Department of Biological Sciences, Clemson University, 190 Collings St., Clemson, SC, 29634, USA.
Science Department, Cape Fear Community College, Wilmington, NC, 28401, USA.
J Mol Evol. 2023 Aug;91(4):514-535. doi: 10.1007/s00239-023-10115-2. Epub 2023 Jun 3.
Snake venom can vary both among and within species. While some groups of New World pitvipers-such as rattlesnakes-have been well studied, very little is known about the venom of montane pitvipers (Cerrophidion) found across the Mesoamerican highlands. Compared to most well-studied rattlesnakes, which are widely distributed, the isolated montane populations of Cerrophidion may facilitate unique evolutionary trajectories and venom differentiation. Here, we describe the venom gland transcriptomes for populations of C. petlalcalensis, C. tzotzilorum, and C. godmani from Mexico, and a single individual of C. sasai from Costa Rica. We explore gene expression variation in Cerrophidion and sequence evolution of toxins within C. godmani specifically. Cerrophidion venom gland transcriptomes are composed primarily of snake venom metalloproteinases, phospholipase A[Formula: see text]s (PLA[Formula: see text]s), and snake venom serine proteases. Cerrophidion petlalcalensis shows little intraspecific variation; however, C. godmani and C. tzotzilorum differ significantly between geographically isolated populations. Interestingly, intraspecific variation was mostly attributed to expression variation as we did not detect signals of selection within C. godmani toxins. Additionally, we found PLA[Formula: see text]-like myotoxins in all species except C. petlalcalensis, and crotoxin-like PLA[Formula: see text]s in the southern population of C. godmani. Our results demonstrate significant intraspecific venom variation within C. godmani and C. tzotzilorum. The toxins of C. godmani show little evidence of directional selection where variation in toxin sequence is consistent with evolution under a model of mutation-drift equilibrium. Cerrophidion godmani individuals from the southern population may exhibit neurotoxic venom activity given the presence of crotoxin-like PLA[Formula: see text]s; however, further research is required to confirm this hypothesis.
蛇毒在种内和种间都存在差异。虽然一些新世界响尾蛇（如响尾蛇）已经得到了很好的研究，但对于中美洲高地发现的高山响尾蛇（Cerrophidion）的毒液知之甚少。与分布广泛的大多数研究充分的响尾蛇相比，孤立的高山响尾蛇种群可能促进了独特的进化轨迹和毒液分化。在这里，我们描述了来自墨西哥的 C. petlalcalensis、C. tzotzilorum 和 C. godmani 种群以及来自哥斯达黎加的 C. sasai 单一个体的毒液腺转录组。我们探索了 Cerrophidion 中的基因表达变异和 C. godmani 中毒素的序列进化。Cerrophidion 毒液腺转录组主要由蛇毒金属蛋白酶、磷脂酶 A2（PLA2）和蛇毒丝氨酸蛋白酶组成。Cerrophidion petlalcalensis 种内变异很小；然而，C. godmani 和 C. tzotzilorum 在地理上隔离的种群之间存在显著差异。有趣的是，种内变异主要归因于表达变异，因为我们没有在 C. godmani 毒素中检测到选择信号。此外，我们在除 C. petlalcalensis 以外的所有物种中都发现了类似于 PLA2 的肌毒素，在 C. godmani 的南部种群中发现了类似于 crotoxin 的 PLA2。我们的结果表明 C. godmani 和 C. tzotzilorum 种内毒液存在显著变异。C. godmani 的毒素几乎没有定向选择的证据，毒素序列的变异与突变-漂变平衡模型下的进化一致。鉴于存在类似于 crotoxin 的 PLA2，C. godmani 南部种群的个体可能表现出神经毒性毒液活性；然而，需要进一步的研究来证实这一假设。
