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BACKGROUND: Titi monkeys, Callicebus, comprise the most species-rich primate genus—34 species are currently recognised, five of them described since 2005. The lack of molecular data for titi monkeys has meant that little is known of their phylogenetic relationships and divergence times. To clarify their evolutionary history, we assembled a large molecular dataset by sequencing 20 nuclear and two mitochondrial loci for 15 species, including representatives from all recognised species groups. Phylogenetic relationships were inferred using concatenated maximum likelihood and Bayesian analyses, allowing us to evaluate the current taxonomic hypothesis for the genus. RESULTS: Our results show four distinct Callicebus clades, for the most part concordant with the currently recognised morphological species-groups—the torquatus group, the personatus group, the donacophilus group, and the moloch group. The cupreus and moloch groups are not monophyletic, and all species of the formerly recognized cupreus group are reassigned to the moloch group. Two of the major divergence events are dated to the Miocene. The torquatus group, the oldest radiation, diverged c. 11 Ma; and the Atlantic forest personatus group split from the ancestor of all donacophilus and moloch species at 9–8 Ma. There is little molecular evidence for the separation of Callicebus caligatus and C. dubius, and we suggest that C. dubius should be considered a junior synonym of a polymorphic C. caligatus. CONCLUSIONS: Considering molecular, morphological and biogeographic evidence, we propose a new genus level taxonomy for titi monkeys: Cheracebus n. gen. in the Orinoco, Negro and upper Amazon basins (torquatus group), Callicebus Thomas, 1903, in the Atlantic Forest (personatus group), and Plecturocebus n. gen. in the Amazon basin and Chaco region (donacophilus and moloch groups).

The platyrrhine family Cebidae (capuchin and squirrel monkeys) exhibit among the largest primate encephalization quotients. Each cebid lineage is also characterized by notable lineage-specific traits, with capuchins showing striking similarities to Hominidae such as high sensorimotor intelligence with tool use, advanced cognitive abilities, and behavioral flexibility. Here, we take a comparative genomics approach, performing genome-wide tests for positive selection across five cebid branches, to gain insight into major periods of cebid adaptive evolution. We uncover candidate targets of selection across cebid evolutionary history that may underlie the emergence of lineage-specific traits. Our analyses highlight shifting and sustained selective pressures on genes related to brain development, longevity, reproduction, and morphology, including evidence for cumulative and diversifying neurobiological adaptations across cebid evolution. In addition to generating a high-quality reference genome assembly for robust capuchins, our results lend to a better understanding of the adaptive diversification of this distinctive primate clade.

Platyrrhine primate taxonomy is a rapidly evolving area of research. The recent description of the Parecis titi monkey, Plecturocebus parecis, has raised substantial questions regarding the taxonomy, distribution, and evolutionary history of titi taxa from south-central Amazonia. There is only a single documented record of P. parecis, which is the type locality, with uncertainty regarding species monophyly. Moreover, there are questions surrounding the distribution and pelage patterns of the poorly studied P. cinerascens and P. parecis, which further highlight the uncertainty regarding the taxonomic validity of this new species. Here, we investigate the taxonomy, distribution, and evolutionary history of these lineages through new field work and assessment of pelage pigmentation patterns from 25 localities, as well as maximum likelihood and Bayesian phylogenetic reconstructions based on two mitochondrial and 11 nuclear loci for 19 and 10 specimens of Plecturocebus, respectively. Our mitochondrial results recover a paraphyletic arrangement for the four P. parecis type specimens that show three distinct haplotypes, with the holotype showing a close affinity to P. bernhardi. Our morphological analysis reveals a north–south clinal bleaching gradient through the Aripuanã-Sucundurí/Juruena interfluve from an all-grayish morphotype associated with P. cinerascens, through intermediary morphotypes with increasingly whitish hairs on the beard, hands, feet, and tail, to the most whitish morphotype described as P. parecis. Based on these findings, we present hypotheses to explain the taxonomy, distribution, and evolutionary history of P. cinerascens and P. parecis and discuss the significance of introgression among titi taxa from southern Amazonia given the lack of study systems for natural hybridization in platyrrhine primates.

The pygmy marmoset, the smallest of the anthropoid primates, has a broad distribution in Western Amazonia. Recent studies using molecular and morphological data have identified two distinct species separated by the Napo and SolimöesAmazonas rivers. However, reconciling this new biological evidence with current taxonomy, i.e., two subspecies, Cebuella pygmaea pygmaea (Spix, 1823) and Cebuella pygmaea niveiventris (Lönnberg, 1940), was problematic given the uncertainty as to whether Spix's pygmy marmoset (Cebuella pygmaea pygmaea) was collected north or south of the Napo and Solimöes-Amazonas rivers, making it unclear to which of the two newly revealed species the name pygmaea would apply. Here, we present the first molecular data from Spix's type specimen of Cebuella pygmaea, as well as novel mitochondrial genomes from modern pygmy marmosets sampled near the type locality (Tabatinga) on both sides of the river. With these data, we can confirm the correct names of the two species identified, i.e., C. pygmaea for animals north of the Napo and SolimöesAmazonas rivers and C. niveiventris for animals south of these two rivers. Phylogenetic analyses of the novel genetic data placed into the context of cytochrome b gene sequences from across the range of pygmy marmosets further led us to reevaluate the geographical distribution for the two Cebuella species. We dated the split of these two species to 2.54 million years ago. We discuss additional, more recent, subdivisions within each lineage, as well as potential contact zones between the two species in the headwaters of these rivers.

Abstract The family Cebidae (capuchin and squirrel monkeys) form a remarkable platyrrhine clade exhibiting among the largest primate encephalisation quotients. Each cebid lineage is characterised by notable lineage-specific traits, with capuchins showing striking similarities to Hominidae including high sensorimotor intelligence with tool use, advanced cognitive abilities, and behavioural flexibility. Here, we take a comparative genomics approach, analysing five cebid branches including successive lineages, to infer a stepwise timeline for cebid adaptive evolution. We uncover candidate targets of selection across various periods of cebid evolution that may underlie the emergence of lineage-specific traits. Our analyses highlight shifting and sustained selective pressures on genes related to brain development, longevity, reproduction, and morphology, including evidence for cumulative and diversifying neurobiological adaptations over cebid evolutionary history. In addition to generating a new, high-quality reference genome assembly for robust capuchins, our results lend to a better understanding of the adaptive diversification of this distinctive primate clade. Competing Interest Statement The authors have declared no competing interest. Footnotes * https://doi.org/10.5281/zenodo.5225106

The rich diversity of morphology and behavior displayed across primate species provides an informative context in which to study the impact of genomic diversity on fundamental biological processes. Analysis of that diversity provides insight into long-standing questions in evolutionary and conservation biology, and is urgent given severe threats these species are facing. Here, we present high coverage whole-genome data from 233 primate species representing 86% of genera and all 16 families. This dataset was used, together with fossil calibration, to create a nuclear DNA phylogeny and to reassess evolutionary divergence times among primate clades. We found within-species genetic diversity across families and geographic regions to be associated with climate and sociality, but not with extinction risk. Furthermore, mutation rates differ across species, potentially influenced by effective population sizes. Lastly, we identified extensive recurrence of missense mutations previously thought to be human-specific. This study will open a wide range of research avenues for future primate genomic research. The whole genome sequences of 233 primate species provide insight into the determinants of genetic diversity, phylogenomics, and human uniqueness.

BackgroundSilver-Russell syndrome is an imprinting disorder that restricts growth, resulting in short adult stature that may be ameliorated by treatment. Approximately 50% of patients have loss of methylation of the imprinting control region (H19/IGF2:IG-DMR) on 11p15.5 and 5%–10% have maternal uniparental disomy of chromosome 7. Most published research focuses on the childhood phenotype. Our aim was to describe the phenotypic characteristics of older patients with SRS.MethodsA retrospective cohort of 33 individuals with a confirmed molecular diagnosis of SRS aged 13 years or above were carefully phenotyped.ResultsThe median age of the cohort was 29.6 years; 60.6% had a height SD score (SDS) ≤−2 SDS despite 70% having received growth hormone treatment. Relative macrocephaly, feeding difficulties and a facial appearance typical of children with SRS were no longer discriminatory diagnostic features. In those aged ≥18 years, impaired glucose tolerance in 25%, hypertension in 33% and hypercholesterolaemia in 52% were noted. While 9/33 accessed special education support, university degrees were completed in 40.0% (>21 years). There was no significant correlation between quality of life and height SDS. 9/25 were parents and none of the 17 offsprings had SRS.ConclusionHistorical treatment regimens for SRS were not sufficient for normal adult growth and further research to optimise treatment is justified. Clinical childhood diagnostic scoring systems are not applicable to patients presenting in adulthood and SRS diagnosis requires molecular confirmation. Metabolic ill-health warrants further investigation but SRS is compatible with a normal quality of life including normal fertility in many cases.

Abstract Context Low birth weight, as seen in Silver-Russell syndrome (SRS), is associated with later cardiometabolic disease. Data on long-term outcomes and adult body composition in SRS are limited. Objective To evaluate body composition and metabolic health in adults with SRS. Methods This was an observational study of 25 individuals with molecularly confirmed SRS, aged ≥ 18 years, from research facilities across the UK. Body composition and metabolic health were assessed at a single appointment. Individuals with SRS were compared with unaffected men and women (from the Southampton Women's Survey [SWS]). Fat mass, lean mass, bone mineral density (BMD), blood pressure, lipids, and blood glucose were measured. Results Twenty-five adults with SRS were included (52% female). The median age was 32.9 years (range, 22.0 to 69.7). Fat percentage was greater in the SRS group than the SWS cohort (44.1% vs 30.3%, P < .001). Fat mass index was similar (9.6 vs 7.8, P = .3). Lean mass percentage (51.8% vs 66.2%, P < .001) and lean mass index (13.5 kg/m2 vs 17.3 kg/m2, P < .001) were lower in the SRS group than the SWS cohort. BMD was lower in the SRS group than the SWS cohort (1.08 vs 1.24, P < .001; all median values). Total cholesterol was ≥ 5 mmol/L in 52.0%. Triglyceride levels were ≥ 1.7 mmol/L in 20.8%. Fasting blood glucose levels were ≥ 6.1 mmol/L in 25.0%. Hypertension was present in 33.3%. Conclusion Adults with SRS have an unfavorable body composition and predisposition to cardiometabolic disease. These results support the need for a health surveillance strategy to mitigate adverse outcomes.

IntroductionHepatocellular carcinoma (HCC) is expected to become the third most common cause of cancer death worldwide by 2030. The increase in HCC is in large part due to the rising prevalence of risk factors such as type 2 diabetes mellitus (T2DM). Up to 1 in 20 people living with T2DM have liver cirrhosis, and they have a 1% to 2% incidence of HCC per year. Patients with cirrhosis enter surveillance for HCC to identify early-stage, curable tumours. A diagnosis of T2DM does not mandate testing to identify patients with cirrhosis, with testing restricted to those with additional risks. There has never been a trial and nested cost-effectiveness evaluation comparing screening all patients with T2DM for cirrhosis against usual care.Methods and analysisThe study will use a multi-centre, unblinded individual randomised controlled trial design. The aim will be to determine the effectiveness and cost-effectiveness of screening all adults with T2DM to identify those at high risk of HCC. The recruitment strategy has been supported by patient and public involvement (PPI). Participants will be identified via an automated search of primary care records and invited to participate via text. 320 participants will be randomised for screening. The screening will include measurement of bio-markers for liver fibrosis (ELF and Fib-4) and vibration-controlled transient elastography. Another 320 participants will be randomised to standard care. Demographic and medical history data will be collected at baseline from all participants. Outcome data will be collected remotely from healthcare records. The primary outcome is the proportion of participants in each arm who are referred to HCC surveillance following testing for liver disease within 12 months of randomisation. The results will be used to calculate the incremental cost-effectiveness ratio of screening via a Markov model.Ethics and disseminationThe results of this study will be presented directly to National Health Service England. Additional dissemination via conference proceedings and publication will be supported by our PPI team. Ethical approval was granted by the West of Scotland Research Ethics Service on 2 August 2023, REC reference 23/WS/0102.Trial registration number ISRCTN17017677.

ObjectiveThe psychosocial impact of growing up with Silver-Russell syndrome (SRS), characterised by growth failure and short stature in adulthood, has been explored in adults; however, there are no accounts of contemporary lived experience in adolescents. Such data could inform current healthcare guidance and transition to adult services. We aimed to explore the lived experience of adolescents with SRS.Design/setting/patientsIn-depth, semi-structured interviews were conducted between January 2015 and October 2016 with a sample of eight adolescents aged 13–18 (five girls) with genetically confirmed SRS from the UK. Qualitative interviews were transcribed and coded to identify similarities and differences using thematic analysis; codes were then grouped to form overarching themes.ResultsWe identified four themes from the interview data: (1) the psychosocial challenges of feeling and looking different; (2) pain, disability and fatigue; (3) anticipated stigma; and (4) building resilience and acceptance. Despite adolescents accepting SRS in their lives, they described ongoing psychosocial challenges and anticipated greater problems to come, such as stigma from prospective employers.ConclusionsAdolescents with SRS may experience psychosocial difficulties from as young as 10 years old related to feeling and looking different; pain, disability and fatigue; anticipated stigma; and future challenges around employment. We discuss these findings in relation to recommendations for the care of adolescents with SRS to prepare them for adult life.