Phylogeny and evolutionary history of the silkworm

Wei Sun,Yutaka Banno,Yihong Shen,Zhonghuai Xiang,Hongsong Yu,Ze Zhang

doi:10.1007/s11427-012-4334-7

Abstract

The silkworm, Bombyx mori, played an important role in the old Silk Road that connected ancient Asia and Europe. However, to date, there have been few studies of the origins and domestication of this species using molecular methods. In this study, DNA sequences of mitochondrial and nuclear loci were used to infer the phylogeny and evolutionary history of the domesticated silkworm and its relatives. All of the phylogenetic analyses indicated a close relationship between the domesticated silkworm and the Chinese wild silkworm. Domestication was estimated to have occurred about 4100 years ago (ya), and the radiation of the different geographic strains of B. mori about 2000 ya. The Chinese wild silkworm and the Japanese wild silkworm split about 23600 ya. These estimates are in good agreement with the fossil evidence and historical records. In addition, we show that the domesticated silkworm experienced a population expansion around 1000 ya. The divergence times and the population dynamics of silkworms presented in this study will be useful for studies of lepidopteran phylogenetics, in the genetic analysis of domestic animals, and for understanding the spread of human civilizations.

Highlights

The silkworm, Bombyx mori, played an important role in the old Silk Road that connected ancient Asia and Europe
Nucleotide sequences of two mitochondrial loci and two nuclear loci obtained in the present study showed high similarities between B. mori and Chinese B. mandarina
Japanese B. mandarina has a 216 bp repetitive insertion in the mitochondrial CR region and two large unique insertions in the intron of the period gene. These observations are consistent with a previous finding that a transposon-like sequence was inserted in the Arylphorin gene of Japanese B. mandarina [5]. These observations all indicate that the molecular markers we selected had enough polymorphisms to distinguish the phylogenetic relationships among closely related species and that B. mori and Chinese B. mandarina are more closely related than are B. mori and Japanese B. mandarina

Summary

Introduction

The silkworm, Bombyx mori, played an important role in the old Silk Road that connected ancient Asia and Europe. Two types of wild silkworms exist; one occurs in China and in far eastern Russia (chromosome number 2n=56, as in B. mori), and the other in Japan and southern Korea (2n=54) [1,5] They are usually referred to as Chinese B. mandarina and Japanese B. mandarina, respectively. No. substitution rate of the mitochondrial gene Nd5 from a coleopteran insect (Carabidae), estimated that B. mori split from wild silkworms about 7.1 Ma [12] Both estimates are much older than indicated by the fossil evidence [4]. The aim of this study was to reveal the evolutionary history of the domesticated silkworm Phylogenetic analyses of both mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) sequences were carried out. This study, provides new insights into the evolutionary history of the silkworm

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Conclusion