De novo transcriptome assembly, annotation and SSR mining data of Hellula undalis (Fabr.) (Lepidoptera: Pyralidae), the cabbage webworm

BACKGROUND

The cabbage webworm, Hellula undalis (Fabricius) (Lepidoptera: Pyralidae), is a significant pest of brassicas and other cruciferous plants in warm regions worldwide. Transcriptome analysis is valuable for investigation of molecular mechanisms underlying the insect development and reproduction. De novo assembly is particularly useful for acquiring complete transcriptome information of insect species when there is no reference genome available. In case of Hellula undalis, only 17 nucleotide records are currently available throughout NCBI nucleotide database. Genes associated with metabolic processes, general development, reproduction, defense and functional genomics were not previously predicted in the Hellula undalis at the genomic level.

METHODS & RESULTS

To address this issue, we constructed Hellula undalis transcriptome using Illumina NovaSeq6000 technology. Approximately 48 million 150 bp paired-end reads were obtained from sequencing. A total of 30,451 contigs were generated by de novo assembly of sample and were compared with the sequences in the NCBI non-redundant protein database (Nr). In total, 71 % of contigs were matched to known proteins in public databases including Nr, Gene Ontology (GO), and Cluster Orthologous Gene Database (COG), and then, contigs were mapped to 123 via functional annotation against the Kyoto Encyclopedia of Genes and Genomes pathway database (KEGG). In addition, we compared the ortholog gene family of the Hullula undalis, transcriptome to Spodoptera frugiperda, spodotera litura and spodoptera littoralis and found that 391 orthologous gene families are specific to Hullula undalis. A total of 1,913 potential SSRs was discovered in Hullula undalis contigs.

CONCLUSIONS

This study is the first transcriptome data for Hullula undalis. Additionally, it serves as a valuable resource for identifying target genes and developing effective and environmentally friendly strategies for pest control.

Aseasonal, undirected migration in insects: 'Invisible' but common

Many insect pests are long-distance migrants, moving from lower latitudes where they overwinter to higher latitudes in spring to exploit superabundant, but seasonally ephemeral, host crops. These seasonal long-distance migration events are relatively easy to recognize, and justifiably garner much research attention. Evidence indicates several pest species that overwinter in diapause, and thus inhabit a year-round range, also engage in migratory flight, which is somewhat "invisible" because displacement is nondirectional and terminates among conspecifics. Support for aseasonal, undirected migration is related to recognizing true migratory flight behavior, which differs fundamentally from most other kinds of flight in that it is nonappetitive. Migrating adults are not searching for resources and migratory flight is not arrested by encounters with potential resources. The population-level consequence of aseasonal, undirected migration is spatial mixing of individuals within the larger metapopulation, which has important implications for population dynamics, gene flow, pest management, and insect resistance management.

Movement Ecology of Adult Western Corn Rootworm: Implications for Management

Movement of adult western corn rootworm, Diabrotica virgifera virgifera LeConte, is of fundamental importance to this species' population dynamics, ecology, evolution, and interactions with its environment, including cultivated cornfields. Realistic parameterization of dispersal components of models is needed to predict rates of range expansion, development, and spread of resistance to control measures and improve pest and resistance management strategies. However, a coherent understanding of western corn rootworm movement ecology has remained elusive because of conflicting evidence for both short- and long-distance lifetime dispersal, a type of dilemma observed in many species called Reid's paradox. Attempts to resolve this paradox using population genetic strategies to estimate rates of gene flow over space likewise imply greater dispersal distances than direct observations of short-range movement suggest, a dilemma called Slatkin's paradox. Based on the wide-array of available evidence, we present a conceptual model of adult western corn rootworm movement ecology under the premise it is a partially migratory species. We propose that rootworm populations consist of two behavioral phenotypes, resident and migrant. Both engage in local, appetitive flights, but only the migrant phenotype also makes non-appetitive migratory flights, resulting in observed patterns of bimodal dispersal distances and resolution of Reid's and Slatkin's paradoxes.

De Novo Mining and Validating Novel Microsatellite Markers to Assess Genetic Diversity in Maruca vitrata (F.), a Legume Pod Borer

Maruca vitrata (Fabricius) is an invasive insect pest capable of causing enormous economic losses to a broad spectrum of leguminous crops. Microsatellites are valuable molecular markers for population genetic studies; however, an inadequate number of M. vitrata microsatellite loci are available to carry out population association studies. Thus, we utilized this insect's public domain databases for mining expressed sequence tags (EST)-derived microsatellite markers. In total, 234 microsatellite markers were identified from 10053 unigenes. We discovered that trinucleotide repeats were the most predominant microsatellite motifs (61.53%), followed by dinucleotide repeats (23.50%) and tetranucleotide repeats (14.95%). Based on the analysis, twenty-five markers were selected for validation in M. vitrata populations collected from various regions of India. The number of alleles (Na), observed heterozygosity (Ho), and expected heterozygosity (He) ranged from 2 to 5; 0.00 to 0.80; and 0.10 to 0.69, respectively. The polymorphic loci showed polymorphism information content (PIC), ranging from 0.09 to 0.72. Based on the genetic distance matrix, the unrooted neighbor-joining dendrogram differentiated the selected populations into two discrete groups. The SSR markers developed and validated in this study will be helpful in population-level investigations of M. vitrata to understand the gene flow, demography, dispersal patterns, biotype differentiation, and host dynamics.

Analysis of Genetic Diversity of Banana Weevils (Cosmopolites sordidus) (Coleoptera: Curculionidae) Using Transcriptome-Derived Simple Sequence Repeat Markers

The banana weevil, Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae) is an economically important insect pest of bananas. It causes up to 100% yield losses and substantial lifespan reduction in bananas. Advances in genomics, proteomics, and sequencing technologies have provided powerful pathways to genotyping disastrous pests such as C. sordidus. However, such technologies are often not available to the majority of rural subtropical African banana growers and pest control managers. This study was therefore motivated by the need to create cheap and easily accessible C. sordidus genotyping methods that could be deployed by banana pest control managers to the benefit of C. sordidus control programs in the tropics where such advanced technologies are not readily accessible. We used an in-house C. sordidus transcriptome from the an-ongoing study from which we mined an array of simple sequence repeat (SSR) markers. Of these, six highly polymorphic transcriptome-derived SSR markers were used to successfully genotype within and among banana weevil population genetic diversity of 12 C. sordidus populations collected from four banana-growing agro-ecological zones (AEZs) in Uganda. The developed transcriptome-derived SSR markers can be used by researchers in population genetics for characterization of the C. sordidus and identification of new genes that are linked to traits of particular interest. The significant genetic diversity revealed in C. sordidus provides pertinent information for integrated pest management strategies.

High migratory propensity constitutes a single stock of an exploited cutlassfish species in the Northwest Pacific: A microsatellite approach

Cutlassfishes, also known as hairtails, include multiple predatory fishes of the family Trichiuridae. They constitute a top marine fish commodity globally, yet the knowledge about their composition and intraspecific genetic structures is still limited. Trichiurus japonicus accounts for a major amount in the northwest Pacific fishery. Previous studies based on mitochondrial DNA markers reported incongruences in its population structure, hence prompting the need for high-resolution markers and avoiding possible shortcomings in its management. Here we genotyped ten novel de novo-assembled transcriptome-derived microsatellite markers on a total of 150 samples across five major fishing grounds (encompassing latitudes 22-39°N). These markers presented a high number of alleles and heterozygosity compared to other marine fishes, corresponding to the large effective population size of ~20,000 per location and cohort differentiation. Population structuring analyses suggested T. japonicus to be a homogenous well-mixed population. This configuration is likely attributed to the majority of its effective population migrates across locations, and the absence of oceanographic barriers at the continental shelves. Qingdao with reportedly high ocean productivity could be a genetic pseudosink based on the high heterozygosity and migratory preference. Moreover, the results of sign tests suggest that T. japonicus experienced a recent bottleneck likely concurrent with historical glaciation events. Further, we demonstrated satisfactory cross-amplifications of our markers on several congeners, indicating a great promise to use these markers to study the population genetics of trichiurids. Together, our findings will serve as an essential groundwork for enhancing resource conservation and management of cutlassfishes.

Lack of Genetic Structure Among Populations of Striped Flea Beetle Phyllotreta striolata (Coleoptera: Chrysomelidae) Across Southern China

The striped flea beetle (SFB) Phyllotreta striolata (Fabricius) (Coleoptera: Chrysomelidae) is a major pest of cruciferous vegetables in southern China. The population diversity and genetic structure of SFB are unknown. Here, we assembled a draft genome for the SFB and characterized the distribution of microsatellites. Then, we developed 12 novel microsatellite markers across the genome. We used a segment of the cox1 gene and newly developed microsatellite markers to genotype the genetic diversity of SFB across southern China. There were 44 mitochondrial haplotypes in the SFB populations, with haplotype 2 as the most widespread. The population genetic differentiation was very low, indicated by FST-values (<0.05 except for Guangxi population with other populations based on cox1), high gene flow (4.10 and 44.88 of cox1 and microsatellite, respectively) and Principal Coordinate Analysis across all populations. Mantel test showed genetic distance in SFB was significantly associated with geographic distance based on microsatellites (R2 = 0.2373, P = 0.014) while result based on cox1 (R2 = 0.0365, P = 0.155) showed no significant difference. The phylogenetic analysis did not find any geographically related clades among all haplotypes. Analyses based on microsatellites showed a lack of population genetic structure among all populations. Our study provides a foundation for the future understanding of the ecology and evolution of SFB and its management.

Capsicum chinense MYB Transcription Factor Genes: Identification, Expression Analysis, and Their Conservation and Diversification With Other Solanaceae Genomes

Myeloblastosis (MYB) genes are important transcriptional regulators of plant growth, development, and secondary metabolic biosynthesis pathways, such as capsaicinoid biosynthesis in Capsicum. Although MYB genes have been identified in Capsicum annuum, no comprehensive study has been conducted on other Capsicum species. We identified a total of 251 and 240 MYB encoding genes in Capsicum chinense MYBs (CcMYBs) and Capsicum baccatum MYBs (CbMYBs). The observation of twenty tandem and 41 segmental duplication events indicated expansion of the MYB gene family in the C. chinense genome. Five CcMYB genes, i.e., CcMYB101, CcMYB46, CcMYB6, CcPHR8, and CcRVE5, and two CaMYBs, i.e., CaMYB3 and CaHHO1, were found within the previously reported capsaicinoid biosynthesis quantitative trait loci. Based on phylogenetic analysis with tomato MYB proteins, the Capsicum MYBs were classified into 24 subgroups supported by conserved amino acid motifs and gene structures. Also, a total of 241 CcMYBs were homologous with 225 C. annuum, 213 C. baccatum, 125 potato, 79 tomato, and 23 Arabidopsis MYBs. Synteny analysis showed that all 251 CcMYBs were collinear with C. annuum, C. baccatum, tomato, potato, and Arabidopsis MYBs spanning over 717 conserved syntenic segments. Using transcriptome data from three fruit developmental stages, a total of 54 CcMYBs and 81 CaMYBs showed significant differential expression patterns. Furthermore, the expression of 24 CcMYBs from the transcriptome data was validated by quantitative real-time (qRT) PCR analysis. Eight out of the 24 CcMYBs validated by the qRT-PCR were highly expressed in fiery hot C. chinense than in the lowly pungent C. annuum. Furthermore, the co-expression analysis revealed several MYB genes clustered with genes from the capsaicinoid, anthocyanin, phenylpropanoid, carotenoid, and flavonoids biosynthesis pathways, and related to determining fruit shape and size. The homology modeling of 126 R2R3 CcMYBs showed high similarity with that of the Arabidopsis R2R3 MYB domain template, suggesting their potential functional similarity at the proteome level. Furthermore, we have identified simple sequence repeat (SSR) motifs in the CcMYB genes, which could be used in Capsicum breeding programs. The functional roles of the identified CcMYBs could be studied further so that they can be manipulated for Capsicum trait improvement.

Genome-Wide Novel Genic Microsatellite Marker Resource Development and Validation for Genetic Diversity and Population Structure Analysis of Banana

Trait tagging through molecular markers is an important molecular breeding tool for crop improvement. SSR markers encoded by functionally relevant parts of a genome are well suited for this task because they may be directly related to traits. However, a limited number of these markers are known for Musa spp. Here, we report 35136 novel functionally relevant SSR markers (FRSMs). Among these, 17,561, 15,373 and 16,286 FRSMs were mapped in-silico to the genomes of Musa acuminata, M. balbisiana and M. schizocarpa, respectively. A set of 273 markers was validated using eight accessions of Musa spp., from which 259 markers (95%) produced a PCR product of the expected size and 203 (74%) were polymorphic. In-silico comparative mapping of FRSMs onto Musa and related species indicated sequence-based orthology and synteny relationships among the chromosomes of Musa and other plant species. Fifteen FRSMs were used to estimate the phylogenetic relationships among 50 banana accessions, and the results revealed that all banana accessions group into two major clusters according to their genomic background. Here, we report the first large-scale development and characterization of functionally relevant Musa SSR markers. We demonstrate their utility for germplasm characterization, genetic diversity studies, and comparative mapping in Musa spp. and other monocot species. The sequences for these novel markers are freely available via a searchable web interface called Musa Marker Database.

An empirical comparison of population genetic analyses using microsatellite and SNP data for a species of conservation concern

BACKGROUND

Use of genomic tools to characterize wildlife populations has increased in recent years. In the past, genetic characterization has been accomplished with more traditional genetic tools (e.g., microsatellites). The explosion of genomic methods and the subsequent creation of large SNP datasets has led to the promise of increased precision in population genetic parameter estimates and identification of demographically and evolutionarily independent groups, as well as questions about the future usefulness of the more traditional genetic tools. At present, few empirical comparisons of population genetic parameters and clustering analyses performed with microsatellites and SNPs have been conducted.

RESULTS

Here we used microsatellite and SNP data generated from Gunnison sage-grouse (Centrocercus minimus) samples to evaluate concordance of the results obtained from each dataset for common metrics of genetic diversity (HO, HE, FIS, AR) and differentiation (FST, GST, DJost). Additionally, we evaluated clustering of individuals using putatively neutral (SNPs and microsatellites), putatively adaptive, and a combined dataset of putatively neutral and adaptive loci. We took particular interest in the conservation implications of any differences. Generally, we found high concordance between microsatellites and SNPs for HE, FIS, AR, and all differentiation estimates. Although there was strong correlation between metrics from SNPs and microsatellites, the magnitude of the diversity and differentiation metrics were quite different in some cases. Clustering analyses also showed similar patterns, though SNP data was able to cluster individuals into more distinct groups. Importantly, clustering analyses with SNP data suggest strong demographic independence among the six distinct populations of Gunnison sage-grouse with some indication of evolutionary independence in two or three populations; a finding that was not revealed by microsatellite data.

CONCLUSION

We demonstrate that SNPs have three main advantages over microsatellites: more precise estimates of population-level diversity, higher power to identify groups in clustering methods, and the ability to consider local adaptation. This study adds to a growing body of work comparing the use of SNPs and microsatellites to evaluate genetic diversity and differentiation for a species of conservation concern with relatively high population structure and using the most common method of obtaining SNP genotypes for non-model organisms.

Genetic Structure of Norway Spruce Ecotypes Studied by SSR Markers

Norway spruce is a widespread and economically highly important tree species in Central Europe which occurs there in different morphotypic forms (also known as ecotypes). Previously established common garden experiments indicated that the morphological differentiation is most likely genetically determined. The genetic structure of Norway spruce morphological variants might be an indicator (marker) of specific sustainability in forest ecosystems. In this study, we investigated 436 individuals from autochthonous populations belonging to three different ecotypes. The main aim was to evaluate a level of genetic intra and interpopulation diversity among the low, medium and high-elevation ecotypes using both expressed sequence tag simple sequence repeats (EST – SSR) and genomic SSR markers. Sixteen highly polymorphic microsatellite loci folded in two newly designed multiplexes were used to depicture the genetic structure of targeted trees. Important allele frequency parameters, such as the mean expected (0.722, SE = 0.061) and observed (0.585, SE = 0.062) heterozygosity and mean effective number of alleles (Ne = 5.943, SE = 1.279), were estimated. The low genetic differentiation detected among different ecotypes (Fst = 0.008) was further discussed and clarified.

Genome-wide mining of microsatellites in king cobra (Ophiophagus hannah) and cross-species development of tetranucleotide SSR markers in Chinese cobra (Naja atra)

The complete genome sequence provides the opportunity for genome-wide and coding region analysis of SSRs in the king cobra and for cross-species identification of microsatellite markers in the Chinese cobra. In the Ophiophagus hannah genome, tetranucleotide repeats (38.03%) were the most abundant category, followed by dinucleotides (23.03%), pentanucleotides (13.07%), mononucleotides (11.78%), trinucleotides (11.49%) and hexanucleotides (2.6%). Twenty predominant motifs in the O. hannah genome were (A)n (C)n, (AC)n, (AG)n, (AT)n, (AGG)n, (AAT)n, (AAG)n, (AAC)n, (ATG)n, (ATAG)n, (AAGG)n, (ATCT)n, (CCTT)n, (ATTT)n, (AAAT)n, (AATAG)n, (ATTCT)n, (ATATGT)n, (AGATAT)n. In total, 4344 SSRs were found in coding sequences (CDSs). Tetranucleotides (52.79%) were the most abundant microsatellite type in CDS, followed by trinucleotides (28.50%), dinucleotides (11.02%), pentanucleotides (4.42%), mononucleotides (1.77%), and hexanucleotides (1.50%). A total of 984 CDSs containing microsatellites were assigned 11152 Gene Ontology (GO) functional terms. Gene Ontology (GO) analysis demonstrated that cellular process, cell and binding were the most frequent GO terms in biological process, cellular component and molecular function, respectively. Thirty-two novel highly polymorphic (PIC > 0.5) SSR markers for Naja atra were developed from cross-species amplification based on the tetranucleotide microsatellite sequences in the king cobra genome. The number of alleles (N_A) per locus had between 3 and 11 alleles with an average of 6.5, the polymorphism information content (PIC) value ranged from 0.521 to 0.858 (average = 0.707), the observed heterozygosity (Ho) of 32 microsatellite loci ranged from 0.292 to 0.875 (mean = 0.678), the expected heterozygosity (H_E) ranged from 0.561 to 0.889 (average = 0.761), and 3 microsatellite loci exhibited statistically significant departure from Hardy-Weinberg equilibrium (HWE) after Bonferroni correction (p < 0.003).

Comparative analyses of simple sequence repeats (SSRs) in 23 mosquito species genomes: Identification, characterization and distribution (Diptera: Culicidae)

Simple sequence repeats (SSRs) exist in both eukaryotic and prokaryotic genomes and are the most popular genetic markers, but the SSRs of mosquito genomes are still not well understood. In this study, we identified and analyzed the SSRs in 23 mosquito species using Drosophila melanogaster as reference at the whole-genome level. The results show that SSR numbers (33 076-560 175/genome) and genome sizes (574.57-1342.21 Mb) are significantly positively correlated (R² = 0.8992, P < 0.01), but the correlation in individual species varies in these mosquito species. In six types of SSR, mono- to trinucleotide SSRs are dominant with cumulative percentages of 95.14%-99.00% and densities of 195.65/Mb-787.51/Mb, whereas tetra- to hexanucleotide SSRs are rare with 1.12%-4.22% and 3.76/Mb-40.23/Mb. The (A/T)n, (AC/GT)n and (AGC/GCT)n are the most frequent motifs in mononucleotide, dinucleotide and trinucleotide SSRs, respectively, and the motif frequencies of tetra- to hexanucleotide SSRs appear to be species-specific. The 10-20 bp length of SSRs are dominant with the number of 110 561 ± 93 482 and the frequency of 87.25% ± 5.73% on average, and the number and frequency decline with the increase of length. Most SSRs (83.34% ± 7.72%) are located in intergenic regions, followed by intron regions (11.59% ± 5.59%), exon regions (3.74% ± 1.95%), and untranslated regions (1.32% ± 1.39%). The mono-, di- and trinucleotide SSRs are the main SSRs in both gene regions (98.55% ± 0.85%) and exon regions (99.27% ± 0.52%). An average of 42.52% of total genes contains SSRs, and the preference for SSR occurrence in different gene subcategories are species-specific. The study provides useful insights into the SSR diversity, characteristics and distribution in 23 mosquito species of genomes.

Identification of genes involved in fruit development/ripening in Capsicum and development of functional markers

The molecular mechanism of the underlying genes involved in the process of fruit ripening in Capsicum (family Solanaceae) is not clearly known. In the present study, we identified orthologs of 32 fruit development/ripening genes of tomato in Capsicum, and validated their expression in fruit development stages in C. annuum, C. frutescens, and C. chinense. In silico expression analysis using transcriptome data identified a total of 12 out of 32 genes showing differential expression during different stages of fruit development in Capsicum. Real time expression identified gene LOC107847473 (ortholog of MADS-RIN) had substantially higher expression (>500 folds) in breaker and mature fruits, which suggested the non-climacteric ripening behaviour of Capsicum. However, differential expression of Ehtylene receptor 2-like (LOC107873245) gene during fruit maturity supported the climacteric behaviour of only C. frutescens (hot pepper). Furthermore, development of 49 gene based simple sequence repeat (SSR) markers would help in selection of identified genes in Capsicum breeding.

De novo transcriptome sequencing and SSR markers development for Cedrela balansae C.DC., a native tree species of northwest Argentina

The endangered Cedrela balansae C.DC. (Meliaceae) is a high-value timber species with great potential for forest plantations that inhabits the tropical forests in Northwestern Argentina.Research on this species is scarce because of the limited genetic and genomic information available. Here, we explored the transcriptome of C. balansae using 454 GS FLX Titanium next-generation sequencing (NGS) technology. Following de novo assembling, we identified 27,111 non-redundant unigenes longer than 200 bp, and considered these transcripts for further downstream analysis. The functional annotation was performed searching the 27,111 unigenes against the NR-Protein and the Interproscan databases. This analysis revealed 26,977 genes with homology in at least one of the Database analyzed. Furthermore, 7,774 unigenes in 142 different active biological pathways in C. balansae were identified with the KEGG database. Moreover, after in silico analyses, we detected 2,663 simple sequence repeats (SSRs) markers. A subset of 70 SSRs related to important "stress tolerance" traits based on functional annotation evidence, were selected for wet PCR-validation in C. balansae and other Cedrela species inhabiting in northwest and northeast of Argentina (C. fissilis, C. saltensis and C. angustifolia). Successful transferability was between 77% and 93% and thanks to this study, 32 polymorphic functional SSRs for all analyzed Cedrela species are now available. The gene catalog and molecular markers obtained here represent a starting point for further research, which will assist genetic breeding programs in the Cedrela genus and will contribute to identifying key populations for its preservation.

Development of polymorphic EST microsatellite markers for the sand fly, Phlebotomus papatasi (Diptera: Psychodidae)

Background

Phlebotomus papatasi is a widely distributed sand fly species in different tropical and sub-tropical regions including the Middle East and North Africa. It is considered an important vector that transmits Leishmania major parasites, the causative agents of cutaneous leishmaniasis. The development of microsatellite markers for this sand fly vector is of high interest to understand its population structure and to monitor its geographic dispersal.

Results

Fourteen polymorphic microsatellite markers were developed with simple di-, tri- and tetra-nucleotide repeats. The F statistics calculated for the 14 markers revealed high genetic diversity; expected heterozygosity (He) ranged from 0.407 to 0.767, while observed heterozygosity (Ho) was lower and ranged from 0.083 to 0.514. The number of alleles sampled fall in the range of 9–29. Three out of 14 markers deviated from Hardy-Weinberg expectations, no significant linkage disequilibrium was detected and high values for inbreeding coefficient (F_IS) were likely due to inbreeding.

Conclusions

The development of these functional microsatellites enable a high resolution of P. papatasi populations. It opens a path for researchers to perform multi locus-based population genetic structure analyses, and comparative mapping, a part of the efforts to uncover the population dynamics of this vector, which is an important global strategy for understanding the epidemiology and control of leishmaniasis.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-2770-3) contains supplementary material, which is available to authorized users.

APMicroDB: A microsatellite database of Acyrthosiphon pisum

Pea aphids represent a complex genetic system that could be used for QTL analysis, genetic diversity and population genetics studies. Here, we described the development of first microsatellite repeat database of the pea aphid (APMicroDB), accessible at “http://deepaklab.com/aphidmicrodb”. We identified 3,40,233 SSRs using MIcroSAtellite (MISA) tool that was distributed in 14,067 (out of 23,924) scaffold of the pea aphid. We observed 89.53% simple repeats of which 73.41% were mono-nucleotide, followed by di-nucleotide repeats. This database stored information about the repeats kind, GC content, motif type (mono - hexa), genomic location etc. We have also incorporated the primer information derived from Primer3 software of the 250bp flanking region of the identified marker. Blast tool is also provided for searching the user query sequence for identified marker and their primers. This work has an immense use for scientific community working in the field of agricultural pest management, QTL mapping, and host-pathogen interaction analysis.

Level of genetic differentiation affects relative performances of expressed sequence tag and genomic SSRs

Microsatellites, also called simple sequence repeats (SSRs), are markers of choice to estimate relevant parameters for conservation genetics, such as migration rates, effective population size and kinship. Cross-amplification of SSRs is the simplest way to obtain sets of markers, and highly conserved SSRs have recently been developed from expressed sequence tags (EST) to improve SSR cross-species utility. As EST-SSRs are located in coding regions, the higher stability of their flanking regions reduces the frequency of null alleles and improves cross-species amplification. However, EST-SSRs have generally less allelic variability than genomic SSRs, potentially leading to differences in estimates of population genetic parameters such as genetic differentiation. To assess the potential of EST-SSRs in studies of within-species genetic diversity, we compared the relative performance of EST- and genomic SSRs following a multispecies approach on passerine birds. We tested whether patterns and levels of genetic diversity within and between populations assessed from EST- and from genomic SSRs are congruent, and we investigated how the relative efficiency of EST- and genomic SSRs is influenced by levels of differentiation. EST- and genomic SSRs ensured comparable inferences of population genetic structure in cases of strong genetic differentiation, and genomic SSRs performed slightly better than EST-SSRs when differentiation is moderate. However and interestingly, EST-SSRs had a higher power to detect weak genetic structure compared to genomic SSRs. Our study attests that EST-SSRs may be valuable molecular markers for conservation genetic studies in taxa such as birds, where the development of genomic SSRs is impeded by their low frequency.

Genetic differentiation of the regional Plutella xylostella populations across the Taiwan Strait based on identification of microsatellite markers

Movement of individuals through events, such as storms or crop transportation, may affect survival and distribution of insect pests, as well as population genetic structure at a regional scale. Understanding what factors contribute to gene flow in pest populations remains very important for sustainable pest management. The diamondback moth (Plutella xylostella) is an insect pest well known for its capacity of moving over short to long distances. Here, we used newly isolated microsatellite markers to analyze the genetic structure of nine populations across the Taiwan Strait of China (Taiwan and Fujian). A total of 12,152 simple sequence repeats (SSRs) were initially identified from the P. xylostella transcriptome (~94 Mb), with an average of 129 SSRs per Mb. Nine SSRs were validated to be polymorphic markers, and eight were used for this population genetic study. Our results showed that the P. xylostella populations could be divided into distinct two clusters, which is likely due to the year-round airflows in this region. A pattern of isolation by distance among the local populations within Fujian was found, and may be related to vegetable transportation. Considering the complexity of the P. xylostella population genetic structure from local and regional to global levels, we propose that developing ecologically sound strategies for managing this pest will require knowledge of the link between behavioral and population ecology and its genetic structure.

Genetic structure of Lycorma delicatula (Hemiptera: Fulgoridae) populations in Korea: implication for invasion processes in heterogeneous landscapes

Lycorma delicatula (White) was identified in 2004 as an invasive pest in South Korea, where it causes serious damage to vineyard crops. To investigate the population structure and dispersal pattern of L. delicatula in South Korea, we estimated the population genetic structure and gene flow among nine locations across the country using seven microsatellite markers. Although L. delicatula spread throughout most of its geographical range in South Korea within 5-7 years following invasion, its populations show evidence of genetic structuring across the range with a low but significant global F ST (genetic differentiation across all populations) of 0.0474. Bayesian-based clustering analysis indicates the presence of at least three genetically unique populations in South Korea, including populations in northeastern South Korea, which show a distinct genetic background. However, isolation by distance suggests that populations in South Korea have not yet reached genetic equilibrium. Estimates of the historical rate of gene flow (N e m) indicate that relatively high rates of flow have been maintained among populations within the western region, which may indicate recent range expansion. A population assignment test using the first-generation migrant detection method suggested that long-distance dispersal of L. delicatula may have occurred over large areas of South Korea. More complex dispersal patterns may have occurred during L. delicatula invasion of heterogeneous landscapes in South Korea.

Efficient isolation of polymorphic microsatellites from high-throughput sequence data based on number of repeats

Transcriptome data are a good resource to develop microsatellites due to their potential in targeting candidate genes. However, developing microsatellites can be a time-consuming enterprise due to the numerous primer pairs to be tested. Therefore, the use of methodologies that make it efficient to identify polymorphic microsatellites is desirable. Here we used a 62,038 contigs transcriptome assembly, obtained from pyrosequencing a peacock blenny (Salaria pavo) multi-tissue cDNA library, to mine for microsatellites and in silico evaluation of their polymorphism. A total of 4190 microsatellites were identified in 3670 unique unigenes, and from these microsatellites, in silico polymorphism was detected in 733. We selected microsatellites based either on their in silico polymorphism and annotation results or based only on their number of repeats. Using these two approaches, 28 microsatellites were successfully amplified in twenty-six individuals, and all but 2 were found to be polymorphic, being the first genetic markers for this species. Our results showed that the strategy of selection based on number of repeats is more efficient in obtaining polymorphic microsatellites than the strategy of in silico polymorphism (allelic richness was 8.2±3.85 and 4.56±2.45 respectively). This study demonstrates that combining the knowledge of number of repeats with other predictors of variability, for example in silico microsatellite polymorphism, improves the rates of polymorphism, yielding microsatellites with higher allelic richness, and decreases the number of monomorphic microsatellites obtained.

Use of comparative genomics to develop EST-SSRs for red drum (Sciaenops ocellatus)

Microsatellites physically linked to expressed sequence tags (EST-SSRs) are an important resource for linkage mapping and comparative genomics, and data mining in publicly available EST databases is a common strategy for EST-SSR discovery. At present, many species lack species-specific EST sequence data needed for the efficient characterization of EST-SSRs. This paper describes the discovery and development of EST-SSRs for red drum (Sciaenops ocellatus), an estuarine-dependent sciaenid species of economic importance in the USA and elsewhere, using a phylogenetically informed, comparative genomics approach to primer design. The approach entailed comparing existing genomic resources from species closely allied phylogenetically to red drum, with resources from more distantly related outgroup species. By taking into account the degree to which flanking regions are conserved across taxa, the efficiency of PCR primer design was increased greatly. The amplification success rate for primers designed for red drum was 100 % when using EST libraries from confamilial species and 92 % when using an EST library from a species in the same suborder. The primers developed also amplified EST-SSRs in a wide range of perciform fishes, suggesting potential use in comparative genomics. This study demonstrates that EST-SSRs can be efficiently developed for an organism when limited species-specific data are available by exploiting genomic resources from well-studied species, even those at extended phylogenetic distances.

Genetic evidence for the uncoupling of local aquaculture activities and a population of an invasive species--a case study of Pacific oysters (Crassostrea gigas)

Human-mediated introduction of nonnative species into coastal areas via aquaculture is one of the main pathways that can lead to biological invasions. To develop strategies to counteract invasions, it is critical to determine whether populations establishing in the wild are self-sustaining or based on repeated introductions. Invasions by the Pacific oyster (Crassostrea gigas) have been associated with the growing oyster aquaculture industry worldwide. In this study, temporal genetic variability of farmed and wild oysters from the largest enclosed bay in Ireland was assessed to reconstruct the recent biological history of the feral populations using 7 anonymous microsatellites and 7 microsatellites linked to expressed sequence tags (ESTs). There was no evidence of EST-linked markers showing footprints of selection. Allelic richness was higher in feral than in aquaculture samples (P = 0.003, paired t-test). Significant deviations from Hardy-Weinberg equilibrium due to heterozygote deficiencies were detected for almost all loci and samples, most likely explained by the presence of null alleles. Relatively high genetic differentiation was found between aquaculture and feral oysters (largest pairwise multilocus F(ST) 0.074, P < 0.01) and between year classes of oysters from aquaculture (largest pairwise multilocus F(ST) 0.073, P < 0.01), which was also confirmed by the strong separation of aquaculture and wild samples using Bayesian clustering approaches. A 10-fold higher effective population size (N(e)) and a high number of private alleles in wild oysters suggest an established self-sustaining feral population. The wild oyster population studied appears demographically independent from the current aquaculture activities in the estuary and alternative scenarios of introduction pathways are discussed.

Comparative population genetic analysis of bocaccio rockfish Sebastes paucispinis using anonymous and gene-associated simple sequence repeat loci

Comparative population genetic analyses of traditional and emergent molecular markers aid in determining appropriate use of new technologies. The bocaccio rockfish Sebastes paucispinis is a high gene-flow marine species off the west coast of North America that experienced strong population decline over the past 3 decades. We used 18 anonymous and 13 gene-associated simple sequence repeat (SSR) loci (expressed sequence tag [EST]-SSRs) to characterize range-wide population structure with temporal replicates. No F(ST)-outliers were detected using the LOSITAN program, suggesting that neither balancing nor divergent selection affected the loci surveyed. Consistent hierarchical structuring of populations by geography or year class was not detected regardless of marker class. The EST-SSRs were less variable than the anonymous SSRs, but no correlation between F(ST) and variation or marker class was observed. General linear model analysis showed that low EST-SSR variation was attributable to low mean repeat number. Comparative genomic analysis with Gasterosteus aculeatus, Takifugu rubripes, and Oryzias latipes showed consistently lower repeat number in EST-SSRs than SSR loci that were not in ESTs. Purifying selection likely imposed functional constraints on EST-SSRs resulting in low repeat numbers that affected diversity estimates but did not affect the observed pattern of population structure.

Cross-species transferability of SSR loci developed from transciptome sequencing in lodgepole pine

With the advent of next generation sequencing technologies, transcriptome level sequence collections are arising as prominent resources for the discovery of gene-based molecular markers. In a previous study more than 15,000 simple sequence repeats (SSRs) in expressed sequence tag (EST) sequences resulting from 454 pyrosequencing of Pinus contorta cDNA were identified. From these we developed PCR primers for approximately 4000 candidate SSRs. Here, we tested 184 of these SSRs for successful amplification across P. contorta and eight other pine species and examined patterns of polymorphism and allelic variability for a subset of these SSRs. Cross-species transferability was high, with high percentages of loci producing PCR products in all species tested. In addition, 50% of the loci we screened across panels of individuals from three of these species were polymorphic and allelically diverse. We examined levels of diversity in a subset of these SSRs by collecting genotypic data across several populations of Pinus ponderosa in northern Wyoming. Our results indicate the utility of mining pyrosequenced EST collections for gene-based SSRs and provide a source of molecular markers that should bolster evolutionary genetic investigations across the genus Pinus.

In silico mining and characterization of 12 EST-SSRs for the invasive slipper limpet Crepidula fornicata

In silico mining of an expressed sequence tags (ESTs) library was found to be efficient at isolating simple sequence repeats (SSRs) loci in the non-indigenous marine mollusc Crepidula fornicata. Twelve SSR loci were developed for routine genotyping. Cross-species amplification to 8 other Crepidula species showed that the 12 loci are highly specific for C. fornicata. Mendelian inheritance was shown for 11 of them (1 being monomorphic in the analyzed offspring array). The genetic diversity for 88 adults was found to be variable across the 12 loci (2-40 alleles, expected heterozygosity between 0.023 and 0.898) with a high overall exclusion probability of 0.99. The degree of genetic polymorphism found here is similar to that shown for 7 anonymous SSRs previously developed and here used on the same samples. This set of 12 specific loci is relevant to perform reliable population and relatedness analyses in Crepidula fornicata.

Development of soybean aphid genomic SSR markers using next generation sequencing

Simple sequence repeats (SSRs) or microsatellites are very useful molecular markers, owing to their locus-specific codominant and multiallelic nature, high abundance in the genome, and high rates of transferability across species. The soybean aphid (Aphis glycines Matsumura) has become the most damaging insect pest of soybean (Glycine max (L.) Merr.) in North America, since it was first found in the Midwest of the United States in 2000. Biotypes of the soybean aphid capable of colonizing newly developed aphid-resistant soybean cultivars have been recently discovered. Genetic resources, including molecular markers, to study soybean aphids are severely lacking. Recently developed next generation sequencing platforms offer opportunities for high-throughput and inexpensive genome sequencing and rapid marker development. The objectives of this study were (i) to develop and characterize genomic SSR markers from soybean aphid genomic sequences generated by next generation sequencing technology and (ii) to evaluate the utility of the SSRs for genetic diversity or relationship analyses. In total 128 SSR primer pairs were designed from sequences generated by Illumina GAII from a reduced representation library of A. glycines. Nearly 94% (120) of the primer pairs amplified SSR alleles of expected size and 24 SSR loci were polymorphic among three aphid samples from three populations. The polymorphic SSRs were successfully used to differentiate among 24 soybean aphids from Ohio and South Dakota. Sequencing of PCR products of two SSR markers from four aphid samples revealed that the allelic polymorphism was due to variation in the SSR repeats among the aphids. These markers should be particularly useful for genetic differentiation among aphids collected from soybean fields at different localities and regions. These SSR markers provide the soybean aphid research community with the first set of PCR-based codominant markers developed from the genomic sequences of A. glycines.

Development of novel EST-SSRs from sacred lotus (Nelumbo nucifera Gaertn) and their utilization for the genetic diversity analysis of N. nucifera

Expressed sequence tags (ESTs) provide a valuable resource for the development of simple sequence repeat (SSR) or microsatellite markers. This study identified SSRs within ESTs from Nelumbo nucifera (lotus or sacred lotus), developed markers from them, and assessed the potential of those markers for diversity analysis. Within 2207 ESTs from N. nucifera downloaded from GenBank, 1483 unigenes (303 contigs and 1180 singletons) were identified. After eliminating for redundancy, 125 SSR-containing ESTs were derived, and 71 unique SSRs were detected with an average density of one SSR per 13.04 kb. Dinucleotide repeats were the dominant motif in N. nucifera, whereas the sequences AG/TC/GA/CT, AAG/TTC/GAT/AGA, and AAAGCC were the most frequent of di-, tri-, and hexanucleotide motifs, respectively. The AG/TC (40.85%) and AAG (5.63%) motifs were predominant for the di- and trinucleotide repeats, respectively. Sixty-two SSR-containing ESTs were suitable for primer design. From these sequences, 23 EST-SSR markers were developed and were applied to 39 cultivated varieties of N. nucifera, 10 accessions of wild N. nucifera, and 1 accession of Nelumbo lutea (American lotus). Genetic diversity and genetic relationships were examined by constructing unweighted pair-group method with arithmetic average dendrograms and principal coordinates analysis plots based on SSR polymorphisms. Results indicated genetic differentiation between cultivated and wild lotus and between seed lotus cultivars and rhizome lotus cultivars. These EST-SSR markers will be useful for further studies of the evolution and diversity of Nelumbo.

A genome-wide set of 106 microsatellite markers for the blue tit (Cyanistes caeruleus)

We have characterized a set of 106 microsatellite markers in 26-127 individual blue tits (Cyanistes caeruleus), and assigned their location on the zebra finch (Taeniopygia guttata) and on the chicken (Gallus gallus) genome on the basis of sequence homology. Thirty-one markers are newly designed from zebra finch EST (expressed sequence tags) sequences, 22 markers were developed by others from EST sequences using different methods and the remaining 53 loci were previously designed or modified passerine markers. The 106 microsatellite markers are distributed over 26 and 24 chromosomes in the zebra finch and in the chicken genome respectively and the number of alleles varies between 2 and 49. Eight loci deviate significantly from Hardy-Weinberg equilibrium and show a high frequency of null alleles, and three pairs of markers located in the same chromosome appear to be in linkage disequilibrium. With the exception of these few loci, the polymorphic microsatellite markers presented here provide a useful genome-wide resource for population and evolutionary genetic studies of the blue tit, in addition to their potential utility in other passerine birds.

Comparative performance of single nucleotide polymorphism and microsatellite markers for population genetic analysis

Microsatellite loci are standard genetic markers for population genetic analysis, whereas single nucleotide polymorphisms (SNPs) are more recent tools that require assessment of neutrality and appropriate use in population genetics. Twelve SNP markers were used to describe the genetic structure of Diabrotica virgifera virgifera (LeConte; Coleoptera: Chrysomelidae) in the United States of America and revealed a high mean observed heterozygosity (0.40 +/- 0.059) and low global F(ST) (0.029). Pairwise F(ST) estimates ranged from 0.007 to 0.045, and all but 2 populations showed significant levels of genetic differentiation (P < or = 0.008). Population parameters and conclusions based on SNP markers were analogous to that obtained by use of microsatellite markers from the identical population samples. SNP-based F(ST) estimates were 3-fold higher than corresponding estimates from microsatellites, wherein lower microsatellite F(ST) estimates likely resulted from an overestimate of migration rates between subpopulations due to convergence of allele size (homoplasy). No significant difference was observed in the proportion of SNP or microsatellite markers loci that were nonneutral within populations. SNP markers provided estimates of population genetic parameters consistent with those from microsatellite data, and their low back mutation rates may result in reduced propensity for error in estimation of population parameters.

From conservation genetics to conservation genomics

Although the application of population and evolutionary genetic theory and methods to address issues of conservation relevance has a long history, the formalization of conservation genetics as a research field is still relatively recent. One of the periodic catalysts for increased research effort in the field has been advances in molecular technologies, leading to an increasingly wider variety of molecular markers for application in conservation genetic studies. To date, genetic methods have been applied in conservation biology primarily as selectively neutral molecular tools for resolving questions of conservation relevance. However, there has been renewed interest in complementing the analysis of neutral markers with the assessment of loci that may be directly involved in responses to processes such as environmental change, with a view to identifying the genes involved in them. These kinds of studies are now possible due to the increase in availability of genomic resources for nonmodel organisms, and there will likely be an even more rapid increase in the near future due to the advent of new ultrahigh throughput-sequencing technologies. This review considers the implications of the most recent developments in genomic technologies and their potential for contributing to the conservation of populations and species. Three "conservation genomics" case studies are presented (Atlantic salmon, Salmo sala; the butterfly, Melitaea cinxia; and the California condor, Gymnogyps californianus) in order to demonstrate the diversity of applications now possible. While it is clear that genomics approaches in conservation will not replace other tried-and-true methods, these recent developments open up an exciting new range of possibilities that will enable further diversification of the application of genomics in conservation biology.

Development of EST-SSR markers for the study of population structure in lettuce (Lactuca sativa L.)

A set of 61 simple sequence repeat (SSR) markers was developed from the 19,523 Lactuca sativa and Lactuca serriola unigenes. Approximately 4.5% of the unigenes contained a perfect SSR at least 20 bp long, corresponding to roughly 1 perfect SSR per 14.7 kb. Marker polymorphism was tested on a set comprising 96 accessions representing all major horticultural types and 3 wild species (L. serriola, Lactuca saligna, and Lactuca virosa). Both the average marker heterozygosity (UHe = 0.32) and the number of different alleles per locus (Na = 3.56) were significantly reduced in expressed sequence tag (EST)-SSRs as compared with anonymous SSRs (UHe = 0.59, Na = 5.53). Marker transfer rate to the wild species corresponded to the decreasing sexual compatibility with L. sativa and was higher for EST-SSRs (100% L. serriola, 87% L. saligna, and 75% L. virosa) than for anonymous SSRs (93%, 66%, and 42%, respectively). Assessment of population structure among 90 L. sativa cultivars with SSRs was in good agreement with classification into the horticultural types. The average marker heterozygosity was smallest in iceberg (0.097), Latin (0.140), and romaine-type (0.151) cultivars while highest in leaf (green leaf 0.208 and red leaf 0.240) lettuces. The level of marker heterozygosity is in accord with morphological variability observed in different horticultural types.

Tsetse flies: genetics, evolution, and role as vectors

Tsetse flies (Diptera: Glossinidae) are an ancient taxon of one genus, Glossina, and limited species diversity. All are exclusively haematophagous and confined to sub-Saharan Africa. The Glossina are the principal vectors of African trypanosomes Trypanosoma sp. (Kinetoplastida: Trypanosomatidae) and as such, are of great medical and economic importance. Clearly tsetse flies and trypanosomes are coadapted and evolutionary interactions between them are manifest. Numerous clonally reproducing strains of Trypanosoma sp. exist and their genetic diversities and spatial distributions are inadequately known. Here I review the breeding structures of the principle trypanosome vectors, G. morsitans s.l., G. pallidipes, G. palpalis s.l. and G. fuscipes fuscipes. All show highly structured populations among which there is surprisingly little detectable gene flow. Rather less is known of the breeding structure of T. brucei sensu lato vis à vis their vector tsetse flies but many genetically differentiated strains exist in nature. Genetic recombination in Trypanosoma via meiosis has recently been demonstrated in the laboratory thereby furnishing a mechanism of strain differentiation in addition to that of simple mutation. Spatially and genetically representative sampling of both trypanosome species and strains and their Glossina vectors is a major barrier to a comprehensive understanding of their mutual relationships.

Adaptation and invasiveness of western corn rootworm: intensifying research on a worsening pest

The western corn rootworm, Diabrotica virgifera virgifera LeConte, is an established insect pest of maize (Zea mays L.) in North America. The rotation of maize with another crop, principally soybeans, Glycine max (L.), was the primary management strategy utilized by North American producers and remained highly effective until the mid-1990s. In 1995, widespread and severe root injury occurred in east-central Illinois and northern Indiana maize fields that had been annually rotated with soybeans on a regular basis for several decades. The failure of this cultural tactic from a pest management perspective was attributed to a behavioral adaptation by a variant western corn rootworm that had lost fidelity to maize for egg laying. In 1992, an infestation of western corn rootworm was found within a small maize field near the Belgrade Airport. By 2007, the presence of this insect pest had been confirmed in 20 European countries. More recent molecular studies have confirmed that at least three separate invasions (until 2004) of western corn rootworms have occurred in Europe, increasing the risk that rotation-resistant western corn rootworms will be introduced into a new continent. Although biological control and use of conventional resistant maize hybrids have not achieved widespread success in the management of western corn rootworms in North America, these tactics are being evaluated in Europe.

Microsatellite characterization and marker development from public EST and WGS databases in the reef-building coral Acropora millepora (Cnidaria, Anthozoa, Scleractinia)

Mining for microsatellites (also called simple sequence repeats [SSRs]) in public sequence databases of a common Indo-Pacific coral Acropora millepora identified 191 SSRs from 10 258 expressed sequence tag (EST) and 618 SSRs from 14 625 whole-genome shotgun (WGS) sequences. In contrast to other animals, trinucleotide repeats, rather than dinucleotide repeats, are dominant in the WGS-SSRs, and AAT is the most frequent trinucleotide motif in EST-SSRs. We successfully developed 40 polymorphic markers from EST-SSRs and WGS-SSRs. Both EST- and WGS-SSRs show high levels of polymorphism within corals from the same reef patch. Interestingly, markers WGS079 and WGS227 revealed SSR duplications in a few individuals, suggesting recent duplication events. Genotypic linkage disequilibrium was identified in 5 pairs of SSR markers, which will be invaluable for high-resolution studies of genetic admixture in natural populations of A. millepora. Transferability analysis showed that 25 of these markers can be successfully amplified in one of the most ubiquitous Indo-Pacific corals Acropora hyacinthus. The marker collection reported here is the largest ever developed for any reef-building coral. It holds great potential for addressing coral reef connectivity across the Indo-Pacific with an unprecedented precision, especially taking into account the cross-species transferability of a substantial number of markers.