The invasive zebra mussel, Dreissena polymorpha (ZM), established in Europe for a long time, has recently been joined and commonly outcompeted by a new invader, the quagga mussel, Dreissena rostriformis bugensis (QM). To identify factors contributing to this displacement, we studied behavioural differences between the species: aggregation, movement, and responses to conspecifics, congeners and their alarm cues. Compared to ZM, QM were more aggregated and less motile, crawling shorter distances for a shorter time at a slower speed. Conversely, QM exhibited more nonlocomotor movements. Both species aggregated and burrowed less and showed more nonlocomotor movements in response to conspecific and heterospecific alarm cues. They also moved shorter distances in the presence of conspecific alarm cues. ZM delayed their locomotion and nonlocomotor movements, whereas QM started locomotion earlier in the presence of both alarm cues. Mussel responses to living heterospecifics resembled those to alarm cues. In mixed-species aggregations, ZM attached to conspecifics more often than to QM shells, whereas QM were nonselective. To summarize, QM are less mobile, less selective regarding attachment site and more aggregated than ZM. This allows QM to perform better in mixed-species assemblages by spending less energy on relocation and overgrowing ZM to a higher extent than vice versa. Both species responded to heterospecific signals, which is helpful in mixed-species assemblages, particularly in novel areas occupied by these invasive species. Nevertheless, similar responses to alarm cues and living heterospecifics suggest a negative interaction between the congeners.

中文翻译：

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形成混合物种组合的两个无柄双壳类动物之间的行为差​​异和相互作用

入侵斑马贻贝，Dreissena polymorpha (ZM)，在欧洲建立了很长时间，最近加入了一种新的入侵者，斑马贻贝，Dreissena rostriformis bugensis (QM)，并普遍在竞争中胜出。为了确定导致这种位移的因素，我们研究了物种之间的行为差​​异：聚集、运动和对同种、同源物及其警报线索的反应。与 ZM 相比，QM 更聚合且活动性更小，以更慢的速度在更短的时间内爬行更短的距离。相反，QM 表现出更多的非运动性运动。这两个物种聚集和挖洞较少，并显示出更多的非运动性运动以响应同种和异种警报提示。在存在同种警报提示的情况下，它们还会移动更短的距离。ZM 延迟了他们的运动和非运动性运动，而 QM 在两种警报提示都存在的情况下更早地开始运动。贻贝对异种异种生物的反应类似于对警报线索的反应。在混合物种聚集中，ZM 更频繁地附着在同种物种上，而不是 QM 壳，而 QM 是非选择性的。总而言之，与 ZM 相比，QM 的移动性较低，对附件站点的选择性较低，并且聚合性更强。这使得 QM 通过在迁移和过度生长 ZM 上花费更少的能量而在混合物种组合中表现得更好，反之亦然。这两个物种都对异种特异性信号做出反应，这有助于混合物种组合，特别是在这些入侵物种占据的新区域中。尽管如此，