Genetic variation within native populations of endemic silkmoth Antheraea assamensis (Helfer) from Northeast India indicates need for in situ conservation

Abstract

A. assamensis is a phytophagous Lepidoptera from Northeast India reared on host trees of Lauraceae family for its characteristic cocoon silk. Source of these cocoons are domesticated farm stocks that crash frequently and/or wild insect populations that provide new cultures. The need to reduce dependence on wild populations for cocoons necessitates assessment of genetic diversity in cultivated and wild populations. Molecular markers based on PCR of Inter-simple sequence repeats (ISSR) and simple sequence repeats (SSR) were used with four populations of wild insects and eleven populations of cultivated insects. Wild populations had high genetic diversity estimates (H(i) = 0.25; H(S) = 0.28; H(E) = 0.42) and at least one population contained private alleles. Both marker systems indicated that genetic variability within populations examined was significantly high. Among cultivated populations, insects of the Upper Assam region (H(i) = 0.19; H(S) = 0.18; H(E) = 0) were genetically distinct (F(ST) = 0.38 with both marker systems) from insects of Lower Assam (H(i) =0.24; H(S) =0.25; H(E) = 0.3). Sequencing of polymorphic amplicons suggested transposition as a mechanism for maintaining genomic diversity. Implications for conservation of native populations in the wild and preserving in-farm diversity are discussed.

Figure 1. A map image showing the distribution of collection sites of A. assamensis.

Names on the map correspond to collection sites in Table 1.

Figure 2. Analyses of sampled populations using PCO and STRUCTURE.

Genetic relationships were determined using (A) PCO analyses of 207 ISSR fingerprints obtained for fifteen populations collected from 3 regions. Designations for regions are: Upper Assam or UA (cultivated populations), Lower Assam or LA (cultivated populations) and Shillong plateau or SP (wild populations). Inset shows PCO analyses of ISSR fingerprints from eleven cultivated populations from Upper Assam and Lower Assam regions. Putative population genetic structure (B) was obtained with Admixture (+adm ISSR) and without Admixture (-adm ISSR) settings at K = 3 using ISSR data with STRUCTURE . Each vertical bar represents a moth distributed into 1 of K colored clusters. Populations 1 (BK), 2 (MD), 3(NB), 4 (GP) and 5 (SK) are cultivated populations from Lower Assam (LA); populations 6 (MR), 7 (DM), 8 (D), 9 (KG), 10 (TB) and 11 (LK) are cultivated populations from Upper Assam (UA); populations 12 (HA), 13 (MN), 14 (TR) and 15 (AG) are wild populations from Shillong plateau (SP). Population acronyms are expanded in Table 1. Putative population genetic structure (C) was obtained with Admixture (+adm SSR) setting at K = 3 for 15 populations (189 insects) using SSR data as above.

Figure 3. A map showing positions of motifs resembling putative transposable elements (boxes shown in different colors) within sequenced ISSR amplicons.

Abbreviations are as described in Table 2. Arrows denote tandem repeats. The bold lines ( ) indicate position of nested primers (Fp2 and Ah16) within amplicon EU872512.

Figure 4. Southern hybridization of various silkmoths using a putative transposable element amplicon from A. assamensis as probe.

Genomic DNAs (A) of A. assamensis moths BK12 (lane 1), TR3 (lane 2), TR4 (lane 3), KG8 (lane 4); B. mori (lane5), S. cynthia (lane 6), A. mylitta (lane 7) and A. proylei (lane 8) were digested with Hae III. Southern hybridization of the digested DNAs with an 800 bp amplicon containing a putative mariner-like element are shown after (B) a low stringency wash and (C) a high stringency wash. Lane M shows λ DNA restricted with Hind III as a size marker. Arrows denote hybridization signals that distinguish moths from different populations.