Inducible defenses against predators are widespread among plants and animals. For example, some Daphnia species form neckteeth against predatory larvae of the dipteran genus Chaoborus. Though thoroughly studied in D. pulex, knowledge about neckteeth in other Daphnia species is limited. The occurrence of this trait in the D. longispina species complex is only sporadically reported and the specific shape of neckteeth or the occurrence of other morphological defense traits is scarcely known in this widespread group. Here, we explored neckteeth occurrence in a large number of D. longispina populations across Scandinavia and studied neckteeth formation and other morphological defense traits on three D. longispina clones in the laboratory. In the study region, neckteeth on juvenile D. longispina s. str. were observed frequently in permanent ponds, but only when Chaoborus spp. larvae were present. In the laboratory experiments, all three D. longispina clones developed neckteeth (very similar to D. pulex) in response to Chaoborus kairomone exposure. The D. longispina clones also developed a longer tail spine, wider body, and larger neckteeth pedestal in response to predation threat-likely as a defense against the gape-limited predator. The intensity of neckteeth expression also depended on the clone studied and the concentration of Chaoborus kairomone. Our results demonstrate that neckteeth on D. longispina can be common in nature and that D. longispina can also induce other morphological defenses against predators. The similarity of neckteeth in D. longispina and D. pulex imposes yet unresolved questions on the evolutionary origin in these distantly related Daphnia groups.

中文翻译：

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捕食者诱导的水蚤形态防御特征的生态学（克拉科德拉，节肢动物）。

在植物和动物中广泛存在着对天敌的诱导防御。例如，一些水蚤物种形成颈部，抵制双足类Chaophorus的掠食性幼虫。尽管已在D. pulex中进行了深入研究，但其他水蚤属中有关颈牙的知识仍然有限。仅散发性报道了D. longispina种复合体中该性状的发生，在这一广泛分布的群体中，鲜为人知的是脖子的具体形状或其他形态防御性状的发生。在这里，我们探索了整个斯堪的纳维亚半岛上大量D. longispina种群中的颈齿发生，并在实验室中研究了三个D. longispina克隆的颈齿形成和其他形态防御特征。在研究区域，少年D. longispina s上的脖子。海峡 经常在永久性池塘中观察到 但仅当潮虫属时。幼虫存在。在实验室实验中，所有三个D. longispina克隆均响应于Chaoborus kairomone暴露而形成了颈齿（非常类似于D. pulex）。D. longispina克隆还发展了更长的尾脊，更宽的身体和更大的颈齿基座，以应对掠食威胁，这可能是对有限的掠食者的防御。颈牙表达的强度还取决于研究的克隆和南美白对虾的浓度。我们的研究结果表明，D。longispina上的颈部牙齿在自然界中可能很常见，而D. longispina还可诱导其他针对食肉动物的形态防御。在D. longispina和D. pulex中，颈部的相似性对这些远缘相关的水蚤群体的进化起源提出了尚未解决的问题。