German Primate Center

In humans, frailty, risk-taking behaviors, and unhealthy lifestyles have been linked to shifts in adult sex ratios (ASR), which are heavily female-biased at older ages. Conversely, Madagascar’s group-living primates frequently exhibit male-biased ASRs, defying patterns commonly observed among polygynous mammals. To explore these unusual sex ratio dynamics in wild redfronted lemurs (Eulemur rufifrons), we examined three behavioral proxies of mortality risk. We conducted 150 flight initiation distance (FID) experiments to assess sex differences in risk-taking and collected locomotion and proximity data to gauge variation in frailty and social integration. To achieve the observed male-biased ASR, we expected females to be less physically active than males, to have shorter FIDs, and to maintain less proximity to group members, thereby increasing their risk of predation. Using observational data from six years, we found that males spent less time being physically active than females. Locomotor quality followed an inverted U-shaped pattern, with very young individuals and those over eight years jumping less far than young adults. Older lemurs also had fewer nearby individuals. Individual FIDs decreased with height above the ground. Moreover, females with longer FIDs had a slightly lower risk of disappearing sooner, indicating a relevant behavioral adaptation that may enhance survival. However, weak evidence for sex differences in these proxies suggests that other intrinsic and extrinsic factors more strongly shape mortality and ASR in this species. The predicted effects of risk-taking, agility and social integration on survival therefore merit further study in additional taxa and using alternative proxies.

Autoantibodies elicited by prenatal maternal infections with Neisseria gonorrhoeae (N. gonorrhoeae) are suspected to play a role in the pathogenesis of neurodevelopmental diseases like schizophrenia. This chapter provides an overview on research about cellular interaction partners of such antibodies in choroid plexus epithelial cells. In a first set of experiments, it was revealed that antibodies to N. gonorrhoeae interact with mitochondrial proteins like Hsp60 and ATBP5, leading to impaired energy metabolism in choroid plexus papilloma cells. This interaction was confirmed in postmortem samples of the choroid plexus as well as in choroid plexus epithelium from Callithrix jacchus, a nonhuman primate. In a further set of experiments, employing a multiprotein array, it was shown that the interaction of anti-N. gonorrhoeae antibodies with the SNARE-protein Snap23 was capable of impairing the insulin-dependent membrane translocation of the glucose transporter GluT4 in choroid plexus papilloma cells. These findings show that antibacterial antibodies implicated in the etiology of schizophrenia are capable of interacting with certain proteins in the choroid plexus epithelium, which eventually leads to functional alterations that could play a role in the pathogenesis of this disease.

The most dynamic and repetitive regions of great ape genomes have traditionally been excluded from comparative studies1, 2–3. Consequently, our understanding of the evolution of our species is incomplete. Here we present haplotype-resolved reference genomes and comparative analyses of six ape species: chimpanzee, bonobo, gorilla, Bornean orangutan, Sumatran orangutan and siamang. We achieve chromosome-level contiguity with substantial sequence accuracy (<1 error in 2.7 megabases) and completely sequence 215 gapless chromosomes telomere-to-telomere. We resolve challenging regions, such as the major histocompatibility complex and immunoglobulin loci, to provide in-depth evolutionary insights. Comparative analyses enabled investigations of the evolution and diversity of regions previously uncharacterized or incompletely studied without bias from mapping to the human reference genome. Such regions include newly minted gene families in lineage-specific segmental duplications, centromeric DNA, acrocentric chromosomes and subterminal heterochromatin. This resource serves as a comprehensive baseline for future evolutionary studies of humans and our closest living ape relatives.

Sensory uncertainty jeopardizes accurate movement. During reaching, visual uncertainty can affect the estimation of hand position (feedback) and the desired movement endpoint (target). While impairing motor learning, it is unclear how either form of uncertainty affects cortical reach goal encoding. We show that reach trajectories vary more with higher visual uncertainty of the target, but not the feedback. Accordingly, cortical motor goal activities in male rhesus monkeys are less accurate during planning and movement initiation under target but not feedback uncertainty. Yet, when monkeys critically depend on visual feedback to conduct reaches via a brain-computer interface, then visual feedback uncertainty impairs reach accuracy and neural motor goal encoding around movement initiation. Neural state space analyses reveal a dimension that separates population activity by uncertainty level in all tested conditions. Our findings demonstrate that while both target and feedback uncertainty always reflect in neural activity, uncertain feedback only deteriorates neural reach goal information and behavior when it is task-critical, i.e., when having to rely on the sensory feedback and no other more reliable sensory modalities are available. Further, uncertain target and feedback impair reach goal encoding in a time-dependent manner, suggesting that they are integrated during different stages of reach planning.

The Gaoligong Mountains, located in the southeastern Tibetan Plateau, is one of the world's biodiversity hotspots and provides a refugium for many endangered endemic animals. In this study, we reported a population genetic study on black snub‐nosed monkey ( Rhinopithecus strykeri ), a critically endangered primate endemic to the Gaoligong Mountains, yet their large‐scale population genetic study remains underexplored. Here, we performed population genetic analyses from two geographical populations (Pianma and Luoma) based on targeted genomic single‐nucleotide polymorphism (SNP) data (37.7 K) and mitochondrial DNA (mtDNA) control region (842 bp). Both nuclear SNP data and mtDNA revealed relatively low levels of genetic variation in both populations compared to other reported primates, which is most likely to be explained by loss of historical genetic diversity due to inbreeding and long‐term small effective population size, thus potentially aggravating the effects of inbreeding and genetic depression. Phylogenetic and population structure analyses for mtDNA revealed two deep lineages (approximately 0.69 million years ago), but limited genetic differentiation in nuclear data, which might have been caused by the Late Cenozoic uplift of the Tibetan Plateau and glacial refuge, and subsequent secondary contact as a result of historically high and bidirectional gene flow between populations. Ecological niche modeling and landscape connectivity analyses also showed historical and recent connectivity between two geographical populations. The demographic history inferred from both mtDNA and nuclear data revealed at least two continuous declines in the effective population size occurring around 43 Kya and 8–10 Kya, respectively, probably due to Pleistocene glaciations and subsequent human activities. Our results provide the first detailed and comprehensive genetic insights into the genetic diversity, population structure, and demographic history of a critically endangered species, and provide essential baseline information to guide conservation efforts.

X‐nuclei magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) are powerful tools for the in vivo investigation of metabolism. Most nuclei require a dedicated radio frequency (RF) coil for signal detection; however, RF coils are often expensive. Coupled with the need for experts to create RF coils, X‐nuclei MR measurements are often inaccessible to the general user. In this paper, we present cost‐efficient and easy to assemble ⁷ Li RF coils that achieved comparable signal‐to‐noise ratios (SNRs) to their commercial counterpart. Our ⁷ Li RF coils were built as single resonance, transmit–receive (Tx/Rx) coils with sufficient design flexibility to allow for future implementations for other nuclei. We found that for a mouse surface coil the optimal number of segmentation capacitors was two. In vitro ⁷ Li MRS yielded a 75% SNR increase and in vivo ⁷ Li MRS yielded a 42% SNR increase compared with a commercial dual‐tuned surface coil. Finally, we demonstrated that in vivo ⁷ Li MRI of lithium‐fed mice is possible with a custom‐built, 2‐segment surface coil.

We embrace Moffett's call for more rigorous definitions of social organizations but raise two intersecting critiques: (1) The spaces controlled by societies are not exclusively physical, and (2) cooperation is required to maintain control over spaces, physical or otherwise. We discuss examples of non-physical societal spaces across species and highlight the top-down group cooperation challenge that is maintaining them.

The value of visual stimuli guides learning, decision-making, and motivation. Although stimulus values often depend on multiple attributes, how neurons extract and integrate distinct value components from separate cues remains unclear. Here we recorded the activity of amygdala neurons while two male monkeys viewed sequential cues indicating the probability and magnitude of expected rewards. Amygdala neurons frequently signaled reward probability in an abstract, stimulus-independent code that generalized across cue formats. While some probability-coding neurons were insensitive to magnitude information, signaling ‘pure’ probability rather than value, many neurons showed biphasic responses that signaled probability and magnitude in a dynamic (temporally-patterned) and flexible (reversible) value code. Specific amygdala neurons integrated these reward attributes into risk signals that quantified the variance of expected rewards, distinct from value. Population codes were accurate, mutually transferable between value components, and expressed differently across amygdala nuclei. Our findings identify amygdala neurons as a substrate for the sequential integration of multiple reward attributes into value and risk.

Social learning opportunities shape cognitive skills across species, especially in humans. Although the social environment impacts learning opportunities, the benefits of role model diversity and tolerance on task learning in tool-using species remain poorly understood. To explore these links, we study 2343 peering events (close-range observation of a conspecific) from 35 wild immature (<10 y) chimpanzees (Pan troglodytes verus). We find that chimpanzee peering functions to acquire information more than food, persists during development while peaking around weaning age, and increases with food processing complexity. Role models change throughout development, with increased peering at mothers during early stages and for more complex tasks. Finally, immatures observe many role models, favouring older and more tolerant individuals. We conclude that chimpanzees learn from multiple tolerant individuals, particularly when acquiring complex skills like tool use. Tolerant societies may be necessary for the acquisition and retention of the diverse tool kits rarely found in nature.

We determined the roles of two coevolved and coexpressed human-specific genes, NBPF14 and NOTCH2NLB, on the abundance of the cortical progenitors that underlie the evolutionary expansion of the neocortex, the seat of higher cognitive abilities in humans. Using automated microinjection into apical progenitors (APs) of embryonic mouse neocortex and electroporation of APs in chimpanzee cerebral organoids, we show that NBPF14 promotes the delamination of AP progeny, by promoting oblique cleavage plane orientation during AP division, leading to increased abundance of the key basal progenitor type, basal radial glia. In contrast, NOTCH2NLB promotes AP proliferation, leading to expansion of the AP pool. When expressed together, NBPF14 and NOTCH2NLB exert coor- dinated effects, resulting in expansion of basal progenitors while maintaining self-renewal of APs. Hence, these two human-specific genes orchestrate the behavior of APs, and the lineages of their progeny, in a manner essen- tial for the evolutionary expansion of the human neocortex.

Floodplain forests are currently undergoing substantial reorganization processes due to the combined effects of management-induced altered hydrological conditions, climate change and novel invasive pathogens. Nowadays, the ash dieback is one of the most concerning diseases affecting European floodplain forests, causing substantial tree mortality and threatening the loss of the dominant key tree species of the hardwood floodplain forest, Fraxinus excelsior. Understanding how the increased light availability caused by pathogen-driven mortality in combination with altered hydrological conditions and climate change affects growth responses in a diverse forest community is of crucial importance for conservation efforts. Thus, we examined growth of the main tree species in response to ash dieback and how it depended on altered hydrological conditions under novel climatic conditions for the lower and upper canopy in the floodplain forest of Leipzig, Germany. Our study period encompassed the consecutive drought years from 2018 to 2020. We found that tree growth responded mostly positively to increased light availability, but only on moist sites, while tree growth largely declined on dry sites, suggesting that water availability is a critical factor for tree species to be able to benefit from increased light availability due to canopy disturbances caused by ash dieback. This hydrological effect was species-specific in the lower canopy but not in the upper canopy. While, in the lower canopy, some species such as the competitive shade-tolerant but flood-intolerant Acer pseudoplatanus and Acer platanoides benefited from ash dieback on moist sites, others were less affected or suffered disproportionally, indicating that floodplain forests might turn into a novel ecosystem dominated by competitive Acer species, which may have detrimental effects on ecosystem functioning. Our results give hints on floodplain forests of the future and have important implications for conservation measures, suggesting that a substantial revitalization of natural hydrological dynamics is important to maintain a tree composition that resembles the existing one and thus sustain their conservation status.

Mammalian species with slow life histories invest heavily in offspring care to meet offspring nutritional and developmental requirements, typically at significant costs to mothers. While maternal care has been extensively studied, understanding the mechanisms driving variation in mother‒offspring relationships during key offspring developmental periods require more comparative data from natural populations. Using eight years of behavioral data, we analyzed mother-offspring interactions in 68 infants born to 46 mothers in wild mandrills (Mandrillus sphinx), spanning multiple birth cohorts and the entire first year of infant life, a critical period for individual social and physical development. We found that mothers dynamically adjusted caregiving behavior as infants aged, reducing physical contact while promoting spatial independence and social integration. Maternal traits, such as age, social rank, and reproductive history, shaped maternal phenotypes: high-ranking mothers promoted infant socialization while reducing carrying, and older, multiparous mothers invested more in grooming and physical contact than younger, inexperienced females. Previous infant loss predicted reduced maternal aggression, potentially due to fewer immatures to care for or behavioral adjustments aimed at improving offspring survival. Finally, mothers fostered closer bonds with their daughters while encouraging their sons’ independence, possibly resulting in more frequent tantrums observed in males. This sex-biased pattern likely reflects preparation for contrasting life histories between the sexes in this species. By combining extensive longitudinal observations with fine-scale, individual analyses, our study emphasizes the dynamic and multifaceted nature of early mother-offspring interactions and their evolutionary implications in long-lived mammals.

Optogenetic stimulation has become a promising approach for restoring lost body function. For example, partial restoration of vision has been achieved in a blind patient and preclinical proof-of-concept has been demonstrated for optogenetic hearing restoration. In preparation for clinical translation of hearing restoration, efficient and safe optogenetic modification of spiral ganglion neurons (SGNs) in the mature cochlea remained to be developed. Methods: Here, we established microcatheter-based administration of adeno-associated virus (AAV) into scala tympani of the cochlea of Mongolian gerbils and compared it to the previously developed direct AAV-injection into the spiral ganglion. We probed the potential of AAV-PHP.S to express channelrhodopsins (ChRs) under the control of the human synapsin promotor in mature SGNs of hearing and deafened gerbils. Results: Using the microcatheter approach, but not with the AAV-modiolus injection, we achieved reliable ChR expression in SGN enabling optogenetic stimulation of the auditory pathway in 80% of the treated animals. Yet, the efficiency of SGN transduction was modest with only ~30% ChR-expressing SGNs. Moreover, we encountered off-target expression in hair cells in hearing gerbils in both approaches. We did not detect ChR expression in the central nervous system using microcatheter administration. Comparing optogenetic auditory brainstem responses of gerbils with and without hair cell transduction confirmed that SGNs were the primary site of optogenetic stimulation of the pathway. Conclusions: The AAV.PHP-S microcatheter administration via the round window with pressure relief at the round window is a reliable approach to optogenetically modify the SGNs in order to restore hearing with future optical cochlear implants.

When quantifying animal cognition, memory represents one of the most tested domains and is key to understanding cognitive evolution. Memory tests thus play an important role in comparative cognitive research, yet slight variations in the experimental settings can substantially change the outcome, questioning whether different memory tests tap into different memory systems or whether they test memory at all. Here, we first assessed memory performance of 16 common marmosets (Callithrix jacchus) in two distinct paradigms varying in their format and delay. First, we examined marmoset memory in a 24-h delay memory test (24 h-DMT) in which they could freely explore an environment with three novel objects of which one contained food. We examined their retention the day after, and the procedure was iterated cumulatively with previous objects remaining in the enclosure until the marmosets had to choose the correct out of 30 objects. Second, we administered a classical delayed response test (DRT) in the same animals with three objects and a maximum delay of 30 s. In the DRT, marmoset performance was poor and not better than chance after 15 s already. However, individuals excelled in the 24 h-DMT, performing above chance level after 24 h even with tenfold the number of objects to choose from compared to the DRT. Moreover, individual performances in the two tests were not correlated, and typical age effects on memory could not be detected in both experiments. Together, these results suggest that the two tests explore different domains, and that the 24 h-DMT examines long-term memory. The outcome of the DRT is more difficult to assign to memory since individuals performed only moderately even in the 0-s delay condition. This puts into question whether this task design indeed tests memory or other cognitive processes.

Ongoing ecosystem change and biodiversity decline across the Afrotropics call for tools to monitor the state of biodiversity or ecosystem elements across extensive spatial and temporal scales. We assessed relationships in the co‐occurrence patterns between great apes and other medium to large‐bodied mammals to evaluate whether ape abundance serves as a proxy for mammal diversity across broad spatial scales. We used camera trap footage recorded at 22 research sites, each known to harbor a population of chimpanzees, and some additionally a population of gorillas, across 12 sub‐Saharan African countries. From ~350,000 1‐min camera trap videos recorded between 2010 and 2016, we estimated mammalian community metrics, including species richness, Shannon diversity, and mean animal mass. We then fitted Bayesian Regression Models to assess potential relationships between ape detection rates (as proxy for ape abundance) and these metrics. We included site‐level protection status, human footprint, and precipitation variance as control variables. We found that relationships between detection rates of great apes and other mammal species, as well as animal mass were largely positive. In contrast, relationships between ape detection rate and mammal species richness were less clear and differed according to site protection and human impact context. We found no clear association between ape detection rate and mammal diversity. Our findings suggest that chimpanzees hold potential as indicators of specific elements of mammalian communities, especially population‐level and composition‐related characteristics. Declines in chimpanzee populations may indicate associated declines of sympatric medium to large‐bodied mammal species and highlight the need for improved conservation interventions.Changes in chimpanzee abundance likely precede extirpation of sympatric mammals.

Animal’s cognitive abilities have traditionally been studied in captive settings and only more recently in the wild. Few studies have investigated whether and how captive and wild animals differ in performance in cognitive tasks. We tested the effect of age, sex, and wild versus captive origin on cognitive performance in a problem solving (captive: N = 34; wild: N = 83), an inhibitory control (captive: N = 34; wild: N = 91), and a causal understanding task (captive: N = 34; wild: N = 86) in grey mouse lemurs (Microcebus murinus). The overall success rate of captive grey mouse lemurs in the problem-solving task was 88% (N = 30), whereas wild grey mouse lemurs had a higher success rate of 100% (N = 83). In the causal understanding task, the success rate of captive grey mouse lemurs was 62% (N = 21), whereas wild grey mouse lemurs outperformed captive individuals with 88% (N = 76) success rate. In the inhibitory control task, we found an interaction between age and origin, where the number of correct trials in the inhibitory control task decreased with age in captive individuals but not in their wild counterparts. The differences between the two origins may have been caused by higher explorative tendencies in wild grey mouse lemurs, by age differences in wild and captive individuals, or by differences in motivational state in the two populations. Overall, our study emphasizes the role of origin in primate cognition.

Magnetic resonance imaging (MRI) is widely used in human medicine, offering multiple contrast mechanisms to visualise different tissue types. It is also gaining importance in veterinary medicine, including diagnosing joint disorders. The menisci of the stifle joint play a crucial role in the development of osteoarthritis (OA), and multi-parameter MRI of the menisci may aid in early OA diagnosis, potentially improving therapeutic outcomes. In a previous ex vivo study, we measured T2 relaxation times in menisci of elderly dogs with mild histological signs of degeneration but no clinical symptoms of lameness. As no significant changes in T2 relaxation times were observed in relation to histological scores, the present study extends this investigation by exploring more advanced MR parameters—including T1 relaxation time, T2* relaxation time, magnetisation transfer ratio (MTR), and magnetisation transfer saturation (MTsat)—to assess their potential for detecting early microstructural changes in the menisci. While T2* relaxation times and MTR showed no significant variation across histological scores, MTsat values increased with higher proteoglycan staining. In contrast, the apparent T1 relaxation time (T1app) was lower in menisci with elevated proteoglycan scores and increased with higher cellularity scores. The correlation between MTsat and proteoglycan content suggests that MTsat, along with T1app, could be a promising parameter for characterising the extracellular matrix. However, further research is needed to validate these findings.