Researchers’ interest in marmosets as animal models has driven a sharp increase in demand for them. Presenters discussed the context of wild marmoset populations, challenges and opportunities for transporting marmosets, and innovative approaches to breeding marmosets in captivity.
Maria Adélia Borstelmann de Oliveira, a professor at the Animal Ecophysiology and Behavior Laboratory of the Federal Rural University of Pernambuco in Brazil, and Joanna Malukiewicz addressed the status and habits of marmosets in the wild.
Brazil’s Wild Marmoset Populations
Six marmoset species are part of the genus Callithrix, a relatively young genus under 2.5 million years old (see Figure 6-1). Three of these—C. aurita, C. flaviceps, and C. kuhlii—are endangered. Populations of the other three—C. jacchus, C. geoffroyi, and C. penicillata—are considered stable. C. jacchus is one of the youngest species and has the lowest genetic diversity, while the oldest, C. aurita, is the most genetically diverse.
Brazil is home to an estimated population of more than 10,000 wild mature marmosets across 20,000 square kilometers. Wild marmosets are found mainly in the northeastern Brazilian state of Pernambuco and in the country’s highly threatened Atlantic forest region (Amora et al. 2013), though they are also found in lowland rain forests, dry forest, dry scrub,
and mangroves. Despite being well adapted to these environments, marmosets live in one of the most threatened ecosystems on earth, the remaining 2 percent of which is a fragmented patchwork of small and isolated fragments. In the state of Pernambuco, at least two areas where common marmosets live, are under invasion by the Amazonian squirrel monkey, Saimiri sciureus. Borstelmann de Oliveira described the increased stress and behavioral change of the marmosets in the presence of the larger, and also highly insectivorous, squirrel monkeys, as shown by high levels of fecal cortisol of this population.
Marmosets were introduced to Brazil’s South and Southwest regions by humans and are thriving so well they are now considered pests. They are also spreading into Argentina. To protect other wildlife, the Brazilian Chico Mendes Institute for Biodiversity Conservation1 stresses the importance of controlling and eradicating marmosets in areas where they are invasive.
Wild marmosets live in groups of 3–15 members. They weigh less than 500 grams, are highly reproductive, and highly adaptable. Marmoset species hybridize both naturally and anthropogenically. While they are an invasive pest in some areas, in their native regions they face threats from habitat endangerment, especially in Pernambuco and the Atlantic forest, and competition for resources, especially from the invasive squirrel monkey from the Amazonian basin.
Like other primates in Brazil, marmosets are vulnerable to arboviruses. A recent yellow fever outbreak killed nearly 10 times as many NHPs as humans (Bicca-Marques et al. 2017). Human aggression and maltreatment are also leading causes of death of wild marmosets. According to CITES, approximately 1,600 marmosets were legally traded from 2006–2012, although those were mostly captive born. Legal trade is responsible for removing thousands of primates from the Brazilian wild each year. A recent analysis of CITES permits showed that 90,000 monkeys were legally exported from South American countries to 23 other countries between 1977 and 2013 (de Souza Fialho et al. 2016).
Marmoset Research in Brazil
Among Latin American countries, Brazil has the strongest legal protections for NHPs. All animal research in Brazil is regulated by the National Council for the Control of Animal Experimentation, which requires primate researchers to follow the National Research Council’s (NRC’s) 2011 Guide for the Care and Use of Laboratory Animals. Specific regulations restrict the collection of data and scientific materials in Brazil by foreigners, establish procedures for the scientific use of animals, and define categories of
use and management for wild animals in captivity. However, there remains room for improvement in the translation of these rules into practice both in Brazil and elsewhere; for example, primates under experimental protocols are housed in isolation, and deprived of natural light, despite recommendations emphasizing the importance of social housing.
There are more than 800 primates in private facilities,2 including zoos, research laboratories, rehabilitation centers, and sanctuaries in Brazil, used in more than 33 research areas from virology to toxicology to ophthalmology (Pissinatti et al. 2007). In addition to this basic and translational work, researchers are also working to expand their understanding of wild marmosets by focusing, for example, on marmosets’ taste receptors. Other work is examining the impacts of resource competition between native marmosets and invasive squirrel monkeys.
It is clear that a better understanding and consideration of the effects of captivity on marmosets is needed to inform their care and use as animal models. Researchers in Brazil are advancing knowledge in this area by comparing captive and wild marmoset behavior, including studies of gum eating, social and foraging behavior, and sensorial ecology. One study is examining the diet, food competition, and lipid profiles of both captive and wild marmosets; another has concluded that wild marmosets in competition for resources have a higher level of cortisol than captive marmosets or wild marmosets without competition. Investigations by Malukiewicz characterized differences in the microbiomes of captive and wild marmosets (see Chapter 5, the section Genetic Variation and the Gut Microbiome).
Researchers in Brazil and elsewhere are also working to advance conservation efforts for wild marmoset populations supported by legal protections in place across various countries in Latin America. The demand for marmoset research colonies can add pressures to these wild populations, suggesting a need for careful consideration of how founder marmoset populations are sourced to meet research demands without undermining conservation goals.
Jon Levine is the director of the WNPRC. Saverio “Buddy” Capuano is the associate director and attending veterinarian for the WNPRC. Together with Erika Sasaki these speakers discussed opportunities to address marmoset supply challenges through innovative approaches to breeding and transportation.
2 These facilities do not include the five largest centers of primatology in Brazil, including the Laboratory of Advanced Studies in Primatology (LEAP).
Marmoset Supply Challenges
It is estimated that research facilities currently house more than 6,000 marmosets worldwide, with about 2,500 of those animals located in Japan; 1,900 in North America; 1,000 in Europe; and 800 in South America. An unknown number is located in China. In contrast, macaques are far more widely available for research, supported by a strong infrastructure for their breeding and transportation. Macaques are bred by the U.S. National Primate Research Centers (NPRCs), NIH, and multiple other academic institutions and commercial entities in the United States and abroad. Macaques are also much hardier than marmosets and travel well; each year about 30,000 macaques, compared with only 250 marmosets, are transported for research (see Figure 6-2).
In the United States, marmoset demand is quickly outstripping supply. About 1,900 marmosets are spread among 27 research colonies in the United States, where at least 40 primary investigators are working with them. Querying the NIH RePORTER database3 for the text “marmoset/marmosets” showed that each year for the past 10 years, approximately 50 grants were awarded for marmoset research in the United States—a number that is expected to grow. During the discussion an attendee noted that another sign of this increased demand is the sharp increase in references to marmosets in the Society for Neuroscience annual conference programs
over the past few years. The most recent conference, for example, featured 61 posters of marmoset research.
The increased demand has come somewhat as a surprise. In fact, the WNPRC had until fairly recently been using birth control drugs to keep its marmoset population in check and avoid overtaxing the center’s resources and infrastructure to care for the animals. The WNPRC has also given some marmosets to other institutions to start their own research colonies, though the number of marmosets available for transfer has not been sufficient to meet the current demand.
Japan is seeing a similar gap between marmoset demand and availability. Marmoset research in Japan began in 1978, when leading scientist Tatsuji Nomura identified marmosets as an ideal NHP model. In 1996, Nomura’s breeding colony was transferred to CLEA Japan, Inc. Until around 2000, researchers in Japan showed little interest in marmosets, preferring to work with macaques, leading CLEA to reduce its marmoset breeding program to address persistent oversupply. Today CLEA’s 1,000 marmosets are insufficient to meet the demand and the organization is actively trying to grow this population.
Importing marmosets to Japan is not an option. In a frustrating catch-22, only Air France is allowed to transport marmosets to Japan, but in Japan it is prohibited to import marmosets from France. Another challenge is that marmosets in Japan all come from the same initial colony (imported from the United Kingdom) and so are interrelated, which makes the lack of genetic diversity a serious issue for the researchers working with them.
Drivers of Research Demand
All primates are considered desirable models for high priority research areas across the globe, including cognition, neurodevelopmental disorders, neurodegenerative diseases, aging, behavior, reproductive biology, physiology, and metabolic diseases. For this work, and as other speakers mentioned, marmosets present with specific advantages: they are easier to work with and maintain; they require less space; they have a short generation time and short lifespan; and they have multiple births. Current shortages notwithstanding, marmosets are also relatively inexpensive to acquire and to maintain compared to other primate species.
As discussed in Chapter 2 (the section Current Use and Key Advantages), marmoset demand is also on the rise because they are well suited for emerging transgenic and gene editing techniques. One WNPRC study is using CRISPR/Cas9 gene editing approaches to develop a marmoset model for familial Parkinson’s disease, a process extending over multiple generations of animals that involves much trial and error. Another WNPRC study is using nanoparticles to genetically edit marmoset neurons
for neurogenetic diseases research (Furtado et al. 2018). NIH researchers are studying somatic cell genomic editing in marmosets. These methods and others have contributed to the development of marmoset models for MPTP-induced Parkinson’s and spinal injury and the establishment of marmoset embryonic stem cell lines.
In Japan, much of the increased demand for marmosets has been propelled by two large-scale scientific initiatives: the 2008 Strategic Research Program for Brain Science and the 2014 Brain/MINDS project (Okano et al. 2016). Both use marmosets as a primary model organism.
Approaches to Increase Marmoset Supply
Panelists discussed three possible solutions to improve researchers’ access to marmosets: a consortium of marmoset principal investigators (PIs), a coordinated strategic plan to increase the marmoset population, and an embryo exchange. The first two are already under way, and Sasaki proposed the third in her presentation.
Marmoset PI Consortium: Recently, PIs who use marmosets held an informal meeting to discuss current research, marmoset management issues, and goals for the development of marmoset models. The PIs agreed to create a consortium to facilitate efforts to share information and trade animals. Consortium members discussed several options for improving marmoset supplies. These include the establishment of centralized breeding facilities, a centralized pedigree tracking system and animal locator, and a quarantine facility for imported animals.
The consortium also hopes to improve overall communication, especially with South American colleagues closest to wild marmoset populations, and identify best practices for marmoset transportation and care. Members plan to publish a white paper to enhance the visibility of marmoset supply challenges, and to convene again in 2019.
NIH Strategic Plan: The NPRC directors have been working closely to address the problem of marmoset availability. The group has identified several urgent needs to accurately monitor supply and demand of marmosets, develop a plan to adjust breeding targets, expand facilities, and increase resources to distribute expertise and core services more efficiently, and address the concerns that have been raised about marmoset genetic diversity.
NIH and the Office of Research Infrastructure Programs have taken several concrete steps to address these needs and strategically plan for improving the environment for NHP research more broadly. As a first step, a needs assessment was conducted that recommends developing and expanding colonies, identifying the new techniques driving the research, and helping the NPRCs and other facilities meet the increased demand.
The first phase of this effort focused mainly on macaques, but many of its findings apply to marmosets, as well.
The second part of this effort convened an expert panel discussion including program officers from nearly all NIH institutes. The panel was charged to forecast the future of NHPs in biomedical research, assess existing resources and infrastructure and the potential need for expansion, and identify key challenges. Challenges identified include funding, space, and infrastructure limitations; a lack of standardized data collection and reporting; and needs related to personnel training. Among several recommendations emerging from the discussion, the one most pertinent to marmoset research is that NIH should prioritize, fund, and establish a breeding production site for marmosets as part of a federally distributed system for animal production (NIH 2018).
Embryo Transfer: In Japan, a limited marmoset supply combined with a lack of genetic diversity and restrictions on importing have driven a focus on developing techniques to transfer marmoset embryos, rather than live animals. Sasaki’s team has developed non-surgical techniques to remove fertilized embryos, freeze them, and implant them in a surrogate female for gestation, resulting in successful healthy births (Thompson et al. 1994).
If permitted under CITES, fertilized marmoset embryos (including wildtype embryos and/or genetically modified ones) could be transported among research facilities within and between countries for implantation in surrogate marmosets at the receiving facility. Embryo transfers have a higher success rate than insemination after cryopreservation, and this approach is easier from a technical perspective compared with other procedures. Embryo transfers also entail a complete genetic exchange, whereas sperm transfers result in a transfer of only half of a set of genes.
Amora TD, Beltrão-Mendes R, Ferrari SF. 2013. Use of alternative plant resources by common marmosets (Callithrix jacchus) in the semi-arid caatinga scrub forests of northeastern Brazil. Am J Primatol Apr; 75(4):333–341.
Bicca-Marques JC, Calegaro-Marques C, Rylands A, et al. 2017. Yellow fever threatens Atlantic Forest primates. Science Advances 3.e1600946/tab-e.
de Souza Fialho M, Ludwig G, Valenca-Montenegro MM. 2016. Legal international trade in live neotropical primates originating from South America. Primate Conservation 30:1–6.
Furtado D, Björnmalm M, Ayton S, et al. 2018. Overcoming the blood brain barrier: The role of nanomaterials in treating neurological diseases. Adv Mater 30(46):e1801362.
NIH (National Institutes of Health). 2018. Nonhuman Primate Evaluation and Analysis, Part 2. Report of the Expert Panel Forum on Challenges in Assessing Nonhuman Primate Needs and Resources for Biomedical Research. Available at: https://orip.nih.gov/about-orip/research-highlights/nonhuman-primate-evaluation-and-analysis-part-2-report-expert-panel.
NRC (National Research Council). 2011. Guide for the Care and Use of Laboratory Animals: Eighth Edition. Washington, DC: The National Academies Press. Available at: https://www.nap.edu/catalog/12910.
Okano H, Sasaki E, Yamamori T, et al. 2016. Brain/MINDS: A Japanese national brain project for marmoset neuroscience. Neuron 92(3):582–590.
Pissinatti L, Pissinatti A, Burity CHF, et al. 2007. Ocorrência de acantocephala em Leontopithecus (Lesson, 1840) cativos: Aspectos clínico-patológicos. Callitrichidae—Primates. Arq Bras Med Vet Zootec 59:1473–1477.
Thomson JA, Kalishman J, Hearn JP. 1994. Nonsurgical uterine stage preimplantation embryo collection from the common marmoset. J Med Primatol 23(6):333–336.
This page intentionally left blank.