Konrad Lorenz Institute of Ethology, Department of Integrative Biology and Evolution, University of Veterinary Medicine, Vienna, Savoyenstrasse, Vienna, Austria.
PLoS One. 2012;7(5):e35833. doi: 10.1371/journal.pone.0035833. Epub 2012 May 16.
Predation pressure has long been considered a leading explanation of colonies, where close neighbors may reduce predation via dilution, alarming or group predator attacks. Attacking predators may be costly in terms of energy and survival, leading to the question of how neighbors contribute to predator deterrence in relationship to each other. Two hypotheses explaining the relative efforts made by neighbors are byproduct-mutualism, which occurs when breeders inadvertently attack predators by defending their nests, and reciprocity, which occurs when breeders deliberately exchange predator defense efforts with neighbors. Most studies investigating group nest defense have been performed with birds. However, colonial fish may constitute a more practical model system for an experimental approach because of the greater ability of researchers to manipulate their environment. We investigated in the colonial fish, Neolamprologus caudopunctatus, whether prospecting pairs preferred to breed near conspecifics or solitarily, and how breeders invested in anti-predator defense in relation to neighbors. In a simple choice test, prospecting pairs selected breeding sites close to neighbors versus a solitary site. Predators were then sequentially presented to the newly established test pairs, the previously established stimulus pairs or in between the two pairs. Test pairs attacked the predator eight times more frequently when they were presented on their non-neighbor side compared to between the two breeding sites, where stimulus pairs maintained high attack rates. Thus, by joining an established pair, test pairs were able to reduce their anti-predator efforts near neighbors, at no apparent cost to the stimulus pairs. These findings are unlikely to be explained by reciprocity or byproduct-mutualism. Our results instead suggest a commensal relationship in which new pairs exploit the high anti-predator efforts of established pairs, which invest similarly with or without neighbors. Further studies are needed to determine the scope of commensalism as an anti-predator strategy in colonial animals.
捕食压力一直被认为是群体形成的主要原因之一，因为近邻可以通过稀释、警报或群体攻击来减少捕食者的攻击。攻击捕食者可能会消耗大量的能量和生存资源，因此就出现了一个问题，即邻居之间彼此如何为捕食者防御做出贡献。有两个假说可以解释邻居之间相对努力程度，即副产品互惠，当繁殖者在保护巢穴时无意中攻击捕食者时就会发生这种情况；还有互惠，当繁殖者故意与邻居交换捕食者防御工作时就会发生这种情况。大多数研究群体巢穴防御的研究都是用鸟类进行的。然而，由于研究人员更有能力操纵殖民地鱼类的环境，因此殖民地鱼类可能构成更实用的实验模型系统。我们在群居鱼类 Neolamprologus caudopunctatus 中进行了研究，探究探测对是更喜欢在同种附近繁殖还是独自繁殖，以及繁殖者如何根据邻居的情况投资于防御捕食者。在一个简单的选择测试中，探测对选择靠近邻居的繁殖地点，而不是独自的繁殖地点。然后，依次将捕食者呈现给新建立的测试对、以前建立的刺激对或两个配对之间。与两个繁殖地点之间相比，当测试对在非邻居一侧受到攻击时，它们攻击捕食者的频率要高 8 倍，而刺激对则保持高攻击率。因此，通过加入一个已建立的配对，测试对能够在靠近邻居的地方减少它们的防御捕食者的努力，而对刺激对没有明显的影响。这些发现不太可能用互惠或副产品互惠来解释。我们的结果表明，这更可能是一种共生关系，即新对利用已建立对的高防御捕食者的努力，而不管是否有邻居，它们的投资方式都相似。需要进一步的研究来确定共生关系作为殖民地动物的一种防御捕食者的策略的范围。
