Ya-e Ji

Unexpected relationships of substructured populations in Chinese Locusta migratoria.

BackgroundHighly migratory species are usually expected to have minimal population substructure because strong gene flow has the effect of homogenizing genetic variation over geographical populations, counteracting random drift, selection and mutation. The migratory locust Locusta migratoria belongs to a monotypic genus, and is an infamous pest insect with exceptional migratory ability – with dispersal documented over a thousand kilometers. Its distributional area is greater than that of any other locust or grasshopper, occurring in practically all the temperate and tropical regions of the eastern hemisphere. Consequently, minimal population substructuring is expected. However, in marked contrast to its high dispersal ability, three geographical subspecies have been distinguished in China, with more than nine being biologically and morphologically identified in the world. Such subspecies status has been under considerable debate.ResultsBy multilocus microsatellite genotyping analysis, we provide ample genetic evidence for strong population substructure in this highly migratory insect that conforms to geography. More importantly, our genetic data identified an unexpected cryptic subdivision and demonstrated a strong affiliation of the East China locusts to those in Northwest/Northern China. The migratory locusts in China formed three distinct groups, viz. (1) the Tibetan group, comprising locusts from Tibet and nearby West China high mountain regions; this is congruent with the previously recognized Tibetan subspecies, L. m. tibetensis; (2) the South China group, containing locusts from the Hainan islands; this corresponds to the Southeast Asia oriental tropical subspecies L. m. manilensis; (3) the North China group, including locusts from the Northwest and Northern China (the Asiatic subspecies L. m. migratoria), Central China and Eastern China regions. Therefore, the traditional concept on Locusta subspecies status established from Uvarov in 1930s needs to be revised. The three groups of locusts probably have separate evolutionary histories that were most likely linked to Quaternary glaciations events, and derived from different ancestral refugial populations following postglacial expansions.ConclusionThe migratory locust populations in China have differentiated into three genetically distinct groups despite high dispersal capability. While this clarified long-standing suspicions on the subspecific diversification of this species in China, it also revealed that the locusts in the vast area of East China are not the oriental subspecies but the Asiatic subspecies, an unexpected substructuring pattern. The distribution pattern of the three locust groups in China may be primarily defined by adaptive differentiation coupled to Quaternary glaciations events. Our results are of general significance both for locust research and for phylogeographical study of flora and fauna in China, illustrating the potential importance of phylogeographical history in shaping the divergence and distribution patterns of widespread species with strong dispersal ability.

Impact of climate changes from Middle Miocene onwards on evolutionary diversification in Eurasia: Insights from the mesobuthid scorpions

The aridification from Middle Miocene onwards has transformed the Asian interior into an arid environment, and the Pleistocene glacial–interglacial oscillations exerted further ecological impact. Therefore, both aridification and glaciation would have considerably influenced the evolution of many mid‐latitude species in temperate Asia. Here, we tested this perspective by a phylogeographic study of the mesobuthid scorpions across temperate Asia using one mitochondrial and three nuclear genes. Concordant mitochondrial and nuclear gene trees were obtained, which are consistent with species tree inferred using a Bayesian approach. The age of the most recent common ancestor (MRCA) of all the studied scorpions was estimated to be 12.49 Ma (late Middle Miocene); Mesobuthus eupeus diverged from the clade composing Mesobuthus caucasicus and Mesobuthus martensii in early Late Miocene (10.21 Ma); M. martensii diverged from M. caucasicus at 5.53 Ma in Late Miocene. The estimated MRCA ages of M. martensii and the Chinese lineage of M. eupeus were 2.37 and 0.68 Ma, respectively. Central Asia was identified as the ancestral area for the lineage leading to M. martensii and M. caucasicus and the Chinese lineage of M. eupeus. The ancestral habitat of the genus Mesobuthus is likely to have been characterized by an arid environment; a shift towards more humid habitat occurred in the MRCA of M. martensii and a lineage of M. caucasicus, finally leading to the adaptation of M. martensii to humid environment. Our data strongly support the idea that the stepwise intensified aridifications from Mid‐Miocene onwards drove the diversification of mesobuthid scorpions, and suggest that M. martensii and M. eupeus observed today in China originated from an ancestral lineage distributed in Central Asia. Both the colonization and the ensuing evolution of these species in East Asia appear to have been further moulded by Quaternary glaciations.

Haplotype reconstruction for scnp DNA: a consensus vote approach with extensive sequence data from populations of the migratory locust (Locusta migratoria)

Single copy nuclear polymorphic (scnp) DNA is potentially a powerful molecular marker for evolutionary studies of populations. However, a practical obstacle to its employment is the general problem of haplotype determination due to the common occurrence of heterozygosity in diploid organisms. We explore here a ‘consensus vote’ (CV) approach to this question, combining statistical haplotype reconstruction and experimental verification using as an example an indel‐free scnp DNA marker from the flanking region of a microsatellite locus of the migratory locust. The raw data comprise 251‐bp sequences from 526 locust individuals (1052 chromosomes), with 71 (28.3%) polymorphic nucleotide sites (including seven triallelic sites) and 141 distinct genotypes (with frequencies ranging from 0.2 to 25.5%). Six representative statistical haplotype reconstruction algorithms are employed in our CV approach, including one parsimony method, two expectation–maximization (EM) methods and three Bayesian methods. The phases of 116 ambiguous individuals inferred by this approach are verified by molecular cloning experiments. We demonstrate the effectiveness of the CV approach compared to inferences based on individual statistical algorithms. First, it has the unique power to partition the inferrals into a reliable group and an uncertain group, thereby allowing the identification of the inferrals with greater uncertainty (12.7% of the total sample in this case). This considerably reduces subsequent efforts of experimental verification. Second, this approach is capable of handling genotype data pooled from many geographical populations, thus tolerating heterogeneity of genetic diversity among populations. Third, the performance of the CV approach is not influenced by the number of heterozygous sites in the ambiguous genotypes. Therefore, the CV approach is potentially a reliable strategy for effective haplotype determination of nuclear DNA markers. Our results also show that rare variations and rare inferrals tend to be more vulnerable to inference error, and hence deserve extra surveillance.

Internal algorithm variability and among-algorithm discordance in statistical haplotype reconstruction

The potential effectiveness of statistical haplotype inference makes it an area of active exploration over the last decade. There are several complications of statistical inference, including: the same algorithm can produce different solutions for the same data set, which reflects the internal algorithm variability; different algorithms can give different solutions for the same data set, reflecting the discordance among algorithms; and the algorithms per se are unable to evaluate the reliability of the solutions even if they are unique, this being a general limitation of all inference methods. With the aim of increasing the confidence of statistical inference results, consensus strategy appears to be an effective means to deal with these problems. Several authors have explored this with different emphases. Here we discuss two recent studies examining the internal algorithm variability and among‐algorithm discordance, respectively, and evaluate the different outcomes of these analyses, in light of Orzack (2009) comment. Until other, better methods are developed, a combination of these two approaches should provide a practical way to increase the confidence of statistical haplotyping results.

Eight polymorphic microsatellite markers developed in the Chinese scorpion, Mesobuthus martensii (Scorpiones: Buthidae)

Eight polymorphic di‐ and trinucleotide microsatellite loci were developed in the Chinese scorpion, Mesobuthus martensii. The expected heterozygosity at these loci ranges from 0.019 to 0.860, with the observed allele numbers varying from two to 25. Overall, there were no deviations from Hardy–Weinberg equilibrium and no observed linkage disequilibrium after Bonferroni correction. Cross‐species amplification of these loci in Mesobuthus eupeus revealed that five loci can amplify successfully in this species. The polymorphic microsatellite DNA markers reported here should provide helpful means to address questions concerning phylogeographical patterns and evolutionary history of M. martensii and closely related species.

Black‐spotted pond frog (Pelophylax nigromaculatus) on the Chinese Loess Plateau represents a cryptic species: Evidence from molecular phylogeny and ecological niche modeling

The black‐spotted pond frog Pelophylax nigromaculatus is a typical temperate‐adapted amphibian species, largely endemic to East Asia. It occurs from central, east, and northeast China, to the Russian Far East, the Korean Peninsula, and part of Japan. So far, little is known about this frog from the Loess Plateau, a region that has experienced profound changes in climate and environment since the late Miocene. Particularly, between the Loess Plateau and the North China Plain, stand the Lüliang and Taihang mountain ranges, which form an important geographical divide in East China. Therefore, frogs from the Loess Plateau are indispensable for understanding the biogeography and evolution of this species. In this study, a total of 933 specimens of P. nigromaculatus collected range‐wide were sequenced for the mitochondrial Cyt b gene, with 345 of them being genotyped at 10 nuclear microsatellite loci. Both mitochondrial and microsatellite data resolved four major frog clades: (i) Loess Plateau clade, containing only frogs from the Loess Plateau; (ii) East China clade, containing frogs from the rest of China except those from the Liaodong Peninsula; (iii) Peninsulas clade, comprising frogs from the Korean Peninsula and Liaodong Peninsula; and (iv) Japan clade. Frogs from the Loess Plateau have deeply diverged from frogs in the remaining regions, with 11.5%–13.1% sequence divergence, which is comparable to distances between congeneric ranid species. Ecological niche modeling analysis showed that the potential distribution ranges of the Loess Plateau frogs and the non‐Loess Plateau frogs are rather different; niche identity testing indicated that the environmental niches of frogs from the Loess Plateau and other regions are not equivalent. Our data thus suggest that the Loess Plateau frogs represent a cryptic species. The uplift of the Lüliang Mountains was the most plausible trigger of this cryptic diversification.

A simple and reliable method for discriminating between Helicoverpa armigera and Helicoverpa assulta (Lepidoptera: Noctuidae)

Abstract  The cotton bollworm Helicoverpa armigera and the oriental tobacco budworm H. assulta are sibling species, both being important agricultural pests. Morphologically, the two insects are almost indistinguishable at the egg, larval and pupal stages. One of the big challenges in the study of these insects, in particular in integrated pest management, is a timely and dependable identification of these insects at their early stages of development. Here, we report a H. armigera‐specific nuclear DNA marker, and demonstrate that it can be employed to reliably discriminate between H. armigera and H. assulta by simple polymerase chain reaction amplification experiment.