For weeks, mom feeds her baby with milk that contains four times more protein than the cow. Yet this mother is not a mammal. She is a jumping spider with eight legs and a pronounced taste for fruit flies.
We, the mammals, are named after our mammary glands. Other animals, tsetse flies with pigeons, secrete their own version of milk for their babies. Nursing recently discovered at Toxeus magnus could be the most mammal of all, a team of researchers from China proposes in November 30 Science.
Biologists have recognized T. magnus as a species since 1933, but it was easy to miss a small spider. Spiders hunt animals such as fruit flies and retreat to a small nest, perhaps tied to a leaf, to raise a family.
The co-author of the study, Zhanqi Chen, of the Chinese Academy of Sciences of Menglunzhen, who studies the behavior of the spider, noticed several T. magnus sharing a nest in 2012 and wondered if the species had some kind of extended parental protection. Five years later, he discovered the behavior of breastfeeding when a spider snuggled against his mother's belly during an exciting evening in July 2017.
With a T. magnus A woman under a microscope, a slight finger pressure on the underside of the abdomen will pull out a small pearl of white fluid from a furrow called an epigastric furrow, the researchers say. About a week after the eggs hatch, a spider mum leaves droplets of milk around the nest so that the creepy spots of her cubs can drink. Then, the breastfeeding becomes more mammal, the small ones pressing against the body of their mother.
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How spiders could resume milk intrigues the evolutionary physiologist, Wendy Hood of Auburn University in Alabama, who studies lactation. In the platypus and echidna, also known as thorny anteater, females do not have nipples. Babies take milk that comes out of the mammary glands on the surface of the skin "a bit like water sweat glands," she says. However, in the majority of mammals, the baby sucks rather than turns, which causes the release of milk in the mouth.
The foods contained in spider milk have well-known basic components in mammalian milk: about 2 milligrams of sugar per milliliter of milk, 5 milligrams of fat and 124 milligrams of protein. The researchers report that this is all the spiders have during the first 20 days of their life. In the laboratory spider nests, mothers occasionally hunted fruit flies provided by researchers, but never brought these prey home to feed their offspring.
After 20 days, the spiders began looking for food, but also continued to breastfeed for almost three weeks, the team discovered. With this combined diet, 76% of young people in laboratory nests survived into adulthood. But when the researchers sealed the mother's epigastric furrow with correction fluid typing from the birth of spiders, they died in about 10 days.
The researchers were also curious to know if milk was important when young people started hunting. It made. Depriving these older spiders by sealing their mother's furrow on the twentieth day lowered the survival rate to about 50%, the researchers said.
With such care from mom, T. magnus Spiders eventually share a nest during an unusually long time in the largely solitary and predatory world of spiders, says Cornell University behavioral arachnologist Linda Rayor. Only about 120 of the more than 48,000 known spider species tolerate the company, including their siblings, for more than three weeks. And only about 30 of them have a social life for life. So, an example of spiders sharing a nest for 40 days, says Rayor, is "a big deal".
MEAL TIME Female Toxeus magnus Spiders, native to the tropical and subtropical regions of Asia, produce milk to feed their young for weeks even after the spiders have started to hunt themselves. Here, a 1 week old baby feeds in an area of his mother's abdomen where milk is available.