Taerum Stephen J, De Martini Francesca, Liebig Jürgen, Gile Gillian H
School of Life Sciences, Arizona State University, Tempe, AZ.
Environ Entomol. 2018 Feb 8;47(1):184-195. doi: 10.1093/ee/nvx193.
Coevolution is a major driver of speciation in many host-associated symbionts. In the termite-protist digestive symbiosis, the protists are vertically inherited by anal feeding among nest mates. Lower termites (all termite families except Termitidae) and their symbionts have broadly co-diversified over ~170 million yr. However, this inference is based mainly on the restricted distribution of certain protist genera to certain termite families. With the exception of one study, which demonstrated congruent phylogenies for the protist Pseudotrichonympha and its Rhinotermitidae hosts, coevolution in this symbiosis has not been investigated with molecular methods. Here we have characterized the hindgut symbiotic protists (Phylum Parabasalia) across the genus Zootermopsis (Archotermopsidae) using single cell isolation, molecular phylogenetics, and high-throughput amplicon sequencing. We report that the deepest divergence in the Zootermopsis phylogeny (Zootermopsis laticeps [Banks; Isoptera: Termopsidae]) corresponds with a divergence in three of the hindgut protist species. However, the crown Zootermopsis taxa (Zootermopsis angusticollis [Hagen; Isoptera: Termopsidae], Z. nevadensis nevadensis [Hagen; Isoptera: Termopsidae], and Z. nevadensis nuttingi [Haverty & Thorne; Isoptera: Termopsidae]) share the same protist species, with no evidence of co-speciation under our methods. We interpret this pattern as incomplete co-cladogenesis, though the possibility of symbiont exchange cannot be entirely ruled out. This is the first molecular evidence that identical communities of termite-associated protist species can inhabit multiple distinct host species.
协同进化是许多宿主相关共生体物种形成的主要驱动力。在白蚁-原生生物消化共生关系中，原生生物通过在巢伴之间的肛门取食进行垂直遗传。低等白蚁（除白蚁科外的所有白蚁科）及其共生体在约1.7亿年的时间里广泛地共同分化。然而，这一推断主要基于某些原生生物属在特定白蚁科中的有限分布。除了一项研究表明原生生物伪滴虫及其鼻白蚁科宿主具有一致的系统发育外，这种共生关系中的协同进化尚未用分子方法进行研究。在这里，我们使用单细胞分离、分子系统发育学和高通量扩增子测序对整个Zootermopsis属（木白蚁科）的后肠共生原生生物（披发虫门）进行了表征。我们报告说，Zootermopsis系统发育中最深的分歧（Zootermopsis laticeps [班克斯；等翅目：木白蚁科]）与三种后肠原生生物物种的分歧相对应。然而，Zootermopsis属的冠群分类单元（Zootermopsis angusticollis [哈根；等翅目：木白蚁科]、Z. nevadensis nevadensis [哈根；等翅目：木白蚁科]和Z. nevadensis nuttingi [哈弗蒂和索恩；等翅目：木白蚁科]）共享相同的原生生物物种，在我们的方法下没有协同物种形成的证据。我们将这种模式解释为不完全的共同分支形成，尽管不能完全排除共生体交换的可能性。这是第一个分子证据，表明与白蚁相关的原生生物物种的相同群落可以栖息在多个不同的宿主物种中。
