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Abstract African lungfish estivate every dry season to survive unfavorable environmental conditions. The estivation process is associated with a drastic remodeling of the skin characterized by severe inflammation, granulocyte infiltration, epithelial damage and stem cell depletion which ultimately lead to formation of a cocoon with potent antimicrobial functions. We recently identified a novel toxin molecule that can be detected in the lungfish mucus and cocoon using proteomics. There are two genes in the African lungfish genome encoding for this toxin, one with six exons and the segmented duplicated gene with five exons. The toxin is also found in the Australian lungfish genome as a single exon molecule but appears to be lost in South American lungfish. Our studies show that dermal stem cells express this toxin at the steady state. Upon estivation, toxin mRNA levels are upregulated up to 200-fold and immunofluorescence microscopy shows it co-localizes with extracellular trap markers. 3D structure modeling predicts a pore-forming delta-endotoxin with potential insecticide functions. Current experiments are trying to elucidate the biological roles of this new toxin in the lungfish skin during freshwater and estivating stages. 

Abstract Saline migrants into freshwater habitats constitute among the most destructive invaders in aquatic ecosystems throughout the globe. However, the evolutionary and physiological mechanisms underlying such habitat transitions remain poorly understood. To explore the mechanisms of freshwater adaptation and distinguish between adaptive (evolutionary) and acclimatory (plastic) responses to salinity change, we examined genome‐wide patterns of gene expression between ancestral saline and derived freshwater populations of theEurytemora affinisspecies complex, reared under two different common‐garden conditions (0 versus 15 PSU). We found that evolutionary shifts in gene expression (between saline and freshwater inbred lines) showed far greater changes and were more widespread than acclimatory responses to salinity (0 versus 15 PSU). Most notably, 30–40 genes showing evolutionary shifts in gene expression across the salinity boundary were associated with ion transport function, withinorganic cation transmembrane transportforming the largest Gene Ontology category. Of particular interest was the sodium transporter, the Na⁺/H⁺antiporter (NHA) gene family, which was discovered in animals relatively recently. Thirty key ion regulatory genes, such as NHA paralogue #7, demonstrated concordant evolutionary and plastic shifts in gene expression, suggesting the evolution of ion transporter function and plasticity during rapid invasions into novel salinities. Moreover, freshwater invasions were associated with the evolution of reduced plasticity in the freshwater population, again for the same key ion transporters, consistent with the predicted evolution of canalization following adaptation to stressful conditions. Our results have important implications for understanding evolutionary and physiological mechanisms of range expansions by some of the most widespread invaders in aquatic habitats.