DNA barcodes provide evidence for the independent origin of the cultivated silkworms Samia ricini and Samia cynthia

Abstract

Samia ricini (Wm. Jones) and Samia cynthia (Drury) (Lepidoptera: Saturniidae) have been used as traditional sources of food as well as silk-producing insects. However, the phylogenetic relationship between the two silkworms remains to be addressed. In this study, the mitochondrial cytochrome c oxidase subunit 1 (COI) gene sequences corresponding to DNA barcodes from 13 Samia species were analysed, and a DNA barcode-based phylogenetic framework for these Samia species was provided. Phylogenetic analysis showed that multiple individuals of a species could be clustered together. Our analysis revealed a close relationship among Samia yayukae Paukstadt, Peigler and Paukstadt, Samia abrerai Naumann and Peigler, Samia kohlli Naumann and Peigler, Samia naessigi Naumann and Peigler, Samia naumanni Paukstadt, Peigler and Paukstadt, and Samia kalimantanensis Paukstadt and Paukstadt. The mixed clustering relationship and low Kimura-2-parameter (K2P) genetic distance (0.006) between individuals of S. ricini and Samia canningi (Hutton) indicated that the cultivated silkworm S. ricini was derived from the non-cultivated silkworm S. canningi. The remote phylogenetic relationship and high K2P genetic distance (0.039) indicated that S. ricini and S. cynthia are distinct species, thus providing solid molecular evidence that they had entirely independent origins. The relationships between S. kalimantanensis and S. naumanni and between S. cynthia and Samia wangi Naumann and Peigler, as well as the potential cryptic species within S. abrerai were also discussed. This is the first study to assess the DNA barcodes of the genus Samia, which supplements the knowledge of species identification and provides the first molecular phylogenetic framework for Samia species.