Animal Ecology, Zoological Institute and Museum, University of Greifswald, Greifswald, Germany.
Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biosciences, University of Oslo, Blindern, Oslo, Norway.
Oecologia. 2020 Mar;192(3):687-698. doi: 10.1007/s00442-019-04588-6. Epub 2020 Jan 16.
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.
诱导防御是动植物中广泛存在的现象。例如，一些枝角类动物会形成颈齿来抵御双翅目 Chaoborus 属的幼虫捕食。尽管在 Daphnia pulex 中对此进行了深入研究，但对其他枝角类动物的颈齿知识却有限。在 D. longispina 种复合体中，该特征的出现只是偶有报道，而在这个广泛分布的群体中，颈齿的具体形状或其他形态防御特征的出现则鲜为人知。在这里，我们在斯堪的纳维亚半岛的大量 D. longispina 种群中探索了颈齿的出现，并在实验室中对三个 D. longispina 克隆体的颈齿形成和其他形态防御特征进行了研究。在研究区域中，在永久性池塘中经常观察到幼年 D. longispina s. str. 的颈齿，但只有当 Chaoborus spp. 幼虫存在时才会出现。在实验室实验中，所有三个 D. longispina 克隆体在受到 Chaoborus 信息素的刺激后都发育出了颈齿（与 D. pulex 非常相似）。D. longispina 克隆体还在受到捕食威胁时发育出了更长的尾刺、更宽的身体和更大的颈齿底座，这可能是为了抵御有限张口的捕食者。颈齿表达的强度也取决于所研究的克隆体和 Chaoborus 信息素的浓度。我们的研究结果表明，D. longispina 上的颈齿在自然界中可能很常见，而且 D. longispina 还可以诱导其他针对捕食者的形态防御。D. longispina 和 D. pulex 之间颈齿的相似性对这些亲缘关系较远的枝角类动物群体中的进化起源提出了尚未解决的问题。
