Intercontinental test of constraint-breaking adaptations; testing behavioural plasticity in the face of a predator with novel hunting strategies

1. Constraint-breaking adaptations are evolutionary tools that provide a mechanism for incumbent-replacement between species filling similar ecological roles. 2. In common-garden experiments, we exposed populations of two desert rodents to two different viper species, testing their ability to adjust to novel predators that use different hunting strategies. We aimed to understand whether both predators and prey with constraint-breaking adaptations actually manifest comparative advantage over their counterparts. 3. We used convergent species from desert dunes in the Mojave Desert in North America, Merriam’s kangaroo rat (Dipodomys merriami) and the sidewinder rattlesnake (Crotalus cerastes), and from the Negev Desert in the Middle East, the greater Egyptian gerbil (Gerbillus pyramidum) and the Saharan horned vipers (Cerastes cerastes). Both Mojave species hold constraint-breaking adaptations in relation to their counterparts from the Negev. The rattlesnakes have heat sensing organs (pits) and the kangaroo rats have fur-lined cheek pouches that allow for greater foraging efficiency and food preservation. Using patch-use, we assessed the rodents’ risk-assessment from each snake— separately, together and in combination with barn owls. 4. Initially each rodent species foraged less in the presence of its familiar snake, but within a month both foraged less in the presence of the pit-viper (sidewinder). 5. Our findings indicate a level of learning, and behavioural plasticity, in both rodents and ability to assess the risk from novel predators. The kangaroo rats were capable of harvesting far greater amounts of resources under the same conditions of elevate risk. However, the reason for their advantage may lay in bi-pedal agility and not only their ability collect food more efficiently.

1. 打破约束适应性（Constraint-breaking adaptations）是一类演化工具，可为占据相似生态角色的物种间的现存物种更替提供机制。2. 在同质园实验（common-garden experiments）中，我们将两种荒漠啮齿类种群暴露于两种不同的蝰蛇物种之下，以测试它们适应采用不同捕猎策略的新型捕食者的能力。本研究旨在探究具备打破约束适应性的捕食者与猎物，是否真的相较于其同类物种表现出比较优势。3. 本研究选用了来自北美莫哈韦沙漠荒漠沙丘的趋同物种：梅氏更格卢鼠（Merriam’s kangaroo rat，Dipodomys merriami）与侧响尾蛇（sidewinder rattlesnake，Crotalus cerastes），以及来自中东内盖夫沙漠的趋同物种：大埃及沙鼠（greater Egyptian gerbil，Gerbillus pyramidum）与撒哈拉角蝰（Saharan horned vipers，Cerastes cerastes）。相较于内盖夫沙漠的同类物种，莫哈韦沙漠的两个物种均具备打破约束适应性。响尾蛇拥有热感应器官（颊窝），而更格卢鼠则长有具毛内衬的颊囊，可提升觅食效率与食物保存能力。本研究通过斑块利用（patch-use）实验，在分别、联合以及结合仓鸮（barn owls）的情境下，评估了啮齿类对每种蛇类的风险评估能力。4. 初始阶段，两种啮齿类在其熟悉的蛇类存在时觅食活动均有所减少，但在一个月内，两种啮齿类在颊窝毒蛇（侧响尾蛇）存在时的觅食量均进一步降低。5. 本研究结果表明，两种啮齿类均具备一定的学习能力与行为可塑性（behavioural plasticity），且能够评估新型捕食者带来的风险。在同等风险升高的条件下，梅氏更格卢鼠能够获取远更多的资源。不过，其竞争优势的成因可能源于双足敏捷性，而非仅依靠更高的食物收集效率。