Department of Environmental Biology, Chubu University, Kasugai, 487-8501, Japan.
Animal Systematics Research Unit, Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand.
Sci Rep. 2021 Apr 16;11(1):8407. doi: 10.1038/s41598-021-87984-4.
Pontodrilus litoralis is a cosmopolitan littoral earthworm known to exhibit bioluminescence. Recently, a congeneric species, Pontodrilus longissimus, from Thailand was described. These species are sympatric, but their burrowing depths on Thai beaches are different. In this study, we examined the in vivo and in vitro bioluminescent properties of P. longissimus and P. litoralis. Mechanical stimulation induced in vivo luminescence in P. litoralis, as reported previously, but not in P. longissimus. In vitro cross-reaction tests between these species revealed the absence of luciferin and luciferase activities in P. longissimus. The coelomic fluid of P. litoralis had strong fluorescence that matched the spectral maximum of its bioluminescence, but the same result was not observed for P. longissimus. These results suggest that P. litoralis has luminescence abilities due to the creation of bioluminescent components (i.e., luciferin, luciferase, and light emitters). The presence of both luminous and nonluminous species in a single genus is likely widespread, but only a few examples have been confirmed. Our findings provide insight into the possible functions of bioluminescence in earthworms, such as avoiding predation by littoral earwigs.
扁尾海蚯蚓是一种世界性的沿岸蚯蚓，已知具有生物发光特性。最近，泰国描述了一个同种的物种，即长扁尾海蚯蚓。这些物种是同域的，但它们在泰国海滩上的挖掘深度不同。在这项研究中，我们检查了长扁尾海蚯蚓和扁尾海蚯蚓的体内和体外生物发光特性。如前所述，机械刺激会诱导扁尾海蚯蚓体内发光，但不会诱导长扁尾海蚯蚓体内发光。这些物种之间的体外交叉反应测试表明，长扁尾海蚯蚓中不存在荧光素和荧光酶活性。扁尾海蚯蚓的体腔液具有很强的荧光，与生物发光的光谱最大值相匹配，但长扁尾海蚯蚓没有观察到相同的结果。这些结果表明，扁尾海蚯蚓具有发光能力，这是由于生物发光成分（即荧光素、荧光酶和发光体）的产生。同一属中既有发光物种又有非发光物种的情况可能很普遍，但只有少数几个例子得到了证实。我们的发现为生物发光在蚯蚓中的可能功能提供了一些见解，例如避免被沿岸耳虾捕食。
