Epibacterial cell density measurement and experiment on antifouling activity of native and invasive Gracilaria vermiculophylla populations sampled in 2013 in South Korea, Denmark and Germany

Rapid adaptation to novel biotic interactions and abiotic factors in introduced ranges can be critical to invasion success of both exotic terrestrial and aquatic plants. Seaweeds are extremely successful biological invaders in marine environments. Along with herbivores, foulers ? ubiquitous enemies in the marine environment ? have the potential to determine the success or failure of invasive seaweeds. However, research on the topic of rapid adaptation of seaweeds to biotic challenges is still in its nascent stages and rapid adaptation of seaweeds to fouling is unexplored.
We tested whether the impressive invasion success of the red macroalga Gracilaria vermiculophylla may be enhanced by the rapid adaptation of chemical control (defence) of new bacterial epibionts in the invaded range.
The native and invasive G. vermiculophylla populations investigated were equally well defended against currently co-occurring bacterial epibionts isolated from their respective ranges. In contrast, the native populations were weakly defended against bacterial epibionts from the invaded range, whereas the invasive populations were weakly defended against bacterial epibionts from their native range. Apparently during the invasion process, invasive populations have adapted their control capacity to cope with the new epibionts but have lost the capacity to fend off old epibionts.
Synthesis. These results provide the first evidence that a change in habitat and, thus, confrontation by new enemies, may trigger rapid defence adaptation of seaweeds, which could be necessary for invasiveness. Such adaptation dynamics as found in the current study could be also applicable to other types of host plant - enemy interaction e.g. plant root - microbe interactions, freshwater plant - fouler interactions in general and for cases of shifting plant - enemy interactions in course of climate change.

在入侵分布区（introduced ranges）中，对新型生物相互作用（biotic interactions）与非生物因子（abiotic factors）的快速适应，对外来陆生与水生植物的入侵成功至关重要。海藻（seaweeds）是海洋环境中极具入侵优势的生物入侵者。与草食动物（herbivores）一道，污损生物（foulers）——海洋环境中无处不在的天敌——具备决定入侵海藻成败的潜力。然而，针对海藻应对生物挑战的快速适应研究仍处于萌芽阶段（nascent stages），而海藻对污损生物的快速适应更是尚未被探索。
本研究检验了红大型藻类（red macroalga）细基江蓠（Gracilaria vermiculophylla）卓越的入侵成功能力，是否可通过其在入侵分布区内对新型细菌附生生物（bacterial epibionts）的化学防御（chemical defence）快速适应而得到提升。
本次研究的本土种群（native populations）与入侵种群（invasive populations）细基江蓠，对各自分布范围中当前共存的细菌附生生物均具备同等有效的防御能力。与之相对，本土种群对来自入侵分布区的细菌附生生物防御能力较弱，而入侵种群则对来自其原生分布区的细菌附生生物防御能力较弱。显然，在入侵过程中，入侵种群已调整其防御能力以应对新型附生生物，但却丧失了抵御原有附生生物的能力。
研究总结。本研究结果首次证实，生境改变以及由此遭遇的新型天敌，可能会触发海藻的快速防御适应，而这或许是其具备入侵性的必要条件。本研究揭示的此类适应动态，亦可适用于其他类型的宿主植物-天敌相互作用（host plant - enemy interaction）场景：例如植物根系-微生物相互作用（plant root - microbe interactions）、淡水植物-污损生物相互作用（freshwater plant - fouler interactions），以及气候变化（climate change）过程中植物-天敌相互作用发生转移的各类案例。