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Mol Ecol
2025 Jan 22;351:e70202. doi: 10.1111/mec.70202.
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Coral Venom and Toxins as Protection Against Crown-of-Thorns Sea Star Attack.
Gorman LM, Huffmyer AS, Byrne M, Mills SC, Putnam HM.
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Crown-of-thorns sea star (CoTS) outbreaks are a main cause of hard coral cover decline across the Indo-Pacific, posing a major threat to the resilience of coral reefs. However, the drivers underlying CoTS feeding on preferred (e.g., Acropora species) versus non-preferred (e.g., Porites species) are poorly understood. We hypothesised that coral venom may influence CoTS prey preferences. To investigate this hypothesis, we compared the coral venom toxin families across the genomes of preferred (A. digitifera, A. hyacinthus, A. millepora and A. tenuis) and non-preferred (P. australiensis, P. compressa, P. lutea and P. rus) prey species of CoTS. We also included one species from each genus inhabiting the Caribbean, where CoTS are absent (A. cervicornis and P. astreoides), to broaden our identification of venom constituents shared within each genus and investigate geographic differences. We collected known cnidarian toxins, and along with the cnidarian Tox-Prot database, used these to identify putative toxins and investigate their phylogeny. The most abundant toxins across all coral species included neurotoxins (kunitz-type and SCRiPS) and pore-forming toxins (actinoporins and MAC-PFs). We found genera-specific differences with jellyfish toxins (CFXs) only present in Porites species. Similarly, only Acropora species harboured pore-forming toxins with the aerolysin domain. Two toxin homologues only present in Indo-Pacific corals (CFX and MAC-PF homologues) showed evidence of positive selection, suggesting their evolution is shaped by environmental pressures, including exposure to CoTS. These findings provide a foundation for future studies of scleractinian venoms, which have direct applications to assessing reef coral's susceptibility to future CoTS outbreaks and active reef management.
FIGURE 1. Putative coral venom protein families found across each coral species identified by custom BLAST searches and discovery bioinformatics (Tables S1–S11).
FIGURE 2. Main differences found in venom proteins across Acropora and Porites species and a coral's exposure to CoTS (corals native to the Pacific = CoTS exposed vs. corals native to the Caribbean = not exposed to CoTS). Black boxes represent the presence of protein found in that coral species. Actinoporin, MAC‐PF, CFX and SCRiP group terminology on the y‐axis is informed by phylogenetic analysis conducted in our current study (Figures 3, 4, 5, 6). Asterisks (*) refers to actinoporin phylogenetic groups with low support (blue font; Figure 3). Hashed boxes represent proteins that were found in a previous study (Barroso et al. 2024) but not in our current study. Graph created in BioRender (Gorman 2025; https://BioRender.com/hbygxgm) and figure edited in InkScape. Images of CoTS and coral species downloaded from the media library at the Integration Network University of Maryland Centre for Environmental science (https://ian.umces.edu/media‐library/).
FIGURE 3. Maximum likelihood tree of actinoporins across Cnidaria. Putative actinoporins from the current study are denoted in green (Acropora species) and brown (Porites species). Model of evolution and tree constructed in IQ tree (Trifinopoulos et al. 2016) and tree visualised and edited in Interactive tree of life (iTOL; Letunic and Bork 2024). SH‐aLRT/Ultrafast bootstrap (UFBoot) support values are shown on branches. Branches are coloured based on SH‐aLRT support (maximum support—light green; minimum support—purple). Blue font represents groups that have a < 70% SH‐aLRT support. The asterisk ‘*’ group denotes two Acropora actinoporins containing the aerolisin/ETX pore‐forming domain (SUPERFAMILY ID: SSF56973), whilst the delta ‘∆’ group represents a putative actinoporin in
Acropora hyacinthus
grouping separately from all other actinoporins investigated. The dagger ‘†’ symbol indicates potential pseudogenes.
FIGURE 4. Maximum likelihood tree of Membrane Attack Complex/Perforin toxins (MAC‐PF) across Cnidaria. Putative MAC‐PFs from the current study are denoted in green (Acropora species) and brown (Porites species). Model of evolution and tree constructed in IQ tree (Trifinopoulos et al. 2016) and tree visualised and edited in Interactive tree of life (iTOL; Letunic and Bork 2024). SH‐aLRT/Ultrafast bootstrap (UFBoot) support values are shown on branches. Branches are coloured based on SH‐aLRT support (maximum support—light green; minimum support—purple). The dagger ‘†’ symbol indicates potential pseudogenes.
FIGURE 5. Maximum likelihood tree of jellyfish toxins (JFTs) and their homologues. JFTs gathered from Klompen et al. (2021) and aligned with putative CFXs from the current study which are denoted in brown (Porites species). Model of evolution and tree constructed in IQ tree (Trifinopoulos et al. 2016) and tree visualised and edited in Interactive tree of life (iTOL; Letunic and Bork 2024). Groupings named as in Klompen et al. (2021). SH‐aLRT/Ultrafast bootstrap (UFBoot) support values are shown on branches. Branches are coloured based on SH‐aLRT support (maximum support—light green; minimum support—purple).
FIGURE 6. Small Cysteine‐Rich Proteins (SCRiPs) maximum likelihood tree. Putative SCRiP homologues from this current study are denoted in green (Acropora species) and brown (Porites species). Other sequences were taken from Barroso et al. (2024). Groups named accordingly with those named in Barroso et al. (2024). Model of evolution and tree constructed in IQ tree (Trifinopoulos et al. 2016) and tree visualised and edited in Interactive tree of life (iTOL; Letunic and Bork 2024). Groupings named as in Klompen et al. (2021). SH‐aLRT/Ultrafast bootstrap (UFBoot) support values are shown on branches. Branches are coloured based on SH‐aLRT support (maximum support—light green; minimum support—purple). The dagger ‘†’ symbol indicates potential pseudogenes.
