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Scientists use poop to study endangered monkeys’ mating behavior

In the lush Atlantic forest of Brazil, Northern muriquis, a critically of monkey, face an uncertain future. Understanding their mating behaviors is crucial for their survival. Researchers from the University of Texas at Austin and the –Madison embarked on a unique journey, delving into the monkeys' poop to unravel the secrets of mate selection.

Published in the journal Proceedings of the Royal Society B on Aug. 2, the paper combines analysis with long-term behavioral observations to shed light on the reproductive patterns of these rare primates. Unlike most primates, muriquis live in peaceful, egalitarian societies, with related males and their mothers forming the core. Over four decades, Karen Strier, a professor of anthropology at UW–Madison, has meticulously studied these monkeys in a preserved Brazilian forest, making her an expert in identifying individual monkeys and their relations.

By collecting fecal samples and providing them to Anthony Di Fiore, a professor of anthropology at UT Austin, and Paulo Chaves, Di Fiore's former graduate student, the team used DNA extracted from the samples to analyze the muriquis' mating behaviors. This non-invasive approach provides valuable insights into their intricate mating lives, essential for their species' long-term survival.

A group of northern muriquis sit together in a tree. The peaceful egalitarian structure of northern muriquis groups makes them different from many other groups of primates which tend to see more violence. Credit: Carla Possamai

Strier's field crew played a crucial role in this unique study, as their knowledge of which fecal sample belonged to each muriqui enabled the research team to ask specific genetic questions.

By combining behavioral observations and genetic analysis, the team made intriguing discoveries. The absence of mother-son pairings indicated that muriquis might possess the ability to recognize their kin, effectively avoiding incestuous mating. Furthermore, the lab analysis conducted by Chaves and Di Fiore revealed that females tended to mate with males who possessed a more diverse set of genes related to the major histocompatibility complex (MHC). These genes play a vital role in the body's immune response to pathogens and environmental stressors, highlighting the importance of in the species' reproductive choices.

Karen Strier of the University of Wisconsin–Madison during fieldwork in Brazil. Credit: João Marcos Rosa

The research team's findings offer valuable insights into the mating behaviors of muriquis. Di Fiore notes that the higher MHC diversity in male sires aligns with the idea that such diversity could contribute to male fitness, ensuring offspring have better chances of survival. This in MHC genes may also provide enhanced protection against pathogens and environmental stressors, proving evolutionarily advantageous.

Ideally, females should select males with both high MHC diversity and genetic variants different from their own to maximize the benefits for their offspring. Surprisingly, while females seemed to prioritize mates with higher MHC diversity, they didn't necessarily choose males with different MHC genes.

This study is significant, as it is among the few to explore the link between MHC variation and reproductive patterns in wild primates. Moreover, it stands as the only one to investigate an egalitarian species like muriquis, shedding light on the intricate dynamics of mate selection in these endangered monkeys.

Anthony Di Fiore of the University of Texas at Austin during fieldwork in Brazil. Credit: Anthony Di Fiore

The collaboration between Strier, Di Fiore, and Chaves brought excitement and reinforced the validity of Strier's long-term behavioral observations. Their collective findings have not only deepened our understanding of muriqui mating patterns but have also sparked intriguing questions for future research.

Chaves, the lead author of the study, pursued under Di Fiore's guidance through a prestigious fellowship from the Brazilian government. After completing his lab work, he returned to Brazil and secured a civil service position as a forensic geneticist with the government of the state of Goiás.

Looking ahead, the team plans to explore additional factors that might influence muriqui mate choice for both males and females, beyond MHC diversity. Unraveling these factors could provide further insights into how the monkeys optimize offspring survival.

Future collaborations hold great promise in unraveling the complexities of muriqui behavior and contributing to the ongoing efforts to conserve and protect this endangered species in the Atlantic forest of Brazil.

Source: University of Wisconsin-Madison

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