麻豆淫院

Researchers peered inside the brains of huntsman and crab spiders using microCT scanners and found that while spiders' brains don't have to be bigger for them to live in groups, social spiders are wired for better memory, recognition and collaboration.

In bushland near Melbourne last year, Dr. Vanessa Penna-Gon莽alves was collecting certain "social" species of huntsman and crab spiders for her Ph.D. research, and peeled back a strip of eucalyptus bark to uncover a remarkable sight鈥攁 society of huntsman spiders living together in social harmony under a single piece of bark.

"When I opened the bark, I was so surprised鈥攖here were over a hundred spiders living in their little social community," says the Macquarie University data scientist and Ph.D. candidate.

New findings from Dr. Penna-Gon莽alves ongoing research into spider brains and behavior, just in Integrative Zoology, shows while social and solitary spiders have similar overall brain sizes, the internal structures tell a completely different story.

The findings represent the first robust test of a theory called "The Social Brain Hypothesis" in non-web-building spiders, examining whether animals living in groups need bigger brains to manage complex social relationships.

Social spiders scurry against the trend

Sociality in spiders is extraordinarily rare鈥攐nly 0.1% of the world's 53,000 spider species live in groups. Most spiders are hostile territorial loners, who, given the chance, will cannibalize their neighbors.

"Spiders are typically very aggressive towards other individuals," says Dr. Penna-Gon莽alves.

Spiders' social tendencies appear to stem from what Dr. Penna-Gon莽alves calls being "lazy to launch," where young spiders stay home longer instead of dispersing after their first molt.

"In those spider species who show an extended maternal care timeframe for young, we found the young don't eat each other, and they start sharing prey," she says.

Her laboratory experiments revealed striking behavioral differences between social and solitary species when presented with large prey such as a live grasshopper.

"Social spider species babies will collaborate to hunt, or one individual might hunt the prey, but the others come by and stay to share the meal," she says. "I didn't see this behavior in the solitary babies."

Mapping microscopic minds

To study the inner workings of spider brains, Dr. Penna-Gon莽alves developed new techniques that pushed the boundaries of neuroscience technology, spending almost two years perfecting brain staining methods so she could get meaningful images via micro CT scanning.

"We use a complex staining process that fixes different tissues inside the brain so you can see contrast between different structures," she says. "Without using staining that reacts to different tissues, everything inside the brain just looks gray."

Some samples required more than 100 days of staining before they were ready for microCT scanning, in a partnership with the University of Melbourne.

Spider's brains are particularly tricky to study because of their location.

"Most insects and animals have a separate head that contains their brain, but the brain of a spider sits inside of its fused head and thorax, the cephalothorax, surrounded by muscle and many other tissues, so it's difficult to isolate," she says.

Once scanned, each spider brain image required painstaking manual mapping of individual structures鈥攁 process that can't yet be automated.

"We don't have AI to do these things, we don't yet have enough data and the edges of the structures of spiders' brains requires a trained eye to be able to distinguish, so it takes a long time," says Dr. Penna-Gon莽alves.

Size isn't everything

The team compared brains from six species: social huntsman spiders (Delena cancerides), social crab spiders (Xysticus bimaculatus), and four closely related solitary species.

To their surprise, they discovered that the overall size of the brain and central nervous system showed no significant differences between social and solitary species.

However, internal brain structures revealed important differences. Social huntsman spiders had distinctly larger brain areas called "arcuate bodies" and "mushroom bodies," both regions of the brain that are linked with memory and cognitive processing.

Dr. Penna-Gon莽alves believes these enlarged structures probably support the complex social behaviors observed in huntsman spider colonies, such as recognizing kin or friendly spiders from their own society, and group coordination.

Another interesting finding was the quite different patterns emerging from within the brains of social crab spiders, which had enlarged visual processing areas but similar cognitive regions to their solitary relatives.

"This makes sense when you think about their different social structures, because crab spiders live in small family groups in dark leaf nests, while huntsman groups can be complex communities with multiple adult females and males," she says.

Sharing the load

One of the study's most intriguing discoveries was that social huntsman spiders have smaller venom glands compared to their solitary cousins鈥攄irect evidence that cooperation within the species gives them an evolutionary advantage.

"Because the social huntsmen share the prey, each of them only needs to use a little bit of venom to kill the prey," says Dr. Penna-Gon莽alves. "Creating venom is very energy-expensive for them, so this makes all of the spiders in this species better off."

This finding supports the idea that cooperative behaviors reduce the investment that individuals need to make in costly biological systems, such as venom production.

While collecting specimens across different seasons, Dr. Penna-Gon莽alves discovered that social structure varies throughout the year.

"In the summer, we found more spider mothers with babies, but we also found more groups of females together and more eggs, which shows the society is more complex than we first thought," she says.

Do spiders dream?

Recent research suggests that some spiders may even sleep and dream.

"Discovering that spider brains can support sophisticated social behaviors challenges assumptions about intelligence in invertebrates," says supervising author Professor Marie Herberstein.

She says that Dr. Penna-Gon莽alves' mapping of the neural landscapes of tiny spider brains along with observations of their behaviors, could deliver insights beyond spider biology to help understand how social intelligence evolved across the animal kingdom.

"We've shown that the volume of the brain is not a key indicator for intelligence, but rather intelligence reflects the amount of neurons and their connections in the brain," says Dr. Penna-Gon莽alves.

Future research could employ new techniques like "brain soup"鈥攍iterally dissolving brains to count individual neurons鈥攚hich may provide more accurate measures of cognitive capacity than brain volume alone. The team also plans to test how social experiences during development shape brain structure.

This content was originally published on The Macquarie University .