氨对蚤状溞诱导型反捕食生活史防御的抑制效应

Inhibitory Effects of Ammonia on the Predator-induced Life-history Defense of Daphnia pulex

氨是水体中常见且毒性较强的含氮污染物之一,不仅会对水生生物产生直接毒害作用,甚至在不产生直接危害的情况下严重威胁水生生物的种间关系。诱导型防御是猎物应对捕食风险所表现出的典型的适应性响应,是重要的捕食与防御关系。目前,尚不清楚氨是否会干扰猎物诱导型反捕食防御性状的表达。为此,研究选择浮游动物代表性物种蚤状溞(Daphnia pulex)作为受试生物,检验了不同浓度氨对蚤状溞反捕食(鳑鲏鱼作为捕食风险源)生活史防御策略的影响以及处于诱导防御的蚤状溞对氨胁迫敏感性的变化。结果表明,氨会对蚤状溞的生活史表现产生毒害作用,例如,当氨浓度达到0.6 mg·L^(-1)时,首窝产卵时间延迟了4.2 h,成熟体长和尾刺长分别缩短了5.72%和3.74%,后代数量降低了39.7%。就蚤状溞的生活史防御而言,随着氨浓度的升高,蚤状溞响应鱼类捕食风险而表现出的体长减小(-11.13%)、生长速率减缓(-24.18%)、产卵提前等防御表现被明显抑制,并且这种对蚤状溞诱导型防御的抑制作用随着氨暴露时间的延长而累积。此外,经捕食者信息素诱导后形成反捕食防御的蚤状溞更容易受到环境压力的胁迫,即捕食风险会削弱蚤状溞对氨的耐受性。该研究不仅从种间关系的角度揭示了氨的广泛负面效应,同时也为捕食风险下生物个体应对环境胁迫能力的变化提供了新的见解。

Ammonia is one of the most common and highly toxic nitrogenous pollutants in water,which not only directly poisons aquatic organisms,but also seriously threatens the interspecific relationships of aquatic organisms without causing direct harm.Induced defense is a typical adaptive response of prey to the predation risk,and it is an important relationship between predation and defense.However,whether ammonia interfere with the responses of prey to their predators is still unclear.In this study,the effects of ammonia with different concentrations on the induced anti-predation(Rhodeus ocellatus as the predator)life-history defense responses of Daphnia pulex,a representative species of zooplankton,were examined and the changes in susceptibility of D.pulex under induced defense to ammonia stress were investigated.Results show that ammonia had an inhibitory effect on the life-history traits of D.pulex.For example,at an ammonia concentration of 0.6 mg·L^(-1),there was a delay of 4.2 hours in the first brood time,a 5.72%and 3.74%reduction in maturation body size and spine length,respectively,and a 39.7%decrease in offspring numbers.As to the induced life-history defense of D.pulex,with the increase of ammonia concentrations,the performance of D.pulex in response to predation risk,i.e.,body size reduction(-11.13%)and somatic growth rate slowdown(-24.18%),were significantly inhibited.The inhibitory effect accumulated with prolonged ammonia exposure.In addition,the predator-induced defense makes D.pulex more susceptible to ammonia,i.e.,predation risk weakens D.pulex′s tolerance to ammonia.This study not only further reveals the extensive negative effects of ammonia from the perspective of interspecific relationships,but also provides new insights into the ability changes of organisms in response to environmental stress under predation risk.