Hellsten M, Lagergren R, Stenson J
Department of Zoology, Section of Animal Ecology, University of Göteborg, Box 463, SE-40530 Göteborg, Sweden e-mail:
Oecologia. 1999 Jan;118(1):23-8. doi: 10.1007/s004420050699.
Bosmina (Cladocera) populations, especially within the subgenus Eubosmina, show a variety of phenotypes that exhibit large differences in body size and shape and antennule length. In some populations, the morphological traits also vary during the season, with the most extreme forms occurring in periods with high densities of certain invertebrate predators. However, while temporal phenotypic variation in other cladocerans, as in the family Daphnidae, has been shown to be an adaptation to reduce the risk of predation by invertebrate predators, the reason for such changes in Bosmina is much less clear. We examined whether certain morphological traits in Bosmina species could act as a defence against invertebrate predators. We tested three Bosmina forms (subgenus Eubosmina), differing in morphology from each other, which are found in lakes together with the predator Leptodora kindtii (Cladocera). Bosmina (E.) longispina has a relatively low and elongated carapace with a caudal mucro, and short antennule, B. (E.) coregoni gibbera has a higher and more protruding carapace without caudal mucro, and a much longer antennule. Finally, B. (E.) coregoni retro extensa has a carapace like that of B. longispina but with no caudal mucro and a much longer antennule. In one experiment, B. longispina and B. gibbera were exposed for 12 h to Leptodora in Petri dishes. In a second experiment, we observed directly the escape efficiency of B. longispina, B. gibbera and B. retro extensa, and the handling time of Leptodora. The two Bosmina forms with more extreme morphological features had a lower death rate and higher escape efficiency than B. longispina. Prey that escaped did so, in most cases, within 5 min. Predator handling time was correlated to predator body length and antennule length of the prey. The results suggests that Bosmina species with extreme morphological traits may be less vulnerable to invertebrate predators.
薄皮溞（枝角类）种群，尤其是真薄皮溞亚属内的种群，呈现出多种表型，这些表型在体型、形状以及触角长度上存在很大差异。在一些种群中，形态特征在季节变化中也会有所不同，最极端的形态出现在某些无脊椎动物捕食者密度较高的时期。然而，虽然像水蚤科的其他枝角类动物的时间表型变化已被证明是一种为降低被无脊椎动物捕食者捕食风险的适应性变化，但薄皮溞这种变化的原因却不太清楚。我们研究了薄皮溞物种的某些形态特征是否能作为抵御无脊椎动物捕食者的防御手段。我们测试了三种形态各异的薄皮溞形态（真薄皮溞亚属），它们与捕食者长刺溞（枝角类）共同存在于湖泊中。长刺薄皮溞（真薄皮溞亚属）有一个相对较低且细长的背甲，有尾刺，触角短；驼背薄皮溞（真薄皮溞亚属）有一个更高且更突出的背甲，无尾刺，触角长得多。最后，后延薄皮溞（真薄皮溞亚属）有一个与长刺薄皮溞类似的背甲，但无尾刺，触角长得多。在一个实验中，将长刺薄皮溞和驼背薄皮溞在培养皿中与长刺溞接触12小时。在第二个实验中，我们直接观察了长刺薄皮溞、驼背薄皮溞和后延薄皮溞的逃逸效率以及长刺溞的处理时间。两种具有更极端形态特征的薄皮溞形态的死亡率低于长刺薄皮溞，逃逸效率更高。逃脱的猎物在大多数情况下在5分钟内逃脱。捕食者的处理时间与捕食者体长以及猎物的触角长度相关。结果表明，具有极端形态特征的薄皮溞物种可能较不易受到无脊椎动物捕食者的攻击。
