Chimerism in Callitrichids

The immersion Internship at Pacific Primate Sanctuary (PPS) provides Interns with an opportunity to expand their knowledge of New World Primate species, both through hands-on experience as well as making use of educational resources. The monthly Talk Story- Special Topic encourages Interns to gain a more in depth understanding of each of the species here at PPS.  Following is a Special Topic written by Intern Holly.

 Special Topic by Intern Holly

Genetic chimerism occurs when an organism has cells that are genetically distinct from one another. This organism may have blood cells of differing blood types, or two differently-colored eyes, or they may even have a mix of male and female reproductive organs. In most animals, chimerism develops when multiple fertilized eggs merge together while in utero, creating a single organism with multiple cells that are different from rest of the body’s genetic structure; thus, chimerism is often the result of a zygote absorbing their twin. Chimerism can also occur in plants, but the chimera is often the result of a mutation during cell division, rather than two early-developed organisms merging together.

All species of Callitrichidae, aside from the Goeldi’s marmoset (Callimico goeldii), routinely give birth to fraternal twins. Early in development, the placentas of the twin embryos fuse together. This placental fusion allows the twins to exchange stem cells, specifically germ cells and hematopoietic cells. Germs cells are the cells that will give rise to gametes (ovum and sperm) in reproductive organs, while hematopoietic cells will become blood cells. These mixed hematopoietic cells can be found in blood, bone marrow, and internal organs, which means that every tamarin and marmoset is a composite of cells from multiple individuals: a chimera. 

Callitrichids also routinely engage in germline chimerism, a trait that is unique to them specifically due to its regular occurrence, rather than by chance. As mentioned, germ cells will become gametes, the cells that an organism uses to reproduce. During cell exchange through the fused placenta the twins’ germ cells exchange alleles. Alleles are the expressed variants of genes, i.e.: whether an animal will have blue or green eyes. Not only is every tamarin and marmoset a chimera, they also carry reproductive alleles of their fraternal twin, in addition to their own. 

One implication of germline chimerism is that a tamarin or marmoset could sire or give birth to offspring that are more genetically related to their twin than to them. Evidence suggests that chimerism is a contributor for the cooperative breeding system found in Callitrichids. In a cooperative breeding system, all members of a family group help care for offspring, not just parents. Personal reproductive fitness is the number of offspring that an individual bears, while inclusive reproductive fitness is the number of offspring equivalents that an individual raises. The non-reproducing “helpers” in a cooperative breeding system are engaging in inclusive fitness: by taking care of their siblings or nieces/nephews, they are ensuring that their family line lives on, even if they do not reproduce themselves. Due to germline chimerism and the resulting interrelatedness of the family group, it becomes very important for a tamarin or marmoset to help care for their siblings/niece/nephew, because that offspring may actually be more closely related to them than to their biological parents. 

Many of the tamarins and marmosets at Pacific Primate Sanctuary come from the same family groups. With the knowledge of chimerism, it becomes evident that the level of interrelatedness is more complicated than a standard family tree diagram would suggest. When attempting to pair a male and female, we have had the most success with pairing two completely unrelated individuals. Not only does this kind of pairing have the most resemblance to wild Callitrichid breeding pairs, but it is possible that tamarins and marmosets may recognize family traits, even in an individual they have never met before, and prefer not to partner with a closely related individual, although, more evidence is needed to support this hypothesis. (Male Callitrichids at PPS have been vasectomized.)

References

• Rutherford, J. N. & Tardif, S. “Mother’s Little Helper? The Placenta and Its Role in Intrauterine Maternal Investment in the Common Marmoset (Callithrix jacchus).” 
• The Smallest Anthropoids: The Marmoset/Callimico Radiation, edited by Susan M. Ford, Leila M. Porter, & Lesa C. Davis, Springer, 2009, pp. 301-329.

The Amazon Rainforest, here and now

The immersion Internship at Pacific Primate Sanctuary (PPS) provides Interns with an opportunity to expand their knowledge of New World Primate species, both through hands-on experience as well as making use of educational resources. The monthly Talk Story- Special Topic encourages Interns to gain a more in depth understanding of each of the species here at PPS.  Following is a Special Topic written by Intern Cookie.

Intern Cookie: Special Topic

Spanning three million square miles, constituting 30% of South America’s surface area, housing over 30% of the world’s insect, plant, and animal species, harboring a rich mosaic of tropical vegetation that each moment transpires oxygen and water, stores carbon, indiscriminately shelters vast populations and holistically provides for its contingent, the Amazon Rainforest is the cradle of the world’s biodiversity and fragile ecosystem. Why does the Amazon Rainforest play this critical role? Perhaps because nature spent millions of years implementing and refining delicate, specific, and effective practices. Practices that could (can) be capricious, arbitrary, callous at times, but also processes that were (are) dependable, self-sustaining, mechanistic, and not only account for but wholly depend upon variation. If a country were to govern and provide for its population in a similar manner, we would deem it a success. With the increasing global economic initiatives dependent on its destruction, we have deemed the Amazon rainforest a success to be exploited.

In the last 50 years, one fifth of the of the Amazon Rainforest has been slashed and burned, mostly in Brazil, whose borders contain over two thirds of the Amazon basin. More land, not accounted for by this proportion, has been fragmented and degraded. 

Why is this happening? Industrial agricultural practices, mining, logging, and cattle farming are the major contributors, but there are also other culprits in the ongoing destruction. The displacement/destruction of indigenous communities, the removal of keystone species, the construction of dams, and the expansion of urban areas also cause forest loss. Humans have proven incredibly adept at occupying any ecological niche, mostly because technology and social collaboration allows for the acquisition of resources from nature. And the Amazon Rainforest is the richest, densest repository of natural resources in the world.   

Yet even small changes to the Amazon Rainforest have a ripple effect. With the abundance of trees that store carbon in their trunks, branches, and leaves, the Amazon acts as a carbon sink. As the forest is degraded and disturbed, as it has been in recent years, carbon gains have begun to exceed carbon losses. Carbon storage negates temperature elevation on a global scale, but the release of carbon exacerbates this issue. Daily, the earth is warmed by the sun, and this heat rises into the atmosphere. Atmospheric gases, especially carbon dioxide, capture solar heat and radiate it back towards earth. More atmospheric carbon, therefore, creates higher global temperatures. As temperatures rise, the delicate tropical balance of rainy and dry seasons is disrupted, and the Amazon rainforest (as well as other forests and lands across the globe) becomes increasingly susceptible to drought and the continued loss of vegetation. While humans exploit the Amazon’s land, timber, and minerals, countless other species depend on, and symbiotically contribute to, the Rainforest’s rich and complex ecosystem. Deforestation of the Amazon is their loss, too. 

Pacific Primate Sanctuary (PPS) is home to five different primate species, all of which are endemic to the Amazon Rainforest in South and Central America. In nature, these primates serve as ecological engineers through seed dispersal, exudativory and insectivory. Due to their feeding ecology as well as their role as both predator and prey in the wild, marmosets, tamarins, capuchins, and spider monkeys represent keystone species in the Amazon biosystem. While these individual animals have found refuge at PPS, their species have nowhere else to go. Their habitat has been destroyed, and their contributions to growing, maintaining, and sustaining the Amazon Rainforest have been negated. 

Climate change, habitat loss, and elimination of biodiversity are all environmental buzzwords—buzzwords that in 2000 incited a change in Brazil’s environmental protection policies. By implementing governmental incentives to conserve Amazon lands, regulating agriculture, practicing sustainable development, and collaborating with activists and researchers, Brazil slowed the rate of forest destruction. In 2012, the country reached the lowest rate of deforestation since record-keeping began. Sadly, in 2018, the election of the country’s new president, Jair Bolsanaro, has led to the prioritization of agribusiness initiatives over conserving this massive terrestrial ecosystem. Since his election in October, environmental protection policies have been lifted and conservation efforts undermined. Recent reports have shown that even in a short time period, from October to July 2019, the rate of Rainforest destruction has exceeded 50% of the deforestation rate during the same time period last year. While Brazil was once a global leader in preservation, recent policy changes have led to a role reversal. The country’s shift from environmental protection to promoting environmental degradation suggests that the significance of conservation has been dampened and its implications ignored and overruled. As the rate of climate change, habitat loss, and biodiversity elimination accelerates, no one seems to be watching and listening.

While human actions are the root cause of the destruction and fragmentation of the Rainforest, our actions are also the only way that these practices can be halted and their effects prevented. Living in a first-world country, far removed from the vibrant web of life in the Amazon basin, it not only easy but natural to feel aloof, guiltless, and uninvolved in its systematic destruction.

Yet, we are living in an era of globalization and vast social interconnectedness. Now, more than ever, it is imperative that we also feel connected to nature, attuned to its needs and effected by its devastation. This relationship is one of mutual dependence, and we are the gatekeepers of change to our earth, our home. 

Literature Cited

-Baccini, A, et al. “Tropical Forests Are a Net Carbon Source Based on Aboveground Measurements of Gain and Loss.” Science (New York, N.Y.), vol. 358, no. 6360, 2017, pp. 230–234.

-“Brazil’s Sustainability Needs Social Sciences.” Nature Sustainability, vol. 1, no. 11, 2018, p. 607.

-Carson, Walter P., et al. Tropical Forest Community Ecology. Wiley-Blackwell Pub., 2008.

-Casado, Letícia, and Ernesto Londoño. “Under Brazil’s Far-Right Leader, Amazon Protections Slashed and Forests Fall.” New York Times, 28 July 2019.

-Link, A., and Di Fiore, A. “Seed Dispersal by Spider Monkeys and Its Importance in the Maintenance of Neotropical Rain-Forest Diversity.” Journal of Tropical Ecology, vol. 22, 2006, pp. 235–246.

-Sussman, R. W., and W. G. Kinzey. “The Ecological Role of the Callitrichidae: A Review.” American Journal of Physical Anthropology, vol. 64, no. 4, 1984, pp. 419–449.