What is a marmoset?

Twinning in wild, endangered lion-tailed macaques Macaca silenus in the Anamalai Hills of the Western Ghats, India

Many primate species show various behavioural and ecological adaptations to provisioning, one of which is the unusual occurrence of twins. Here, we report observations on two pairs of surviving twins in lion-tailed macaques Macaca silenus in the Anamalai Hills of the Western Ghats, India. The Puthuthottam population of lion-tailed macaques has historically been restricted to a rainforest fragment measuring 92 ha, situated adjacent to human settlements. Over the last 10 years, however, several groups from this population have begun to directly interact with the local human communities, visiting settlements at a rate of 0.52 events/day and exploiting various anthropogenic food resources. We followed and opportunistically collected behavioural ad libitum data on two sets of twins for a year, between March 2019 and March 2020. Both of the mothers were primarily terrestrial, although the mother with the younger set of twins also used the tree canopy and other precarious substrates, such as cables. Although two previous cases of twinning have been reported in this population, one in the late 1990s and one between 2000 and 2002, neither of those sets of twins survived beyond a few weeks, with at least one infant in each pair dying of unknown causes. We discuss, but discount, the possibility that one of the infants in either set of twins was an adoptee. Our observations indicate that some lion-tailed macaque twins can survive under free-ranging conditions if they receive adequate care from their biological mother or another female. Our findings also provide further evidence of increased rates of twinning as a consequence of dietary changes in synanthropic non-human primate populations.

Adaptation in the face of internal conflict: the paradox of the organism revisited

The paradox of the organism refers to the observation that organisms appear to function as coherent purposeful entities, despite the potential for within-organismal components like selfish genetic elements and cancer cells to erode them from within. While it is commonly accepted that organisms may pursue fitness maximisation and can be thought to hold particular agendas, there is a growing recognition that genes and cells do so as well. This can lead to evolutionary conflicts between an organism and the parts that reside within it. Here, we revisit the paradox of the organism. We first outline its conception and relationship to debates about adaptation in evolutionary biology. Second, we review the ways selfish elements may exploit organisms, and the extent to which this threatens organismal integrity. To this end, we introduce a novel classification scheme that distinguishes between selfish elements that seek to distort transmission versus those that seek to distort phenotypic traits. Our classification scheme also highlights how some selfish elements elude a multi-level selection decomposition using the Price equation. Third, we discuss how the organism can retain its status as the primary fitness-maximising agent in the face of selfish elements. The success of selfish elements is often constrained by their strategy and further limited by a combination of fitness alignment and enforcement mechanisms controlled by the organism. Finally, we argue for the need for quantitative measures of both internal conflicts and organismality.

The common marmoset as a model of neurodegeneration

Human life expectancy has increased over the past few centuries, and the incidence of dementia in the older population is also projected to continue to rise. Neurodegenerative diseases are complex multifactorial conditions for which no effective treatments are currently available. Animal models are necessary to understand the causes and progression of neurodegeneration. Nonhuman primates (NHPs) offer significant advantages for the study of neurodegenerative disease. Among them, the common marmoset, Callithrix jacchus, stands out due to its easy handling, complex brain architecture, and occurrence of spontaneous beta-amyloid (Aβ) and phosphorylated tau aggregates with aging. Furthermore, marmosets present physiological adaptations and metabolic alterations associated with the increased risk of dementia in humans. In this review, we discuss the current literature on the use of marmosets as a model of aging and neurodegeneration. We highlight aspects of marmoset physiology associated with aging, such as metabolic alterations, which may help understand their vulnerability to developing a neurodegenerative phenotype that goes beyond normal aging.

Paternal genome elimination promotes altruism in viscous populations

Population viscosity has long been thought to promote the evolution of altruism. However, in the simplest scenarios, the potential for altruism is invariant with respect to dispersal-a surprising result that holds for haploidy, diploidy, and haplodiploidy (arrhenotoky). Here, we develop a kin-selection model to investigate how population viscosity affects the potential for altruism in species with male paternal genome elimination (PGE), exploring altruism enacted by both females and males, and both juveniles and adults. We find that (1) PGE promotes altruistic behaviors relative to the other inheritance systems, and to a degree that depends on the extent of paternal genome expression. (2) Under PGE, dispersal increases the potential for altruism in juveniles and decreases it in adults. (3) The genetics of PGE can lead to striking differences in sex-specific potentials for altruism, even in the absence of any sex differences in ecology.

After short interbirth intervals, captive callitrichine monkeys have higher infant mortality

Life history theory predicts a trade-off between the quantity and quality of offspring. Short interbirth intervals-the time between successive births-may increase the quantity of offspring but harm offspring quality. In contrast, long interbirth intervals may bolster offspring quality while reducing overall reproductive output. Further research is needed to determine whether this relationship holds among primates, which have intensive parental investment. Using Cox proportional hazards models, we examined the effects of interbirth intervals (short, normal, or long) on infant survivorship using a large demographic dataset (n = 15,852) of captive callitrichine monkeys (marmosets, tamarins, and lion tamarins). In seven of the nine species studied, infants born after short interbirth intervals had significantly higher risks of mortality than infants born after longer interbirth intervals. These results suggest that reproduction in callitrichine primates may be limited by physiologic constraints, such that short birth spacing drives higher infant mortality.

On Being a Monkey's Uncle: Germline Chimerism in the Callitrichinae and the Evolution of Sibling Rivalry

AbstractA typical monkey of the subfamily Callitrichinae has two or more cell lineages occupying its tissues: one from "itself," and one from its co-twin(s). Chimerism originates in utero when the twin placentae fuse, vascular anastomoses form between them, and cells are exchanged between conceptuses through their shared circulation. Previously it was thought that chimerism was limited to tissues of the hematopoietic cell lineage and that the germline was clonal, but subsequent empirical work has shown that chimerism may extend to many tissues, including the germline. To explore how natural selection on chimeric organisms should shape their social behavior, I construct an inclusive fitness model of sibling interactions that permits differing degrees of chimerism in the soma and germline. The model predicts that somatic chimerism should diminish sibling rivalry but that germline chimerism should typically intensify it. A further implication of the model is the possibility for intraorganismal conflict over developing phenotypes; as tissues may differ in their extent of chimerism-for example, placenta versus brain-their respective inclusive fitness may be maximized by different phenotypes. Communication between tissues in chimeric organisms might therefore be noisy, rapidly evolving, and fraught, as is common in systems with internal evolutionary conflicts of interest.

Noninvasive cardiac psychophysiology as a tool for translational science with marmosets

The importance of marmosets for comparative and translational science has grown in recent years because of their relatively rapid development, birth cohorts of twins, family social structure, and genetic tractability. Despite this, they remain understudied in investigations of affective processes. In this methodological note, we establish the validity of using noninvasive commercially available equipment to record cardiac physiology and compute indices of autonomic nervous system activity-a major component of affective processes. Specifically, we recorded electrocardiogram and impedance cardiogram, from which we derived heart rate, respiration rate, measures of high-frequency heart rate variability (indices of parasympathetic autonomic nervous system activity), and ventricular contractility (an index of sympathetic autonomic nervous system activity). Our methods produced physiologically plausible data, and further, animals with increased heart rates during testing were also more reactive to isolation from their social partner and presentation of novel objects, though no relationship was observed between reactivity and specific indices of parasympathetic or sympathetic nervous system activity.

A comparative study of litter size and sex composition in a large dataset of callitrichine monkeys

In many birds and mammals, the size and sex composition of litters can have important downstream effects for individual offspring. Primates are model organisms for questions of cooperation and conflict, but the factors shaping interactions among same-age siblings have been less-studied in primates because most species bear single young. However, callitrichines (marmosets, tamarins, and lion tamarins) frequently bear litters of two or more, thereby providing the opportunity to ask whether variation in the size and sex composition of litters affects development, survival, and reproduction. To investigate these questions, we compiled a large dataset of nine species of callitrichines (n = 27,080 individuals; Callithrix geoffroyi, Callithrix jacchus, Cebuella pygmaea, Saguinus imperator, Saguinus oedipus, Leontopithecus chrysomelas, Leontopithecus chrysopygus, Leontopithecus rosalia, and Callimico goeldii) from zoo and laboratory populations spanning 80 years (1938-2018). Through this comparative approach, we found several lines of evidence that litter size and sex composition may impact fitness. Singletons have higher survivorship than litter-born peers and they significantly outperform litter-born individuals on two measures of reproductive performance. Further, for some species, individuals born in a mixed-sex litter outperform isosexually-born individuals (i.e., those born in all-male or all-female litters), suggesting that same-sex competition may limit reproductive performance. We also document several interesting demographic trends. All but one species (C. pygmaea) has a male-biased birth sex ratio with higher survivorship from birth to sexual maturity among females (although this was significant in only two species). Isosexual litters occurred at the expected frequency (with one exception: C. pygmaea), unlike other animals, where isosexual litters are typically overrepresented. Taken together, our results indicate a modest negative effect of same-age sibling competition on reproductive output in captive callitrichines. This study also serves to illustrate the value of zoo and laboratory records for biological inquiry.

Experimental autoimmune encephalomyelitis in the common marmoset: a translationally relevant model for the cause and course of multiple sclerosis

Aging Western societies are facing an increasing prevalence of chronic autoimmune-mediated inflammatory disorders (AIMIDs) for which treatments that are safe and effective are scarce. One of the main reasons for this situation is the lack of animal models, which accurately replicate clinical and pathological aspects of the human diseases. One important AIMID is the neuroinflammatory disease multiple sclerosis (MS), for which the mouse experimental autoimmune encephalomyelitis (EAE) model has been frequently used in preclinical research. Despite some successes, there is a long list of experimental treatments that have failed to reproduce promising effects observed in murine EAE models when they were tested in the clinic. This frustrating situation indicates a wide validity gap between mouse EAE and MS. This monography describes the development of an EAE model in nonhuman primates, which may help to bridge the gap.

Full allogeneic fusion of embryos in a holothuroid echinoderm

Whole-body chimaeras (organisms composed of genetically distinct cells) have been directly observed in modular/colonial organisms (e.g. corals, sponges, ascidians); whereas in unitary deuterostosmes (including mammals) they have only been detected indirectly through molecular analysis. Here, we document for the first time the step-by-step development of whole-body chimaeras in the holothuroid Cucumaria frondosa, a unitary deuterostome belonging to the phylum Echinodermata. To the best of our knowledge, this is the most derived unitary metazoan in which direct investigation of zygote fusibility has been undertaken. Fusion occurred among hatched blastulae, never during earlier (unhatched) or later (larval) stages. The fully fused chimaeric propagules were two to five times larger than non-chimaeric embryos. Fusion was positively correlated with propagule density and facilitated by the natural tendency of early embryos to agglomerate. The discovery of natural chimaerism in a unitary deuterostome that possesses large externally fertilized eggs provides a framework to explore key aspects of evolutionary biology, histocompatibility and cell transplantation in biomedical research.

Animal models of multiple sclerosis: Focus on experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is a chronic, progressive disorder of the central nervous system (CNS) that affects more than two million people worldwide. Several animal models resemble MS pathology; the most employed are experimental autoimmune encephalomyelitis (EAE) and toxin- and/or virus-induced demyelination. In this review we will summarize our knowledge on the utility of different animal models in MS research. Although animal models cannot replicate the complexity and heterogeneity of the MS pathology, they have proved to be useful for the development of several drugs approved for treatment of MS patients. This review focuses on EAE because it represents both clinical and pathological features of MS. During the past decades, EAE has been effective in illuminating various pathological processes that occur during MS, including inflammation, CNS penetration, demyelination, axonopathy, and neuron loss mediated by immune cells.

Cytogenetics and Molecular Genetic Analysis of Chimerism in Marmosets (Callithrix: Primates)

The birth of fraternal twins is a characteristic frequently observed in callitrichids. Cytogenetic studies have demonstrated hematopoietic chimerism in marmosets with the occurrence of two cell lines 2n=46,XX/46,XY in females and males co-twins, without phenotypic changes. Amplification by PCR have also been used to verify the presence of the SRY gene in female chimaeras. Our aim was to verify the occurrence of chimerism in Callithrix sp. individuals considered as hybrids according to their intermediate phenotypes between C. jacchus and C. penicillata. Blood samples from 37 Callithrix sp. individuals were collected. Hematopoietic chimerism 2n=46,XX/46,XY was detected by cytogenetic analysis in five individuals, three males and two females. A fragment of approximately 200bp of the SRY gene was amplified in seven females with normal external genitalia. The percentage of 32% of chimeric individuals detected in the present study is similar to that observed for pure specimens of Callithrix. These data suggests that hybridization probably does not interfere with the occurrence of twin gestation, nor of chimerism. Although cytogenetics is the main tool to identify the two cell lineages present in cases of chimerism, the amplification of the SRY gene by PCR has proved to be more efficient to identify the Y chromosome in cases of chimeric female marmoset.

Primate autoimmune disease models; lost for translation?

Replacement, reduction and refinement (the 3R's) are the leading principles in translational research with animals. To be useful a model should also be clinically Relevant (the 4th R). Work in a non-human primate model of multiple sclerosis, the experimental autoimmune encephalomyelitis model, reveals an inherent conflict among these 4R principles. The impossibility to harmonize all 4R's forms a major challenge when the model is applied in preclinical drug development.

Anatomical and functional neuroimaging in awake, behaving marmosets

The common marmoset (Callithrix jacchus) is a small New World monkey that has gained significant recent interest in neuroscience research, not only because of its compatibility with gene editing techniques, but also due to its tremendous versatility as an experimental animal model. Neuroimaging modalities, including anatomical (MRI) and functional magnetic resonance imaging (fMRI), complemented by two-photon laser scanning microscopy and electrophysiology, have been at the forefront of unraveling the anatomical and functional organization of the marmoset brain. High-resolution anatomical MRI of the marmoset brain can be obtained with remarkable cytoarchitectonic detail. Functional MRI of the marmoset brain has been used to study various sensory systems, including somatosensory, auditory, and visual pathways, while resting-state fMRI studies have unraveled functional brain networks that bear great correspondence to those previously described in humans. Two-photon laser scanning microscopy of the marmoset brain has enabled the simultaneous recording of neuronal activity from thousands of neurons with single cell spatial resolution. In this article, we aim to review the main results obtained by our group and by our colleagues in applying neuroimaging techniques to study the marmoset brain. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 373-389, 2017.

The common marmoset (<i>Callithrix jacchus</i>): a relevant preclinical model of human (auto)immune-mediated inflammatory disease of the brain

Abstract. The increasing prevalence of chronic autoimmune-mediated inflammatory disorders (AIMIDs) in aging human populations creates a high unmet need for safe and effective medications. However, thus far the translation of pathogenic concepts developed in animal models into effective treatments for the patient has been notoriously difficult. The main reason is that currently used mouse-based animal models for the pipeline selection of promising new treatments were insufficiently predictive for clinical success. Regarding the high immunological similarity between human and non-human primates (NHPs), AIMID models in NHPs can help to bridge the translational gap between rodent and man. Here we will review the preclinical relevance of the experimental autoimmune encephalomyelitis (EAE) model in common marmosets (Callithrix jacchus), a small-bodied neotropical primate. EAE is a generic AIMID model projected on the human autoimmune neuro-inflammatory disease multiple sclerosis (MS).

Experimental Autoimmune Encephalomyelitis in Marmosets

Experimental autoimmune encephalomyelitis (EAE) in the common marmoset, a small-bodied Neotropical primate, is a well-known and validated animal model for multiple sclerosis (MS). This model can be used for exploratory research, i.e., investigating the pathogenic mechanisms involved in MS, and applied research, testing the efficacy of new potential drugs.In this chapter, we will describe a method to induce EAE in the marmoset. In addition, we will explain the most common immunological techniques involved in the marmoset EAE research, namely isolation of mononuclear cells (MNC) from peripheral blood and lymphoid tissue, assaying T cell proliferation by thymidine incorporation, MNC phenotyping by flow cytometry, antibody measurement by ELISA, generation of B cell lines and antigen-specific T cell lines, and assaying cytotoxic T cells.

Does microchimerism mediate kin conflicts?

Fetal microchimerism (FMc) is predicted to promote the fitness of the fetus and maternal microchimerism (MMc) to promote the fitness of the mother. Offspring and mothers benefit from each other's health. Therefore, microchimeric cells should usually not be harmful to their host. However, the evolutionary interests of mothers and offspring diverge when there is competition among siblings for maternal investment. Fetal cells in mothers' bodies could benefit their own offspring at the expense of its sibs by promoting lactogenesis or by extending the interbirth interval. Maternal cells in fetal bodies could benefit from the suppression of sibling rivalry. Non-inherited haplotypes in MMc or sibling microchimerism (SMc) gain no direct benefit from their hosts' health and could be associated with substantial detrimental effects.

Current models of the marmoset brain

Since the availability of the common marmoset monkey as a primate model in neuroscience research has recently increased, much effort has been made to develop a reliable guide of the brain structures of this species. In this article, we review the development of the marmoset brain atlas and discuss a newly developed brain model, which was reconstructed from histological sections under volume-rendering technology. This kind of brain model allows virtual sections to be constructed on any axis, with nomenclatural annotations to structures in situ. This model is also applicable for the identification of structures revealed in magnetic resonance imaging studies. The brain model is accessible at the following web address: http://brainatlas.brain.riken.jp/marmoset/modules/xoonips/listitem.php?index_id=66.

Identification of MHC I class genes in two Platyrrhini species

The major histocompatibility complex is a diverse gene family that plays a crucial role in the adaptive immune system. In humans, the MHC class I genes consist of the classical loci of HLA-A, -B, and -C, and the nonclassical loci HLA-E, -F, and -G. In Platyrrhini species, few MHC class I genes have been described so far and were classified as MHC-E, MHC-F, and MHC-G, with MHC-G possibly representing a classical MHC class I locus while there were arguments about the existence of the MHC-B locus in Platyrrhini. In this study, MHC class I genes were identified in eight common marmosets (Callithrix jacchus) and two brown-headed spider monkeys (Ateles fusciceps). For common marmosets, 401 cDNA sequences were sequenced and 18 alleles were detected, including 14 Caja-G alleles and 4 Caja-B alleles. Five to eleven Caja-G alleles and one to three Caja-B alleles were detected in each animal. For brown-headed spider monkeys, 102 cDNA sequences were analyzed, and 9 new alleles were identified, including 5 Atfu-G and 4 Atfu-B alleles. Two or three Atfu-G and two Atfu-B alleles were obtained for each of animal. In phylogenetic analyses, the MHC-G and -B alleles from the two species and other Platyrrhini species show locus-specific clusters with bootstrap values of 86% and 50%. The results of pairwise sequence comparisons and an excess of non-synonymous nucleotide substitutions in the PBR region are consistent with the suggestion that Caja-G and Atfu-G may be classical MHC class I loci in the Platyrrhini species… But it appears that MHC-B locus of the two Platyrrhini species shares features with both classical and nonclasical MHC class I loci. Our results are an important addition to the limited MHC immunogenetic information available for the Platyrrhini species.

PROGRESS ON THE PATERNAL BRAIN: THEORY, ANIMAL MODELS, HUMAN BRAIN RESEARCH, AND MENTAL HEALTH IMPLICATIONS

With a secure foundation in basic research across mammalian species in which fathers participate in the raising of young, novel brain-imaging approaches are outlining a set of consistent brain circuits that regulate paternal thoughts and behaviors in humans. The newest experimental paradigms include increasingly realistic baby-stimuli to provoke paternal cognitions and behaviors with coordinated hormone measures to outline brain networks that regulate motivation, reflexive caring, emotion regulation, and social brain networks with differences and similarities to those found in mothers. In this article, on the father brain, we review all brain-imaging studies on PubMed to date on the human father brain and introduce the topic with a selection of theoretical models and foundational neurohormonal research on animal models in support of the human work. We discuss potentially translatable models for the identification and treatment of paternal mood and father-child relational problems, which could improve infant mental health and developmental trajectories with potentially broad public health importance.

Evolutionary genetics and implications of small size and twinning in callitrichine primates

New World monkeys (NWMs) are characterized by an extensive size range, with clawed NWMs (subfamily Callitrichinae, or callitrichines) such as the common marmoset manifesting diminutive size and unique reproductive adaptations. Perhaps the most notable of these adaptations is their propensity toward multiple gestations (i.e., dichorionic twins and trichorionic triplets). Indeed, with the exception of Goeldi's monkey (Callimico), callitrichine singleton pregnancies rarely occur. Multiple gestations seem to have coevolved with a suite of reproductive adaptations, including hematopoetic chimerism of siblings, suppression of reproduction in nondominant females, and cooperative alloparenting. The sequencing of the common marmoset (Callithrix jacchus) genome offers the opportunity to explore the genetic basis of these unusual traits within this primate lineage. In this study, we hypothesized that genetic changes arising during callitrichine evolution resulted in multiple ovulated ova with each cycle, and that these changes triggered adaptations that minimized complications common to multiple gestations in other primates, including humans. Callitrichine-specific nonsynonymous substitutions were identified in GDF9, BMP15, BMP4, and WFIKKN1. WFIKKN1, a multidomain protease inhibitor that binds growth factors and bone morphogenetic proteins, has nonsynonymous changes found exclusively in common marmosets and other tested callitrichine species that twin. In the one callitrichine species that does not produce twins (Callimico), this change has reverted back to the ancestral (nontwinning) primate sequence. Polymorphisms in GDF9 occur among human cohorts with a propensity for dizygotic twins, and polymorphisms in GDF9 and BMP15 are associated with twinning in sheep. We postulate that positive selection affected NWM growth patterns, with callitrichine miniaturization coevolving with a series of reproductive adaptations.

Interbirth intervals: Intrafamilial, intragenomic and intrasomatic conflict

BACKGROUND AND OBJECTIVES

Interbirth intervals (IBIs) mediate a trade-off between child number and child survival. Life history theory predicts that the evolutionarily optimal IBI differs for different individuals whose fitness is affected by how closely a mother spaces her children. The objective of the article is to clarify these conflicts and explore their implications for public health.

METHODOLOGY

Simple models of inclusive fitness and kin conflict address the evolution of human birth-spacing.

RESULTS

Genes of infants generally favor longer intervals than genes of mothers, and infant genes of paternal origin generally favor longer IBIs than genes of maternal origin.

CONCLUSIONS AND IMPLICATIONS

The colonization of maternal bodies by offspring cells (fetal microchimerism) raises the possibility that cells of older offspring could extend IBIs by interfering with the implantation of subsequent embryos.

The development of small primate models for aging research

Nonhuman primate (NHP) aging research has traditionally relied mainly on the rhesus macaque. But the long lifespan, low reproductive rate, and relatively large body size of macaques and related Old World monkeys make them less than ideal models for aging research. Manifold advantages would attend the use of smaller, more rapidly developing, shorter-lived NHP species in aging studies, not the least of which are lower cost and the ability to do shorter research projects. Arbitrarily defining "small" primates as those weighing less than 500 g, we assess small, relatively short-lived species among the prosimians and callitrichids for suitability as models for human aging research. Using the criteria of availability, knowledge about (and ease of) maintenance, the possibility of genetic manipulation (a hallmark of 21st century biology), and similarities to humans in the physiology of age-related changes, we suggest three species--two prosimians (Microcebus murinus and Galago senegalensis) and one New World monkey (Callithrix jacchus)--that deserve scrutiny for development as major NHP models for aging studies. We discuss one other New World monkey group, Cebus spp., that might also be an effective NHP model of aging as these species are longer-lived for their body size than any primate except humans.

Preclinical models of multiple sclerosis in nonhuman primates

Biotechnology has enabled the development of specifically acting therapies for immune-mediated inflammatory disorders (IMIDs) based on biological molecules. The high species specificity precludes safety and effectivity testing in lower species (mice and rats), thus creating a need for valid experimental models in nonhuman primates (NHPs). Here, we review the creation of relevant NHP model(s) for multiple sclerosis (MS), an IMID of the human CNS. We will also discuss how the model(s) can help in the translation of a scientific principle developed in lower species into a therapy for MS.

Development of microsatellite DNA markers and their chromosome assignment in the common marmoset

This study was performed to develop microsatellite DNA markers, which are useful for linkage analyses, gene mapping and blood chimera analyses in the common marmoset (Callithrix jacchus). We searched 153 of 295 bacterial artificial clone DNA sequences of the common marmoset that were archived in the NCBI database in 2004. On the basis of the search, we designed 186 PCR primer sets. When tested using 5 unrelated individuals, we successfully detected 154 markers with PCR products, of which 80 (52%) were polymorphic and 74 (48%) were monomorphic. We assigned each of the 154 markers to a human chromosome based on BLAST searches, which was achieved by searching the entire human genome sequences using an approximately 3 kb section of each forward primer sequence, including approximately 1.5 kb of the upstream and approximately 1.5 kb of the downstream sequences. Combining our assignment data and the chromosome painting-assisted karyotype of the common marmoset [Sherlock et al., Genomics 33:214-219, 1996], we prepared a list of 154 microsatellite DNA markers that were assigned to human chromosomes, except for the Y chromosome, which is equivalent to a chromosome map. Using five microsatellite DNA markers, we have established a fragment analysis method with a sequencer, which can be routinely used for blood chimera analysis, parentage diagnosis and individual identification.

Nepotistic cooperation in non-human primate groups

Darwin was struck by the many similarities between humans and other primates and believed that these similarities were the product of common ancestry. He would be even more impressed by the similarities if he had known what we have learned about primates over the last 50 years. Genetic kinship has emerged as the primary organizing force in the evolution of primate social organization and the patterning of social behaviour in non-human primate groups. There are pronounced nepotistic biases across the primate order, from tiny grey mouse lemurs (Microcebus murinus) that forage alone at night but cluster with relatives to sleep during the day, to cooperatively breeding marmosets that rely on closely related helpers to rear their young, rhesus macaque (Macaca mulatta) females who acquire their mother's rank and form strict matrilineal dominance hierarchies, male howler monkeys that help their sons maintain access to groups of females and male chimpanzees (Pan troglodytes) that form lasting relationships with their brothers. As more evidence of nepotism has accumulated, important questions about the evolutionary processes underlying these kin biases have been raised. Although kin selection predicts that altruism will be biased in favour of relatives, it is difficult to assess whether primates actually conform to predictions derived from Hamilton's rule: br > c. In addition, other mechanisms, including contingent reciprocity and mutualism, could contribute to the nepotistic biases observed in non-human primate groups. There are good reasons to suspect that these processes may complement the effects of kin selection and amplify the extent of nepotistic biases in behaviour.

A combined histological and MRI brain atlas of the common marmoset monkey, Callithrix jacchus

The common marmoset, Callithrix jacchus, is of growing importance for research in neuroscience and related fields. In the present work, we describe a combined histological and magnetic resonance imaging (MRI) atlas constructed from the brains of two adult female marmosets. Histological sections were processed from Nissl staining and digitized to produce an atlas in a large format that facilitates visualization of structures with significant detail. Naming of identifiable brain structures was performed utilizing current terminology. The histological sections and a simplified schematic atlas are available online at http://udn.nichd.nih.gov/brainatlas_home.html.

A fully resolved genus level phylogeny of neotropical primates (Platyrrhini)

There are more than 125 species of extant New World monkeys (Primates: Platyrrhini) found in approximately 15 genera. The phylogenetic relationships of these neotropical primates have been extensively studied from a molecular perspective. While these studies have been successful at inferring many of the relationships within the platyrrhines, key questions remain. The current study provides a framework for using non-genic, non-coding markers in comparative primate phylogenomic studies in species whose genomes are not yet scheduled for complete sequencing. A random genomic shotgun library was generated from the nocturnal Owl monkey Aotus lemurinus. Eleven unlinked, non-coding, non-genic, non-repetitive, nuclear DNA markers derived from this library were sequenced in at least one representative species of every platyrrhine genus. The combined sequence from these markers yielded a 7.7 kb multiple sequence alignment of 22 taxa. We analyzed these markers independently and combined with a 10 kb dataset consisting of "traditional," previously published markers located within or directly adjacent to genes. Parsimony, maximum likelihood, and Bayesian analysis converged on a single topology for the platyrrhine generic relationships. Notably, we confidently inferred that Pitheciidae is the sister taxon to the other two platyrrhine families (Cebidae, Atelidae). This relationship is supported by high values of branch support as well as topology tests. Additionally, Aotus formed a sister taxon to a clade comprising Cebus and Saimiri. With a fully resolved platyrrhine phylogeny in place it is now possible to design and test hypotheses regarding the evolution and diversification of platyrrhine phenotypes and life histories.

Developmental plasticity of the microscopic placental architecture in relation to litter size variation in the common marmoset monkey (Callithrix jacchus)

Fetal demand, shaped by factors such as number of fetuses, may alter placental regulation of exchange, even when maternal nutrition restriction is not overt. The marmoset is an interesting model in which to examine this aspect of placental function due to unique placentation that leads to multiple fetuses sharing a unified placental mass. We demonstrated previously that the triplet marmoset placenta exhibits significantly higher efficiency than does the twin placenta. Here, we test the hypothesis that this increased efficiency is due to increases in changes in the microscopic morphology of the placenta. Stereology was employed to analyze the microscopic architecture of placentas from twin and triplet pregnancies. Compartments of interest were the trabeculae, intertrabecular space, fetal capillaries, and the surface area of the maternal-fetal interface. Placentas from the two litters did not differ significantly in overall volume or individual volumetric compartments, but triplet placentas exhibited significant expansion of the trabecular surface area in comparison to twins (p=0.039). Further, the two groups differed in the isomorphy coefficient, with triplet placentas having a significantly higher coefficient (p=0.001) and potentially a more complex microscopic topography. Differences in the maternal-fetal interface may be due to developmental constraints on gross placental growth that occur earlier in gestation, such that the only option for maintaining sufficient access to maternal resources or signaling pathways late in gestation is via an expansion of the interface. Despite the significant increase in overall surface area, individual triplet fetuses are associated with much less surface area than are individual twins, suggestive of alterations in metabolic efficiency, perhaps via differential amino acid transport regulation.

Fast progression of recombinant human myelin/oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis in marmosets is associated with the activation of MOG34-56-specific cytotoxic T cells

The recombinant human (rh) myelin/oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE) model in the common marmoset is characterized by 100% disease incidence, a chronic disease course, and a variable time interval between immunization and neurological impairment. We investigated whether monkeys with fast and slow disease progression display different anti-MOG T or B cell responses and analyzed the underlying pathogenic mechanism(s). The results show that fast progressor monkeys display a significantly wider specificity diversification of anti-MOG T cells at necropsy than slow progressors, especially against MOG(34-56) and MOG(74-96). MOG(34-56) emerged as a critical encephalitogenic peptide, inducing severe neurological disease and multiple lesions with inflammation, demyelination, and axonal injury in the CNS. Although EAE was not observed in MOG(74-96)-immunized monkeys, weak T cell responses against MOG(34-56) and low grade CNS pathology were detected. When these cases received a booster immunization with MOG(34-56) in IFA, full-blown EAE developed. MOG(34-56)-reactive T cells expressed CD3, CD4, or CD8 and CD56, but not CD16. Moreover, MOG(34-56)-specific T cell lines displayed specific cytotoxic activity against peptide-pulsed B cell lines. The phenotype and cytotoxic activity suggest that these cells are NK-CTL. These results support the concept that cytotoxic cells may play a role in the pathogenesis of multiple sclerosis.

Germ-line chimerism and paternal care in marmosets (Callithrix kuhlii)

The formation of viable genetic chimeras in mammals through the transfer of cells between siblings in utero is rare. Using microsatellite DNA markers, we show here that chimerism in marmoset (Callithrix kuhlii) twins is not limited to blood-derived hematopoietic tissues as was previously described. All somatic tissue types sampled were found to be chimeric. Notably, chimerism was demonstrated to be present in germ-line tissues, an event never before documented as naturally occurring in a primate. In fact, we found that chimeric marmosets often transmit sibling alleles acquired in utero to their own offspring. Thus, an individual that contributes gametes to an offspring is not necessarily the genetic parent of that offspring. The presence of somatic and germ-line chimerism may have influenced the evolution of the extensive paternal and alloparental care system of this taxon. Although the exact mechanisms of sociobiological change associated with chimerism have not been fully explored, we show here that chimerism alters relatedness between twins and may alter the perceived relatedness between family members, thus influencing the allocation of parental care. Consistent with this prediction, we found a significant correlation between paternal care effort and the presence of epithelial chimerism, with males carrying chimeric infants more often than nonchimeric infants. Therefore, we propose that the presence of placental chorionic fusion and the exchange of cell lines between embryos may represent a unique adaptation affecting the evolution of cooperative care in this group of primates.

Response to novel food and the role of social influences in common marmosets (Callithrix jacchus) and Goeldi's monkeys (Callimico goeldii)

Neophobia, defined as showing caution toward novel features of the environment, is widespread in birds and mammals; it can be affected by ecology, early experience, and social context. In this study, we aimed to (i) investigate the response to novel food in adult common marmosets and Goeldi's monkeys and (ii) assess the role of social influences. We used an experimental paradigm employed previously with capuchin monkeys and children, in which a subject (observer) was presented with a novel food under three conditions: (i) Presence: group members did not have food; (ii) Different color: group members received familiar food whose color differed from that of the observer's novel food; (iii) Same color: group members received familiar food of the same color as the observer's novel food. Although most common marmosets tasted and/or ate the novel food, none of the Goeldi's monkeys ate it and only two sampled it. Differences in home range size and early social experience might explain the divergent behavior of the two species. Observers of both species similarly attended to group members and their visual attention increased with the number of group members eating, especially when the observer's and group members' foods were perceptually similar. However, we observed social influences on explorative behavior in Goeldi's monkeys but not on explorative or eating behavior in common marmosets. This result might be explained by the different pattern of response to novel food observed in the two species. Moreover, social influences on Goeldi's monkeys' behavior were nonspecific, i.e. they were not based on an appreciation that the food is safe because eaten by group members.

MHC Class II DRB genotyping is highly predictive of in-vitro alloreactivity in the common marmoset

The common marmoset (Callithrix jacchus) is emerging as a promising alternative pre-clinical model for transplantation and immunological research. It is therefore important to establish a rapid and reliable method of confirming alloreactivity between donor-recipient pairs. In this study of a large marmoset colony (n=49), we firstly characterised MHC Class II genes (Caja-DRB*W1201, Caja-DRB1*03, Caja-DRB*W16) using, for the first time in this species, sequence-based allelic typing techniques. Exon 2 was amplified using M13-tailed PCR primers specific for known marmoset alleles, and sequenced using universal M13 sequencing primers and dye terminator cycle sequencing. Twenty-six genotypes involving monomorphic Caja-DRB*W1201, 8 Caja-DRB*W16 and 5 Caja-DRB1*03 alleles were observed. Two new DRB*W16 alleles were identified. Subsequently we investigated whether matching at MHC-DRB loci alone could accurately predict in-vitro alloreactivity as assessed by mixed lymphocyte reactions. Peripheral blood mononuclear cells (PBMC) isolated from fully and partially DRB-matched and fully mismatched animal pairs were mixed and co-cultured for T-cell proliferation. PBMC co-cultured from fully or partially mismatched pairs exhibited significant T cell proliferation above single cell controls (p<0.01). Mixed PBMC from fully DRB-matched pairs exhibited no proliferation over controls (p=0.3). Thus using Caja-DRB genotyping, suitably alloreactive donor-recipient pairs can be rapidly and accurately identified for use in further studies of cellular and solid organ transplantation.

Paternity and kinship patterns in polyandrous moustached tamarins (Saguinus mystax)

We studied patterns of genetic relatedness and paternity in moustached tamarins, small Neotropical primates living in groups of 1-4 adult males and 1-4 adult females. Generally only one female per group breeds, mating with more than one male. Twin birth are the norm. In order to examine the genetic consequences of this mating pattern, DNA was extracted from fecal samples collected from two principal and six neighboring groups. DNA was characterized at twelve microsatellite loci (average: seven alleles/locus). We addressed the following questions: Do all adult males have mating access to the reproductive female of the group? How is paternity distributed across males in a group? Can polyandrous mating lead to multiple paternity? Are nonparental animals more closely related to the breeders than to the population mean? And, are mating partners unrelated? Breeding females mated with all nonrelated males. In at least one group the father of the older offspring did not sire the youngest infant although he was still resident in the group. We also found evidence for multiple paternity in a supposed twin pair. Yet, within each group the majority (67-100%) of infants had the same father, suggesting reproductive skew. Relatedness within groups was generally high (average R = 0.31), although both nonrelated males and females occurred, i.e., immigrations of both sexes are possible. Mating partners were never found to be related, hence inbreeding seems to be uncommon. The results suggest that while the social mating system is polyandry, paternity is often monopolized by a single male per group.

Non-human primate models of experimental autoimmune encephalomyelitis: Variations on a theme

Despite years of intensive research into multiple sclerosis (MS) scientists have not yet succeeded in developing an absolute therapy for the treatment of this disabling disease of the human central nervous system. The wide immunological gap between inbred rodent strains and the heterogeneous human population is probably the single most important factor that hampers the translation of scientific principles developed in rodents into effective therapies for MS. Because of the closer immunological proximity to humans, non-human primates provide useful experimental models that may help to bridge this gap. Here we review the models of experimental autoimmune encephalomyelitis in rhesus macaques and common marmosets. We will discuss the salient points of the models and suggest how these may represent the spectrum of inflammatory demyelinating diseases of the central nervous system in humans.

Review on testicular development, structure, function, and regulation in common marmoset

BACKGROUND

The common marmoset (Callithrix jacchus) is a New World primate that has been used increasingly in toxicological evaluations including testing for testicular toxicity of pharmaceutical and environmental chemicals. Information on structural and functional characteristics of the testis in common marmosets ("marmoset" in this review) is critical for designing experiments, interpreting data collected, and determining relevance to humans in risk assessment.

METHODS

This study provides a comprehensive review on testicular development, structure, function, and regulation in common marmosets.

RESULTS

There is little information regarding testicular formation and development during gestation. Based on the overall pattern of embryonic development in marmosets, it is postulated that gonadal formation and testicular differentiation most likely takes place during gestational Week 6-12. After birth, the neonatal period of the first 2-3 weeks and the pubertal period from Months 6-12 are critical for establishment of spermatogenesis in the adult. In the adult, a nine-stage model has been used to describe the organization of seminiferous epithelium and multiple stages per tubular cross-section have been observed. Seminiferous epithelium is organized in a wave or partial-wave manner. There are on average two stages per cross-section of seminiferous tubules in adult marmoset testis. Sertoli cells in the marmoset have a uniform morphology. Marmoset spermatogenesis has a high efficiency. The prime determinant of germ cell production is proliferation and survival of spermatogonia. Sertoli cell proliferation during the neonatal period is regulated by follicle-stimulating hormone (FSH), but chorionic gonadotropin (CG), instead of luteinizing hormone (LH), is the only gonadotropin with luteinizing function in marmoset. The receptor gene for CG in marmoset is unique in that it does not have exon 10. Marmosets have a "generalized steroid hormone resistance," i.e., relatively high levels of steroid hormones in circulation and relatively low response to exogenous steroids. Blockage of FSH, CG, and testosterone production during the first 3 months after birth does not cause permanent damage to the male reproductive system. Initiation of spermatogenesis in the marmoset requires unique factors that are probably not present in other mammals. Normal male marmosets respond to estradiol injection positively (increased LH or CG levels), a pattern seen in normal females or castrated males, but not usually in normal males of other mammalian species.

CONCLUSIONS

It seems that the endocrine system including the testis in marmosets has some unique features that have not been observed in rodents, Old World primates, and humans, but detailed comparison in these features among these species will be presented in another review. Based on the data available, marmoset seems to be an interesting model for comparative studies. However, interpretation of experimental findings on the testicular effects in marmosets should be made with serious caution. Depending on potential mode of testicular actions of the chemical under investigation, marmoset may have very limited value in predicting potential testicular or steroid hormone-related endocrine effects of test chemicals in humans.

The strange case of the armored scale insect and its bacteriome

Armored scale insects are unusual in that a part of their bodies is genetically distinct from the rest. This extraordinary phenomenon challenges the notion of identity

Non-invasive measurement of brain damage in a primate model of multiple sclerosis

Early recognition of whether a product has potential as a new therapy for treating multiple sclerosis (MS) relies upon the quality of the animal models used in the preclinical trials. The promising effects of new treatments in rodent models of experimental autoimmune encephalomyelitis (EAE) have rarely been reproduced in patients suffering from MS. EAE in outbred marmoset monkeys, Callithrix jacchus, is a valid new model, and might provide an experimental link between EAE in rodent models and human MS. Using magnetic resonance imaging techniques similar to those used in patients suffering from MS pathological abnormalities in the brain, white matter of the animal can be visualized and quantified. Moreover, NMR spectroscopy, in combination with pattern recognition, offers an advanced uroscopic technique for the identification of biomarkers of inflammatory demyelination.

The common marmoset (Callithrix jacchus) as a model in toxicology

The common marmoset, Callithrix jacchus, is the smallest nonhuman primate commonly used in biomedical research. Marmoset characteristics and propensities have enabled them to be used in a wide range of research as a model of human disease, physiology, drug metabolism, general toxicology, and reproductive biology. This paper provides a general overview of the marmoset with special emphasis on the benefits and disadvantages of this species as a model for inclusion in preclinical drug development programmes. In view of its small size in comparison with other nonrodent species marmosets have become of value for toxicology studies with biotechnology products where compound supply is limited. In general toxicology studies, marmosets have been successfully used to meet regulatory endpoints also for specific investigatory purposes. The widespread use of this species has allowed extensive background information to become available and a summary of the most frequently measured parameters are presented. Marmosets apparently represent an interesting animal model for comparative research on primate reproductive physiology. However, several basic aspects of reproductive processes exhibit cardinal discrepancies to those described for macaques and human. Thus, from the viewpoint of reproductive toxicology, the relevance of the marmoset primate model for human reproduction remains unclear to date and further research is obviously needed. Given our current knowledge of marmoset reproductive features, the use of this animal model cannot be recommended for reproductive toxicology assessment.