Nuclear insertions help and hinder inference of the evolutionary history of gorilla mtDNA

Interrogating 1000 insect genomes for NUMTs: A risk assessment for estimates of species richness

The nuclear genomes of most animal species include NUMTs, segments of the mitogenome incorporated into their chromosomes. Although NUMT counts are known to vary greatly among species, there has been no comprehensive study of their frequency/attributes in the most diverse group of terrestrial organisms, insects. This study examines NUMTs derived from a 658 bp 5' segment of the cytochrome c oxidase I (COI) gene, the barcode region for the animal kingdom. This assessment is important because unrecognized NUMTs can elevate estimates of species richness obtained through DNA barcoding and derived approaches (eDNA, metabarcoding). This investigation detected nearly 10,000 COI NUMTs ≥ 100 bp in the genomes of 1,002 insect species (range = 0-443). Variation in nuclear genome size explained 56% of the mitogenome-wide variation in NUMT counts. Although insect orders with the largest genome sizes possessed the highest NUMT counts, there was considerable variation among their component lineages. Two thirds of COI NUMTs possessed an IPSC (indel and/or premature stop codon) allowing their recognition and exclusion from downstream analyses. The remainder can elevate species richness as they showed 10.1% mean divergence from their mitochondrial homologue. The extent of exposure to "ghost species" is strongly impacted by the target amplicon's length. NUMTs can raise apparent species richness by up to 22% when a 658 bp COI amplicon is examined versus a doubling of apparent richness when 150 bp amplicons are targeted. Given these impacts, metabarcoding and eDNA studies should target the longest possible amplicons while also avoiding use of 12S/16S rDNA as they triple NUMT exposure because IPSC screens cannot be employed.

The impact of endogenous content, replicates and pooling on genome capture from faecal samples

Target-capture approach has improved over the past years, proving to be very efficient tool for selectively sequencing genetic regions of interest. These methods have also allowed the use of noninvasive samples such as faeces (characterized by their low quantity and quality of endogenous DNA) to be used in conservation genomic, evolution and population genetic studies. Here we aim to test different protocols and strategies for exome capture using the Roche SeqCap EZ Developer kit (57.5 Mb). First, we captured a complex pool of DNA libraries. Second, we assessed the influence of using more than one faecal sample, extract and/or library from the same individual, to evaluate its effect on the molecular complexity of the experiment. We validated our experiments with 18 chimpanzee faecal samples collected from two field sites as a part of the Pan African Programme: The Cultured Chimpanzee. Those two field sites are in Kibale National Park, Uganda (N = 9) and Loango National Park, Gabon (N = 9). We demonstrate that at least 16 libraries can be pooled, target enriched through hybridization, and sequenced allowing for the genotyping of 951,949 exome markers for population genetic analyses. Further, we observe that molecule richness, and thus, data acquisition, increase when using multiple libraries from the same extract or multiple extracts from the same sample. Finally, repeated captures significantly decrease the proportion of off-target reads from 34.15% after one capture round to 7.83% after two capture rounds, supporting our conclusion that two rounds of target enrichment are advisable when using complex faecal samples.

Morphometric, Behavioral, and Genomic Evidence for a New Orangutan Species

Six extant species of non-human great apes are currently recognized: Sumatran and Bornean orangutans, eastern and western gorillas, and chimpanzees and bonobos [1]. However, large gaps remain in our knowledge of fine-scale variation in hominoid morphology, behavior, and genetics, and aspects of great ape taxonomy remain in flux. This is particularly true for orangutans (genus: Pongo), the only Asian great apes and phylogenetically our most distant relatives among extant hominids [1]. Designation of Bornean and Sumatran orangutans, P. pygmaeus (Linnaeus 1760) and P. abelii (Lesson 1827), as distinct species occurred in 2001 [1, 2]. Here, we show that an isolated population from Batang Toru, at the southernmost range limit of extant Sumatran orangutans south of Lake Toba, is distinct from other northern Sumatran and Bornean populations. By comparing cranio-mandibular and dental characters of an orangutan killed in a human-animal conflict to those of 33 adult male orangutans of a similar developmental stage, we found consistent differences between the Batang Toru individual and other extant Ponginae. Our analyses of 37 orangutan genomes provided a second line of evidence. Model-based approaches revealed that the deepest split in the evolutionary history of extant orangutans occurred ∼3.38 mya between the Batang Toru population and those to the north of Lake Toba, whereas both currently recognized species separated much later, about 674 kya. Our combined analyses support a new classification of orangutans into three extant species. The new species, Pongo tapanuliensis, encompasses the Batang Toru population, of which fewer than 800 individuals survive. VIDEO ABSTRACT.

Unbiased Mitoproteome Analyses Confirm Non-canonical RNA, Expanded Codon Translations

Proteomic MS/MS mass spectrometry detections are usually biased towards peptides cleaved by experimentally added digestion enzyme(s). Hence peptides resulting from spontaneous degradation and natural proteolysis usually remain undetected. Previous analyses of tryptic human proteome data (cleavage after K, R) detected non-canonical tryptic peptides translated according to tetra- and pentacodons (codons expanded by silent mono- and dinucleotides), and from transcripts systematically (a) deleting mono-, dinucleotides after trinucleotides (delRNAs), (b) exchanging nucleotides according to 23 bijective transformations. Nine symmetric and fourteen asymmetric nucleotide exchanges (X ↔ Y, e.g. A ↔ C; and X → Y → Z → X, e.g. A → C → G → A) produce swinger RNAs. Here unbiased reanalyses of these proteomic data detect preferentially non-canonical tryptic peptides despite assuming random cleavage. Unbiased analyses couldn't reconstruct experimental tryptic digestion if most detected non-canonical peptides were false positives. Detected non-tryptic non-canonical peptides map preferentially on corresponding, previously described non-canonical transcripts, as for tryptic non-canonical peptides. Hence unbiased analyses independently confirm previous trypsin-biased analyses that showed translations of del- and swinger RNA and expanded codons. Accounting for natural proteolysis completes trypsin-biased mitopeptidome analyses, independently confirms non-canonical transcriptions and translations.

Chimeric mitochondrial peptides from contiguous regular and swinger RNA

Previous mass spectrometry analyses described human mitochondrial peptides entirely translated from swinger RNAs, RNAs where polymerization systematically exchanged nucleotides. Exchanges follow one among 23 bijective transformation rules, nine symmetric exchanges (X ↔ Y, e.g. A ↔ C) and fourteen asymmetric exchanges (X → Y → Z → X, e.g. A → C → G → A), multiplying by 24 DNA's protein coding potential. Abrupt switches from regular to swinger polymerization produce chimeric RNAs. Here, human mitochondrial proteomic analyses assuming abrupt switches between regular and swinger transcriptions, detect chimeric peptides, encoded by part regular, part swinger RNA. Contiguous regular- and swinger-encoded residues within single peptides are stronger evidence for translation of swinger RNA than previously detected, entirely swinger-encoded peptides: regular parts are positive controls matched with contiguous swinger parts, increasing confidence in results. Chimeric peptides are 200 × rarer than swinger peptides (3/100,000 versus 6/1000). Among 186 peptides with > 8 residues for each regular and swinger parts, regular parts of eleven chimeric peptides correspond to six among the thirteen recognized, mitochondrial protein-coding genes. Chimeric peptides matching partly regular proteins are rarer and less expressed than chimeric peptides matching non-coding sequences, suggesting targeted degradation of misfolded proteins. Present results strengthen hypotheses that the short mitogenome encodes far more proteins than hitherto assumed. Entirely swinger-encoded proteins could exist.

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Chimeric peptides are translated from contiguous regular and swinger RNA

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They are 200x rarer than mitochondrial swinger peptides

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Chimeric peptides integrated in regular mitochondrial proteins are downregulated

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Contiguous regular parts are matched positive controls for swinger parts

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The last point validates results beyond other statistical tests for robustness

Looking back on a decade of barcoding crustaceans

Species identification represents a pivotal component for large-scale biodiversity studies and conservation planning but represents a challenge for many taxa when using morphological traits only. Consequently, alternative identification methods based on molecular markers have been proposed. In this context, DNA barcoding has become a popular and accepted method for the identification of unknown animals across all life stages by comparison to a reference library. In this review we examine the progress of barcoding studies for the Crustacea using the Web of Science data base from 2003 to 2014. All references were classified in terms of taxonomy covered, subject area (identification/library, genetic variability, species descriptions, phylogenetics, methods, pseudogenes/numts), habitat, geographical area, authors, journals, citations, and the use of the Barcode of Life Data Systems (BOLD). Our analysis revealed a total number of 164 barcoding studies for crustaceans with a preference for malacostracan crustaceans, in particular Decapoda, and for building reference libraries in order to identify organisms. So far, BOLD did not establish itself as a popular informatics platform among carcinologists although it offers many advantages for standardized data storage, analyses and publication.

Rampant nuclear insertion of mtDNA across diverse lineages within Orthoptera (Insecta)

Nuclear mitochondrial pseudogenes (numts) are non-functional fragments of mtDNA inserted into the nuclear genome. Numts are prevalent across eukaryotes and a positive correlation is known to exist between the number of numts and the genome size. Most numt surveys have relied on model organisms with fully sequenced nuclear genomes, but such analyses have limited utilities for making a generalization about the patterns of numt accumulation for any given clade. Among insects, the order Orthoptera is known to have the largest nuclear genome and it is also reported to include several species with a large number of numts. In this study, we use Orthoptera as a case study to document the diversity and abundance of numts by generating numts of three mitochondrial loci across 28 orthopteran families, representing the phylogenetic diversity of the order. We discover that numts are rampant in all lineages, but there is no discernable and consistent pattern of numt accumulation among different lineages. Likewise, we do not find any evidence that a certain mitochondrial gene is more prone to nuclear insertion than others. We also find that numt insertion must have occurred continuously and frequently throughout the diversification of Orthoptera. Although most numts are the result of recent nuclear insertion, we find evidence of very ancient numt insertion shared by highly divergent families dating back to the Jurassic period. Finally, we discuss several factors contributing to the extreme prevalence of numts in Orthoptera and highlight the importance of exploring the utility of numts in evolutionary studies.

Identification of species-specific nuclear insertions of mitochondrial DNA (numts) in gorillas and their potential as population genetic markers

The first hyper-variable region (HV1) of the mitochondrial control region (MCR) has been widely used as a molecular tool in population genetics, but inadvertent amplification of nuclear translocated copies of mitochondrial DNA (numts) in gorillas has compromised the use of mitochondrial DNA in population genetic studies. At least three putative classes (I, II, III) of gorilla-specific HV1 MCR numts have been uncovered over the past decade. However, the number, size and location of numt loci in gorillas and other apes are completely unknown. Furthermore, little work to date has assessed the utility of numts as candidate population genetic markers. In the present study, we screened Bacterial Artificial Chromosome (BAC) genomic libraries in the chimpanzee and gorilla to compare patterns of mitochondrial-wide insertion in both taxa. We conducted an intensive BLAST search for numts in the gorilla genome and compared the prevalence of numt loci originating from the MCR with other great ape taxa. Additional gorilla-specific MCR numts were retrieved either through BAC library screens or using an anchored-PCR (A-PCR) amplification using genomic DNA from five unrelated gorillas. Locus-specific primers were designed to identify numt insertional polymorphisms and evaluate their potential as population genetic markers. Mitochondrial-wide surveys of chimpanzee and gorilla BACs showed that the number of numts does not differ between these two taxa. However, MCR numts are more abundant in chimpanzees than in other great apes. We identified and mapped 67 putative gorilla-specific numts, including two that contain the entire HV1 domain, cluster with sequences from two numt classes (I, IIb) and will likely co-amplify with mitochondrial sequences using most published HV1 primers. However, phylogenetic analysis coupled with post-hoc analysis of mitochondrial variation can successfully differentiate nuclear sequences. Insertional polymorphisms were evident in three out of five numts examined, indicating their potential utility as molecular markers. Taken together, these findings demonstrate the potentially powerful insight that numts could make in uncovering population history in gorillas and other mammals.

Complete mitochondrial genome sequence of the Eastern gorilla (Gorilla beringei) and implications for african ape biogeography

The Western and Eastern species of gorillas (Gorilla gorilla and Gorilla beringei) began diverging in the mid-Pleistocene, but in a complex pattern with ongoing gene flow following their initial split. We sequenced the complete mitochondrial genomes of 1 Eastern and 1 Western gorilla to provide the most accurate date for their mitochondrial divergence, and to analyze patterns of nucleotide substitutions. The most recent common ancestor of these genomes existed about 1.9 million years ago, slightly more recent than that of chimpanzee and bonobo. We in turn use this date as a calibration to reanalyze sequences from the Eastern lowland and mountain gorilla subspecies to estimate their mitochondrial divergence at approximately 380000 years ago. These dates help frame a hypothesis whereby populations became isolated nearly 2 million years ago with restricted maternal gene flow, followed by ongoing male migration until the recent past. This process of divergence with prolonged hybridization occurred against the backdrop of the African Pleistocene, characterized by intense fluctuations in temperature and aridity, while at the same time experiencing tectonic uplifting and consequent shifts in the drainage of major river systems. Interestingly, this same pattern of introgression following divergence and discrepancies between mitochondrial and nuclear loci is seen in fossil hominins from Eurasia, suggesting that such processes may be common in hominids and that living gorillas may provide a useful model for understanding isolation and migration in our extinct relatives.

Heteroplasmy and ancient translocation of mitochondrial DNA to the nucleus in the Chinese Horseshoe Bat (Rhinolophus sinicus) complex

The utility and reliability of mitochondrial DNA sequences in phylogenetic and phylogeographic studies may be compromised by widespread and undetected nuclear mitochondrial copies (numts) as well as heteroplasmy within individuals. Both numts and heteroplasmy are likely to be common across diverse taxa yet few studies have characterised their frequencies and variation at the intra-specific level. Here we report the presence of both numts and heteroplasmy in the mitochondrial control region of the Chinese horseshoe bat Rhinolophus sinicus. In total we generated 123 sequences from 18 bats, which contained two different numt clades (i.e. Numt-1 and Numt-2) and one mtDNA clade. The sequence divergence between Numt-1 and Numt-2 was 16.8% and each numt type was found in all four R. sinicus taxa, suggesting either two ancient translocations of mitochondrial DNA into the nucleus from the same source taxon, or a single translocation from different source taxa that occurred before the split of R. sinicus into different lineages. Within the mtDNA clade, phylogenetic relationships among the four taxa of R. sinicus were similar to those seen in previous results. Based on PCR comparisons, heteroplasmy was inferred between almost all individuals of R. sinicus with respect to sequence variation. Consistent with introgression of mtDNA between Central sinicus and septentrionalis, individuals from these two taxa exhibited similar signatures of repeated sequences in the control region. Our study highlights the importance of testing for the presence of numts and heteroplasmy when applying mtDNA markers to phylogenetic studies.

A genome-wide survey of genetic variation in gorillas using reduced representation sequencing

All non-human great apes are endangered in the wild, and it is therefore important to gain an understanding of their demography and genetic diversity. Whole genome assembly projects have provided an invaluable foundation for understanding genetics in all four genera, but to date genetic studies of multiple individuals within great ape species have largely been confined to mitochondrial DNA and a small number of other loci. Here, we present a genome-wide survey of genetic variation in gorillas using a reduced representation sequencing approach, focusing on the two lowland subspecies. We identify 3,006,670 polymorphic sites in 14 individuals: 12 western lowland gorillas (Gorilla gorilla gorilla) and 2 eastern lowland gorillas (Gorilla beringei graueri). We find that the two species are genetically distinct, based on levels of heterozygosity and patterns of allele sharing. Focusing on the western lowland population, we observe evidence for population substructure, and a deficit of rare genetic variants suggesting a recent episode of population contraction. In western lowland gorillas, there is an elevation of variation towards telomeres and centromeres on the chromosomal scale. On a finer scale, we find substantial variation in genetic diversity, including a marked reduction close to the major histocompatibility locus, perhaps indicative of recent strong selection there. These findings suggest that despite their maintaining an overall level of genetic diversity equal to or greater than that of humans, population decline, perhaps associated with disease, has been a significant factor in recent and long-term pressures on wild gorilla populations.

Historical sampling reveals dramatic demographic changes in western gorilla populations

BACKGROUND

Today many large mammals live in small, fragmented populations, but it is often unclear whether this subdivision is the result of long-term or recent events. Demographic modeling using genetic data can estimate changes in long-term population sizes while temporal sampling provides a way to compare genetic variation present today with that sampled in the past. In order to better understand the dynamics associated with the divergences of great ape populations, these analytical approaches were applied to western gorillas (Gorilla gorilla) and in particular to the isolated and Critically Endangered Cross River gorilla subspecies (G. g. diehli).

RESULTS

We used microsatellite genotypes from museum specimens and contemporary samples of Cross River gorillas to infer both the long-term and recent population history. We find that Cross River gorillas diverged from the ancestral western gorilla population ~17,800 years ago (95% HDI: 760, 63,245 years). However, gene flow ceased only ~420 years ago (95% HDI: 200, 16,256 years), followed by a bottleneck beginning ~320 years ago (95% HDI: 200, 2,825 years) that caused a 60-fold decrease in the effective population size of Cross River gorillas. Direct comparison of heterozygosity estimates from museum and contemporary samples suggests a loss of genetic variation over the last 100 years.

CONCLUSIONS

The composite history of western gorillas could plausibly be explained by climatic oscillations inducing environmental changes in western equatorial Africa that would have allowed gorilla populations to expand over time but ultimately isolate the Cross River gorillas, which thereafter exhibited a dramatic population size reduction. The recent decrease in the Cross River population is accordingly most likely attributable to increasing anthropogenic pressure over the last several hundred years. Isolation of diverging populations with prolonged concomitant gene flow, but not secondary admixture, appears to be a typical characteristic of the population histories of African great apes, including gorillas, chimpanzees and bonobos.

Elucidating population histories using genomic DNA sequences

In 1993, Cliff Jolly suggested that rather than debating species definitions and classifications, energy would be better spent investigating multidimensional patterns of variation and gene flow among populations. Until now, however, genetic studies of wild primate populations have been limited to very small portions of the genome. Access to complete genome sequences of humans, chimpanzees, macaques, and other primates makes it possible to design studies surveying substantial amounts of DNA sequence variation at multiple genetic loci in representatives of closely related but distinct wild primate populations. Such data can be analyzed with new approaches that estimate not only when populations diverged but also the relative amounts and directions of subsequent gene flow. These analyses will reemphasize the difficulty of achieving consistent species and subspecies definitions by revealing the extent of variation in the amount and duration of gene flow accompanying population divergences.

Testing mitochondrial sequences and anonymous nuclear markers for phylogeny reconstruction in a rapidly radiating group: molecular systematics of the Delphininae (Cetacea: Odontoceti: Delphinidae)

BACKGROUND

Many molecular phylogenetic analyses rely on DNA sequence data obtained from single or multiple loci, particularly mitochondrial DNA loci. However, phylogenies for taxa that have undergone recent, rapid radiation events often remain unresolved. Alternative methodologies for discerning evolutionary relationships under these conditions are desirable. The dolphin subfamily Delphininae is a group that has likely resulted from a recent and rapid radiation. Despite several efforts, the evolutionary relationships among the species in the subfamily remain unclear.

RESULTS

Here, we compare a phylogeny estimated using mitochondrial DNA (mtDNA) control region sequences to a multi-locus phylogeny inferred from 418 polymorphic genomic markers obtained from amplified fragment length polymorphism (AFLP) analysis. The two sets of phylogenies are largely incongruent, primarily because the mtDNA tree provides very poor resolving power; very few species' nodes in the tree are supported by bootstrap resampling. The AFLP phylogeny is considerably better resolved and more congruent with relationships inferred from morphological data. Both phylogenies support paraphyly for the genera Stenella and Tursiops. The AFLP data indicate a close relationship between the two spotted dolphin species and recent ancestry between Stenella clymene and S. longirostris. The placement of the Lagenodelphis hosei lineage is ambiguous: phenetic analysis of the AFLP data is consistent with morphological expectations but the phylogenetic analysis is not.

CONCLUSION

For closely related, recently diverged taxa, a multi-locus genome-wide survey is likely the most comprehensive approach currently available for phylogenetic inference.

Morphological and molecular evidence reveals recent hybridization between gorilla taxa

Molecular studies have demonstrated a deep lineage split between the two gorilla species, as well as divisions within these taxa; estimates place this divergence in the mid-Pleistocene, with gene flow continuing until approximately 80,000 years ago. Here, we present analyses of skeletal data indicating the presence of substantial recent gene flow among gorillas at all taxonomic levels: between populations, subspecies, and species. Complementary analyses of DNA sequence variation suggest that low-level migration occurred primarily in a westerly-to-easterly direction. In western gorillas, the locations of hybrid phenotypes map closely to expectations based on population refugia and riverine barrier hypotheses, supporting the presence of significant vicariance-driven structuring and occasional admixture within this taxon. In eastern lowland gorillas, the high frequency of hybrid phenotypes is surprising, suggesting that this region represents a zone of introgression between eastern gorillas and migrants from the west, and underscoring the conservation priority of this critically endangered group. These results highlight the complex nature of evolutionary divergence in this genus, indicate that historical gene flow has played a major role in structuring gorilla diversity, and demonstrate that our understanding of the evolutionary processes responsible for shaping biodiversity can benefit immensely from consideration of morphological and molecular data in conjunction.

Mitochondrial pseudogenes in the nuclear genome of Aedes aegypti mosquitoes: implications for past and future population genetic studies

Background

Mitochondrial DNA (mtDNA) is widely used in population genetic and phylogenetic studies in animals. However, such studies can generate misleading results if the species concerned contain nuclear copies of mtDNA (Numts) as these may amplify in addition to, or even instead of, the authentic target mtDNA. The aim of this study was to determine if Numts are present in Aedes aegypti mosquitoes, to characterise any Numts detected, and to assess the utility of using mtDNA for population genetics studies in this species.

Results

BLAST searches revealed large numbers of Numts in the Ae. aegypti nuclear genome on 146 supercontigs. Although the majority are short (80% < 300 bp), some Numts are almost full length mtDNA copies. These long Numts are not due to misassembly of the nuclear genome sequence as the Numt-nuclear genome junctions could be recovered by amplification and sequencing. Numt evolution appears to be a complex process in Ae. aegypti with ongoing genomic integration, fragmentation and mutation and the secondary movement of Numts within the nuclear genome.

The PCR amplification of the putative mtDNA nicotinamide adenine dinucleotide dehydrogenase subunit 4 (ND4) gene from 166 Southeast Asian Ae. aegypti mosquitoes generated a network with two highly divergent lineages (clade 1 and clade 2). Approximately 15% of the ND4 sequences were a composite of those from each clade indicating Numt amplification in addition to, or instead of, mtDNA. Clade 1 was shown to be composed at least partially of Numts by the removal of clade 1-specific bases from composite sequences following enrichment of the mtDNA. It is possible that all the clade 1 sequences in the network were Numts since the clade 2 sequences correspond to the known mitochondrial genome sequence and since all the individuals that produced clade 1 sequences were also found to contain clade 2 mtDNA-like sequences using clade 2-specific primers. However, either or both sets of clade sequences could have Numts since the BLAST searches revealed two long Numts that match clade 2 and one long Numt that matches clade 1. The substantial numbers of mutations in cloned ND4 PCR products also suggest there are both recently-derived clade 1 and clade 2 Numt sequences.

Conclusion

We conclude that Numts are prevalent in Ae. aegypti and that it is difficult to distinguish mtDNA sequences due to the presence of recently formed Numts. Given this, future population genetic or phylogenetic studies in Ae. aegypti should use nuclear, rather than mtDNA, markers.

Mitochondrial COII Introgression into the Nuclear Genome of Gorilla gorilla

Numts are nonfunctional mitochondrial sequences that have translocated into nuclear DNA, where they evolve independently from the original mitochondrial DNA (mtDNA) sequence. Numts can be unintentionally amplified in addition to authentic mtDNA, complicating both the analysis and interpretation of mtDNA-based studies. Amplification of numts creates particular issues for studies on the noncoding, hypervariable 1 mtDNA region of gorillas. We provide data on putative numt sequences of the coding mitochondrial gene cytochrome oxidase subunit II (COII). Via polymerase chain reaction (PCR) and cloning, we obtained COII sequences for gorilla, orangutan, and human high-quality DNA and also from a gorilla fecal DNA sample. Both gorilla and orangutan samples yielded putative numt sequences. Phylogenetically more anciently transferred numts were amplified with a greater incidence from the gorilla fecal DNA sample than from the high-quality gorilla sample. Data on phylogenetically more recently transferred numts are equivocal. We further demonstrate the need for additional investigations into the use of mtDNA markers for noninvasively collected samples from gorillas and other primates.

Phylogeography and population structure of the Yunnan snub-nosed monkey (Rhinopithecus bieti) inferred from mitochondrial control region DNA sequence analysis

Rhinopithecus bieti, the Yunnan snub-nosed monkey, is the nonhuman primate with the highest altitudinal distribution and is also one of the 25 most globally endangered primate species. Currently, R. bieti is found in forests between 3000 and 4500 m above sea level, within a narrow area on the Tibetan Plateau between the Yangtze and Mekong rivers, where it is suffering from loss of habitat and shrinking population size (approximately 1500). To assess the genetic diversity within this species, its population structure and to infer its evolutionary history, we sequenced 401 bp of the hypervariable I (HVI) segment from the mitochondrial DNA control region (CR) for 157 individuals from 11 remnant patches throughout the fragmented distribution area. Fifty-two variable sites were observed and 30 haplotypes were defined. Compared with other primate species, R. bieti cannot be regarded as a taxon with low genetic diversity. Phylogenetic analysis partitioned haplotypes into two divergent haplogroups (A and B). Haplotypes from the two mitochondrial clades were found to be mixed in some patches although the distribution of haplotypes displayed local homogeneity, implying a strong population structure within R. bieti. Analysis of molecular variance detected significant differences among the different geographical regions, suggesting that R. bieti should be separated into three management units (MUs) for conservation. Based on our results, it can be hypothesized that the genetic history of R. bieti includes an initial, presumably allopatric divergence between clades A and B 1.0-0.7 million years ago (Ma), which might have been caused by the Late Cenozoic uplift of the Tibetan Plateau, secondary contact after this divergence as a result of a population expansion 0.16-0.05 Ma, and population reduction and habitat fragmentation in the very recent past.

Detection of mitochondrial insertions in the nucleus (NuMts) of Pleistocene and modern muskoxen

Background

Nuclear insertions of mitochondrial sequences (NuMts) have been identified in a wide variety of organisms. Trafficking of genetic material from the mitochondria to the nucleus has occurred frequently during mammalian evolution and can lead to the production of a large pool of sequences with varying degrees of homology to organellar mitochondrial DNA (mtDNA) sequences. This presents both opportunities and challenges for forensics, population genetics, evolutionary genetics, conservation biology and the study of DNA from ancient samples. Here we present a case in which difficulties in ascertaining the organellar mtDNA sequence from modern samples hindered their comparison to ancient DNA sequences.

Results

We obtained mitochondrial hypervariable region (HVR) sequences from six ancient samples of tundra muskox (Ovibos moschatus) that were reproducible but distinct from modern muskox sequences reported previously. Using the same PCR primers applied to the ancient specimens and the primers used to generate the modern muskox DNA sequences in a previous study, we failed to definitively identify the organellar sequence from the two modern muskox samples tested. Instead of anticipated sequence homogeneity, we obtained multiple unique sequences from both hair and blood of one modern specimen. Sequencing individual clones of a >1 kb PCR fragment from modern samples did not alleviate the problem as there was not a consistent match across the entire length of the sequences to Ovibos when compared to sequences in GenBank.

Conclusion

In specific taxa, due to nuclear insertions some regions of the mitochondrial genome may not be useful for the characterization of modern or ancient DNA.

Y-chromosome analysis confirms highly sex-biased dispersal and suggests a low male effective population size in bonobos (Pan paniscus)

Dispersal is a rare event that is difficult to observe in slowly maturing, long-lived wild animal species such as the bonobo. In this study we used sex-linked (mitochondrial DNA sequence and Y-chromosome microsatellite) markers from the same set of individuals to estimate the magnitude of difference in effective dispersal between the sexes and to investigate the long-term demographic history of bonobos. We sampled 34 males from four distinct geographical areas across the bonobo distribution range. As predicted for a female-dispersing species, we found much higher levels of differentiation among local bonobo populations based upon Y-chromosomal than mtDNA genetic variation. Specifically, almost all of the Y-chromosomal variation distinguished populations, while nearly all of the mtDNA variation was shared between populations. Furthermore, genetic distance correlated with geographical distance for mtDNA but not for the Y chromosome. Female bonobos have a much higher migration rate and/or effective population size as compared to males, and the estimate for the mitochondrial TMRCA (time to most recent common ancestor) was approximately 10 times greater than the estimate for the Y chromosome (410,000 vs. 40,000-45,000). For humans the difference is merely a factor of two, suggesting a more stable demographic history in bonobos in comparison to humans.

Origin, evolution and genetic effects of nuclear insertions of organelle DNA

In eukaryotes, nuclear genomes are subject to an influx of DNA from mitochondria and plastids. The nuclear insertion of organellar sequences can occur during the illegitimate repair of double-stranded breaks. After integration, nuclear organelle DNA is modified by point mutations, and by deletions. Insertion of organelle DNA into nuclear genes is not rare and can potentially have harmful effects. In humans, some insertions of nuclear mitochondrial DNA are associated with heritable diseases. It remains to be determined whether nuclear organelle DNA can contribute beneficially to gene evolution.

Discovery of a large number of previously unrecognized mitochondrial pseudogenes in fish genomes

Nuclear inserted copies of mitochondrial origin (numts) vary widely among eukaryotes, with human and plant genomes harboring the largest repertoires. Numts were previously thought to be absent from fish species, but the recent release of three fish nuclear genome sequences provides the resource to obtain a more comprehensive insight into the extent of mtDNA transfer in fishes. From the sequence analyses of the genomes of Fugu rubripes, Tetraodon nigroviridis, and Danio rerio, we have identified 2, 5, and 10 recent numt integrations, respectively, which integrated into those genomes less than 0.6 million years (Myr) ago. Such results contradict the hypothesis of absence or rarity of numts in fishes, as (i) the ratio of numts to the total size of the nuclear genome in T. nigroviridis was superior to the ratio observed in several higher vertebrate species (e.g., chicken, mouse, and rat), and only surpassed by humans, and (ii) the mtDNA coverage transferred to the nuclear genome of D. rerio is exceeded only by human and mouse, within the whole range of eukaryotic genomes surveyed for numts. Additionally, 335, 336, and 471 old numts (>12.5 Myr) were detected in F. rubripes, T. nigroviridis, and D. rerio, respectively. Surprisingly, old numts are inserted preferentially into known or predicted genes, as inferred for recent numts in human. However, because in fish genomes such integrations are old, they are likely to represent evolutionary successes and they may be considered a potential important evolutionary mechanism for the enhancement of genomic coding regions.