Animal reproduction under stressful conditions is often reduced, with current survival and future reproduction being generally traded off against current reproductive activity. This study examines the impacts of physical and chemical stressors on the rates of asexual reproduction of the invasive planarian Girardia tigrina. 320 wild-caught planaria (mixed size class) were kept individually in Petri dishes such that their individual rates of fission through fragmentation could be easily monitored. Four treatment groups were compared, one chemical (5 mg/L ammonia) and one physical (decapitation), in comparison to a negative control (animals were starved of food) and a positive control where the animals were given an abundance of food. The two treatment groups immediately began reproducing asexually and accumulated the highest number of fissions over the course of the 12-day investigation period, while the positive control only began to fission after 7 days. We propose that the reproductive response observed here is an adaptive one to stressful conditions, whereby the likelihood of survival through numerical abundance is enhanced, although the size and vulnerability of resulting fragments may impose a balancing cost. The response may play a role in the invasiveness of G. tigrina by making it able to colonize environments where adverse conditions prevail.

动物在压力条件下的繁殖往往会减少，当前的生存和未来的繁殖通常与当前的繁殖活动进行权衡。本研究探讨了物理和化学应激源对入侵性涡虫虎虎鞭毛虫无性繁殖率的影响。320 只野生捕获的涡虫（混合大小的类别）被单独饲养在培养皿中，以便可以轻松监测它们各自的破碎率。比较了四个治疗组，一种是化学治疗组（5 mg/L 氨），一种是物理治疗组（斩首），与阴性对照组（动物饥饿）和阳性对照组（给动物提供大量食物）进行比较。两个处理组立即开始无性繁殖，并在 12 天的调查期间累积最高数量的裂变，而阳性对照仅在 7 天后才开始裂变。我们认为，这里观察到的生殖反应是对压力条件的适应性反应，尽管由此产生的碎片的大小和脆弱性可能会带来平衡成本，但通过数量丰富而生存的可能性得到了提高。这种反应可能在虎虎蜥的入侵中发挥作用，使其能够在不利条件盛行的环境中定殖。