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Acute die-offs of amphibian populations worldwide have been linked to the emergence of viral and fungal diseases. Inter and intra specific immunogenetic differences may influence the out come of infection. Toll-like receptors (TLRs) are a nessential component of innateimmunity andals oprimeacquired defenses. We report the first comprehensive assessment of TLR genevariation for urodele amphibians. The Lissotriton newt TLR repertoire includes representatives of 13 families and iscompositionally most similar to that of the an uranXenopus. Bothancient and recent geneduplication shave occurred in ur odeles, bringing the total number of TLR genes to atleast 21. Purifying selection has predominated the evolution of newt TLRs in both long (~70Ma)and medium (~18Ma) times cales. However, we find evidence for both purifying and positive selection acting on TLRs in two recently diverged (2–5Ma) allopatric evolutionary lineages (Lissotriton montandoni and L. vulgaris graecus). Overall, both forms of selection have been stronger in L. v. graecus, while constrainton most TLR genes in L.montandoni appears relaxed. The differences in selection regimesare unlikely tobe biased by demographic effects because these were controlled by means of a historical demographic model derived from an independent data set of 62loci. We infer that TLR genes under go distinct trajectories of adaptive evolution in closely related amphibian line ages, highlight the potential of TLRs to capture the signatures of different assemblages of pathogenic microorganisms, and suggest differences between lineages in the relative roles of innate and acquired immunity.
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Kembali