Mtgenome organization
A total of 19 species of mtgenomes in Tenebrionoidea are completely sequenced in the present study (accession numbers in Table 1), and 11 species of them are reported for the first time with all in Lagriidae. All 82 species of complete mtgenomes investigated contain the typical 37 genes (including 13 PCGs, 2 rRNAs and 22 tRNAs) and one control region (CR). There are 22 genes (nine PCGs and 13 tRNAs) located on the majority coding strand (J-strand), while the other 15 genes (four PCGs, nine tRNAs and two rRNAs) are on the minority strand (N-strand; Fig. 1). These mtgenome sequences range in length from 14 777 bp (Cerogria kikuchii ) to 16 861 bp (Heterotarsus carinula ) with an average of 15 763 bp, and the length variation mainly results from the control region, intergenic overlap and spacers. They all display obvious AT bias with A+T content ranging from 62.7% (Casnonidea terminata ) to 81.6% (Pyrochroidae sp.) and an average being 73.6%. AT-skew values range from -0.141 (Paramarygmus sp.) to 0.219 (Strongylium pinfaense ), and GC-skew from -0.375 (S. pinfaense ) to 0.366 (Paramarygmus sp.) (Fig. 2).
The tRNAs sizes range from 57 bp to 82 bp, and all of the tRNAs can be folded into a typical clover-leaf structure except fortRNA -Ser (AGN), in which the dihydrouridine (DHU) arm is absent and a UCU anticodon is present (Fig. S1). The most frequently occurred base mismatches are U-G, U–U and A-G, and the mismatch A-G is only occurred in tRNA-Trp . For rRNAs, rrnL is located between the trnL1 and trnV , ranging from 750 bp (Anthicidae sp.) to 1 323 bp (Alcidodes juglans ). The length of the rrnS ranges from 740 bp (Cerogira popularis ) to 1 269 bp (Uloma sp.), which is located between the trnVand CR region. The percentage of AT content in rRNAs is 68.3-84.3%. The CRs are located between the rrnS andtrnI , and the percentage of AT content in this region is 72.2-96.1%.