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Institute
Although many large mammal species went extinct at the end of the Pleistocene epoch, their DNA may persist due to past episodes of interspecies admixture. However, direct empirical evidence of the persistence of ancient alleles remains scarce. Here, we present multifold coverage genomic data from four Late Pleistocene cave bears (Ursus spelaeus complex) and show that cave bears hybridized with brown bears (Ursus arctos) during the Pleistocene. We develop an approach to assess both the directionality and relative timing of gene flow. We find that segments of cave bear DNA still persist in the genomes of living brown bears, with cave bears contributing 0.9 to 2.4% of the genomes of all brown bears investigated. Our results show that even though extinction is typically considered as absolute, following admixture, fragments of the gene pool of extinct species can survive for tens of thousands of years in the genomes of extant recipient species.
Targeted capture coupled with high-throughput sequencing can be used to gain information about nuclear sequence variation at hundreds to thousands of loci. Divergent reference capture makes use of molecular data of one species to enrich target loci in other (related) species. This is particularly valuable for nonmodel organisms, for which often no a priori knowledge exists regarding these loci. Here, we have used targeted capture to obtain data for 809 nuclear coding DNA sequences (CDS) in a nonmodel organism, the Eurasian lynx Lynx lynx, using baits designed with the help of the published genome of a related model organism (the domestic cat Felis catus). Using this approach, we were able to survey intraspecific variation at hundreds of nuclear loci in L. lynx across the species’ European range. A large set of biallelic candidate SNPs was then evaluated using a high-throughput SNP genotyping platform (Fluidigm), which we then reduced to a final 96 SNP-panel based on assay performance and reliability; validation was carried out with 100 additional Eurasian lynx samples not included in the SNP discovery phase. The 96 SNP-panel developed from CDS performed very successfully in the identification of individuals and in population genetic structure inference (including the assignment of individuals to their source population). In keeping with recent studies, our results show that genic SNPs can be valuable for genetic monitoring of wildlife species.
The prevalence of contaminant microbial DNA in ancient bone samples represents the principal limiting factor for palaeogenomic studies, as it may comprise more than 99% of DNA molecules obtained. Efforts to exclude or reduce this contaminant fraction have been numerous but also variable in their success. Here, we present a simple but highly effective method to increase the relative proportion of endogenous molecules obtained from ancient bones. Using computed tomography (CT) scanning, we identify the densest region of a bone as optimal for sampling. This approach accurately identifies the densest internal regions of petrous bones, which are known to be a source of high-purity ancient DNA. For ancient long bones, CT scans reveal a high-density outermost layer, which has been routinely removed and discarded prior to DNA extraction. For almost all long bones investigated, we find that targeted sampling of this outermost layer provides an increase in endogenous DNA content over that obtained from softer, trabecular bone. This targeted sampling can produce as much as 50-fold increase in the proportion of endogenous DNA, providing a directly proportional reduction in sequencing costs for shotgun sequencing experiments. The observed increases in endogenous DNA proportion are not associated with any reduction in absolute endogenous molecule recovery. Although sampling the outermost layer can result in higher levels of human contamination, some bones were found to have more contamination associated with the internal bone structures. Our method is highly consistent, reproducible and applicable across a wide range of bone types, ages and species. We predict that this discovery will greatly extend the potential to study ancient populations and species in the genomics era.
Being at the western fringe of Europe, Iberia had a peculiar prehistory and a complex pattern of Neolithization. A few studies, all based on modern populations, reported the presence of DNA of likely African origin in this region, generally concluding it was the result of recent gene flow, probably during the Islamic period. Here, we provide evidence of much older gene flow from Africa to Iberia by sequencing whole genomes from four human remains from northern Portugal and southern Spain dated around 4000 years BP (from the Middle Neolithic to the Bronze Age). We found one of them to carry an unequivocal sub-Saharan mitogenome of most probably West or West-Central African origin, to our knowledge never reported before in prehistoric remains outside Africa. Our analyses of ancient nuclear genomes show small but significant levels of sub-Saharan African affinity in several ancient Iberian samples, which indicates that what we detected was not an occasional individual phenomenon, but an admixture event recognizable at the population level. We interpret this result as evidence of an early migration process from Africa into the Iberian Peninsula through a western route, possibly across the Strait of Gibraltar.
Objective
Plant carnivory is distributed across the tree of life and has evolved at least six times independently, but sequenced and annotated nuclear genomes of carnivorous plants are currently lacking. We have sequenced and structurally annotated the nuclear genome of the carnivorous Roridula gorgonias and that of a non-carnivorous relative, Madeira’s lily-of-the-valley-tree, Clethra arborea, both within the Ericales. This data adds an important resource to study the evolutionary genetics of plant carnivory across angiosperm lineages and also for functional and systematic aspects of plants within the Ericales.
Results
Our assemblies have total lengths of 284 Mbp (R. gorgonias) and 511 Mbp (C. arborea) and show high BUSCO scores of 84.2% and 89.5%, respectively. We used their predicted genes together with publicly available data from other Ericales’ genomes and transcriptomes to assemble a phylogenomic data set for the inference of a species tree. However, groups of orthologs showed a marked absence of species represented by a transcriptome. We discuss possible reasons and caution against combining predicted genes from genome- and transriptome-based assemblies.
Comparing mitogenomic timetrees for two African savannah primate genera (Chlorocebus and Papio)
(2017)
Complete mitochondrial (mtDNA) genomes have proved to be useful in reconstructing primate phylogenies with higher resolution and confidence compared to reconstructions based on partial mtDNA sequences. Here, we analyse complete mtDNA genomes of African green monkeys (genus Chlorocebus), a widely distributed primate genus in Africa representing an interesting phylogeographical model for the evolution of savannah species. Previous studies on partial mtDNA sequences revealed nine major clades, suggesting several cases of para- and polyphyly among Chlorocebus species. However, in these studies, phylogenetic relationships among several clades were not resolved, and divergence times were not estimated. We analysed complete mtDNA genomes for ten Chlorocebus samples representing major mtDNA clades to find stronger statistical support in the phylogenetic reconstruction than in the previous studies and to estimate divergence times. Our results confirmed para- and polyphyletic relationships of most Chlorocebus species, while the support for the phylogenetic relationships between the mtDNA clades increased compared to the previous studies. Our results indicate an initial west-east division in the northern part of the Chlorocebus range with subsequent divergence into north-eastern and southern clades. This phylogeographic scenario contrasts with that for another widespread African savannah primate genus, the baboons (Papio), for which a dispersal from southern Africa into East and West Africa was suggested.
Molecular identification of late and terminal Pleistocene Equus ovodovi from northeastern China
(2019)
The extant diversity of horses (family Equidae) represents a small fraction of that occurring over their evolutionary history. One such lost lineage is the subgenus Sussemionus, which is thought to have become extinct during the Middle Pleistocene. However, recent molecular studies and morphological analysis have revealed that one of their representatives, E. ovodovi, did exist in Siberia during the Late Pleistocene. Fossil materials of E. ovodovi have thus far only been found in Russia. In this study, we extracted DNA from three equid fossil specimens excavated from northeastern China dated at 12,770-12,596, 29,525-28,887 and 40,201-38,848 cal. yBP, respectively, and retrieved three near-complete mitochondrial genomes from the specimens. Phylogenetic analyses cluster the Chinese haplotypes together with previously published Russian E. ovodovi, strongly supporting the assignment of these samples to this taxon. The molecular identification of E. ovodovi in northeastern China extends the known geographical range of this fossil species by several thousand kilometers to the east. The estimated coalescence time of all E. ovodovi haplotypes is approximately 199 Kya, with the Chinese haplotypes coalescing approximately 130 Kya. With a radiocarbon age of 12,770-12,596 cal. yBP, the youngest sample in this study represents the first E. ovodovi sample dating to the terminal Pleistocene, moving the extinction date of this species forwards considerably compared to previously documented fossils. Overall, comparison of our three mitochondrial genomes with the two published ones suggests a genetic diversity similar to several extant species of the genus Equus.
Historically, the giant panda was widely distributed from northern China to southwestern Asia [1]. As a result of range contraction and fragmentation, extant individuals are currently restricted to fragmented mountain ranges on the eastern margin of the Qinghai-Tibet plateau, where they are distributed among three major population clusters [2]. However, little is known about the genetic consequences of this dramatic range contraction. For example, were regions where giant pandas previously existed occupied by ancestors of present-day populations, or were these regions occupied by genetically distinct populations that are now extinct? If so, is there any contribution of these extinct populations to the genomes of giant pandas living today? To investigate these questions, we sequenced the nuclear genome of an similar to 5,000-year-old giant panda from Jiangdongshan, Teng-chong County in Yunnan Province, China. We find that this individual represents a genetically distinct population that diverged prior to the diversification of modern giant panda populations. We find evidence of differential admixture with this ancient population among modern individuals originating from different populations as well as within the same population. We also find evidence for directional gene flow, which transferred alleles from the ancient population into the modern giant panda lineages. A variable proportion of the genomes of extant individuals is therefore likely derived from the ancient population represented by our sequenced individual. Although extant giant panda populations retain reasonable genetic diversity, our results suggest that this represents only part of the genetic diversity this species harbored prior to its recent range contractions.
Horse domestication revolutionized warfare and accelerated travel, trade, and the geographic expansion of languages. Here, we present the largest DNA time series for a non-human organism to date, including genome-scale data from 149 ancient animals and 129 ancient genomes (>= 1-fold coverage), 87 of which are new. This extensive dataset allows us to assess the modem legacy of past equestrian civilisations. We find that two extinct horse lineages existed during early domestication, one at the far western (Iberia) and the other at the far eastern range (Siberia) of Eurasia. None of these contributed significantly to modern diversity. We show that the influence of Persian-related horse lineages increased following the Islamic conquests in Europe and Asia. Multiple alleles associated with elite-racing, including at the MSTN "speed gene," only rose in popularity within the last millennium. Finally, the development of modem breeding impacted genetic diversity more dramatically than the previous millennia of human management.
As limits on O2 availability during submergence impose severe constraints on aerobic respiration, the oxygen binding globin proteins of marine mammals are expected to have evolved under strong evolutionary pressures during their land-to-sea transition. Here, we address this question for the order Sirenia by retrieving, annotating, and performing detailed selection analyses on the globin repertoire of the extinct Steller’s sea cow (Hydrodamalis gigas), dugong (Dugong dugon), and Florida manatee (Trichechus manatus latirostris) in relation to their closest living terrestrial relatives (elephants and hyraxes). These analyses indicate most loci experienced elevated nucleotide substitution rates during their transition to a fully aquatic lifestyle. While most of these genes evolved under neutrality or strong purifying selection, the rate of nonsynonymous/synonymous replacements increased in two genes (Hbz-T1 and Hba-T1) that encode the α-type chains of hemoglobin (Hb) during each stage of life. Notably, the relaxed evolution of Hba-T1 is temporally coupled with the emergence of a chimeric pseudogene (Hba-T2/Hbq-ps) that contributed to the tandemly linked Hba-T1 of stem sirenians via interparalog gene conversion. Functional tests on recombinant Hb proteins from extant and ancestral sirenians further revealed that the molecular remodeling of Hba-T1 coincided with increased Hb–O2 affinity in early sirenians. Available evidence suggests that this trait evolved to maximize O2 extraction from finite lung stores and suppress tissue O2 offloading, thereby facilitating the low metabolic intensities of extant sirenians. In contrast, the derived reduction in Hb–O2 affinity in (sub)Arctic Steller’s sea cows is consistent with fueling increased thermogenesis by these once colossal marine herbivores.