a competent strain of Symbiodinium. While yet to be applied for larval studies, symbiosis-specific genes have been identified recently in Aiptasia anemones (Bucher et al, 2016;Wolfowicz et al, 2016). From the symbiont perspective, apart from the identification of protein kinases that may be involved in the establishment of symbiosis (Rosic et al, 2014), a symbiosisspecific gene was identified in Symbiodinium clade A, an H + -ATPase (Bertucci et al, 2010).…”

Evidence for a role of protein phosphorylation in the maintenance of the cnidarian–algal symbiosis

“…Notably, studying the cnidarian–dinoflagellate symbiosis in corals is difficult for several reasons, including the challenges with maintaining corals in aquarium settings, long reproductive cycles and the obligate dependency on their symbiotic association, that is, the absence of a “control” aposymbiotic (symbiont‐free) state (Voolstra, ). To this end, the sea anemone Aiptasia (sensu Exaiptasia pallida ) is becoming increasingly popular as a model system for the study of coral–algal symbiosis (Baumgarten et al, ; Lehnert, Burriesci, & Pringle, ; Rädecker et al, ; Wolfowicz et al, ). Aiptasia is easily reared in laboratory tanks, has a short asexual reproductive cycle and can be kept in an aposymbiotic state, enabling direct comparison between symbiotic and aposymbiotic conditions.…”

Molecular signatures of host specificity linked to habitat specialization in Exaiptasia sea anemones

“…We observed no evidence in our dataset indicating overall enrichment of SNPs strongly associated with PC1 in scavenger receptors ( p  =   .31; Neubauer et al., 2016) or genes differentially regulated during symbiosis establishment in larvae ( p =  .52; Wolfowicz et al., 2016). …”

“…Larval settlement of Fungia scutaria , a scleractinian coral that also acquires symbionts horizontally, occurred earlier when larvae were colonized by Symbiodinium (Schwarz, Krupp, & Weis, 1999) . Exaiptasia larvae similarly take up Symbiodinium prior to settlement and metamorphosis (Wolfowicz et al., 2016). Additionally, both temperature and the identity of ex‐hospite symbiont types can influence settlement behavior and substrate choice in larvae of broadcast‐spawning corals (Winkler, Pandolfi, & Sampayo, 2015).…”