Sabre teeth, those iconic elongated upper canine teeth, have long fascinated both scientists and the general public, notably because they have appeared several times in the fossil record, including two particularly well-known lineages of sabre-toothed tigers: the felids (the family of our domestic cats, lions, tigers, etc.) and the nimravids (a completely extinct family). However, the process by which these lineages acquired their elongated upper canines remains rather unclear.

Narimane Chatar, lead author of the study, who completed her doctorate at the EDDy Lab at the University of Liège and is now a post-doctoral fellow at UC Berkeley in the United States, has led an ambitious study to uncover the secrets of sabre tooth evolution. Using state-of-the-art 3D scanners and analytical methods, the team meticulously collected and analysed data from a diverse set of current and extinct species. “We quantified the shape of 99 mandibles and 91 skulls, from different eras and continents, giving us a better understanding of the evolution of these animals,” explains Dr Chatar. “Unlocking the secrets of sabre tooth evolution not only enriches our understanding of the Earth’s past, but also documents the mechanisms leading to evolutionary convergence,” says Professor Valentin Fischer, Director of the EDDyLab at ULiège.

The study revealed some surprising results. The first is that rather than contrasting two distinct cranial morphologies in species with elongated upper canines and those with short teeth, there is instead a continuum of form linking the smallest present-day cats and their extinct sabre-toothed counterparts. “From a morphological point of view, the skull of a present-day small cat is just as strange and modified as that of a large sabre-toothed felid,” says Dr Margot Michaud, a researcher at the University of French Guyana in Cayenne. These are therefore the two extremes of a continuum of forms that feline predators have seen evolve over geological time. “Our study suggests that what we often think of as examples of evolutionary patterns in textbooks are actually simplified for educational purposes. However, when we immerse ourselves in statistical analyses, we discover much more complex scenarios in these cases, as suggested by the results of our convergence tests,” explains Davide Tamagnini, post-doctoral researcher at the University of Rome La Sapienza.

The second surprise concerns the path taken by evolution to produce sabre-toothed species. In fact, the team’s work has revealed that sabre-toothed species show faster rates of morphological evolution at the start of their evolutionary history than species with shorter canines. “Among other fascinating discoveries, we have shown that craniomandibular integration in sabre-toothed species is reduced, facilitating greater adaptability and diversification in the jaw and cranial morphology,” points out Margot Michaud. Thus, rapid morphological diversification and a fairly plastic skull have been identified as two key components that facilitated the emergence of elongated upper canines in both felids and nimravids. “As a result, there appears to be a common recipe for evolving into sabre-toothed feline-like predators,” says Dr Chatar.

Finally, the team’s research highlighted the decline of sabre-toothed forms as well as the broader trends of feline-like predators over the course of their evolutionary history. Despite the relatively recent extinction of sabre-toothed forms ‘only’ a few thousand years ago, feline predators have in fact been in decline since the Miocene epoch (between -23 and -5 million years ago). “Some of these feline predators, particularly the sabre-toothed species, rapidly occupied fairly specialised niches, which made them more susceptible to extinction,” explains Dr Tamagnini. This phenomenon, known as ‘ratchet’ or macroevolutionary ratchet, has been proposed as a potential driver for the decline of certain groups, where evolution favours the loss of early generalised forms, leading to the emergence of more specialised, but also more vulnerable, forms later in the history of the lineage.

“Predators have their own evolutionary pathways and risks of extinction. Studying how ancient predators prospered and declined provides us with information about the possible futures of our ecosystems,” concludes Professor Fischer.

Patients who underwent infertility were particularly likely — 2.16 times as likely as those who conceived naturally — to undergo hospitalization for dangerously high blood pressure or hypertension.

“Postpartum checkups are necessary for all patients, but this study indicates they are particularly important for patients who undergo infertility treatment to achieve a conception,” said Rei Yamada, an obstetrics and gynecology resident at Rutgers Robert Wood Johnson Medical School and lead author of the study.

The study authors say their results support standards of care that now call for an initial postpartum checkup three weeks after delivery, standards that some health systems have yet to adopt. Much of the elevated risk came in the first month after delivery, particularly for patients who developed dangerously high blood pressure.

“And these results aren’t the only ones to indicate that follow-up should occur early,” said Cande Ananth, chief of the Division of Epidemiology and Biostatistics in the Department of Obstetrics, Gynecology, and Reproductive Sciences at Rutgers Robert Wood Johnson Medical School and senior author of the study. “We have been involved in a series of studies over the past few years that have found serious risks of heart disease and stroke to various high-risk patient populations within those initial 30 days after delivery — risks that could be mitigated with earlier follow-up care.”

The study analyzed the Nationwide Readmissions Database, which contains nationally representative data on about 31 million hospital discharges and readmissions per year. The database contains diagnosis codes, which let researchers find specific populations and identify reasons for readmission.

The researchers used data from more than 31 million patients who were discharged following delivery from 2010 to 2018, including 287,813 patients who had undergone any infertility treatment.

Although infertility treatment predicted a sharply elevated risk of heart disease, the study authors said the relative youth of infertility treatment patients kept their overall risk fairly low. Just 550 of every 100,000 women who received infertility treatment and 355 of every 100,000 who conceived naturally were hospitalized with cardiovascular disease in the year after delivery.

The cause of the elevated risk of heart disease associated with infertility treatment remains unclear. The increase in heart disease could stem from the infertility treatments themselves, the underlying medical issues that made patients infertile or some other cause.

“Looking forward, I’d like to see if different types of infertility treatment and, importantly, medications are associated with different risk levels,” said Yamada. “Our data gave no information about which patients had undergone which treatment. More detailed information might also provide insight into how infertility treatment impacts cardiovascular outcomes.”

Knowing more about nature’s effects on our bodies could not only help our well-being, but could also improve how we care for land, preserve ecosystems and design cities, homes and parks. Yet studies on the benefits of contact with nature have typically focused primarily on how seeing nature affects us. There has been less focus on what the nose knows. That is something a group of researchers wants to change.

“We are immersed in a world of odorants, and we have a sophisticated olfactory system that processes them, with resulting impacts on our emotions and behavior,” said Gregory Bratman, a University of Washington assistant professor of environmental and forest sciences. “But compared to research on the benefits of seeing nature, we don’t know nearly as much about how the impacts of nature’s scents and olfactory cues affect us.”

In a paper published May 15 in Science Advances, Bratman and colleagues from around the world outline ways to expand research into how odors and scents from natural settings impact our health and well-being. The interdisciplinary group of experts in olfaction, psychology, ecology, public health, atmospheric science and other fields are based at institutions in the U.S., the U.K., Taiwan, Germany, Poland and Cyprus.

At its core, the human sense of smell, or olfaction, is a complex chemical detection system in constant operation. The nose is packed with hundreds of olfactory receptors, which are sophisticated chemical sensors. Together, they can detect more than one trillion scents, and that information gets delivered directly to the nervous system for our minds to interpret — consciously or otherwise.

The natural world releases a steady stream of chemical compounds to keep our olfactory system busy. Plants in particular exude volatile organic compounds, or VOCs, that can persist in the air for hours or days. VOCs perform many functions for plants, such as repelling herbivores or attracting pollinators. Some researchers have studied the impact of exposures to plant VOCs on people.

“We know bits and pieces of the overall picture,” said Bratman. “But there is so much more to learn. We are proposing a framework, informed by important research from many others, on how to investigate the intimate links between olfaction, nature and human well-being.”

Nature’s smell-mediated impacts likely come through different routes, according to the authors. Some chemical compounds, including a subset of those from the invisible realm of plant VOCs, may be acting on us without our conscious knowledge. In these cases, olfactory receptors in the nose could be initiating a “subthreshold” response to molecules that people are largely unaware of. Bratman and his co-authors are calling for vastly expanded research on when, where and how these undetected biochemical processes related to natural VOCs may affect us.

Other olfactory cues are picked up consciously, but scientists still don’t fully understand all their impacts on our health and well-being. Some scents, for example, may have “universal” interpretations to humans — something that nearly always smells pleasant, like a sweet-smelling flower. Other scents are closely tied to specific memories, or have associations and interpretations that vary by culture and personal experience, as research by co-author Asifa Majid of the University of Oxford has shown.

“Understanding how olfaction mediates our relationships with the natural world and the benefits we receive from it are multi-disciplinary undertakings,” said Bratman. “It involves insights from olfactory function research, Indigenous knowledge, Western psychology, anthropology, atmospheric chemistry, forest ecology, Shinrin-yoku — or ‘forest bathing’ — neuroscience, and more.”

Investigation into the potential links between our sense of smell and positive experiences with nature includes research by co-author Cecilia Bembibre at University College London, which shows that the cultural significance of smells, including those from nature, can be passed down in communities to each new generation. Co-author Jieling Xiao at Birmingham City University has delved into the associations people have with scents in built environments and urban gardens.

Other co-authors have shown that nature leaves its signature in the very air we breathe. Forests, for example, release a complex chemical milieux into the air. Research by co-author Jonathan Williams at the Max Planck Institute for Chemistry and the Cyprus Institute shows how natural VOCs can react and mix in the atmosphere, with repercussions for olfactory environments.

The authors are also calling for more studies to investigate how human activity alters nature’s olfactory footprint — both by pollution, which can modify or destroy odorants in the air, and by reducing habitats that release beneficial scents.

“Human activity is modifying the environment so quickly in some cases that we’re learning about these benefits while we’re simultaneously making them more difficult for people to access,” said Bratman. “As research illuminates more of these links, our hope is that we can make more informed decisions about our impacts on the natural world and the volatile organic compounds that come from it. As we say in the paper, we live within the chemical contexts that nature creates. Understanding this more can contribute to human well-being and advance efforts to protect the natural world.”

The researchers used drone footage and biological data from tags suction-cupped to 11 northern and southern resident killer whales off the coast of B.C. to gather information on the animals’ habits.

Whaley fun facts

Published in PLOS ONE, the study found that residents spend most of their time making shallow dives, with the majority of dives less than one minute. The longest dive recorded was 8.5 minutes, for an adult male. “Killer whales are like sprinters who don’t have the marathon endurance of blue and humpback whales to make deep and prolonged dives,” said co-author Dr. Andrew Trites, professor in the UBC Institute for the Oceans and Fisheries (IOF).

For how many fish could an orca wish?

Confirming orcas take only one breath between dives allowed the researchers to calculate how many litres of oxygen adults and juveniles consume per minute. This provides another piece of the puzzle in estimating orca energy expenditure, and eventually, how many fish the animals need to eat per day. “Researchers can then work out if the orcas are getting enough food, including the endangered southern residents, a key factor in their conservation,” said first author Tess McRae, IOF masters student.

Breathe like an orca

Killer whales in the study took 1.2 to 1.3 breaths per minute while resting and 1.5 to 1.8 while travelling or hunting. Comparatively, humans tend to take about 15 breaths per minute when resting and from 40 to 60 while exercising. “It’s the equivalent of holding your breath and running to the grocery store, shopping, and coming back before breathing again,” said co-author Dr. Beth Volpov, IOF postdoctoral fellow.