Assessing the utility of whole genome amplified DNA for next-generation molecular ecology

Integrating genomic and epidemiologic data to accelerate progress toward schistosomiasis elimination

The global community has adopted ambitious goals to eliminate schistosomiasis as a public health problem, and new tools are needed to achieve them. Mass drug administration programs, for example, have reduced the burden of schistosomiasis, but the identification of hotspots of persistent and reemergent transmission threaten progress toward elimination and underscore the need to couple treatment with interventions that reduce transmission. Recent advances in DNA sequencing technologies make whole-genome sequencing a valuable and increasingly feasible option for population-based studies of complex parasites such as schistosomes. Here, we focus on leveraging genomic data to tailor interventions to distinct social and ecological circumstances. We consider two priority questions that can be addressed by integrating epidemiological, ecological, and genomic information: (1) how often do non-human host species contribute to human schistosome infection? and (2) what is the importance of locally acquired versus imported infections in driving transmission at different stages of elimination? These questions address processes that can undermine control programs, especially those that rely heavily on treatment with praziquantel. Until recently, these questions were difficult to answer with sufficient precision to inform public health decision-making. We review the literature related to these questions and discuss how whole-genome approaches can identify the geographic and taxonomic sources of infection, and how such information can inform context-specific efforts that advance schistosomiasis control efforts and minimize the risk of reemergence.

Evolution, systematics and historical biogeography of sand flies of the subgenus Paraphlebotomus (Diptera, Psychodidae, Phlebotomus) inferred using restriction-site associated DNA markers

Phlebotomine sand flies are the main natural vectors of Leishmania, which cause visceral and tegumentary tropical diseases worldwide. However, their taxonomy and evolutionary history remain poorly studied. Indeed, as for many human disease vectors, their small size is a challenge for morphological and molecular works. Here, we successfully amplified unbiased copies of whole genome to sequence thousands of restriction-site associated DNA (RAD) markers from single specimens of phlebotomines. RAD markers were used to infer a fully resolved phylogeny of the subgenus Paraphlebotomus (11 species + 5 outgroups, 32 specimens). The subgenus was not recovered as monophyletic and we describe a new subgenus Artemievus subg. nov. Depaquit for Phlebotomus alexandri. We also confirm the validity of Ph. riouxi which is reinstated as valid species. Our analyses suggest that Paraphlebotomus sensu nov. originated ca 12.9-8.5 Ma and was possibly largely distributed from peri-Mediterranean to Irano-Turanian regions. Its biogeographical history can be summarized into three phases: i) a first split between Ph. riouxi + Ph. chabaudi and other species that may have resulted from the rise of the Saharan belt ca 8.5 Ma; ii) a Messinian vicariant event (7.3-5.3 Ma) during which the prolonged drought could have resulted in the divergence of main lineages; iii) a recent radiation event (3-2 Ma) that correspond to cycles of wet and dry periods in the Middle East and the East African subregions during the Pleistocene. Interestingly these cycles are also hypothetical drivers of the diversification of rodents, in the burrows of which Paraphlebotomus larvae develop. By meeting the challenge of sequencing pangenomics markers from single, minute phlebotomines, this work opens new avenues for improving our understanding of the epidemiology of leishmaniases and possibly other human diseases transmitted by arthropod vectors.

Relevance of ddRADseq method for species and population delimitation of closely related and widely distributed wolf spiders (Araneae, Lycosidae)

Although species delimitation is often controversial, emerging DNA-based and classical morphology-based methods are rarely compared using large-scale samplings, even less in the case of widely distributed species that have distant, allopatric populations. In the current study, we examined species boundaries within two wolf spider species of the genus Pardosa (Araneae, Lycosidae), P. riparia and P. palustris. Wolf spiders constitute an excellent model for testing the relevance of traditional vs. modern methods in species and population delimitation because several closely related species are distributed over cross-continental geographic ranges. Allopatric populations of the two Pardosa species were sampled across Europe to Far East Russia (latitudinal range > 150°) and several dozen individuals were studied using morphological characters (morphometry of three measures for both sexes, plus five in males only and two in females only), DNA barcoding (COI sequencing) and double-digest restriction site associated DNA sequencing (ddRADseq). The results obtained allow for changing the taxonomic status of two Far East Russian populations to subspecies and ddRADseq proved to be a powerful tool for taxonomic research despite scarce sampling and inherent subjectivity of species delimitation in allopatry. Overall, this study pleads for both multi-criteria and more population-based studies in taxonomy.

Double-digest RAD-sequencing: do pre- and post-sequencing protocol parameters impact biological results?

Next-generation sequencing technologies have opened a new era of research in population genetics. Following these new sequencing opportunities, the use of restriction enzyme-based genotyping techniques, such as restriction site-associated DNA sequencing (RAD-seq) or double-digest RAD-sequencing (ddRAD-seq), has dramatically increased in the last decade. From DNA sampling to SNP calling, the laboratory and bioinformatic parameters of enzyme-based techniques have been investigated in the literature. However, the impact of those parameters on downstream analyses and biological results remains less documented. In this study, we investigated the effects of sevral pre- and post-sequencing settings on ddRAD-seq results for two biological systems: a complex of butterfly species (Coenonympha sp.) and several populations of common beech (Fagus sylvatica). Our results suggest that pre-sequencing parameters (i.e., DNA quantity, number of PCR cycles during library preparation) have a significant impact on the number of recovered reads and SNPs, on the number of unique alleles and on individual heterozygosity. In the same way, we found that post-sequencing settings (i.e., clustering and minimum coverage thresholds) influenced loci reconstruction (e.g., number of loci, mean coverage) and SNP calling (e.g., number of SNPs; heterozygosity) but had only a marginal impact on downstream analyses (e.g., measure of genetic differentiation, estimation of individual admixture, and demographic inferences). In addition, replication analyses confirmed the reproducibility of the ddRAD-seq procedure. Overall, this study assesses the degree of sensitivity of ddRAD-seq data to pre- and post-sequencing protocols, and illustrates its robustness when studying population genetics.

Disjunction between canola distribution and the genetic structure of its recently described pest, the canola flower midge (Contarinia brassicola)

Population genomics is a useful tool to support integrated pest management as it can elucidate population dynamics, demography, and histories of invasion. Here, we use a restriction site-associated DNA sequencing approach combined with whole-genome amplification (WGA) to assess genomic population structure of a newly described pest of canola, the diminutive canola flower midge, Contarinia brassicola. Clustering analyses recovered little geographic structure across the main canola production region but differentiated several geographically disparate populations at edges of the agricultural zone. Given a lack of alternative hypotheses for this pattern, we suggest these data support alternative hosts for this species and thus our canola-centric view of this midge as a pest has limited our understanding of its biology. These results speak to the need for increased surveying efforts across multiple habitats and other potential hosts within Brassicaceae to improve both our ecological and evolutionary knowledge of this species and contribute to effective management strategies. We additionally found that use of WGA prior to library preparation was an effective method for increasing DNA quantity of these small insects prior to restriction site-associated DNA sequencing and had no discernible impact on genotyping consistency for population genetic analysis; WGA is therefore likely to be tractable for other similar studies that seek to randomly sample markers across the genome in small organisms.

Optimization of Genotype by Sequencing data for phylogenetic purposes

• Herein we propose a framework for assembling and analyzing Genotype by Sequencing (GBS) data to better understand evolutionary relationships within a group of closely related species using the mastiff bats (Molossus) as our model system. Many species within this genus have low-levels of genetic variation within and between morphologically distinct species, and the relationships among them remain unresolved using traditional Sanger sequencing methods. Given that both de novo and reference genome pipelines can be used to assemble next generation sequences, and that several tree inference methodologies have been proposed for single nucleotide polymorphism (SNP) data, we test whether different alignments and phylogenetic approaches produce similar results. We also examined how the process of SNP identification and mapping can affect the consistency of the analyses. Different alignments and phylogenetic inferences produced consistent results, supporting the GBS approach for answering evolutionary questions on a macroevolutionary scale when the genetic distance among phenotypically identifiable clades is low. We highlight the importance of exploring the relationships among groups using different assembly assumptions and also distinct phylogenetic inference methods, particularly when addressing phylogenetic questions in genetic and morphologically conservative taxa. • The method uses the comparison of several filter settings, alignments, and tree inference approaches on Genotype by Sequencing data. • Consistent results were found among several approaches. • The methodology successfully recovered well supported species boundaries and phylogenetic relationships among species of mastiff bats not hypothesized by previous methods.

Pushing the limits of whole genome amplification: successful sequencing of RADseq library from a single microhymenopteran (Chalcidoidea, Trichogramma)

A major obstacle to high-throughput genotyping of microhymenoptera is their small size. As species are difficult to discriminate, and because complexes may exist, the sequencing of a pool of specimens is hazardous. Thus, one should be able to sequence pangenomic markers (e.g., RADtags) from a single specimen. To date, whole genome amplification (WGA) prior to library construction is still a necessity as at most 10 ng of DNA can be obtained from single specimens (sometimes less). However, this amount of DNA is not compatible with manufacturer's requirements for commercial kits. Here we test the accuracy of the GenomiPhi kit V2 on Trichogramma wasps by comparing RAD libraries obtained from the WGA of single specimens (F0 and F1 generation, about1 ng input DNA for the WGA (0.17-2.9 ng)) and a biological amplification of genomic material (the pool of the progeny of the F1 generation). Globally, we found that 99% of the examined loci (up to 48,189 for one of the crosses, 109 bp each) were compatible with the mode of reproduction of the studied model (haplodiploidy) and Mendelian inheritance of alleles. The remaining 1% (0.01% of the analysed nucleotides) could represent WGA bias or other experimental/analytical bias. This study shows that the multiple displacement amplification method on which the GenomiPhi kit relies, could also be of great help for the high-throughput genotyping of microhymenoptera used for biological control, or other organisms from which only a very small amount of DNA can be extracted, such as human disease vectors (e.g.,  sandflies, fleas, ticks etc.).

A RAD-sequencing approach to genome-wide marker discovery, genotyping, and phylogenetic inference in a diverse radiation of primates

Until recently, most phylogenetic and population genetics studies of nonhuman primates have relied on mitochondrial DNA and/or a small number of nuclear DNA markers, which can limit our understanding of primate evolutionary and population history. Here, we describe a cost-effective reduced representation method (ddRAD-seq) for identifying and genotyping large numbers of SNP loci for taxa from across the New World monkeys, a diverse radiation of primates that shared a common ancestor ~20-26 mya. We also estimate, for the first time, the phylogenetic relationships among 15 of the 22 currently-recognized genera of New World monkeys using ddRAD-seq SNP data using both maximum likelihood and quartet-based coalescent methods. Our phylogenetic analyses robustly reconstructed three monophyletic clades corresponding to the three families of extant platyrrhines (Atelidae, Pitheciidae and Cebidae), with Pitheciidae as basal within the radiation. At the genus level, our results conformed well with previous phylogenetic studies and provide additional information relevant to the problematic position of the owl monkey (Aotus) within the family Cebidae, suggesting a need for further exploration of incomplete lineage sorting and other explanations for phylogenetic discordance, including introgression. Our study additionally provides one of the first applications of next-generation sequencing methods to the inference of phylogenetic history across an old, diverse radiation of mammals and highlights the broad promise and utility of ddRAD-seq data for molecular primatology.

Whole-genome amplification in double-digest RADseq results in adequate libraries but fewer sequenced loci

Whole-genome amplification by multiple displacement amplification (MDA) is a promising technique to enable the use of samples with only limited amount of DNA for the construction of RAD-seq libraries. Previous work has shown that, when the amount of DNA used in the MDA reaction is large, double-digest RAD-seq (ddRAD) libraries prepared with amplified genomic DNA result in data that are indistinguishable from libraries prepared directly from genomic DNA. Based on this observation, here we evaluate the quality of ddRAD libraries prepared from MDA-amplified genomic DNA when the amount of input genomic DNA and the coverage obtained for samples is variable. By simultaneously preparing libraries for five species of weevils (Coleoptera, Curculionidae), we also evaluate the likelihood that potential contaminants will be encountered in the assembled dataset. Overall, our results indicate that MDA may not be able to rescue all samples with small amounts of DNA, but it does produce ddRAD libraries adequate for studies of phylogeography and population genetics even when conditions are not optimal. We find that MDA makes it harder to predict the number of loci that will be obtained for a given sequencing effort, with some samples behaving like traditional libraries and others yielding fewer loci than expected. This seems to be caused both by stochastic and deterministic effects during amplification. Further, the reduction in loci is stronger in libraries with lower amounts of template DNA for the MDA reaction. Even though a few samples exhibit substantial levels of contamination in raw reads, the effect is very small in the final dataset, suggesting that filters imposed during dataset assembly are important in removing contamination. Importantly, samples with strong signs of contamination and biases in heterozygosity were also those with fewer loci shared in the final dataset, suggesting that stringent filtering of samples with significant amounts of missing data is important when assembling data derived from MDA-amplified genomic DNA. Overall, we find that the combination of MDA and ddRAD results in high-quality datasets for population genetics as long as the sequence data is properly filtered during assembly.

Mitonuclear discordance in wolf spiders: Genomic evidence for species integrity and introgression

Systematists and taxonomists have benefited greatly from the emergence of molecular methods. Species identification has become straightforward through DNA barcoding and the rapid build-up of massive DNA barcode reference libraries. In animals, mitonuclear discordance can significantly complicate the process of species identification and delimitation. The causes of mitonuclear discordance are either biological (e.g., introgression, incomplete lineage sorting, horizontal gene transfer androgenesis) or induced by operational factors (e.g., human error with specimen misidentification or incorrect species delimitation). Moreover, endosymbionts may play an important role in promoting fixation of mitochondrial genomes. Here, we study the mitonuclear discordance of wolf spiders species (Lycosidae) (independent cases from Alopecosa aculeata and Pardosa pullata groups) that share identical COI DNA barcodes. We approached the case utilizing double-digest restriction site-associated DNA sequencing (ddRADseq) to obtain and analyse genomic-scale data. Our results suggest that the observed cases of mitonuclear discordance are not due to operational reasons but result from biological processes. Further analysis indicated introgression and that incomplete lineage sorting is unlikely to have been responsible for the observed discrepancy. Additional survey of endosymbionts provided ideas on further research and their role in shaping mitochondrial DNA distribution patterns. Thus, ddRADseq grants an efficient way to study the taxonomy of problematic groups with insight into underlying evolutionary processes.

Review of Current Conservation Genetic Analyses of Northeast Pacific Sharks

Conservation genetics is an applied science that utilizes molecular tools to help solve problems in species conservation and management. It is an interdisciplinary specialty in which scientists apply the study of genetics in conjunction with traditional ecological fieldwork and other techniques to explore molecular variation, population boundaries, and evolutionary relationships with the goal of enabling resource managers to better protect biodiversity and identify unique populations. Several shark species in the northeast Pacific (NEP) have been studied using conservation genetics techniques, which are discussed here. The primary methods employed to study population genetics of sharks have historically been nuclear microsatellites and mitochondrial (mt) DNA. These markers have been used to assess genetic diversity, mating systems, parentage, relatedness, and genetically distinct populations to inform management decisions. Novel approaches in conservation genetics, including next-generation DNA and RNA sequencing, environmental DNA (eDNA), and epigenetics are just beginning to be applied to elasmobranch evolution, physiology, and ecology. Here, we review the methods and results of past studies, explore future directions for shark conservation genetics, and discuss the implications of molecular research and techniques for the long-term management of shark populations in the NEP.

Identifying hybridization and admixture using SNPs: application of the DArTseq platform in phylogeographic research on vertebrates

Next-generation sequencing (NGS) approaches are increasingly being used to generate multi-locus data for phylogeographic and evolutionary genetics research. We detail the applicability of a restriction enzyme-mediated genome complexity reduction approach with subsequent NGS (DArTseq) in vertebrate study systems at different evolutionary and geographical scales. We present two case studies using SNP data from the DArTseq molecular marker platform. First, we used DArTseq in a large phylogeographic study of the agamid lizard Ctenophorus caudicinctus, including 91 individuals and spanning the geographical range of this species across arid Australia. A low-density DArTseq assay resulted in 28 960 SNPs, with low density referring to a comparably reduced set of identified and sequenced markers as a cost-effective approach. Second, we applied this approach to an evolutionary genetics study of a classic frog hybrid zone (Litoria ewingii-Litoria paraewingi) across 93 individuals, which resulted in 48 117 and 67 060 SNPs for a low- and high-density assay, respectively. We provide a docker-based workflow to facilitate data preparation and analysis, then analyse SNP data using multiple methods including Bayesian model-based clustering and conditional likelihood approaches. Based on comparison of results from the DArTseq platform and traditional molecular approaches, we conclude that DArTseq can be used successfully in vertebrates and will be of particular interest to researchers working at the interface between population genetics and phylogenetics, exploring species boundaries, gene exchange and hybridization.

Whole Genome Amplification and Reduced-Representation Genome Sequencing of Schistosoma japonicum Miracidia

Background

In areas where schistosomiasis control programs have been implemented, morbidity and prevalence have been greatly reduced. However, to sustain these reductions and move towards interruption of transmission, new tools for disease surveillance are needed. Genomic methods have the potential to help trace the sources of new infections, and allow us to monitor drug resistance. Large-scale genotyping efforts for schistosome species have been hindered by cost, limited numbers of established target loci, and the small amount of DNA obtained from miracidia, the life stage most readily acquired from humans. Here, we present a method using next generation sequencing to provide high-resolution genomic data from S. japonicum for population-based studies.

Methodology/Principal Findings

We applied whole genome amplification followed by double digest restriction site associated DNA sequencing (ddRADseq) to individual S. japonicum miracidia preserved on Whatman FTA cards. We found that we could effectively and consistently survey hundreds of thousands of variants from 10,000 to 30,000 loci from archived miracidia as old as six years. An analysis of variation from eight miracidia obtained from three hosts in two villages in Sichuan showed clear population structuring by village and host even within this limited sample.

Conclusions/Significance

This high-resolution sequencing approach yields three orders of magnitude more information than microsatellite genotyping methods that have been employed over the last decade, creating the potential to answer detailed questions about the sources of human infections and to monitor drug resistance. Costs per sample range from $50-$200, depending on the amount of sequence information desired, and we expect these costs can be reduced further given continued reductions in sequencing costs, improvement of protocols, and parallelization. This approach provides new promise for using modern genome-scale sampling to S. japonicum surveillance, and could be applied to other schistosome species and other parasitic helminthes.

Schistosomiasis is a devastating tropical disease that affects more than 200 million people worldwide. Over the past several decades, transmission control strategies implemented in China have reduced the prevalence and morbidity of Schistosoma japonicum in many areas. Infections still persist, however, and it is therefore of great interest to determine the sources of recurring infections. Genetic analysis is a promising means to achieve this. Towards this aim, we conducted a pilot study to assess the feasibility of using high-throughput sequencing to assess the geographic distribution of schistosome genetic variants. Because DNA yields from miracidia, the most easily accessible life stage, are insufficient for high throughput sequencing, we first employed whole genome amplification to obtain sufficient quantities of DNA. We then employed a technique that reproducibly sequences the same fraction of a genome across numerous samples. We successfully sequenced 6-year old S. japonicum samples from Sichuan Province, China, easily and economically identifying tens of thousands of variable loci, a sufficient number to discriminate fine-scale population structure. Further population sampling will help answer important questions concerning the persistence of infections, the sources of new infections, and whether parasite populations have undergone incipient evolution of drug resistance.

Genotyping of whole genome amplified reduced representation libraries reveals a cryptic population of Culicoides brevitarsis in the Northern Territory, Australia

BACKGROUND

The advent of genotyping by Next Generation Sequencing has enabled rapid discovery of thousands of single nucleotide polymorphism (SNP) markers and high throughput genotyping of large populations at an affordable cost. Genotyping by sequencing (GBS), a reduced representation library sequencing method, allows highly multiplexed sequencing of genomic subsets. This method has limitations for small organisms with low amounts of genomic DNA, such as the bluetongue virus (BTV) vectors, Culicoides midges.

RESULTS

This study employed the GBS method to isolate SNP markers de novo from whole genome amplified Culicoides brevitarsis genomic DNA. The individuals were collected from regions representing two different Australian patterns of BTV strain distribution: the Northern Territory (NT) and the east coast. We isolated 8145 SNPs using GBS. Phylogenetic analysis conducted using the filtered 3263 SNPs revealed the presence of a distinct C. brevitarsis sub-population in the NT and this was confirmed by analysis of mitochondrial DNA. Two loci showed a very strong signal for selection and were unique to the NT population. Bayesian analysis with STRUCTURE indicated a possible two-population cluster.

CONCLUSIONS

The results suggest that genotyping vectors with high density markers in combination with biological and environmental data is useful. However, more extensive sampling over a wider spatial and temporal range is needed. The presence of sub-structure in populations and loci under natural selection indicates the need for further investigation of the role of vectors in shaping the two Australian systems of BTV transmission. The described workflow is transferable to genotyping of small, non-model organisms, including arthropod vectors of pathogens of economic and medical importance.

Geogenetic patterns in mouse lemurs (genus Microcebus) reveal the ghosts of Madagascar's forests past

Phylogeographic analysis can be described as the study of the geological and climatological processes that have produced contemporary geographic distributions of populations and species. Here, we attempt to understand how the dynamic process of landscape change on Madagascar has shaped the distribution of a targeted clade of mouse lemurs (genus Microcebus) and, conversely, how phylogenetic and population genetic patterns in these small primates can reciprocally advance our understanding of Madagascar's prehuman environment. The degree to which human activity has impacted the natural plant communities of Madagascar is of critical and enduring interest. Today, the eastern rainforests are separated from the dry deciduous forests of the west by a large expanse of presumed anthropogenic grassland savanna, dominated by the Family Poaceae, that blankets most of the Central Highlands. Although there is firm consensus that anthropogenic activities have transformed the original vegetation through agricultural and pastoral practices, the degree to which closed-canopy forest extended from the east to the west remains debated. Phylogenetic and population genetic patterns in a five-species clade of mouse lemurs suggest that longitudinal dispersal across the island was readily achieved throughout the Pleistocene, apparently ending at ∼55 ka. By examining patterns of both inter- and intraspecific genetic diversity in mouse lemur species found in the eastern, western, and Central Highland zones, we conclude that the natural environment of the Central Highlands would have been mosaic, consisting of a matrix of wooded savanna that formed a transitional zone between the extremes of humid eastern and dry western forest types.

Next-generation genotyping of hypervariable loci in many individuals of a non-model species: technical and theoretical implications

BACKGROUND

Across species, diversity at the Major Histocompatibility Complex (MHC) is critical to disease resistance and population health; however, use of MHC diversity to quantify the genetic health of populations has been hampered by the extreme variation found in MHC genes. Next generation sequencing (NGS) technology generates sufficient data to genotype even the most diverse species, but workflows for distinguishing artifacts from alleles are still under development. We used NGS to evaluate the MHC diversity of over 300 captive and wild ring-tailed lemurs (Lemur catta: Primates: Mammalia). We modified a published workflow to address errors that arise from deep sequencing individuals and tested for evidence of selection at the most diverse MHC genes.

RESULTS

In addition to evaluating the accuracy of 454 Titanium and Ion Torrent PGM for genotyping large populations at hypervariable genes, we suggested modifications to improve current methods of allele calling. Using these modifications, we genotyped 302 out of 319 individuals, obtaining an average sequencing depth of over 1000 reads per amplicon. We identified 55 MHC-DRB alleles, 51 of which were previously undescribed, and provide the first sequences of five additional MHC genes: DOA, DOB, DPA, DQA, and DRA. The additional five MHC genes had one or two alleles each with little sequence variation; however, the 55 MHC-DRB alleles showed a high dN/dS ratio and trans-species polymorphism, indicating a history of positive selection. Because each individual possessed 1-7 MHC-DRB alleles, we suggest that ring-tailed lemurs have four, putatively functional, MHC-DRB copies.

CONCLUSIONS

In the future, accurate genotyping methods for NGS data will be critical to assessing genetic variation in non-model species. We recommend that future NGS studies increase the proportion of replicated samples, both within and across platforms, particularly for hypervariable genes like the MHC. Quantifying MHC diversity within non-model species is the first step to assessing the relationship of genetic diversity at functional loci to individual fitness and population viability. Owing to MHC-DRB diversity and copy number, ring-tailed lemurs may serve as an ideal model for estimating the interaction between genetic diversity, fitness, and environment, especially regarding endangered species.