First identification of tetrodotoxin (TTX) in the flatworm Stylochoplana sp.; a source of TTX for the sea slug Pleurobranchaea maculata.

Abstract

High concentrations of the neurotoxin tetrodotoxin (TTX) were detected by liquid chromatography-mass spectrometry (LC-MS) in the Platyhelminthes Stylochoplana sp. from Pilot Bay (Tauranga, New Zealand). This is the first detection of TTX in this genus. Concentrations were monitored from March to November (2013) and found to significantly decrease from a peak in July (avg. 551mgkg(-1)) to November (avg. 140mgkg(-1)). Stylochoplana sp. co-occurred with TTX-containing Pleurobranchaea maculata (Opisthobranchia). A Stylochoplana sp.-specific real-time PCR assay was developed targeting the mitochondrial cytochrome c oxidase subunit I gene to determine if P.maculata consumed Stylochoplana sp.Positive Stylochoplana sp. signals were obtained for 7 of 19 P.maculata tested. Mass calculations indicate Stylochoplana sp. could supply Pilot Bay P.maculata with the TTX required to account for the concentrations reported in previous studies (ca. 1.04mg TTX per individual) based on an ingestion rate of one individual every 2-3 days throughout their lifetime. However, due to the lack of Stylochoplana sp. in areas with dense P.maculata populations, and high concentration (ca. 1400mgkg(-1)) of TTX detected in some individuals, it is unlikely that Stylochoplana sp. represent the sole source of TTX in P.maculata.