Expression of a symbiosis-specific gene in type A1 associated with coral, nudibranch and giant clam larvae.

are responsible for the majority of primary production in coral reefs and found in a mutualistic symbiosis with multiple animal phyla. However, little is known about the molecular signals involved in the establishment of this symbiosis and whether it initiates during host larval development. To address this question, we monitored the expression of a putative symbiosis-specific gene (H-ATPase) in A1 and in association with larvae of a scleractinian coral (), a nudibranch () and a giant clam (). We acquired broodstock for each host, induced spawning and cultured the larvae. cells were offered and larval samples taken for each host during the first 72 h after symbiont addition. In addition, control samples including free-living and broodstock tissue containing symbionts for each host were collected. RNA extraction and RT-PCR were performed and amplified products cloned and sequenced. Our results show that H-ATPase was expressed in associated with coral and giant clam larvae, but not with nudibranch larvae, which digested the symbionts. Broodstock tissue for coral and giant clam also expressed H-ATPase, but not the nudibranch tissue sample. Our results of the expression of H-ATPase as a marker gene suggest that symbiosis between and and is established during host larval development. Conversely, in the case of larvae, evidence does not support a mutualistic relationship. Our study supports the utilization of H-ATPase expression as a marker for assessing invertebrate relationships with applications for the differentiation of symbiotic and non-symbiotic associations. At the same time, insights from a single marker gene approach are limited and future studies should direct the identification of additional symbiosis-specific genes, ideally from both symbiont and host.