Department of Biological Sciences, Virginia Tech, Blacksburg, VA, 24061, USA.
Department of Anthropology, Washington University in St. Louis, St. Louis, MO, 63130, USA.
Oecologia. 2024 Aug;205(3-4):669-680. doi: 10.1007/s00442-024-05600-4. Epub 2024 Aug 3.
Organismal invasions have repeatedly been cited as a driving force behind the loss of biodiversity. Unlike many other impacts of invasion, the effect of invasion on native symbiont communities has received less attention. The introduction of invasive hosts presents a potential opportunity to native symbionts; invasive hosts could benefit native symbionts through providing a novel host environment that improves symbiont fitness relative to their fitness on native hosts. Alternatively, invasive hosts could noncompetent hosts for native symbionts, resulting in negative impacts on native symbiont abundance and diversity. Crayfish in the northern hemisphere host diverse assemblages of obligate annelid symbionts (P: Anellida, O: Branchiobdellida). Two invasive crayfish hosts in the genus Faxonius have been introduced and are interacting with the native crayfish hosts and their symbionts in three watersheds in western Virginia, USA. Previous studies suggest that the invasive host F. cristavarius is a less competent host for symbionts compared to native hosts in the genus Cambarus. We carried out an extensive survey in these watersheds to determine impacts of varying degrees of invasion on branchiobdellidan abundance and diversity. We also conducted a complementary host replacement experiment to investigate how increases in the relative abundance of invasive hosts contributes to observed patterns of symbiont abundance and diversity in the field. In our survey, as the proportion of invasive hosts at a site increased, branchiobdellidan abundance and diversity declined significantly. In the experiment, the worms dispersed onto both native and invasive hosts. As the percentage of noncompetent F. cristavarius hosts increased, the survival of branchiobdellidans declined. Both symbiont survival and opportunities for successful dispersal are reduced as this noncompetent invasive host progressively displaces native hosts, which imperils the integrity of native host-symbiont systems. Given that many native hosts accrue significant fitness benefits from their relationships with native symbionts, including hosts in our study system, losses of beneficial symbionts may produce a positive feedback loop that decreases invasion resistance of native species, exacerbates the effects of invasions, and presents a major conservation issue in invaded systems.
生物入侵被反复认为是生物多样性丧失的驱动力之一。与入侵的许多其他影响相比，入侵对本地共生体群落的影响受到的关注较少。入侵宿主的引入为本地共生体提供了一个潜在的机会；入侵宿主可以通过提供一个改善共生体相对于其在本地宿主上适应性的新宿主环境，从而使本地共生体受益。或者，入侵宿主可能是本地共生体的非竞争宿主，从而对本地共生体的丰度和多样性产生负面影响。北半球的淡水小龙虾宿主有多种专性环节动物共生体（P：环节动物门，O：颤蚓目）。在北美的三个流域，已经引入了两种入侵的淡水小龙虾宿主，即 Faxonius 属的两种淡水小龙虾宿主，它们与本地淡水小龙虾宿主及其共生体相互作用。先前的研究表明，与 Cambarus 属的本地宿主相比，入侵宿主 F. cristavarius 是一种不太适合共生体的宿主。我们在这些流域进行了广泛的调查，以确定不同程度的入侵对颤蚓目丰度和多样性的影响。我们还进行了一项补充的宿主替代实验，以调查入侵宿主相对丰度的增加如何导致野外共生体丰度和多样性的观察模式。在我们的调查中，随着一个地点的入侵宿主比例的增加，颤蚓目丰度和多样性显著下降。在实验中，这些蠕虫分散到本地和入侵的宿主上。随着非竞争的 F. cristavarius 宿主的百分比增加，颤蚓目生物的存活率下降。由于这种非竞争的入侵宿主逐渐取代本地宿主，共生体的生存和成功传播的机会减少，这危及了本地宿主-共生体系统的完整性。鉴于许多本地宿主从与本地共生体的关系中获得了显著的适应性益处，包括我们研究系统中的宿主，有益共生体的丧失可能会产生一个正反馈循环，降低本地物种的入侵抵抗力，加剧入侵的影响，并成为入侵系统中的一个主要保护问题。
