Anemonefish dads do almost anything to support their offspring
Like the father in "Finding Nemo," anemonefish dads will do almost anything to support their offspring. Their parenting instincts are so strong that if you give a bachelor anemonefish a scoop of anemonefish eggs from an unrelated nest, he will care for them -- constantly nipping at them to remove debris and fanning them with oxygen-rich waters -- as if they were his own. (Any other fish would eat them, researchers say.)
A new study of this species, Amphiprion ocellaris, reveals some of the potent hormonal signals that regulate this gallant paternal instinct. Researchers report that anemonefish rely on a signaling molecule that is almost identical to oxytocin -- known as the love hormone in humans and also associated with mothering -- to maintain their fatherly fidelity. When researchers blocked this hormone, known as isotocin, in the male fish, the dads stopped tending to their young.
This is not the first study to show that isotocin regulates paternal care in fish, but it is the first to focus on the anemonefish, which the researchers describe as a paragon of fatherly love.
"Because the fish are so committed to their role as fathers, we're able in the lab to dissociate their parental behavior -- the fanning and the nipping -- from behaviors associated with courtship, territory defense and nest defense," said University of Illinois graduate student Ross DeAngelis, who led the study with psychology professor Justin Rhodes. "This allows us to look at how the brain regulates male parental care in isolation from other behaviors that occur simultaneously."
The researchers also analyzed how another hormone, arginine vasotocin, influences paternal care in anemonefish. Other studies suggest the hormone plays a role in regulating dominance, aggression and courtship. It also has a homolog in humans, known as arginine vasopressin.
"All these peptides -- isotocin and oxytocin, arginine vasopressin and vasotocin -- have very similar genetics and very similar molecular structures across species," Rhodes said. "They all evolved from the same gene."
When the researchers blocked vasotocin in one of a pair of male anemonefish, the treated males displayed significantly less aggression than their untreated counterparts. Blocking vasotocin in anemonefish fathers, however, yielded an unexpected result: The dutiful dads became even more attentive to their offspring.
"We were surprised by this because these fish display such a high level of parental effort in the laboratory that it's hard to imagine there being an increase," DeAngelis said. "Our hypothesis is that by blocking vasotocin signaling, you're reducing vigilance and nest defense, allowing a greater allotted effort to be directed toward parental care."
Whether the patterns in anemonefish also hold true for humans remains to be seen, the researchers said. Paternal care is rare in vertebrates, and mammalian fathers tend to be indifferent to the survival of their offspring, they said.
The anemonefish is particularly faithful to his mate and offspring because he's trapped with them on a single anemone that offers the family shelter and defense, the researchers said.
But the similarities between anemonefish and other species likely outweigh the differences, they said. There is evidence, for example, that oxytocin also plays a role in human fathering.
"There has been a lot of recent research showing that these behaviors -- like aggression or reproduction or parental care -- are sort of ubiquitously distributed across vertebrates, and the mechanisms that promote and maintain those behaviors are similar in all species," DeAngelis said.
"Vertebrates evolved over 400 million years, and 300 million years of that were fish," Rhodes said. "Paternal care has very deep origins, and the molecular mechanisms or genetics of that are going to be similar across species. I think we can learn a lot from our fish ancestors."
Story Source:
Materials provided by University of Illinois at Urbana-Champaign. Original written by Diana Yates. Note: Content may be edited for style and length.
Journal Reference:
- Ross DeAngelis, Joseph Gogola, Logan Dodd, Justin S. Rhodes. Opposite effects of nonapeptide antagonists on paternal behavior in the teleost fish Amphiprion ocellaris. Hormones and Behavior, 2017; 90: 113 DOI: 10.1016/j.yhbeh.2017.02.013
New theory on how Earth's crust was created
More than 90% of Earth's continental crust is made up of silica-rich minerals, such as feldspar and quartz. But where did this silica-enriched material come from? And could it provide a clue in the search for life on other planets?
Conventional theory holds that all of the early Earth's crustal ingredients were formed by volcanic activity. Now, however, McGill University earth scientists Don Baker and Kassandra Sofonio have published a theory with a novel twist: some of the chemical components of this material settled onto Earth's early surface from the steamy atmosphere that prevailed at the time.
First, a bit of ancient geochemical history: Scientists believe that a Mars-sized planetoid plowed into the proto-Earth around 4.5 billion years ago, melting the Earth and turning it into an ocean of magma. In the wake of that impact -- which also created enough debris to form the moon -- the Earth's surface gradually cooled until it was more or less solid. Baker's new theory, like the conventional one, is based on that premise.
The atmosphere following that collision, however, consisted of high-temperature steam that dissolved rocks on the Earth's immediate surface -- "much like how sugar is dissolved in coffee," Baker explains. This is where the new wrinkle comes in. "These dissolved minerals rose to the upper atmosphere and cooled off, and then these silicate materials that were dissolved at the surface would start to separate out and fall back to Earth in what we call a silicate rain."
To test this theory, Baker and co-author Kassandra Sofonio, a McGill undergraduate research assistant, spent months developing a series of laboratory experiments designed to mimic the steamy conditions on early Earth. A mixture of bulk silicate earth materials and water was melted in air at 1,550 degrees Celsius, then ground to a powder. Small amounts of the powder, along with water, were then enclosed in gold palladium capsules, placed in a pressure vessel and heated to about 727 degrees Celsius and 100 times Earth's surface pressure to simulate conditions in the Earth's atmosphere about 1 million years after the moon-forming impact. After each experiment, samples were rapidly quenched and the material that had been dissolved in the high temperature steam analyzed.
The experiments were guided by other scientists' previous experiments on rock-water interactions at high pressures, and by the McGill team's own preliminary calculations, Baker notes. Even so, "we were surprised by the similarity of the dissolved silicate material produced by the experiments" to that found in the Earth's crust.
Their resulting paper, published in the journal Earth and Planetary Science Letters, posits a new theory of "aerial metasomatism" -- a term coined by Sofonio to describe the process by which silica minerals condensed and fell back to earth over about a million years, producing some of the earliest rock specimens known today.
"Our experiment shows the chemistry of this process," and could provide scientists with important clues as to which exoplanets might have the capacity to harbor life Baker says.
"This time in early Earth's history is still really exciting," he adds. "A lot of people think that life started very soon after these events that we're talking about. This is setting up the stages for the Earth being ready to support life."
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Materials provided by McGill University. Note: Content may be edited for style and length.
Journal Reference:
- Don R. Baker, Kassandra Sofonio. A metasomatic mechanism for the formation of Earth's earliest evolved crust. Earth and Planetary Science Letters, 2017; 463: 48 DOI: 10.1016/j.epsl.2017.01.022
The liver increases by half during the day
In mammals, the liver plays a pivotal role in metabolism and the elimination of toxins, and reaches its maximum efficiency when they are active and feed. Biologists from the University of Geneva (UNIGE), Switzerland, have discovered how this organ adapts to the cycles of feeding and fasting, and the alternation of day and night within 24 hours. The researchers showed in mice that the size of the liver increases by almost half before returning to its initial dimensions, according to the phases of activity and rest. Published in the journal Cell, their study describes the cellular mechanisms of this fluctuation, which disappears when the normal biological rhythm is reversed. The disruption of our circadian clock due to professional constraints or private habits therefore probably has important repercussions on our liver functions.
Mammals have adapted to diurnal and nocturnal rhythms using a central clock located in the brain. The latter, which is resettled every day by the light, synchronizes the subordinate clocks present in most of our cells. In the liver, more than 350 genes involved in metabolism and detoxification are expressed in a circadian fashion, with a biological rhythm of 24 hours. "Many of them are also influenced by the rhythm of food intake and physical activity, and we wanted to understand how the liver adapts to these fluctuations," says Ueli Schibler, professor emeritus at the Department of Molecular Biology of the UNIGE Faculty of Science.
The liver oscillates, but not the other organs
The mice forage and feed at night, while the day is spent resting. "In rodents following a usual circadian rhythm, we observed that the liver gradually increases during the active phase to reach a peak of more than 40% at the end of the night, and that it returns to its initial size during the day," notes Flore Sinturel, researcher of the Geneva group and first author of the study.
The cellular mechanisms of this adaptation were discovered in collaboration with scientists from the Nestlé Institute of Health Sciences (NIHS) and the University of Lausanne (UNIL) in Switzerland. Researchers have shown that the size of liver cells and their protein content oscillate in a daily manner.
The number of ribosomes, the organelles responsible for producing the proteins required for the various functions of the liver, fluctuates together with the size of the cell. "The latter adapts the production and assembly of new ribosomes to ensure a peak of protein production during the night. The components of ribosomes produced in excess are then identified, labeled, and degraded during the resting phase," explains Flore Sinturel.
Asynchronous clock genes
The amplitude of the variations observed by the biologists depends on the cycles of feeding and fasting, as well as diurnal and nocturnal phases. Indeed, the fluctuations disappear when the phases of feeding no longer correspond to the biological clock, which evolved in the course of hundreds of millions of years: "the size of the liver and the hepatocytes, as well as their contents in ribosomes and proteins, remain nearly stable when mice are fed during the day. Yet, these animals ingest similar amounts of food, irrespective of whether they are fed during the night or during the day," points out Frédéric Gachon of the NIHS, who co-directed the study.
Many human subjects no longer live according to the rhythm of their circadian clock, due to night work hours, alternating schedules or frequent international travels. A previous study (Leung et al., Journal of Hepatology, 1986) determining the volume of the human liver during six hours using methods based on ultrasound, suggests that this organ also oscillates within us. If mechanisms similar to those found in mice exist in humans, which is likely to be the case, the deregulation of our biological rhythms would have a considerable influence on hepatic functions.
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Materials provided by Université de Genève. Note: Content may be edited for style and length.
Journal Reference:
- Flore Sinturel, Alan Gerber, Daniel Mauvoisin, Jingkui Wang, David Gatfield, Jeremy J. Stubblefield, Carla B. Green, Frédéric Gachon, Ueli Schibler. Diurnal Oscillations in Liver Mass and Cell Size Accompany Ribosome Assembly Cycles. Cell, 2017; 169 (4): 651 DOI: 10.1016/j.cell.2017.04.015
