Dong Zhang , Ivan Jakovlić , Hong Zou , Fei Liu , Chuan-Yu Xiang , Qunzong Gusang , Sonam Tso , Shenggui Xue , Wen-Jin Zhu , Zhenxin Li , Jihua Wu , Gui-Tang Wang
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引用次数: 0
Abstract
The genomic evolution of Polyopisthocotylea remains poorly understood in comparison to the remaining three classes of Neodermata: Monopisthocotylea, Cestoda, and Trematoda. Moreover, the evolutionary sequence of major events in the phylogeny of Neodermata remains unresolved. Herein we sequenced the mitogenome and transcriptome of the polyopisthocotylean Diplorchis sp., and conducted comparative evolutionary analyses using nuclear (nDNA) and mitochondrial (mtDNA) genomic datasets of Neodermata. We found strong mitonuclear discordance in the phylogeny of Neodermata. Polyopisthocotylea exhibited striking mitonuclear discordance in relative evolutionary rates: the fastest-evolving mtDNA in Neodermata and a comparatively slowly-evolving nDNA genome. This was largely attributable to its very long stem branch in mtDNA topologies, not exhibited by the nDNA data. We found indications that the fast evolution of mitochondrial genomes of Polyopisthocotylea may be driven both by relaxed purifying selection pressures and elevated levels of directional selection. We identified mitochondria-associated genes encoded in the nuclear genome: they exhibited unique evolutionary rates, but not correlated with the evolutionary rate of mtDNA, and there is no evidence for compensatory evolution (they evolved slower than the rest of the genome). Finally, there appears to exist an exceptionally large (≈6.3 kb) nuclear mitochondrial DNA segment (numt) in the nuclear genome of newly sequenced Diplorchis sp. A 3′-end segment of the 16S rRNA gene encoded by the numt was expressed, suggesting that this gene acquired novel, regulatory functions after the transposition to the nuclear genome. In conclusion, Polyopisthocotylea appears to be the lineage with the fastest-evolving mtDNA sequences among all of Bilateria, but most of the substitutions were accumulated deep in the evolutionary history of this lineage. As the nuclear genome does not exhibit a similar pattern, the circumstances underpinning this evolutionary phenomenon remain a mystery.
期刊介绍:
International Journal for Parasitology offers authors the option to sponsor nonsubscriber access to their articles on Elsevier electronic publishing platforms. For more information please view our Sponsored Articles page. The International Journal for Parasitology publishes the results of original research in all aspects of basic and applied parasitology, including all the fields covered by its Specialist Editors, and ranging from parasites and host-parasite relationships of intrinsic biological interest to those of social and economic importance in human and veterinary medicine and agriculture.