Although you wouldn't choose microscopic roundworms to be the nurturing type, here's an interesting fact: These commonly studied nematodes make a form of egg-milk from their vulvas.
A new study has shown that Caenorhabditis Elegans larvae that eat yolk milk grow faster than those who don't. This gives the next generation of worms, just as with mammals who give milk to their babies. It also helps them to be more fit to face new challenges.
It comes at a terrible cost to the mother.
Mother C. Elegans are hermaphrodites. This means they have both males and female reproductive organs. Although males are also possible, they are very rare in the wild.
While they can fertilize their eggs by conceiving, mother worms are more likely to fertilize themselves. Their supply of self-sperm is very limited. Once they stop conceiving young, their bodies begin to produce the yolk milk.
These transparent, microscopic wriggle-beasts conceive more eggs than their body weight. They excrete the egg cells as either yolks or fully intact egg cells (oocytes). They make them by melting down their own organs, such as intestines, and repurposing them.
C. elegans pour yolk milk through their eyes. (UCL
Carina Kern, University College London bioscientist, says that "the worms are destroying their own bodies in the process to transfer nutrients to their offspring."
"And all those unfertilized egg are full of milk, so that they act like milk bottles to help milk transport to feed babyworms."
Although it may seem strange, C. elegans is not the only invertebrate that provides highly nutritious excretions to their young. Cockroaches and jumping spiders also do this. Many other animals, such as salmon and octopuses, also offer their young for sacrifice.
Kern and his colleagues showed that larvae that ate egg yolk grew faster than those that ate it, even though they were given E. coli again.
Their lifespans are cut by the insulin-like signaling pathway, a biochemical circuit that triggers conversion of organs to eggs within their mother. This pathway is actually one of many reasons C. elegans is so well studied. It is evolutionary and well preserved across many animals including humans.
Since the 1960s, scientists have used mini soil worms for research on memory, aging, and other strange things. Their research value is so high that they were the first multicellular animals to have their genome sequenced.
Kern and his colleagues believe that the time of the worms's production of yolk milk may coincide with the time when the colony begins to deplete its food. C. elegans can reproduce rapidly in the wild as they take over new territory and eat bacteria from their dirt homes. They build large colonies, which can experience massive booms and busts of population.
The likelihood of surviving a process known as kin selection is higher if the mother gives her offspring a head start when food supplies are scarce.
This self-sacrificing feat may also mean that exciting research about C. elegans genes which massively increase the lifespan of roundworms may not be possible because they prevent reproductive suicide.
However, this doesn't mean that we can't still learn a lot from them about aging. Researchers believe that many of the worm's aging mechanisms are similar to those in other animals. This gives them insight into many diseases we face.
This research was published in Nature Communications, with a review in Frontiers in Cell and Developmental Biology.
