Do larger male elk have proportionally larger antlers? The answer is no. In fact, larger individuals tend to have disproportionately larger antlers -- a phenomenon known as positive allometry. This pattern, where certain body parts grow disproportionately large relative to body size, is observed not only in mammals but also in animals such as beetles and fiddler crabs. Evolutionary biologists interpret such traits as evidence of sexual selection -- a process in which physical features evolve because they offer an advantage in competing for mates.

Male earwigs are known to show positive allometry in their forceps -- pincer-like appendages at the tip of the abdomen -- which are believed to have evolved as weapons in battles with rivals. But what about females? Female earwigs also have forceps -- so what purpose do they serve?

Tomoki Matsuzawa (then an undergraduate) and Associate Professor Junji Konuma from Toho University's Department of Biology conducted the first quantitative study of female earwig forceps. Using morphometric analysis on the maritime earwigs Anisolabis maritima, they found that female forceps also display positive allometry -- suggesting that they, too, may have evolved through sexual selection.

The team measured the head, thorax, abdomen, and bilateral forceps dimensions and analyzed shape differences in both sexes. They found that males have thick, short, and curved forceps, while females have thin, long, and straight ones -- indicating clear sexual dimorphism. When they plotted body size against forceps width and length on a log-log scale, the results revealed a pattern of positive allometry in males: forceps width increased disproportionately with body size. Surprisingly, positive allometry was also found in females -- in the length of the forceps. These results suggest that while the sexes differ in forceps shape, both may have evolved them as weapons -- albeit in different ways.

Associate Professor Konuma explains:"A previous behavioral study has shown that female earwigs compete for small, non-aggressive males. Our findings suggest that female forceps may have evolved as effective weapons in such competition. While most earlier research focused only on males, our study highlights the importance of considering female traits as well when studying the evolution of insect morphologies."

These findings were published on June 12, 2025, in the Biological Journal of the Linnean Society.

Scientists have discovered a specific group of brain cells that create memories of meals, encoding not just what food was eaten but when it was eaten. The findings, published today in Nature Communications, could explain why people with memory problems often overeat and why forgetting about a recent meal can trigger excessive hunger and lead to disordered eating.

During eating, neurons in the ventral hippocampus region of the brain become active and form what the team of researchers call "meal engrams" -- specialized memory traces that store information about the experience of food consumption. While scientists have long studied engrams for their role in storing memories and other experiences in the brain, the new study identified engrams dedicated to meal experiences.

"An engram is the physical trace that a memory leaves behind in the brain," said Scott Kanoski, professor of biological sciences at the USC Dornsife College of Letters, Arts and Sciences and corresponding author of the study. "Meal engrams function like sophisticated biological databases that store multiple types of information such as where you were eating, as well as the time that you ate."

Distracted eating implications

The discovery has immediate relevance for understanding human eating disorders. Patients with memory impairments, such as those with dementia or brain injuries that affect memory formation, may often consume multiple meals in quick succession because they cannot remember eating.

Furthermore, distracted eating -- such as mindlessly snacking while watching television or scrolling on a phone -- may impair meal memories and contribute to overconsumption.

Based on the experiment's findings, meal engrams are formed during brief pauses between bites when the brain of laboratory rats naturally survey the eating environment. These moments of awareness allow specialized hippocampal neurons to integrate multiple streams of information.

Kanoski said it can be assumed a human's brain would undergo a similar phenomenon. When someone's attention is focused elsewhere -- on phone or television screens -- these critical encoding moments are compromised. "The brain fails to properly catalog the meal experience," said Lea Decarie-Spain, postdoctoral scholar at USC Dornsife and the study's first author, "leading to weak or incomplete meal engrams."

Mechanism of 'meal memories'

The research team used advanced neuroscience techniques to observe the brain activity of laboratory rats as they ate, providing the first real-time view of how meal memories form.

The meal memory neurons are distinct from brain cells involved in other types of memory formation. When researchers selectively destroyed these neurons, lab rats showed impaired memory for food locations but retained normal spatial memory for non-food-related tasks, indicating a specialized system dedicated to meal-related information processing. The study revealed that meal memory neurons communicate with the lateral hypothalamus, a brain region long known to control hunger and eating behavior. When this hippocampus-hypothalamus connection was blocked, the lab rats overate and could not remember where meals were consumed.

Eating management implications

Kanoski said the findings could eventually inform new clinical approaches for treating obesity and weight management. Current weight management strategies often focus on restricting food intake or increasing exercise, but the new research suggests that enhancing meal memory formation could be equally important.

"We're finally beginning to understand that remembering what and when you ate is just as crucial for healthy eating as the food choices themselves," Kanoski said.

In addition to Kanoski, other study authors include Lea Decarie-Spain, Cindy Gu, Logan Tierno Lauer, Alicia E. Kao, Iris Deng, Molly E. Klug, Alice I. Waldow, Ashyah Hewage Galbokke, Olivia Moody, Kristen N. Donohue, Keshav S. Subramanian, Serena X. Gao, Alexander G. Bashaw and Jessica J. Rea of USC; and Samar N. Chehimi, Richard C. Crist, Benjamin C. Reiner and Matthew R. Hayes from the University of Pennsylvania's Perelman School of Medicine; and Mingxin Yang and Guillaume de Lartigue from the Monell Chemical Senses Center; and Kevin P. Myers from the Department of Psychology at Bucknell University.

The study was supported by a Quebec Research Funds Postdoctoral Fellowship (315201), an Alzheimer's Association Research Fellowship (AARFD-22-972811), a National Science Foundation Graduate Research Fellowship (DK105155), and a National Institute of Diabetes and Digestive and Kidney Diseases grant (K104897).

The study found that oleic acid, a monounsaturated fat associated with obesity, causes the body to make more fat cells. By boosting a signaling protein called AKT2 and reducing the activity of a regulating protein called LXR, high levels of oleic acid resulted in faster growth of the precursor cells that form new fat cells.

"We know that the types of fat that people eat have changed during the obesity epidemic. We wanted to know whether simply overeating a diet rich in fat causes obesity, or whether the composition of these fatty acids that make up the oils in the diet is important. Do specific fat molecules trigger responses in the cells?" said Michael Rudolph, Ph.D., assistant professor of biochemistry and physiology at the University of Oklahoma College of Medicine and member of OU Health Harold Hamm Diabetes Center.

Rudolph and his team, including Matthew Rodeheffer, Ph.D., of Yale University School of Medicine and other collaborators at Yale and New York University School of Medicine, fed mice a variety of specialized diets enriched in specific individual fatty acids, including those found in coconut oil, peanut oil, milk, lard and soybean oil. Oleic acid was the only one that caused the precursor cells that give rise to fat cells to proliferate more than other fatty acids.

"You can think of the fat cells as an army," Rudolph said. "When you give oleic acid, it initially increases the number of 'fat cell soldiers' in the army, which creates a larger capacity to store excess dietary nutrients. Over time, if the excess nutrients overtake the number of fat cells, obesity can occur, which can then lead to cardiovascular disease or diabetes if not controlled."

Unfortunately, it's not quite so easy to isolate different fatty acids in a human diet. People generally consume a complex mixture if they have cream in their coffee, a salad for lunch and meat and pasta for dinner. However, Rudolph said, there are increasing levels of oleic acid in the food supply, particularly when access to food variety is limited and fast food is an affordable option.

"I think the take-home message is moderation and to consume fats from a variety of different sources," he said. "Relatively balanced levels of oleic acid seem to be beneficial, but higher and prolonged levels may be detrimental. If someone is at risk for heart disease, high levels of oleic acid may not be a good idea."