Forest Pathology Laboratory, Forestry and Forest Products Research Institute, Tsukuba, Japan.
Department of Biology, Institute of Ecology and Evolution, University of Oregon, Eugene, OR, USA.
BMC Ecol. 2018 Aug 21;18(1):26. doi: 10.1186/s12898-018-0182-z.
Biotic interactions are ubiquitous and require information from ecology, evolutionary biology, and functional genetics in order to be understood. However, study systems that are amenable to investigations across such disparate fields are rare. Figs and fig wasps are a classic system for ecology and evolutionary biology with poor functional genetics; Caenorhabditis elegans is a classic system for functional genetics with poor ecology. In order to help bridge these disciplines, here we describe the natural history of a close relative of C. elegans, Caenorhabditis inopinata, that is associated with the fig Ficus septica and its pollinating Ceratosolen wasps.
To understand the natural context of fig-associated Caenorhabditis, fresh F. septica figs from four Okinawan islands were sampled, dissected, and observed under microscopy. C. inopinata was found in all islands where F. septica figs were found. C.i nopinata was routinely found in the fig interior and almost never observed on the outside surface. C. inopinata was only found in pollinated figs, and C. inopinata was more likely to be observed in figs with more foundress pollinating wasps. Actively reproducing C. inopinata dominated early phase figs, whereas late phase figs with emerging wasp progeny harbored C. inopinata dauer larvae. Additionally, C. inopinata was observed dismounting from Ceratosolen pollinating wasps that were placed on agar plates. C. inopinata was not found on non-pollinating, parasitic Philotrypesis wasps. Finally, C. inopinata was only observed in F. septica figs among five Okinawan Ficus species sampled.
These are the first detailed field observations of C. inopinata, and they suggest a natural history where this species proliferates in early phase F. septica figs and disperses from late phase figs on Ceratosolen pollinating fig wasps. While consistent with other examples of nematode diversification in the fig microcosm, the fig and wasp host specificity of C. inopinata is highly divergent from the life histories of its close relatives and frames hypotheses for future investigations. This natural co-occurrence of the fig/fig wasp and C. inopinata study systems sets the stage for an integrated research program that can help to explain the evolution of interspecific interactions.
生物相互作用无处不在，为了理解它们，需要生态学、进化生物学和功能遗传学方面的信息。然而，适合跨学科研究的系统却很少。榕果和榕小蜂是生态学和进化生物学的经典系统，但功能遗传学方面的研究却很少；秀丽隐杆线虫是功能遗传学的经典系统，但生态学方面的研究却很少。为了帮助弥合这些学科之间的差距，我们在这里描述了秀丽隐杆线虫的近亲——无钩线虫的自然历史，它与榕果榕属植物及其传粉榕小蜂有关。
为了了解与榕果相关的秀丽隐杆线虫的自然背景，我们从四个冲绳岛屿采集了新鲜的榕果榕属植物果实，进行解剖并在显微镜下观察。无钩线虫在有榕果榕属植物果实的所有岛屿都有发现。无钩线虫通常存在于榕果内部，几乎从未在外部表面观察到。无钩线虫只存在于已授粉的榕果中，并且在有更多产卵榕小蜂的榕果中更有可能被观察到。活跃繁殖的无钩线虫占据早期阶段的榕果，而晚期阶段有即将出现的榕小蜂后代的榕果中则存在无钩线虫的持久幼虫。此外，我们还观察到无钩线虫从放在琼脂平板上的传粉榕小蜂身上脱落。无钩线虫未在非传粉、寄生的榕小蜂 Philotrypesis 上被发现。最后，在我们采集的五个冲绳榕属植物物种的榕果中，只观察到了榕果榕属植物果实。
这些是无钩线虫的首次详细野外观察结果，它们表明该物种在早期阶段的榕果榕属植物果实中大量繁殖，并通过传粉榕小蜂传播到晚期阶段的榕果中。虽然这与其他在榕果微生境中发生的线虫多样化的例子一致，但无钩线虫与榕果和榕小蜂的宿主特异性高度不同于其近亲的生活史，并为未来的研究提供了假说。这种榕果/榕小蜂和无钩线虫研究系统的自然共存为一个综合研究计划奠定了基础，该计划可以帮助解释种间相互作用的进化。
