Mammal-like milk provisioning and parental care discovered in jumping spider

November 30, 2018, Chinese Academy of Sciences
Jumping Spider. Credit: CHEN Zhanqi

Lactation is the production and secretion of milk for the young and is a mammalian attribute. However, there have been several examples of milk provisioning in non-mammals. In a study published in the journal Science on November 30, researchers at the Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences report milk provisioning in Toxeus magnus (Araneae: Salticidae), a jumping spider that mimics ants.

In a field study, the researchers observed a species whose breeding nest is composed of either several large individuals, with two or more adults, or one adult female and several juveniles. "It's a puzzling observation for a species assumed to be noncolonial. It's possible that the jumping spider might provide either prolonged maternal care or delayed dispersal. We decided to test it," said Dr. Chen Zhanqi, the first author of the study.

The researchers assessed how offspring developed and behaved under maternal care both in laboratory conditions and in the field. No spiderlings were observed leaving the nest for foraging until they were 20 days old. Closer observation revealed that the mother provided a seemingly nutritive fluid, hereafter called milk, to the offspring.

Milk provisioning in T. magnus involves a specialized organ over an extended period, similar to mammalian lactation. Observations under the microscope showed droplets leaking from the mother's epigastric furrow where the spiderlings sucked milk.

The spiderlings ingest nutritious milk droplets secreted from the mother's epigastric furrow until the subadult stage (around 40 days). If blocked from obtaining milk, the newly emerged spiders will stop development and die within 10 days, showing that milk is indispensable for offspring survival in the early stage.

Moreover, the researchers tested why and milk provisioning were continued after 20 days when the spiderlings were able to forage for themselves.

The mother continued nest maintenance throughout, carrying out spiderlings' exuviae and repairing nest damage. When receiving both and milk, 76 percent of the hatched offspring survived to adulthood (around 52 days).

Milk provisioning after 20 days did not affect adult survivorship, body size, or development time, but the mother's presence played a key role in assuring a high adult survival rate and normal body size. Thus, milk provisioning complemented their foraging in later stages.

Although the mother apparently treated all juveniles the same, only daughters were allowed to return to the breeding nest after sexual maturity. Adult sons were attacked if they tried to return. This may reduce inbreeding depression.

The findings show that in the jumping spider species, the mother invests much more than the male invests, predicting a female-biased sex ratio to be optimal for reproductive success with a polygamous mating system.

"Our findings demonstrate that mammal-like provisioning and parental care for sexually mature offspring have also evolved in invertebrates," said Dr. Chen. "We anticipate that our findings will encourage a reevaluation of the evolution of lactation and extended parental care and their occurrences across the animal kingdom."

Explore further: Lactation hormone also helps a mother's brain

More information: Zhanqi Chen et al. Prolonged milk provisioning in a jumping spider, Science (2018). DOI: 10.1126/science.aat3692

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Jeffhans1
5 / 5 (2) Nov 30, 2018
I wonder how many other species do this as well. We have assumed for too long that milk production for the young is a mammal only trait.
Surveillance_Egg_Unit
2.3 / 5 (6) Dec 01, 2018
It was a shock for me to read this article. At first I thought that it was some kind of a joke - after all, arachnids don't have mammary glands as do mammals. And spiders, as well, are known to sometimes eat their young under certain conditions.
So, it appears that humans still have a lot to learn about Life and Nature where certain spiders are being good mothers with something that passes for 'milk ducts', as in this case.
However, I am left wondering if the reason for a spider mum's need for doting on her offspring so well is that there may be something that also benefits HER as long as she continues to produce "milk" for them and nurtures them into adulthood. It may be a matter of preserving her own good health by exuding the liquid from her body.
It is a bit of a surprise to find this out. Are these spiders mimicking mammals due to having evolved in this way for survival of the specie/genus?
Da Schneib
3 / 5 (4) Dec 01, 2018
@SEU demonstrates why YECs don't get evolution.

The measure is not "how well" the mother spider does. It's about the extent to which her genes get replicated. It's called "evolution by natural selection." Perhaps you should study up on it.
Da Schneib
3 / 5 (4) Dec 01, 2018
You see, evolution by natural selection is very simple. It proceeds by how many offspring your conspecifics have.

And variation comes from conservation of mutations in so-called "junk DNA." That's what the so-called "junk DNA" is there for: to enable novel adaptations. This is called evolving the ability to evolve. It's one of those things YECs don't get.

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