Some sea creatures cover themselves with hard shells and spines; vertebrates build skeletons out of the same minerals.
Profs. Lia Addadi and Steve Weiner of the Weizmann Institute of Science’s structural biology department asked themselves how creatures get the calcium they need to build these strong mineral structures.
The answer they found surprised them, and it could change the way scientists think about the process of biomineralization.
Sea urchins need to extract calcium ions from sea water to build their spines. Several years ago, Addadi and Weiner discovered that sea urchins build their spines with tiny packets of “unorganized” material that hardens into crystal when laid in place.
“So the question went back a step: How do they get the calcium ions they need to make this material in the first place?” said Addadi.
“Free calcium is not abundant in seawater,” added Weiner, “so they need an efficient way to extract and concentrate the ions.”
To answer the question the researchers, including Netta Vidavsky, needed methods to observe the animal’s cells in their natural environment. For this the group turned to Dr.
Andreas Schertel of Carl Zeiss Microscopy in Germany and Dr. Sefi Addadi of Weizmann’s life sciences core facilities. Cutting-edge techniques enabled them to observe thin slices of the cells in sea urchin embryos and then to reconstruct three-dimensional images of these cells and their intake of labeled calcium ions.
“Even a few years ago, we could not have done this study,” said Addadi.
The 3D images showed that sea urchin larval cells actually “drink” seawater, taking in drops of water and manipulating the ions in the water within the confines of the cell.
This is in contrast to the theory that these cells take in only ions, one at a time, through special channels in their outer membranes. The cells they observed were filled with networks of bubbles called vacuoles that collect the calcium ions, evidently creating concentrated packages of calcium for building the spines.
This method may be more energy efficient than taking in ions through channels (which the cells also did), but it presents another problem: the cells must be able to pick out the calcium as well as expel other ions in the seawater, especially the sodium and chloride.
“Researchers may be busy for years figuring out how these cells manipulate the ions in the seawater they drink,” says Weiner.
Addadi and Weiner note that this is not the first time this type of calcium ion intake has been observed. Prof. Jonathan Erez of the Hebrew University described this phenomenon in single-celled, hard-shelled microorganisms called foraminifera a decade ago. At the time, it was thought to be a “curiosity,” but finding the same process in two very different creatures suggests that it may be quite widespread.
Although we humans do not live in seawater, it may be that the cells that build our bones use a similar method to obtain calcium.
CHIMPS USE BABYSITTERS TO WEAN YOUNG FASTER
A babysitter can make a big difference in a parent’s life. For wild chimpanzees in Uganda, it may even mean that mothers can wean their infants faster, enabling them to reproduce again more quickly.
A University of Toronto study looked at 42 pairs of chimp mothers and infants at Kibale National Park in Uganda. They wanted to better understand the impact of “alloparenting” – or babysitting – when individuals other than the mother assist with infant care.
In a paper published in the Royal Society’s journal Open Science, they describe looking at two particular aspects of care that these other individuals provided: infant handling, that is carrying and holding the infants; and natal attraction, the interest in infants demonstrated through behaviors like grooming and playing.
The researchers compared whether the extent of involvement of these individuals impacted the proportion of time that mothers spent foraging, the rates that infants nursed and the contribution of milk to infants’ diets.
“Infants who were held and carried more by babysitters nursed less often and drank less milk,” said lead author and anthropology doctoral student Iulia Badescu of the University of Toronto.
“This means that they were becoming more nutritionally independent compared to infants of the same age who were babysat less or not at all. They were going through the weaning process quicker, and would likely be done weaning at a younger age. Babysitting may thus benefit mothers by enabling females to invest in their next offspring sooner through this accelerated weaning.”
But not all chimp mothers relied on babysitters, and in fact, in other chimpanzee communities, babysitting may be a behavior that rarely occurs. Our findings emphasize the significance of babysitting as a flexible component of female reproductive strategies in some species.”
In a separate study, Badescu and her colleagues found that chimpanzee mothers let their “toddlers” nurse for comfort, even after lactation was over and they were receiving no milk.
“The young chimps were already weaned but continued to make contact with their mothers’ nipple not for nutrition, but presumably for emotional purposes, when they needed to be comforted,” said Badescu of the related study published in the American Journal of Physical Anthropology.
The researchers analyzed samples of feces to determine what the contribution of maternal milk was to the diet of the chimpanzee infants. Until now, it has been very difficult to actually measure what animal infants eat in the wild, and Badescu and her colleagues are the first to use this non-invasive method with wild primates in large numbers.
“This novel method quantifies infant diets for us, so that we can know more precisely when weaning occurs for wild mammals, and also provides a biological way to determine if some infants are developing quicker than others,” Badescu said.