On a summer night in 2017, Chen Zhanqi made a curious discovery in his laboratory in Yunnan Province of China. In an artificial nest, he spotted a juvenile jumping spider attached to his mother, recalling a mammalian baby sucking on her mother's breasts. Looking more closely, the spider mum seemed to really love her little ones, he says. "She had to invest so much in the baby's care."
Chen and Quan Rui-Chang, behavioral ecologists at the Center for Integrative Conservation of the Chinese Academy of Sciences in Menglunzhen, confirmed that females jumping spiders actually produced milk for their offspring – and that they have continued to do so even after the spiders have become teenagers, they and their colleagues are reporting today.
Providing milk and long-term care together is virtually unknown in insects and other invertebrates. And with the exception of mammals, it's not even as common in vertebrates. As such, the findings "help to improve our understanding of the evolving origins of complex forms of parental protection," says Nick Royle, behavioral ecologist at Exeter University in the UK, who n & # 39; 39 did not participate in the work. According to them, prolonged maternity may not require the complex brain power assumed by the researchers, he says.
Females of this species of jumping spider (Toxeus magnus) lay between two and 36 eggs at a time. As soon as the eggs hatch, the mother begins to drop tiny milky droplets around the nest, Chen and colleagues at the lab observed. When the team members analyzed the fluid, they found that it contained four times as much protein from cow's milk, fat and sugar.
The researchers observed that spider babies drank drops of milk from this spider around the nest during the first few days. But soon, they started queuing at the mother's birth canal alley to nurse. At 20 days, they started to hunt outside the nest, but they still completed their diet with breast milk until sexual maturity – an additional 20 days.
When Chen painted the mothers' birth channels to cut the milk supply, spiders less than 20 days old died. When he removed the mother from the nest, older spiders grew more slowly, left the nest earlier, and were more likely to die before adulthood. Science. Other spiders can stay around their young for a few days but rarely feed them.
"Milk" can be liquefied eggs that come out prematurely from the genital industry, says Quan. Some amphibians and other invertebrates lay similar "trophic eggs", he notes, although these young children are really very young. Cockroaches also produce "milk", but this food is simply passively absorbed through the shell of their eggs and is not part of the diet of roach roaches.
The long-term parental care that the team observed in jumping spiders generally only exists in very few long-lived social vertebrates, such as humans and elephants, explains Quan. "Prolonged maternal care indicates that invertebrates have also evolved [this] aptitude."
Rosemary Gillespie, an ecologist of evolution at the University of California at Berkeley, notes that some other species of spiders also seem to feed their young. A study conducted in the 1990s showed that funnel spider spiders coelotes ate light yellow drops of liquid or brownish clusters deposited on the band. Mothers of another spider called Amaurobius place bags of "naked" eggs that spiders devour immediately.
Such care often means a need for more than normal offspring, says Royle. For example, if there is a chance that there is no food for newborns, or that young spiders are likely to be eaten by other predators before they have a chance to grow up and to reproduce, it can then be logical for the mother to become a parent "helicopter", he explains. Because this behavior taxes the mother, he adds, it will probably only evolve in extreme situations.