Genetic diversity and differentiation among populations of the Indian eri silkworm, Samia cynthia ricini, revealed by ISSR markers

Abstract

Samia cynthia ricini (Lepidoptera:Saturniidae), the Indian eri silkworm, contributes significantly to the production of commercial silk and is widely distributed in the Brahmaputra river valley in North-Eastern India. Due to over exploitation coupled with rapid deforestation, most of the natural populations of S. cynthia ricini are dwindling rapidly and its preservation has become an important goal. Assessment of the genetic structure of each population is a prerequisite for a sustainable conservation program. DNA fingerprinting to detect genetic variation has been used in different insect species not only between populations, but also between individuals within a population. Since, information on the genetic basis of phenotypic variability and genetic diversity within the S. cynthia ricini populations is scanty, inter simple sequence repeat (ISSR) system was used to assess genetic diversity and differentiation among six commercially exploited S. cynthia ricini populations. Twenty ISSR primers produced 87% of inter population variability among the six populations. Genetic distance was lowest between the populations Khanapara (E5) and Mendipathar (E6) (0.0654) and highest between Dhanubhanga (E4) and Titabar (E3) (0.3811). Within population, heterozygosity was higher in Borduar (E2) (0.1093) and lowest in Titabar (E3) (0.0510). Highest gene flow (0.9035) was between E5 and E6 and the lowest (0.2172) was between E3 and E5. Regression analysis showed positive correlation between genetic distance and geographic distance among the populations. The high GST value (0.657) among the populations combined with low gene flow contributes significantly to the genetic differentiation among the S. cynthia ricini populations. Based on genetic diversity, these populations can be considered as different ecotypes and in situ conservation of them is recommended.

Comparative genetic diversity and genetic structure of three chinese silkworm species Bombyx mori L. (Lepidoptera: Bombycidae), Antheraea pernyi Guérin-Meneville and Samia cynthia ricini donovan (Lepidoptera: Saturniidae)

“…However, the genetic diversity of S. cynthia ricini at the strain level (PPB = 20.83%; h = 0.0858; I = 0.1244) was well within the range calculated by Vijayan et al (2006). UPGMA analysis of Indian populations showed that the individuals grouped according to their population affi nity, and none changed its population cluster, which was different from that found in Chinese populations (Fig 1).…”

“…This is a pattern frequently observed in wild plants (Zhang et al 2007, Tahan et al 2009 and wild insects (Moya et al 2001, Gallusser et al 2004. However, only 16% of genetic variation occurred within strains and 84% among strains of B. mori in China, as observed in Indian populations of S. cynthia ricini (Vijayan et al 2006). This pattern is also found in many domesticated animals (Huang et al 1996, Hao et al 2000 and cultivated plants .…”

“…Therefore, the results reported here revealed high genetic diversity at the species level for A. pernyi (PPB = 78.57%; h = 0.2666; I = 0.3983) and B. mori (PPB = 61.54%; h = 0.2654; I = 0.3835), whereas low genetic diversity for the Chinese populations of S. cynthia ricini (PPB = 37.97%; h = 0.1407; I = 0.2079). A high genetic diversity for Indian populations of S. cynthia ricini at the species level (PPB = 64.13%; h = 0.3334; I = 0.3475), as well as at the population level (PPB = 14.43-31.52%; h = 0.051-0.109; I = 0.076-0.162) was assessed based on ISSR markers (Vijayan et al 2006). Compared to the data found in Indian populations, the genetic diversity of Chinese populations observed in this study (PPB = 37.97%; h = 0.1407; I = 0.2079) was very low at the species level.…”

“…Its exploitation for sericulture was initiated in the Brahmaputra valley, Northeastern India (Vijayan et al 2006). In 1950s, this silkworm species was successfully introduced into China for silk production.…”

“…Furthermore, the large number of strains within one species has been the focus of study on the role of genetic diversity during and after domestication (Goldsmith et al 2005). Recently, many studies have been carried out to assess the genetic diversity of silkmoths , Kar et al 2005, Vijayan et al 2006, Li et al 2007, Mirhoseini et al 2007; however, the information on genetic diversity within and between strains of the three economically important silkworm species is also scanty.…”