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According to a new study, jumping spider mums provide milk to their spiders long before their development, which could change your understanding of the parenting role of invertebrates.
Animals offer all sorts of provisions to their offspring, whether by regurgitation, unfertilized eggs or, in extreme cases, by their own flesh. But specialized secretions resembling milk are wrongly attributed to mammals only. Other non-mammals and even invertebrates also produce secretions resembling milk. What is exciting in this new study is not only the fact that spiders produce milk, but also the duration of their production.
"This poses interesting questions about why this is happening in the first place," Nathan Gwynodo told Nathan Morehouse, assistant professor at the University of Cincinnati who was not involved in the study. . "Why do these spiders act like college kids coming home to live with their parents?"
We often think that invertebrates are robotic beings that reproduce and feed and that's all, but that's not really the case. Spiders take care of their young in different ways: some only keep eggs, others regurgitate or lay unfertilized "trophic" eggs. But jumping spiders providing milk are an extreme case of parental protection in invertebrates.
The researchers behind the new study, all from the Chinese Academy of Sciences, knew that Toxeus magnus or "jumping spiders" reared in nests made up of parents and several juveniles. They wondered if the spider provided long-term parental care. They observed spiders in the nest. They then noticed that the spiders did not leave the nest until about 21 days, during which time the mother was never observed feeding food while the young spiders were growing.
They took a closer look and noticed that the mother secreted fluid from the upper part of her abdomen on the surface of the nest, which the spiders ate. After a week, the spiders sucked the milk directly from the mother. Although they were able to leave the nest and feed after 20 days, they continued to breastfeed milk for another 18 days. If they were humans, they would appear in a cable TV show. Once the spiders matured, the mother attacked the males who came back while the females were still allowed to enter, possibly to prevent inbreeding, according to the study published today in Science.
For those of you who have doubts about the importance of secretion, the researchers then blocked the breast milk glands with white veil and the spiders died at 10 days. When the mother was removed from the nest after 20 days, this reduced the overall survival of the spider babies and their overall size.
Scientists have previously observed that non-mammals previously produced milk-like secretions, such as pigeons, cockroaches and tsetse flies; Earwigs also provide extended care to their youth, said Joshua Benoit, also an assistant professor at the University of Cincinnati, who did not participate in the study. The research impressed and convinced him, but he thought that it was perhaps time to rethink who is credited with breastfeeding young children. After all, invertebrates make up over 95% of the planet's species.
"The production of milk-like systems may have evolved more often in invertebrate systems than in vertebrates," said Benoit.
The study has its limits. It is unclear whether jumping spiders in the wild – and not confined to a laboratory enclosure – would continue to return to their mothers after 20 days, Benoit said. And Morehouse noted that this does not really explain why these spiders continue to breastfeed so long and why other spiders do not produce milk. The authors of the study declined Gizmodo's request for comment.
The book recalls that mammals are not the only animals that care for their young, and that others do so in a way that should be appreciated. Morehouse felt that it was time to look for other examples of milk production in invertebrates. He said: "The message to remember for me is that this study breaks down the particularity of mammals."
[Science]
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