Male bonobos track females’ reproductive cycle to maximize mating success

Female sexual swelling is an unreliable fertility signal, but males can time matings anyway

Peer-Reviewed Publication

PLOS

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Male–male agonistic interaction during a mating attempt in wild bonobos.

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Credit: Heungjin Ryu (CC-BY 4.0, https://creativecommons.org/licenses/by/4.0/)

Male bonobos can decipher females’ unreliable fertility signals, allowing them to focus their efforts on matings with the highest chance of conception, according to a study by Heungjin Ryu at Kyoto University, Japan, and colleagues publishing December 9th in the open-access journal PLOS Biology.

In most mammals, females are only receptive to mating during ovulation, allowing males to time their mating efforts to maximize the chances of conception. But in some primates, such as bonobos (Pan paniscus), females become sexually receptive and display a conspicuous pink swelling around the genitals for a prolonged period of time.

To investigate how males cope with this unreliable fertility signal, researchers studied a group of wild bonobos at Wamba in the Luo Scientific Reserve in the Democratic Republic of the Congo. During daily observations, they recorded sexual behaviors and visually estimated the status of each female’s genital swelling. They also used filter paper to collect urine samples of the females, allowing them to measure estrogen and progesterone levels and estimate the timing of ovulation. They found that ovulation probability peaked between 8 and 27 days after females reached maximum swelling, making it difficult for males to predict. Despite this, males’ sexual advances were closely aligned with the timing of ovulation. Males concentrated their mating efforts on females that had reached maximum swelling earlier, and whose infant offspring were older — two key sources of information indicating a higher probability of ovulation.

The results show that males focus their mating efforts on the most fertile females by combining information about the timing of swelling and reproductive history. Because male bonobos can effectively estimate female fertility despite an unreliable signal, there has likely been little evolutionary pressure for the signal to become more precise. This may explain how this system has been maintained over evolutionary time, the authors say.

The authors add, “In this study, we found that bonobo males, instead of trying to predict precise ovulation timing, use a flexible strategy—paying attention to the end-signal cue of the sexual swelling along with infant age—to fine-tune their mating efforts. This finding reveals that even imprecise signals can remain evolutionarily functional when animals use them flexibly rather than expecting perfect accuracy. Our results help explain how conspicuous but noisy ovulatory signals, like those of bonobos, can persist and shape mating strategies in complex social environments.”

“The male bonobos weren’t the only ones paying close attention to sexual swelling—we spent countless days in the rainforest at Wamba, DRC doing exactly the same thing! All that watching, sweating, and scribbling in our notebooks eventually paid off. By tracking these daily changes, we uncovered just how impressively bonobos can read meaning in a signal that seems noisy and confusing to us.”

 

In your coverage, please use this URL to provide access to the freely available paper in PLOS Biology: https://plos.io/4r584R0

Citation: Ryu H, Hashimoto C, Hill DA, Mouri K, Shimizu K, Furuichi T (2025) Male bonobo mating strategies target female fertile windows despite noisy ovulatory signals during sexual swelling. PLoS Biol 23(12): e3003503. https://doi.org/10.1371/journal.pbio.3003503

Author countries: Japan

Funding: This study was supported by the Global Environment Research Fund (D-1007 to TF) of the Japanese Ministry of the Environment, the Japan Society for the Promotion of Science (JSPS) Grants-in-Aid for Scientific Research (22255007 to TF; https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-22255007/, and 25304019 to CH; https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-25304019/), and the JSPS Asia-Africa Science Platform Program (2012–2014 to TF). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Male bonobos track females’ reproductive cycle to maximize mating success [VIDEO] 

In this clip, the beta male Nobita carefully looks at the sexual swelling of the female Sala while they forage for fungi on the forest floor. Male bonobos take this task seriously—watching and checking swelling changes so they do not miss potential ovulatory periods.

Credit

Heungjin Ryu (CC-BY 4.0, https://creativecommons.org/licenses/by/4.0/)

Male bonobos track females’ reproductive cycle to maximize mating success [VIDEO] 

In this video, two male bonobos and one female engage in a mating-related conflict. The beta male, Nobita, solicits copulation from a female, Fuku. Once they begin copulating, the alpha male, Kitaro—Nobita’s younger brother—attempts to intervene. Despite his efforts, Nobita and Fuku continue and complete the copulation. Afterward, Fuku becomes upset and briefly chases Kitaro.

Credit

Heungjin Ryu (CC-BY 4.0, https://creativecommons.org/licenses/by/4.0/)

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Journal

PLOS Biology

DOI

10.1371/journal.pbio.3003503 

Method of Research

Observational study

Subject of Research

Animals

COI Statement

Competing interests: The authors have declared that no competing interests exist.

 

Humans rank between meerkats and beavers in monogamy ‘league table’

University of Cambridge

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Humans are far closer to meerkats and beavers for levels of exclusive mating than we are to most of our primate cousins, according to a new University of Cambridge study that includes a table ranking monogamy rates in various species of mammal.

Previous evolutionary research has used fossil records and anthropological fieldwork to infer human sexual selection. While in other species, researchers have conducted long-term observations of animal societies and used paternity tests to study mating systems.

Now, a new approach by Dr Mark Dyble from Cambridge’s Department of Archaeology analyses the proportions of full versus half-siblings in a host of species, as well as several human populations throughout history, as a measure for monogamy.

Species and societies with higher levels of monogamy are likely to produce more siblings that share both parents, says Dyble, while those with more polygamous or promiscuous mating patterns are likely to see more half-siblings.

He devised a computational model that maps sibling data collected from recent genetic studies onto known reproductive strategies to calculate an estimated monogamy rating.

While still a rough guide, Dyble argues this is a more direct and concrete way to gauge patterns of monogamy than many previous methods when looking at a spectrum of species, and human societies over thousands of years.    

“There is a premier league of monogamy, in which humans sit comfortably, while the vast majority of other mammals take a far more promiscuous approach to mating,” said Dyble, an evolutionary anthropologist at the University of Cambridge.

“The finding that human rates of full siblings overlap with the range seen in socially monogamous mammals lends further weight to the view that monogamy is the dominant mating pattern for our species.”

The question of human monogamy has been debated for centuries. It has long been hypothesised that monogamy is a cornerstone of the social cooperation that allowed humans to dominate the planet.

However, anthropologists find a wide range of mating norms among humans. For example, previous research shows that 85% of pre-industrial societies permitted polygynous marriage – where a man is married to several women at the same time.

To calculate human monogamy rates, Dyble used genetic data from archaeological sites, including Bronze Age burial grounds in Europe and Neolithic sites in Anatolia, and ethnographic data from 94 human societies around the world: from Tanzanian hunter-gatherers the Hadza, to the rice-farming Toraja of Indonesia.

“There is a huge amount of cross-cultural diversity in human mating and marriage practices, but even the extremes of the spectrum still sit above what we see in most non-monogamous species,” said Dyble.

The study, published in Proceedings of the Royal Society: Biological Sciences, has humans at an overall 66% rate for full siblings, placing us seventh of eleven species in the study considered socially monogamous and preferring long-term pair bonds.

Meerkats come in at a 60% full sibling rate while beavers just beat humans for monogamy with a 73% rate. As with humans, this suggests a significant trend towards monogamy for these species, but with a solid amount of flexibility.

The white-handed gibbon comes closest to humans in the study, with a monogamy rate of 63.5%. It’s the only other top-ranked “monotocous” species, meaning it usually has one offspring per pregnancy, unlike the litters had by other monogamous mammals.

The only other non-human primate in the top division is the moustached tamarin: a small Amazonian monkey that typically produces twins or triplets, and has a full sibling rate of almost 78%.   

All other primates in the study are known to have either polygynous or polygynandrous (where both males and females have multiple partners) mating systems, and rank way down the monogamy table.  

Mountain gorillas manage a 6% full sibling rate, while chimpanzees come in at just 4% – on a par with dolphins. Various macaque species, from Japanese (2.3%) to Rhesus (1%), sit almost at the bottom of the table.

“Based on the mating patterns of our closest living relatives, such as chimpanzees and gorillas, human monogamy probably evolved from non-monogamous group living, a transition that is highly unusual among mammals,” said Dyble.  

Among the few with a similar evolutionary shift are species of wolf and fox, which have a degree of social monogamy and cooperative care, whereas the ancestral canid was likely to have been group-living and polygynous.

The Grey Wolf and Red Fox sneak into the upper league with full sibling rates of almost half (46% and 45% respectively), while African species have much higher rates: the Ethiopian wolf comes in at 76.5%, and the African Wild dog is ranked second for monogamy with a rating of 85%.

Top of the table is the California deermouse that stays paired for life once mated, with a 100% rating. Ranked bottom is Scotland’s Soay sheep, with 0.6% full siblings, as each ewe mates with several rams.

“Almost all other monogamous mammals either live in tight family units of just a breeding pair and their offspring, or in groups where only one female breeds,” said Dyble. “Whereas humans live in strong social groups in which multiple females have children.”

The only other mammal believed to live in a stable, mixed-sex, multi-adult group with several exclusive pair bonds is a large rabbit-like rodent called the Patagonian mara, which inhabits warrens containing a number of long-term couples. 

Dyble added: “This study measures reproductive monogamy rather than sexual behaviour. In most mammals, mating and reproduction are tightly linked. In humans, birth control methods and cultural practices break that link.”

“Humans have a range of partnerships that create conditions for a mix of full and half-siblings with strong parental investment, from serial monogamy to stable polygamy.”

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Journal

Proceedings of the Royal Society B Biological Sciences

DOI

10.1098/rspb.2025.2163 

Method of Research

Data/statistical analysis

Article Title

Human monogamy in mammalian context

Article Publication Date

10-Dec-2025

 

New method to accelerate vaccine and drug development for norovirus

Researchers from The University of Osaka have developed a simple and efficient system for understanding the functions of specific norovirus genes, providing new avenues for developing antivirals and vaccines

The University of Osaka

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Outline of Recombinant Human Norovirus Generation Using Zebrafish Embryos

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Credit: Takeshi Kobayashi (Created with Biorender.com)

Osaka, Japan – Norovirus is the leading cause of gastroenteritis and is responsible for hundreds of thousands of deaths every year. However, research progress into antiviral treatments and vaccines has been hindered by the absence of a robust ‘reverse genetics’ system.

Now, a team at The University of Osaka has successfully overcome this long-standing barrier to norovirus research, developing a simple and efficient research system for human norovirus.

Reverse genetics systems allow the functions of genes to be determined by changing an individual gene and observing the result, creating what is known as a ‘recombinant’ virus. They are powerful tools for studying how viruses replicate and cause disease, and aid in the development of novel antiviral therapies and vaccines. The team at The University of Osaka applied virological techniques to a zebrafish model to create a novel reverse genetics system capable of generating infectious human noroviruses.

The system they developed involves the direct injection of norovirus cDNA clones into zebrafish embryos, which is a very simple and efficient method to generate infectious noroviruses. The team demonstrated the utility of this system by generating genetically manipulated noroviruses, possessing specific mutations or tagged with ‘reporter genes’.

Reporter genes are genetic modifications, such as chemiluminescent molecules, that can tag the virus and report on its activity and location within a host cell, enabling visualization of the virus in action. This ability to manipulate the virus enables the mechanisms of viral replication and pathogenesis to be investigated.

“This will also allow the development of novel vaccines with controlled antigenicity and pathogenicity,” explains senior author Takeshi Kobayashi.

This system fills a critical gap in human norovirus research. The ability to support antiviral screening and accelerate vaccine development could make it a transformative tool for the field. As this approach becomes more widely used, it will lay the groundwork for more effective public health strategies and a markedly reduced global burden of norovirus infection.

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The article, “Recovery of infectious recombinant human norovirus using zebrafish embryos”, was published in PNAS at DOI: https://doi.org/10.1073/pnas.2526726122

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Journal

Proceedings of the National Academy of Sciences

DOI

10.1073/pnas.2526726122 

Method of Research

Experimental study

Subject of Research

Animals

Article Title

Recovery of Infectious Recombinant Human Norovirus Using Zebrafish Embryos

Article Publication Date

4-Dec-2025

 

Houston Methodist partners with CEPI and international scientific institutions to advance first AI-designed mRNA vaccine against deadly Tick-borne disease

Exemplar vaccine to accelerate response to future epidemics and pandemics

Houston Methodist

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Houston Methodist Research Institute is collaborating with the Coalition for Epidemic Preparedness Innovations (CEPI) and leading scientific institutions in the Republic of Korea to develop what could become the world’s first mRNA vaccine against severe fever with thrombocytopenia syndrome (SFTS)—a tick-borne viral disease associated with this condition. 

Symptoms typically emerge after people are bitten by infected ticks or possibly infected domestic animals such as cats. They may range from fever and vomiting to multi-organ failure and death, especially in older adults. Severe SFTS cases have been reported in China, Japan, Korea, Taiwan and Vietnam. 

Jimmy Gollihar, Ph.D., chief of translational sciences and head of Antibody Discovery and Accelerated Protein Therapeutics at Houston Methodist Research Institute, said Houston Methodist will apply cutting-edge AI and computational techniques to accelerate vaccine design—reducing timelines from weeks or months to hours while ensuring safety and broad immune protection. 

"We are applying advanced AI and computational immunology to dramatically shorten the time it takes to move from a viral genome to a rationally designed vaccine candidate,” Gollihar said. “By working hand-in-hand with our partners in Korea and CEPI on this SFTS 'prototype' vaccine, we aim to design components that are both safer and capable of eliciting broad, durable protection, while generating insights that can be rapidly transferred to other phenuiviruses.” 

 Phenuiviruses are a large and diverse family of viruses that infect plants and animals—including humans and livestock. They are commonly transmitted by arthropod vectors, which are invertebrates with segmented bodies and jointed limbs, such as ticks and mosquitoes. 

The collaboration aligns with the 100 Days Mission—a global goal, spearheaded by CEPI, prepping the world to respond in as little as 100 days when the next pandemic threat emerges. 

“We don’t know what the next pandemic will be, but we know that we need to be prepared,” CEPI CEO Dr. Richard Hatchett said. “By advancing an SFTS vaccine, we will both help to address an increasingly menacing viral threat in Asia and generate scientific knowledge that could dramatically accelerate our response to the next Disease X. That way, we won’t be wasting valuable time creating a new vaccine from scratch if a deadly new phenuivirus emerges in the future.” 

Other collaborators in the project include the International Vaccine Institute (IVI), ST Pharm, Seoul National University and the Korea Disease Control Agency. CEPI will invest up to $16 million to support preclinical and Phase I/II trials in Korea, led by IVI.