Abstract
Symbiotic interactions are ubiquitous across biology. Understanding them is therefore fundamental to the study of biology. In the well-known anemonefish-sea anemone symbiosis, anemonefish mucus allows the fish to swim in contact with the deadly stinging tentacles of the host. While anemonefish are the only obligate symbionts,this lifestyle has evolved independently multiple times, and fish from the Dascyllus and cardinalfish clades form facultative associations. This protection relies on the mucus of the fish, but the properties that confer this protection across clades remain unknown. I tested the functional protection and gene expression of skin tissues in symbiotic and non-symbiotic species across these clades. When tested against the bubble-tip anemone(Entacmaea quadricolor), symbiotic species in each clade appear to be protected, while their non-symbiotic relatives are not. In contrast, when tested against Haddon's carpet anemone (Stichodactyla haddoni), only symbiotic fishes from the anemonefish clade were clearly protected, confirming that the symbiosis is species-specific. In symbiotic species from all clades, ortholog groups involved in protein post-translational modification and membrane trafficking were upregulated. In the anemonefish clade, an ortholog group coding for a protein involved in the post-translational modification of a mucin protein was upregulated. In the cardinalfish clade, an ortholog group encoding one subtype of mucus protein was downregulated. Altering the structure or type of mucus present may impair the anemone's ability to detect the fish as food. The fact that the ortholog groups were different in these two clades indicates a pattern of convergent evolution in modification of mucin-related ortholog groups, but with different specific mechanisms in each. With no mucin-related ortholog groups differentially expressed in the Dascyllus clade, protection in this group appears to rely on something else entirely.This research is the first step in further investigating the molecular mechanism of the anemonefish protection, and will provide guidance to specific avenues of inquiry.