Phylogenetic analysis of combined mitochondrial genome and 32 nuclear genes provides key insights into molecular systematics and historical biogeography of Asian warty newts of the genus Paramesotriton(Caudata: Salamandridae)

The Paramesotriton Chang, 1935 genus of Asian warty newts is the second most diverse genus in the family Salamandridae, currently containing 14recognized species from northern Vietnam to southwest-central and southern China. Although species of this genus have been included in previous phylogenetic studies, the origin and interspecific relationships of the genus are still not fully resolved,especially at key nodes in the phylogeny. In this study, we sequenced mitochondrial genomes and 32nuclear genes from 27 samples belonging to 14species to reconstruct the interspecific phylogenetic relationships within Paramesotriton and explore its historical biogeography in southern China. Both Bayesianinferenceandmaximum-likelihood analyses highly supported the monophyly of Paramesotriton and its two recognized species groups(P. caudopunctatus and P. chinensis groups)and further identified five hypothetical phylogenetic cryptic species. Biogeographic analyses indicated that Paramesotriton originated in southwestern China(Yunnan-Guizhou Plateau/South China) during the late Oligocene. The time of origin of Paramesotriton corresponded to the second uplift of the Himalayan/Qinghai-Xizang(Tibetan) Plateau(QTP), rapid lateral extrusion of Indochina, and formation of karst landscapes in southwestern China.Principal component analysis(PCA), independent sample t-tests, and niche differentiation using bioclimatic variables based on locations of occurrence suggested that Paramesotriton habitat conditions in the three current regions(West, South,and East) differ significantly, with different levels of climatic niche differentiation. Species distribution model(SDM) predictions indicated that the most suitable distribution areas for the P. caudopunctatus and P. chinensis species groups are western and southern/eastern areas of southern China. This study increases our knowledge of the taxonomy,biodiversity, origin, and suitable distribution areas of the genus Paramesotriton based on phylogenetic,biogeographic, and species distribution models.

Two novel sodium channel mutations associated with resistance to indoxacarb and metaflumizone in the diamondback moth, Plutella xylostella

Indoxacarb and metaflumizone belong to a relatively new class of sodium channel blocker insecticides （SCBIs）. Due to intensive use of indoxacarb, field-evolved indoxacarb resistance has been reported in several lepidopteran pests, including the dia- mondback moth Plutella xylostella, a serious pest of cruciferous crops. In particular, the BY 12 population of P. xylostella, collected from Baiyun, Guangdong Province of China in 2012, was 750-fold more resistant to indoxacarb and 70-fold more resistant to metaflu- mizone compared with the susceptible Roth strain. Comparison of complementary DNA sequences encoding the sodium channel genes of Roth and BY12 revealed two point mu- tations （F1845Y and V1848I） in the sixth segment of domain IV of the PxNav protein in the BY population. Both mutations are located within a highly conserved sequence region that is predicted to be involved in the binding sites of local anesthetics and SCBIs based on mammalian sodium channels. A significant correlation was observed among 10 field-collected populations between the mutant allele （Y 1845 or I 1848） frequencies （1.7% to 52.5%） and resistance levels to both indoxacarb （34- to 870-fold） and metaflumizone （1- to 70-fold）. The two mutations were never found to co-exist in the same allele of PxNav, suggesting that they arose independently. This is the first time that sodium channel muta- tions have been associated with high levels of resistance to SCBIs. F 1845Y and V 1848I are molecular markers for resistance monitoring in the diamondback moth and possibly other insect pest species.

Identification of the ryanodine receptor mutation I4743M and its contribution to diamide insecticide resistance in Spodoptera exigua (Lepidoptera: Noctuidae)

Insect ryanodine receptors(RyRs)are the targets of diamide insecticides.Two point mutations G4946E and I4790M(numbering according to Plutella xylostella,PxRyR)in the transmembrane domain of the insect RyRs associated with diamide resistance have so far been identified in three lepidopteran pests,P.xylostella,Tuta absoluta and Chilo suppressalis.In this study,we identified one of the known RyR target site resistance mutations(I4790M)in a field-collected population of Spodoptera exigua.The field-collected WF population of S.exigua exhibited 154 fold resistance to chlorantraniliprole when compared with the susceptible WH-S strain.Sequencing the transmembrane domains of S.exigua RyR(SeRyR)revealed that the resistant WF strain was homozygous for the 14743M mutation(corresponding to I4790M in PxRyR),whereas the G4900E allele(corresponding to G4946E of PxRyR)was not detected.The 4743M allele was introgressed into the susceptible WH-S strain by crossing WF with WH-S,followed by three rounds of backcrossing with WH-S.The introgressed strain 4743M was homozygous for the mutant 4743M allele and shared about 94%of its genetic background with that of the recipient WH-S strain.Compared with WH-S,the near-isogenic 4743M strain showed moderate levels of resistance to chlorantraniliprole(21 fold),cyantraniliprole(25 fold)and flubendiamide(22 fold),suggesting that the I4743M mutation confers medium levels of resistance to all three diamides.Genetic analysis showed diamide resistance in the 4743M strain was inherited as an autosomal and recessive trait.Results from this study have direct implications for the design of appropriate resistance monitoring and management practices to sustainably control S.exigua.