Lass Sandra, Bittner Kerstin
Department of Limnology, EAWAG/ETH, Überlandstrasse 133, P.O. Box 611, 8600, Dübendorf, Switzerland.
Limnology Institute, University of Constance, Mainaustrasse 252, 78464, Konstanz, Germany.
Oecologia. 2002 Aug;132(3):344-349. doi: 10.1007/s00442-002-0982-9. Epub 2002 Aug 1.
During their lifetime most organisms are exposed to various enemies influencing their victims in multiple direct and indirect ways. Most studies concentrate on the effects of one enemy at a time, thereby not taking into account that in nature organisms are often simultaneously exposed to more than one enemy. We conducted a life-history experiment to investigate the simultaneous effects of predators (fish, Leuciscus idus) and parasites (microparasite, Caullerya mesnili) on their victim (Daphnia galeata). D. galeata were exposed to predator kairomones, parasites or both. D. galeata are able to sense the presence of fish predators via chemical cues (= kairomones). Both fish predator kairomones and microparasite infections influence the life history of Daphnia. Some of the effects of fish predator kairomones are directly opposed to microparasite effects; fecundity, for example, is increased in the presence of fish kairomones and decreased in Daphnia parasitised with C. mesnili. We investigated the influence of both threats on age at maturity, body size at different adult instars, fecundity and survival of one D. galeata clone. In the presence of fish kairomones, all D. galeata matured significantly earlier and increased the number of eggs in the second brood significantly. Parasitised D. galeata matured significantly earlier than non-parasitised ones in the absence and presence of fish kairomones. An infection with the microparasite C. mesnili led to significantly lower clutch sizes at the second adult instar, to significantly smaller body sizes from adult instar three onwards and to significantly reduced survival. No significant interaction effect between the responses to fish presence and to parasite infection was found for any of the investigated life-history traits. The lack of interaction effects between the exposure to predator kairomones and parasite infection was most likely due to the different timing of the effects. Fish kairomones affected D. galeata early in its life history whereas C. mesnili increased in its effects over time. Our results show that parasitised D. galeata are able to exhibit life-history responses to fish predator presence early in their lives. Thus, D. galeata parasitised with C. mesnili have a similar chance as non-parasitised D. galeata to escape from fish predation via life-history changes. Since older parasitised D. galeata are smaller, they may have an even better chance to escape visual predators under actual predation.
在其一生中，大多数生物会遭遇各种敌人，这些敌人会以多种直接和间接的方式影响它们的受害者。大多数研究一次只关注一种敌人的影响，因此没有考虑到在自然界中，生物常常同时面临不止一种敌人。我们进行了一项生活史实验，以研究捕食者（鱼类，赤梢鱼）和寄生虫（微寄生虫，梅氏考氏虫）对它们的受害者（盔形溞）的同时影响。将盔形溞暴露于捕食者信息素、寄生虫或两者同时存在的环境中。盔形溞能够通过化学信号（即信息素）感知鱼类捕食者的存在。鱼类捕食者信息素和微寄生虫感染都会影响盔形溞的生活史。鱼类捕食者信息素的一些影响与微寄生虫的影响直接相反；例如，在有鱼类信息素存在时，繁殖力会增加，而感染梅氏考氏虫的盔形溞的繁殖力则会下降。我们研究了这两种威胁对一个盔形溞克隆体的成熟年龄、不同成虫龄期的体型、繁殖力和存活率的影响。在有鱼类信息素存在的情况下，所有盔形溞成熟得明显更早，并且第二窝的卵数显著增加。在没有和有鱼类信息素存在的情况下，感染寄生虫的盔形溞都比未感染的盔形溞成熟得明显更早。感染微寄生虫梅氏考氏虫会导致第二成虫龄期的产卵量显著降低，从第三成虫龄期开始体型显著变小，存活率显著降低。对于任何所研究的生活史特征，在对鱼类存在的反应和对寄生虫感染的反应之间均未发现显著的交互作用。捕食者信息素暴露和寄生虫感染之间缺乏交互作用，很可能是由于影响的时间不同。鱼类信息素在盔形溞生命史早期就对其产生影响，而梅氏考氏虫的影响则随着时间推移而增强。我们的结果表明，感染寄生虫的盔形溞在其生命早期就能对鱼类捕食者的存在表现出生活史反应。因此，感染梅氏考氏虫的盔形溞与未感染的盔形溞有类似的机会通过生活史变化逃避鱼类捕食。由于感染寄生虫的老龄盔形溞体型较小，在实际捕食情况下，它们可能有更好的机会逃避视觉捕食者。
