Department of Biological Sciences, University of Calgary, Calgary, Canada.
Museum of Southwestern Biology and Department of Biology, University of New Mexico, Alburquerque, NM, USA.
Int J Parasitol. 2019 Sep;49(10):789-796. doi: 10.1016/j.ijpara.2019.05.007. Epub 2019 Jul 27.
Despite the economic, social and ecological importance of the ostertagiine abomasal nematode Marshallagia marshalli, little is known about its life history traits and its adaptations to cope with environmental extremes. Conserved species-specific traits can act as exaptations that may enhance parasite fitness in changing environments. Using a series of experiments, we revealed several unique adaptations of the free-living stages of M. marshalli that differ from other ostertagiines. Eggs were isolated from the feces of bighorn sheep (Ovis canadensis) from the Canadian Rocky Mountains and were cultured at different temperatures and with different media. Hatching occurred primarily as L1s in an advanced stage of development, morphologically very similar to a L2. When cultured at 20 °C, however, 2.86% of eggs hatched as L3, with this phenomenon being significantly more common at higher temperatures, peaking at 30 °C with 28.95% of eggs hatching as L3s. After hatching, free-living larvae of M. marshalli did not feed nor grow as they matured from L1 to infective L3. These life history traits seem to be adaptations to cope with the extreme environmental conditions that Marshallagia faces across its extensive latitudinal distribution in North America and Eurasia. In order to refine the predictions of parasite dynamics under scenarios of a changing climate, basic life history traits and temperature-dependent phenotypic behaviour should be incorporated into models for parasite biology.
尽管 ostertagiine 胃线虫 Marshallagia marshalli 具有重要的经济、社会和生态意义，但人们对其生活史特征及其适应环境极端条件的能力知之甚少。保守的物种特异性特征可以作为适应，可能会增强寄生虫在不断变化的环境中的适应性。通过一系列实验，我们揭示了 M. marshalli 自由生活阶段的几个独特适应特性，这些特性与其他 ostertagiines 不同。虫卵从加拿大落基山脉的大角羊（Ovis canadensis）粪便中分离出来，并在不同温度和不同培养基中进行培养。孵化主要以发育后期的 L1 形式发生，形态上非常类似于 L2。然而，在 20°C 下培养时，有 2.86%的卵孵化为 L3，这种现象在较高温度下更为常见，在 30°C 时达到峰值，有 28.95%的卵孵化为 L3。孵化后，M. marshalli 的自由生活幼虫在从 L1 成熟为感染性 L3 的过程中既不进食也不生长。这些生活史特征似乎是为了适应 Marshallagia 在北美和欧亚大陆广泛分布的极端环境条件而产生的适应。为了完善气候变化情景下寄生虫动态的预测，应将基本生活史特征和温度依赖性表型行为纳入寄生虫生物学模型。
