Complementary mechanisms for neurotoxin resistance in a copepod

Area of Science:

• Evolutionary Biology
• Marine Ecology
• Molecular Toxicology

Background:

• Predators consuming toxic prey evolve resistance mechanisms.
• Neurotoxins like saxitoxin (STX) target voltage-gated sodium channels (Na_V) in vertebrates.
• The copepod Calanus finmarchicus consumes STX-producing dinoflagellates without apparent harm.

Purpose of the Study:

• To identify the molecular mechanisms of STX resistance in Calanus finmarchicus.
• To investigate the role of sodium channel variants and detoxification pathways in copepod toxin resistance.
• To understand the interplay between physiological adaptations and ecological interactions in toxic environments.

Main Methods:

• Transcriptomic analysis was employed to identify genes and splice variants associated with STX resistance.
• Gene expression levels were monitored in response to toxin exposure across different developmental stages.
• Investigated genes involved in multi-xenobiotic resistance (MXR) and detoxification pathways (phases I and II).

Main Results:

• Toxin-resistant Na_V splice variants were identified but their expression was unresponsive to STX challenge.
• No significant up-regulation of MXR or classical detoxification genes was observed.
• Adult copepods upregulated digestive enzyme genes, potentially limiting STX assimilation, while susceptible nauplii did not.

Conclusions:

• Calanus finmarchicus employs a multi-faceted resistance strategy against STX, involving both modified sodium channels and digestive enzyme regulation.
• Limiting toxin assimilation through digestive processes appears crucial for adult resistance, complementing direct channel resistance.
• Deep-sequencing technologies reveal complex molecular adaptations linking organismal physiology to ecological interactions with toxic prey.