Department of Environmental Science, Policy, and Management, College of Natural Resources, University of California, Berkeley, California, United States of America.
Museum of Vertebrate Zoology, University of California, Berkeley, California, United States of America.
PLoS One. 2018 Mar 13;13(3):e0194265. doi: 10.1371/journal.pone.0194265. eCollection 2018.
Spatial heterogeneity in the strength or agents of selection can lead to geographic variation in ecologically important phenotypes. Many dendrobatid frogs sequester alkaloid toxins from their diets and often exhibit fixed mutations at NaV1.4, a voltage-gated sodium ion channel associated with alkaloid toxin resistance. Yet previous studies have noted an absence of resistance mutations in individuals from several species known to sequester alkaloid toxins, suggesting possible intraspecific variation for alkaloid resistance in these species. Toxicity and alkaloid profiles vary substantially between populations in several poison frog species (genus Dendrobates) and are correlated with variation in a suite of related traits such as aposematic coloration. If resistance mutations are costly, due to alterations of channel gating properties, we expect that low toxicity populations will have reduced frequencies and potentially even the loss of resistance alleles. Here, we examine whether intraspecific variation in toxicity in three dendrobatid frogs is associated with intraspecific variation in alleles conferring toxin resistance. Specifically, we examine two species that display marked variation in toxicity throughout their native ranges (Dendrobates pumilio and D. granuliferus) and one species with reduced toxicity in its introduced range (D. auratus). However, we find no evidence for population-level variation in alkaloid resistance at NaV1.4. In fact, contrary to previous studies, we found that alkaloid resistance alleles were not absent in any populations of these species. All three species exhibit fixed alkaloid resistance mutations throughout their ranges, suggesting that these mutations are maintained even when alkaloid sequestration is substantially reduced.
选择压力的强度或因素在空间上的异质性可能导致生态重要表型的地理变异。许多树蛙从食物中摄取生物碱毒素，并经常在与生物碱毒素抗性相关的电压门控钠离子通道 NaV1.4 上发生固定突变。然而，之前的研究表明，在已知摄取生物碱毒素的几个物种的个体中，没有发现抗性突变，这表明这些物种的生物碱抗性可能存在种内变异。在几种毒蛙物种（Dendrobates 属）中，种群之间的毒性和生物碱谱存在很大差异，并且与一系列相关特征（如警戒色）的变异相关。如果由于通道门控特性的改变，抗性突变是有代价的，那么我们预计低毒性种群的抗性等位基因的频率会降低，甚至可能会丢失。在这里，我们研究了三种树蛙的种内毒性变异是否与赋予毒素抗性的等位基因的种内变异有关。具体来说，我们研究了两种在其原生范围内表现出明显毒性变异的物种（Dendrobates pumilio 和 D. granuliferus）和一种在引入范围内毒性降低的物种（D. auratus）。然而，我们没有发现 NaV1.4 上生物碱抗性的种群水平变异的证据。事实上，与之前的研究相反，我们发现这些物种的任何种群都没有缺失生物碱抗性等位基因。这三个物种在其分布范围内都表现出固定的生物碱抗性突变，这表明即使生物碱的摄取大大减少，这些突变也能被维持。
