ABSTRACT A multitude of malaria species (genus Plasmodium ) infects primates. Due to their public health importance, the human-infective species have garnered the most focus, but increased knowledge of non-human primate malaria species is warranted to improve our evolutionary understanding of host-parasite interactions. Additionally, the broad host tropism of some primate malaria parasites and their realized or theorized zoonotic potential add urgency to understanding of primate-parasite interactions. Here, we use comparative transcriptomics to understand the rhesus macaque ( Macaca mulatta ) response to two malaria parasites used as analogues to human-infective species of differing severity and which may represent emerging zoonotic threats: P. coatneyi , comparable to human-infective P. falciparum , and P. cynomolgi , comparable to human-infective P. vivax . We first validate our transcriptomics-based proxy of parasite load through comparison to gold-standard microscopy-based measures. We then find that malaria-associated host genes have functional links to immune system regulation and blood cells. Host genes with differing expression by malaria species were more likely to be involved in brain-linked functions, perhaps due to the differential central nervous system involvement of the two parasite species. Such comparative work on primate malaria species may help elucidate the essential and species-specific molecular mechanisms that underlie differing clinical presentations and zoonotic risk.

The critically endangered western gorillas (Gorilla gorilla) are divided into two subspecies: the western lowland (G. g. gorilla) and the Cross River (G. g. diehli) gorilla. Given the difficulty in sampling wild great ape populations and the small estimated size of the Cross River gorilla population, only one whole genome of a Cross River gorilla has been sequenced to date, hindering the study of this subspecies at the population level. In this study, we expand the number of whole genomes available for wild western gorillas, generating 41 new genomes (25 belonging to Cross River gorillas) using single shed hairs collected from gorilla nests. By combining these genomes with publicly available wild gorilla genomes, we confirm that Cross River gorillas form three population clusters. We also found little variation in genome-wide heterozygosity among them. Our analyses reveal long runs of homozygosity (>10 Mb), indicating recent inbreeding in Cross River gorillas. This is similar to that seen in mountain gorillas but with a much more recent bottleneck. We also detect past gene flow between two Cross River sites, Afi Mountain Wildlife Sanctuary and the Mbe Mountains. Furthermore, we observe past allele sharing between Cross River gorillas and the northern western lowland gorilla sites, as well as with the eastern gorilla species. This is the first study using single shed hairs from a wild species for whole genome sequencing to date. Taken together, our results highlight the importance of implementing conservation measures to increase connectivity among Cross River gorilla sites.

A large brain is a defining feature of modern humans, and much work has been dedicated to exploring the molecular underpinnings of this trait. Although numerous studies have focused on genes associated with human microcephaly, no studies have explicitly focused on genes associated with megalencephaly. Here, we investigate 16 candidate genes that have been linked to megalencephaly to determine if: (1) megalencephaly-associated genes evolved under positive selection across primates; and (2) selection pressure on megalencephaly-associated genes is linked to primate brain size. We found evidence for positive selection for only one gene, OFD1 , with 1.8% of the sites estimated to have d N /d S values greater than 1; however, we did not detect a relationship between selection pressure on this gene and brain size across species, suggesting that selection for changes to non-brain size traits drove evolutionary changes to this gene. In fact, our primary analyses did not identify significant associations between selection pressure and brain size for any candidate genes. While we did detect positive associations for two genes ( GPC3 and TBC1D7 ) when two phyletic dwarfs (i.e., species that underwent recent evolutionary decreases in brain size) were excluded, these associations did not withstand FDR correction. Overall, these results suggest that sequence alterations to megalencephaly-associated genes may have played little to no role in primate brain size evolution, possibly due to the highly pleiotropic effects of these genes. Future comparative studies of gene expression levels may provide further insights. This study enhances our understanding of the genetic underpinnings of brain size evolution in primates and identifies candidate genes that merit further exploration.

Malaria is infamous for the massive toll it exacts on human life and health. In the face of this intense selection, many human populations have evolved mechanisms that confer some resistance to the disease, such as sickle-cell hemoglobin or the Duffy null blood group. Less understood are adaptations in other vertebrate hosts, many of which have a longer history of co-evolution with malaria parasites. By comparing malaria resistance adaptations across host species, we can gain fundamental insight into host-parasite co-evolution. In particular, understanding the mechanisms by which non-human primate immune systems combat malaria may be fruitful in uncovering transferable therapeutic targets for humans. However, most research on primate response to malaria has focused on a single or few loci, typically in experimentally-infected captive primates. Here, we report the first transcriptomic study of a wild primate response to a malaria-like parasite, investigating gene expression response of red colobus monkeys ( Piliocolobus tephrosceles ) to natural infection with the malaria-like parasite, Hepatocystis . We identified colobus genes with expression strongly correlated with parasitemia, including many implicated in human malaria and suggestive of common genetic architecture of disease response. For instance, the expression of ACKR1 (alias DARC ) gene, previously linked to resistance in humans, was found to be positively correlated with parasitemia. Other similarities to human parasite response include induction of changes in immune cell type composition and, potentially, increased extramedullary hematopoiesis and altered biosynthesis of neutral lipids. Our results illustrate the utility of comparative immunogenetic investigation of malaria response in primates. Such inter-specific comparisons of transcriptional response to pathogens afford a unique opportunity to compare and contrast the adaptive genetic architecture of disease resistance, which may lead to the identification of novel intervention targets to improve human health. Author Summary The co-evolutionary arms race between humans and malaria parasites has been ongoing for millennia. Fully understanding the evolved human response to malaria is impossible without comparative study of parasites in our non-human primate relatives. Though laboratory primates are fruitful models, the complexity of wild primates infected in a natural transmission system may be a more suitable comparison for contextualizing malaria infections in human patients. Here, we investigate the genetic mechanisms underlying the immune response to Hepatocystis , a close relative of human-infective malaria, in a population of wild Ugandan red colobus monkeys. We find that the genes involved have considerable overlap with those active in human malaria patients. Like Plasmodium , Hepatocystis induces changes in blood cell type and may cause the host to produce blood components outside of the bone marrow or alter metabolism related to the production of lipids. Our work helps to identify the genetic mechanisms underlying the arms race between primates and malaria parasites, providing fundamental evolutionary insight. Such comparative work on the interaction between wild non-human primates and malaria parasites can identify ways in which primates have evolved resistance to malaria parasites, and further investigation of such implicated genes may lead to novel potential therapeutic and vaccine targets.

Supplemental data for analysis of gene expression response of Ugandan red colobus monkeys (Piliocolobus tephrosceles) to Hepatocystis, a malaria-like parasite.