Toxin-resistant isoforms of Na+/K+-ATPase in snakes do not closely track dietary specialization on toads

Toads are chemically defended by bufadienolides, a class of cardiotonic steroids that exert toxic effects by binding to and disabling the Na+/K+-ATPases of cell membranes. Some predators, including a number of snakes, have evolved resistance to the toxic effects of bufadienolides and prey regularly on toads. Resistance in snakes to the acute effects of these toxins is conferred by at least two amino acid substitutions in the cardiotonic steroid binding pocket of the Na+/K+-ATPase. We surveyed 100 species of snakes from a broad phylogenetic range for the presence or absence of resistance-conferring mutations. We found that such mutations occur in a much wider range of taxa than previously believed. Although all sequenced species known to consume toads exhibited the resistance mutations, many of the species possessing the mutations do not feed on toads, much less specialize on that food source. This suggests that either there is little performance cost associated with these mutations or t...

蟾蜍凭借蟾毒配基类（bufadienolides）获得化学防御能力，该类物质属于强心甾体类（cardiotonic steroids），可通过结合并抑制细胞膜上的钠钾ATP酶（Na+/K+-ATPases）发挥毒性作用。包括多种蛇类在内的部分捕食者已演化出对该类毒素急性毒性的抗性，并可常规捕食蟾蜍。蛇类对这类毒素的抗性，由钠钾ATP酶的强心甾体结合口袋中至少两处氨基酸替换所赋予。我们对涵盖广泛系统发育类群的100种蛇类开展了调查，以检测其是否携带上述抗性相关突变。研究发现，这类抗性突变在演化类群中的分布范围远较此前认知更广。尽管所有已知以蟾蜍为食的测序蛇类均携带该抗性突变，但诸多携带该突变的蛇类并不会捕食蟾蜍，更不会将其作为特化食物来源。这提示，要么这类突变几乎不会带来适应性成本，要么……