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Why aren't human babies considered larvae?

Why aren't human babies considered larvae?


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I've seen people who are anti-baby describe babies, or children in general, as human larvae. This is generally done in order to make them seem weird. While I feel like this statement is wrong, I can't quite put my finger on exactly why.

Many definitions of "larva" specify that they must metamorphosize, or go through significant morphological changes on the path to adulthood. However, tadpoles gradually change form, rather than metamorphosizing, and hemimetabolic insects have larval instars that aren't substantially different from adults, aside from being sexually immature and smaller. "Sexually immature and smaller", of course, also describes babies fairly well.

Unfortunately, I'm no biologist and my knowledge of what defines animal young as larval vs. non-larval is rudimentary, at best, so I'm not sure if there's a more precise definition of "larva" than the one I found on wikipedia, which would disqualify human babies. What traits differentiate larva from non-larva, and which of those traits to babies lack?


For animals with a clear larval stage, the presence of such a stage indicates that there is a metamorphosis, a change in body morphology at some point in development.

Metamorphosis does not necessarily refer to an 'instant' transformation or one that requires a pupation step or something similar; gradual change can still be metamorphosis, as long as there is a clear 'before' and 'after.'

Human infants, on the other hand, don't go through much of a metamorphosis: sure, they grow quite a bit, but their general body plan does not change. Contrast this with insects, or your tadpole example, and it is clear there are major body plan changes from larvae to adult stages.

The Wikipedia page on larvae describes the characteristics of larvae fairly clearly. Like most traits in biology that vary across taxa, you are likely to find some intermediate creatures where the presence of a larval stage is somewhat controversial or depends on opinion. There could be a difference of opinion on how much of a change is sufficient to describe a juvenile form as a larvae. Humans don't have a postnatal stage that approaches that potential boundary.

The part in your question about people who are "anti-baby" sounds a bit judgmental, but I think what you are describing is just a phrasing meant to be somewhat humorous and to evoke images of "gross" larvae; I wouldn't take that for any biological meaning and I wouldn't focus your time on proving it "wrong" - the actual difference of opinion you have is something entirely different.


Children certainly are not human larvae biologically, for the reasons explained in the accepted answer.

However, calling children larvae is a metaphor that refers to child's mental and social development rather than morphological. Stepping back and looking at a kid as human larva can give adults important insight:

  • A larva has entirely different needs and capabilities than imago. Adults sometimes forget that.
  • Important milestones of development (walking, talking, social training, adolescence) resemble instars: behavior and needs of a kid at given milestone have little in common with needs at previous stage.
  • The purpose of a larva is to molt into adult form. Which is something that many parents tend to forget: that the only purpose of their kid is to grow into a functioning adult eventually.
  • Actions of the larva make no sense for the imago, and imago can't be held responsible for it's previous instar actions. That's somehow a trope for family embarrassing teens/young adults with things they've done as kids. Larva analogy helps to deal with such situations and memories.

This analogy is anti-baby only used in context against babies. In some parenting books, this analogy is used to help parents understand their children better. The only inherently bad thing about it I can think of is exploiting some people's aversion to insects in general and larvae in particular.


Why Science Can't Say When a Baby's Life Begins

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Scott Gilbert was walking through the halls of Swarthmore when he saw the poster, from a campus religious group: “Philosophers and theologians have argued for centuries about when personhood begins,” it read. “But scientists know when it begins. It begins at fertilization.” What troubled Gilbert, who is a developmental biologist, was the assertion that “scientists know.” “I couldn’t say when personhood begins, but I can say with absolute certainty scientists don’t have a consensus,” he says.

When life begins is, of course, the central disagreement that fuels the controversy over abortion. Attacks on abortion rights are now more veiled and indirect---like secret videos pointing to Planned Parenthood’s fetal tissue donations, or state legislation that makes operating abortion clinics so onerous they have to shut down. But make no mistake, the ultimate question is, when does a fetus become a person---at fertilization, at birth, or somewhere in between?

Here, modern science offers no clarity. If anything, the past century of scientific advances have only made the answer more complicated. As scientists have peered into wombs with ultrasound and looked directly at sperm entering an egg, they’ve found that all the bright lines they thought existed dissolving.

Before ultrasounds and long before Roe v. Wade, it was obvious when life began. The “quickening,” the first time a woman felt her baby’s kick, was the moment the baby came alive, the moment it got a soul. When Henry VIII’s wife felt her quickening, it was cause for celebratory bonfires across London. In the 19th century, abortion in Britain was legal---until the quickening.

But the importance of the quickening---a concept that had been around since at least Aristotle---is now a relic. Before a mother can feel her baby kick, at around 20 weeks, she can already hear its heartbeat and see the blurry outline of its face with ultrasound. In a 2012 vice presidential debate, Paul Ryan explained his views on abortion by talking about seeing the bean shape of his unborn daughter on an ultrasound. He and his wife nicknamed her “Bean.” Ryan would later sponsor a bill for fetal personhood, which gives full legal rights to a zygote after fertilization.

In a way, science made possible the argument for fetal personhood. It's only tenable because people can peer inside the womb, at one time a black box. Indeed, when American physicians began collecting humans embryos and charting embryonic development in the late 19th and early 20th centuries, they began considering fertilization as the beginning of fetal life. Around the same time, writes historian Sara Dubow in her book Ourselves Unborn: A History of the Fetus in Modern America, some physicians began to argue that abortion should be illegal. (Dubow declined to be interviewed for this story, citing concerns about being misquoted on abortion politics.)

The next century of developmental biology made things even more complicated. With in vitro fertilization---combining sperm and egg in a lab---scientists could directly observe the process of sperm entering the egg for the first time. It actually takes place over as long as 24 hours a series of biochemical changes need to happen before the sperm can enter. Inside the body, fertilization can happen hours or even days after insemination, as the sperm travels up the fallopian tube. This journey also induces changes in the membrane of the sperm, called capacitation, that ready it to fertilize eggs. (The discovery of artificial capacitation was key to making in vitro fertilization possible.) As the fertilization researcher Harvey Florman has said, “Fertilization doesn’t take place in a moment of passion. It takes place the next day in the laundromat or the library.”

But even fertilization isn't a clean indicator of anything. The next step is implantation, when the fertilized egg travels down the fallopian tube and attaches to the mother’s uterus. “There’s an incredibly high rate of fertilized eggs that don’t implant,” says Diane Horvath-Cosper, an OB-GYN in Washington, DC. Estimates run from 50 to 80 percent, and even some implanted embryos spontaneously abort. The woman might never know she was pregnant.


The unborn is a human being: What science tells us about unborn children

Before we can know how to treat unborn children (an ethical question), we must know what they are biologically. This is a question of science.

Here's what science tells us about the unborn.

Why the unborn is a human being

When a sperm successfully fertilizes an oocyte (egg), a new cell, called a zygote, is generated by their union. The zygote represents the first stage in the life of a human being. This individual, if all goes well, develops through the embryonic (first eight weeks) and fetal (eight weeks until birth) periods and then through infancy, childhood, and adolescence before reaching adulthood.

Four characteristics of the unborn human (the zygote, embryo, or fetus) are important:

Distinct. The unborn has a DNA and body distinct from her mother and father. She develops her own arms, legs, brain, nervous system, heart, and so forth.

Living. The unborn meets the biological criteria for life. She grows by reproducing cells. She turns nutrients into energy through metabolism. And she can respond to stimuli.

Human. The unborn has a human genetic signature. She is also the offspring of human parents, and humans can only beget other humans.

Organism. The unborn is an organism (rather than a mere organ or tissue)—an individual whose parts work together for the good of the whole. Guided by a complete genetic code (46 chromosomes), she needs only the proper environment and nutrition to develop herself through the different stages of life as a member of the species.

These facts about the unborn are established by the science of embryology and developmental biology. They are confirmed by embryology texts, scientific journals, and other relevant authorities.

"Human development begins at fertilization when a sperm fuses with an oocyte to form a single cell, a zygote," explains the textbook The Developing Human: Clinically Oriented Embryology. "This highly specialized, totipotent cell marks the beginning of each of us as a unique individual."

"The development of a human being begins with fertilization," notes Langman's Medical Embryology, "a process by which the spermatozoon from the male and the oocyte from the female unite to give rise to a new organism, the zygote."

The scientific evidence, then, shows that the unborn is a living individual of the species Homo sapiens, the same kind of being as us, only at an earlier stage of development. Each of us was once a zygote, embryo, and fetus, just as we were once infants, toddlers, and adolescents.

Objections to the humanity of the unborn

Many people, however, still dispute the biological humanity of the unborn. Here are some of the most common science-related objections.

Some people point out that the sperm and egg are alive. Indeed, life, in a broad sense, is continuous (stretching back to the beginning of life on Earth). So it's not accurate, they claim, to say that life "begins" at conception.

It's true that life in general is continuous, but the life of an individual human being is not continuous. It has a beginning and an end. The beginning is called conception. "Although life is a continuous process," explains the textbook Human Embryology & Teratology, "fertilization … is a critical landmark because, under ordinary circumstances, a new, genetically distinct human organism is formed."

Many people note that human organs, tissues, and cells (including the sperm and egg) are living and genetically human. But merely being alive and human doesn't make them human beings. Neither, the argument goes, does it make the unborn a human being.

The difference, however, is that the unborn is a whole organism—an individual member of the species—and other cells and tissues are mere parts. So the unborn isn't just living and human (in the adjective sense of those words) she's a life and a human (in the noun sense). None of us was ever a kidney or a skin cell or a sperm cell. But each of us was once an embryo.

Some people think that the cells of a very early embryo are too unspecialized or insufficiently unified for the embryo to count as an individual human being. The embryo, they say, is more akin to a mass or ball of cells.

From the zygote stage forward, however, the unborn human clearly exhibits the molecular composition and behavior characteristic of a self-integrated and self-directed organism rather than a mere collection of cells. That's why she can go on to develop the specialized tissues and organs that she does.

"From the moment of sperm-egg fusion," concludes embryologist Maureen L. Condic, a professor at the University of Utah School of Medicine, in a detailed scientific analysis, "a human zygote acts as a complete whole, with all the parts of the zygote interacting in an orchestrated fashion to generate the structures and relationships required for the zygote to continue developing towards its mature state."

Before about 14 days post-conception, some embryos split into two embryos (identical twins). Therefore, some think, embryos before this point aren't yet individual, unitary human beings.

But the fact than one organism can give rise to two doesn't mean it isn't an individual organism. A flatworm, as Patrick Lee observes, can be cut to produce two separate flatworms, and that doesn't mean a flatworm isn't a flatworm. The evidence of embryology shows that human embryos, likewise, are unitary and individual organisms even if twinning later occurs.

Parallel with brain death

The irreversible cessation of brain function indicates the death of a human being. Some people argue, then, that the life of a human being cannot begin until brain activity begins.

But the reason (total) brain death matters is that it means the body can no longer function as an integrated whole (even if some cells and tissues are still alive). The brain, in older humans, is essential for that purpose. Before the development of the brain in the first place, however, the very young embryo does not require it in order to function as an organism and direct her own growth (including the development of her brain).

Thus, while a brain-dead patient is a corpse in the process of decay, an embryo is a living and growing individual.

Science and morality

If the basic scientific facts pertaining to the nature of the unborn are straightforward, why do so many people claim that "no one knows when life begins" or that a human embryo isn't human? The biggest reason is that science is conflated with morality, philosophy, or religion.

When someone says that the unborn is not yet "human" or "alive," he is often using those terms in a non-scientific way. He doesn't mean that the unborn isn't biologically human or alive. He means that the unborn isn't valuable or doesn't have human rights. He means that the unborn doesn't yet have the characteristics (e.g., "viability," self-awareness, an infant-like appearance) he thinks would make her "human" or "alive" in this philosophical sense.

So there are two distinct issues here. First, the scientific issue: Is the unborn a human being in the biological sense—a living human organism? The answer, unequivocally, is yes.

Second, the moral or philosophical issue: How should we treat these human beings who have not yet been born? Do they have a right to life? Do all members of our species matter, or only some? This is where the controversy actually lies.

Human embryos and fetuses are human beings. That's what science tells us. Is human equality true? That's what the abortion debate is really about.

A version of this article first appeared in the November-December 2017 issue of MCCL News.


Pregnancy: Why mother's immune system does not reject developing fetus as foreign tissue

Researchers at NYU School of Medicine have made an important discovery that partially answers the long-standing question of why a mother's immune system does not reject a developing fetus as foreign tissue.

"Our manuscript addresses a fundamental question in the fields of transplantation immunology and reproductive biology, namely, how do the fetus and placenta, which express antigens that are disparate from the mother, avoid being rejected by the maternal immune system during pregnancy?" explained lead investigator Adrian Erlebacher, MD, PhD, associate professor of pathology and a member of the NYU Cancer Institute at NYU Langone Medical Center. "What we found was completely unexpected at every level."

The researchers discovered that embryo implantation sets off a process that ultimately turns off a key pathway required for the immune system to attack foreign bodies. As a result, immune cells are never recruited to the site of implantation and therefore cannot harm the developing fetus.

The study, funded by grants from the National Institutes of Health and the American Cancer Society, appears in the June 8 issue of Science.

A central feature of the body's natural immune defense against transplanted foreign tissues and pathogens is the production of chemokines as a result of the local inflammatory response. The chemokines recruit various kinds of immune cells, including activated T cells, which accumulate and attack the tissue or pathogen. The chemokine-mediated recruitment of activated T cells to sites of inflammation is an integral part of the immune response.

During pregnancy however, the foreign antigens of the developing fetus and the placenta come into direct contact with cells of the maternal immune system, but fail to evoke the typical tissue rejection response seen with organ transplants.

Several years ago, Erlebacher and his research team found that T cells, poised to attack the fetus as a foreign body, were somehow unable to perform their intended role. The finding prompted the researchers to wonder if perhaps there was some sort of barrier preventing the T cells from reaching the fetus. They turned their attention to studying the properties of the decidua, the specialized structure that encases the fetus and placenta, and there, in a mouse model, they found new answers.

The research team has discovered that the onset of pregnancy causes the genes that are responsible for recruiting immune cells to sites of inflammation to be turned off within the decidua. As a result of these changes, T cells are not able to accumulate inside the decidua and therefore do not attack the fetus and placenta.

Specifically, they revealed that the implantation of an embryo changes the packaging of certain chemokine genes in the nuclei of the developing decidua's stromal cells. The change in the DNA packaging permanently deactivates, or "silences," the chemokine genes. Consequently, the chemokines are not expressed and T cells are not recruited to the site of embryo implantation.

Also of note, the observed change in the DNA packaging was a so-called 'epigenetic' modification, meaning a modification that changes gene expression without the presence of a hereditable gene mutation.

"These findings give insight into mechanisms of fetal-maternal immune tolerance, as well as reveal the epigenetic modification of chemokine genes within tissue stromal cells as a modality for limiting the trafficking of activated T cells," Dr. Erlebacher said. "It turns out that the cells that typically secrete the chemoattractants to bring the T cells to sites of inflammation are inhibited from doing so in the context of the pregnant uterus. The decidua appears instead as a zone of relative immunological inactivity."

Inappropriate regulation of this process, Dr. Erlebacher explained, could cause inflammation and the accumulation of immune cells at the maternal-fetal interface, which could lead to complications of human pregnancy, including preterm labor, spontaneous abortion and preeclampsia.

Erlebacher and his team will next look to see if these epigenetic modifications are also present within the human decidua, and whether the failure to generate them appropriately is associated with complications of human pregnancy. He explained that the study's findings also raise the possibility that the same kind of mechanism could enhance a tumor's ability to survive inside its host. The findings could have implications for autoimmune diseases, organ transplantation and cancer, as well as pregnancy.

"This is a very exciting finding for us because it gives a satisfying explanation for why the fetus isn't rejected during pregnancy, which is a fundamental question for the medical community with clear implications for human pregnancy," Dr. Erlebacher said. "It also reveals a new modality for controlling T cell trafficking in peripheral tissues that could provide insight into a myriad of other conditions and diseases."


The Embryo Project Encyclopedia

A designer baby is a baby genetically engineered in vitro for specially selected traits, which can vary from lowered disease-risk to gender selection. Before the advent of genetic engineering and in vitro fertilization (IVF), designer babies were primarily a science fiction concept. However, the rapid advancement of technology before and after the turn of the twenty-first century makes designer babies an increasingly real possibility. As a result, designer babies have become an important topic in bioethical debates, and in 2004 the term “designer baby” even became an official entry in the Oxford English Dictionary. Designer babies represent an area within embryology that has not yet become a practical reality, but nonetheless draws out ethical concerns about whether or not it will become necessary to implement limitations regarding designer babies in the future.

The prospect of engineering a child with specific traits is not far-fetched. IVF has become an increasingly common procedure to help couples with infertility problems conceive children, and the practice of IVF confers the ability to pre-select embryos before implantation. For example, preimplantation genetic diagnosis (PGD) allows viable embryos to be screened for various genetic traits, such as sex-linked diseases, before implanting them in the mother. Through PGD, physicians can select embryos that are not predisposed to certain genetic conditions. For this reason, PGD is commonly used in medicine when parents carry genes that place their children at risk for serious diseases such as cystic fibrosis or sickle cell anemia. Present technological capabilities point to PGD as the likely method for selecting traits, since scientists have not established a reliable means of in vivo embryonic gene selection.

An early and well-known case of gender selection took place in 1996 when Monique and Scott Collins saw doctors at the Genetics & IVF Institute in Fairfax, Virginia, for in vitro fertilization. The Collins’ intended to conceive a girl, as their first two children were boys and the couple wanted a daughter in the family. This was one of the first highly publicized instances of PGD in which the selection of the embryo was not performed to address a specific medical condition, but to fulfill the parents’ desire to create a more balanced family. The Collins’ decision to have a “designer baby” by choosing the sex of their child entered the public vernacular when they were featured in Time Magazine’s 1999 article "Designer Babies". Though the Collins’ case only involved choice of gender, it raised the issues of selection for other traits such as eye color, hair color, athleticism, or height that are not generally related to the health of the child.

Prior to the Collins’ decision to choose the sex of their child, The Council on Ethical and Judicial Affairs released a statement in 1994 in support of using genetic selection as a means to prevent, cure or specific diseases, but that selection based on benign characteristics was not ethical. Some ethical concerns held by opponents of designer babies are related to the social implications of creating children with preferred traits. The social argument against designer babies is that if this technology becomes a realistic and accessible medical practice, then it would create a division between those that can afford the service and those that cannot. Therefore, the wealthy would be able to afford the selection of desirable traits in their offspring, while those of lower socioeconomic standing would not be able to access the same options. As a result, economic divisions may grow into genetic divisions, with social distinctions delineating enhanced individuals from unenhanced individuals. For example, the science-fiction film Gattaca explores this issue by depicting a world in which only genetically-modified individuals can engage in the upper echelon of society.

Other bioethicists have argued that parents have a right to prenatal autonomy, which grants them the right to decide the fate of their children. George Annas, chair of the Department of Health Law, Bioethics, and Human Rights at Harvard University has offered support for the idea of PGD, and the designer babies that result, as a consumer product that should be open to the forces of market regulation. Additionally, other arguments in favor of designer baby technologies suggest that parents already possess a high degree of control over the outcome of their children’s lives in the form of environmental choices, and that this should absolve some of the ethical concerns facing genetic selection. For example, parents keen on establishing musical appreciation in their children may sign them up for music classes or take them to concerts on a regular basis. These choices affect the way a child matures, much like the decision to select certain genes predisposes a child to develop in ways that the parents have predetermined are desirable.

The increased ability to control and manipulate embryos presents many possibilities for improving the health of children through prenatal diagnosis, but these possibilities are coupled with potential social repercussions that could have negative consequences in the future. Ultimately, designer babies represent great potential in the field of medicine and scientific research, but there remain many ethical questions that need to be addressed.


The Secret Tuna Nursery

It was a little after 10 p.m., and several hundred miles off the coast of Massachusetts, Chrissy Hernandez was counting eyeballs.

Scattered across a dinner plate-sized sieve in front of her was the harvest from yet another tow with a fine-meshed net. Hernandez, a graduate student in the MIT-WHOI Joint Program in Oceanography, shone a light across the sieve, looking for the telltale shine of larval fish eyes. She was hunting for one species in particular—Atlantic bluefin tuna.

Bluefin tuna are the largest species of tuna, growing up to ten feet long and more than a thousand pounds. Their population has been severely depleted by overfishing, as their meat is prized for sushi and can sell at exorbitant prices (one fish sold for more than $1.7 million in Japan in 2013).

A key way to help conserve the species is to protect areas where they go to spawn. But to do that, “you need to know where they spawn,” said Joel Llopiz, a biologist at Woods Hole Oceanographic Institution (WHOI) and Hernandez’s advisor.

In the Atlantic, bluefin tuna generally split into two stocks, which are managed separately. The eastern stock spawns in the Mediterranean Sea, and the western stock spawns in the Gulf of Mexico.

But in the summer of 2017, Hernandez wasn’t in either of these recognized spawning grounds. She was in a third, previously unknown spawning area. It’s tucked into the gap between the continental shelf off the U.S. Eastern Seaboard and the Gulf Stream current as it peels away from the coast—an area known as the Slope Sea.

Some scientists had suspected that the Slope Sea could be a potential spawning ground because they had tracked tagged tuna to this location when the waters were warm enough for spawning. But adult bluefin tuna can swim up to 40 miles per hour and the tags aren’t that accurate. The fish could have just been passing through. Then in 2013, larval bluefin tuna were found in several locations in the Slope Sea during a sampling cruise run by the National Oceanic and Atmospheric Administration (NOAA).

The findings from the cruise were published in 2016, at just the right time for Hernandez. “It was the spring of the first year of my Ph.D. program, and I wasn’t sure what I wanted to do,” she said. “What was going to keep me excited about science?”

The discovery of a potentially new spawning location was definitely exciting. But there’s a big difference between finding larvae and showing that these fish grow up to contribute significantly to the bluefin population. The Slope Sea is a very different environment from the other two spawning locations. Could fish hatched there actually grow and survive, or would they all die off?

Caught in the currents

The first few weeks of a bluefin tuna’s life aren’t easy. A female tuna can lay millions of eggs, but only a small percentage of hatchlings will make it to adulthood. The new larvae are tiny, only a few millimeters long, and they are easily swallowed by a plethora of plankton-eaters. Even if they manage to avoid being eaten, an influx of water that is too warm or too cold can kill them as they are swept along by the currents around them.

The Slope Sea, which is known for both fluctuating currents and temperatures, is a hard place to survive.

“And it’s very close to the Gulf Stream, which is bad for spawning,” said Llopiz. “Your larvae are going to get shot off toward England by the current, and will end up too far away to make it back to the nursery grounds.”

Young tuna could also wind up along the continental shelf, where the waters are too cold for survival.

On the other hand, some of the currents in the Slope Sea might actually help the tuna larvae. As the Gulf Stream wavers along the Slope Sea’s southern edge, it spins off rotating currents to the north, known as eddies or warm-core rings, that can linger for months. As their name suggests, these rings trap warm water in their centers. If that water is the right temperature, the circular motion could cocoon larvae safely within the Slope Sea until they are able to swim independently.

The Slope Sea’s variable currents and fluctuating temperatures makes it a complicated problem to determine if larvae can survive there. Scientists can take measurements of the water temperatures and currents as they study the area, but these only provide brief snapshots of information in one place at one time.

“Field data on currents are valuable,” Llopiz said. “It’s just that you can’t be everywhere at the same time.”

To figure out whether the Slope Sea could be a viable spawning ground for bluefin tuna, the biologists needed a picture of what was happening in the entire area over the course of several months.

Fortunately, Llopiz knew people who could build exactly that.

Biology meets physics

A few years earlier, Llopiz had received an email from two physical oceanographers at WHOI, Larry Pratt and Irina Rypina, who were examining another longstanding ocean larval mystery: how American eels get from their spawning areas in the Sargasso Sea to the mouths of Eastern Seaboard rivers where they spend their adult lives.

Pratt had seen an article in The New York Times claiming that larval eels simply drifted from the middle of the Atlantic to the coast of Maine. He and Rypina study ocean currents, and they had their doubts. But they were not experts in all the biological factors involved, so they enlisted Llopiz.

“Teaming up with physical oceanographers is great,” Llopiz said. “To be able to know what the currents are doing everywhere all the time is mind-blowing. And when these little fish are at the mercy of ocean currents, it’s super valuable information.”

The trio wound up collaborating on a study using a numerical model of currents in the Atlantic Ocean to investigate this mysterious migration. Since then, they have kept an eye out for other opportunities to combine their skills.

“Joel was just telling us about the tuna problem,” Rypina said, “and we thought it might be a good thing to try to model.”

Rypina and Pratt study the physics of ocean movements. They focus on models that view currents as an agglomeration of individual particles of water swirling around. But tuna larvae can also be viewed as tiny individual particles, so “the method for tracking water particles can easily be adapted to track small critters,” Pratt said.

To explore the Slope Sea tuna riddle, the team needed a model that focused on that specific region the model they had used for the eels spanned a larger portion of the Atlantic. For this, they approached Ke Chen, a numerical modeler at WHOI who has been studying the physical processes in the area around the continental shelf in the Northwest Atlantic.

Chen specifically works on modeling and understanding currents on the continental shelf and in the Slope Sea, including Gulf Stream warm-core rings. To improve the accuracy of his regional model, Chen incorporates fresh water flowing out from rivers into the ocean and other processes that typically aren’t considered in open-ocean models.

“Physics tells us how the ocean is moving,” Chen said, “but you have to wonder what that means for biology.”

A virtual ocean

Chen adapted and refined models he had worked on before to create a model of water movement in the Slope Sea. He tested its accuracy against actual data collected during the 2013 NOAA cruise. They focused on the factors that would affect larvae the most: temperatures and currents in the top 30 feet of ocean, where tuna larvae are typically found.

Once they had a working model ready to go, it was time to release the fish. Virtual fish, that is.

As the model replicated the Slope Sea conditions of 2013, the scientists dropped 2,500 “larvae” into the virtual ocean every three hours between May and October and tracked them as they swirled through the currents.

Llopiz and Hernandez provided the biological information to decide whether each virtual larva survived. The larvae had to remain in the right temperatures within the Slope Sea for 25 days—an estimate of how long it might take larval tuna to grow big enough to be able to swim independently of the currents.

At the end of the model run, the researchers had found two spawning hot spots where tuna larvae had the best chance of survival. These areas were warm enough to support the larvae by the end of July, and the nearby currents kept them within the spawning ground. One was in the southwestern part of the Slope Sea, away from the swirls of the Gulf Stream, and the other was farther north, centered on the place where a warm-core ring was located in 2013.

The model identified, on average, the times and places in the Slope Sea where conditions would allow tuna larvae to thrive. The next step was to go out and see if tuna larvae are actually there.

More questions than answers

Hernandez stood on the stern of a NOAA-operated vessel holding a diamond-shaped apparatus made of canvas and bamboo, known as a drifter. She had found bluefin tuna larvae at the last three sampling locations in the ocean.

“A big warm-core ring was in the same place where the model had showed one in 2013,” Hernandez said. “We spent an entire night, well actually more like one and a half nights, doing a transect across it.”

She held a walkie-talkie in her other hand, coordinating with two shipmates who waited to deploy additional drifters.

The drifters plunged into the water, stabilizing a few meters below their buoys at the surface. They would be slowly swept away by the currents, transmitting their locations as they went.

Data from the drifters can help improve and confirm the WHOI physical oceanographers’ models.

“It’s an area of ocean that doesn’t get sampled all the time,” Hernandez said. “We really have to jump on the opportunities that do arise.”

Hernandez is using the larvae she collected to compare growth rates between the Slope Sea population and those in the Gulf of Mexico. Other researchers are looking at the genetics of the samples she collected to determine whether the Slope Sea tuna are related to the eastern or western stocks.

“There’s still a big lack of understanding of the larval ecology of Slope Sea bluefin tuna,” Llopiz said. “There’s just so much that we don’t know: how well they’re eating, how fast they’re growing, why they are where they are. There’s just a lot to learn.”

What these scientists learn will be critical for devising effective conservation strategies. The future of bluefin tuna, both in the ocean and in soy sauce, depends on it.

This research was funded by NOAA, the National Science Foundation, WHOI’s Ocean Life Institute, and WHOI’s NOAA-funded Cooperative Institute for the North Atlantic Region.


Show/hide words to know

Caste: class to which an adult ant belongs.

Larva: the second, "worm-like" stage in the life cycle of insects that undergo complete metamorphosis (like caterpillars).

Larvae: plural of 'larva.'

Metamorphosis: dramatic change in body form. more

Molt: to shed the outer layer of the body.

Pupa: resting stage during which tissues are reorganized from larval form to adult form. The pupa is the third body form in the life cycle of insects that undergo complete metamorphosis (like caterpillars).

Pupae: plural of 'pupa'.

Queen: a female ant that lays eggs.

Worker: a female ant that performs jobs other than reproduction.

Ants undergo complete metamorphosis, passing through a sequence of four stages: egg, larva, pupa, and adult.

An ant’s life begins as an egg. Ant eggs are soft, oval, and tiny – about the size of a period at the end of a sentence. Not all eggs are destined to become adults – some are eaten by nestmates for extra nourishment.

An egg hatches into a worm-shaped larva with no eyes or legs. Larvae are eating machines that rely on adults to provide a constant supply of food. As a result, they grow rapidly, molting between sizes.

When a larva is large enough, it metamorphoses into a pupa. This is a stage of rest and reorganization. Pupae look more like adults, but their legs and antennae are folded against their bodies. They start out whitish and gradually become darker. The pupae of some species spin a cocoon for protection, while others remain uncovered, or naked.

Finally, the pupa emerges as an adult. Young adults are often lighter in color, but darken as they age. The process of development from egg to adult can take from several weeks to months, depending on the species and the environment. Did you know that ants, like all insects, are full-grown when they become adults? Their exoskeletons prevent them from getting any larger.

Furthermore, adult ants belong to one of three castes: queen, worker, or male.

Queens are females that were fed more as larvae. They are larger than workers and lay all the eggs in a colony – up to millions in some species! Queens initially have wings and fly to find a mate(s), but they tear them off before starting a new colony. A queen can live for decades under the right conditions.

Workers are females that were fed less as larvae. They do not reproduce, but perform other jobs, such as taking care of the brood, building and cleaning the nest, and gathering food. Workers are wingless and typically survive for several months.

Males have wings and fly to mate with queens. They live for only a few weeks and never help with the chores of the colony.


BIOACTIVE COMPONENTS AND THEIR SOURCES

Bioactive components of food are defined as elements that �t biological processes or substrates and hence have an impact on body function or condition and ultimately health”. 32 Bioactive components in human milk come from a variety of sources some are produced and secreted by the mammary epithelium, some are produced by cells carried within the milk, 33 while others are drawn from maternal serum and carried across the mammary epithelium by receptor-mediated transport. Further, the secretion of the milk fat globule (MFG) into milk by the mammary epithelium carries with it a diverse collection of membrane-bound proteins and lipids into the milk. 34 Together these methods produce the variety of bioactive components in human milk. For example, in lactating women, antigen-specific B cells home to the mammary gland, where polymeric immunoglobulin receptors (pIgR) transport sIgA into the lumen of the duct. 35 An alternative example is vascular endothelial growth factor (VEGF), which is found at concentrations significantly higher in milk than maternal serum, indicating a mammary gland source. 36,37 Understanding the sources of bioactive components of milk also helps to explain the variability in milk concentrations that are observed following maternal use of specific medications (see article in this issue by Rowe, Baker and Hale).

What are the clinical implications of research on human milk bioactive factors? The depth of scientific evidence is such that in patient or public education, it is valid to clarify that human milk is not “merely nutrition.” Rather, human milk contains a variety of factors with medicinal qualities that have a profound role in infant survival and health. Thus, safe donor milk substitutes are needed for infants at medical risk when mother’s own milk is not available. Proteomic analysis has discovered thematic distinctions in the proteins that compose milk at differing stages of lactation, as well as differences between term and preterm milks. 14,15 These studies suggest that when donor milk is needed, it should be matched to the developmental stage of the infant whenever feasible, although this is often difficult in practice. Furthermore, recognition of potent, bioactive human milk factors indicates the importance of preserving their biologic activity, to the extent possible, through the process of milk collection, storage, and pasteurization. Finally, recognition of the unique mechanisms by which human milk protects and enhances development provides models for new preventive and therapeutic approaches in medicine.

A complete characterization of bioactive factors of human milk is beyond the scope of this review. Here, we focus on a selected set of bioactive factors that vary between mothers of term and preterm infants, or over the course of lactation, and thus represent responsiveness to the changing needs of the infant (see Table 2 ). Many of these factors act synergistically, such that consumption of human milk is superior to supplementation with individual factors or their combinations. 38

Table 2

Major Bioactive Factors in Human Milk

ComponentFunctionReference
Cells
MacrophagesProtection against infection, T-cell
activation
Jarvinen, 2002, Yagi, 2010, Ichikawa, 2003
Stem cellsRegeneration and repair Indumathi, 2012
Immunoglobulins
IgA/sIgAPathogen binding inhibitionVan de Perre, 2003, Cianga, 1999 Brandtzaeg, 2010
Kadaoui, 2007 Corthësy, 2009 Hurley, 2011 Agarwal, 2010
Castellote, 2011
IgGAnti-microbial, activation of phagocytosis
(IgG1, IgG2, IgG3) anti-inflammatory,
response to allergens (IgG4)
Cianga, 1999 Agarwal, 2010
IgMAgglutination, complement activationBrandtzaeg, 2010 Van de Perre, 1993 Agarwal, 2010
Cytokines
IL-6Stimulation of the acute phase response, B
cell activation, pro-inflammatory
Ustundag, 2005 Meki, 2003 Mizuno, 2012 Agarwal, 2010
Castellote, 2011
IL-7Increased thymic size and outputAspinall, 2011 Ngom, 2004
IL-8Recruitment of neutrophils, pro-
inflammatory
Claud, 2003 Ustundag, 2005 Meki, 2003 Maheshwari, 2002
Maheshwari, 2003 Maheshwari, 2004 Hunt, 2012
Agarwal, 2010 Castellote, 2011 Mehta, 2011
IL-10Repressing Th1-type inflammation,
induction of antibody production,
facilitation of tolerance
Meki, 2003 Agarwal, 2010 Castellote, 2011 Mehta, 2011
IFNγPro-inflammatory, stimulates Th1 responseHrdý, 2012 Agarwal, 2010
TGFβAnti-inflammatory, stimulation of T cell
phenotype switch
Penttila, 2010
Kalliomäki, 1999 Saito, 1993 Nakamura, 2009
Letterio, 1994 Ando, 2007 Ozawa, 2009
Donnet-Hughes, 2000 Verhasselt, 2008 Verhasselt, 2010
Penttila, 2003 Mosconi, 2010 Okamoto, 2005
Penttila, 2006 Peroni, 2009 McPherson, 2001
Ewaschuk, 2011 Castellote, 2011
TNFαStimulates inflammatory immune activationRudloff, 1992 Ustundag, 2005 Erbaᇼi, 2005 Meki, 2003
Agarwal, 2010 Castellote, 2011
Chemokines
G-CSFTrophic factor in intestinesGilmore, 1994 Gersting, 2003 Calhoun, 2003 Gersting, 2004
MIFMacrophage Migratory Inhibitory Factor:
Prevents macrophage movement, increases
anti-pathogen activity of macrophages
Magi, 2002 Vigh, 2011
Cytokine Inhibitors
TNFRI and IIInhibition of TNFα, anti-inflammatoryBuescher, 1998 Buescher, 1996 Meki, 2003 Castellote, 2011
Growth Factors
EGFStimulation of cell proliferation and
maturation
Patki, 2012 Kobata, 2008 Hirai, 2002 Wagner, 2008
Dvorak, 2003 Dvorak, 2004 Chang, 2002 Khailova, 2009
Coursodon, 2012 Clark, 2004 Castellote, 2011
Untalan, 2009
HB-EGFProtective against damage from hypoxia
and ischemia
Radulescu, 2011
VEGFPromotion of angiogenesis and tissue repairLoui, 2012 Ozgurtas, 2011
NGFPromotion of neuron growth and maturationRodrigues, 2011 Boesmans 2008 Sánchez 1996
Fichter, 2011
IGFStimulation of growth and development,
increased RBCs and hemoglobin
Chellakooty, 2006 Blum, 2002 Burrin 1997 Philipps, 2002
Milsom, 2008 Prosser, 1996 Elmlinger, 2007
Peterson, 2000 Murali, 2005 Corpeleijn, 2008
Baregamian, 2006 Baregamian, 2012 Büyükkayhan, 2003
Philipps, 2000 Kling, 2006
ErythropoietinErythropoiesis, intestinal developmentCarbonell-Estrany 2000 Juul, 2003 Kling, 2008 Miller-Gilbert, 2001
Pasha, 2008 Soubasi, 1995 Shiou, 2011
Arsenault, 2010 Miller, 2002 Untalan, 2009
Hormones
CalcitoninDevelopment of enteric neuronsStruck, 2002 Wookey, 2012
SomatostatinRegulation of gastric epithelial growthChen, 1999 Rao, 1999 Gama, 1996
Anti-microbial
LactoferrinAcute phase protein, chelates iron, anti-
bacterial, anti-oxidant
Adamkin, 2012 Sherman, 2004 Manzoni, 2009
Hirotani, 2008 Buccigrossi, 2007 Velona, 1999
Lactadherin/
MFG E8
Anti-viral, prevents inflammation by
enhancing phagocytosis of apoptotic cells
Stubbs, 1990 Kusunoki, 2012 Aziz, 2011 Shi, 2004
Chogle, 2011 Baghdadi, 2012 Peterson, 1998
Newburg, 1998 Shah, 2012 Miksa, 2006 Komura, 2009
Miksa, 2009 Wu, 2012 Matsuda, 2011 Silvestre, 2005
Metabolic hormones
AdiponectinReduction of infant BMI and weight, anti-
inflammatory
Martin, 2006 Newburg, 2010 Woo, 2009 Woo, 2012
Ley, 2011 Dundar 2010 Ozarda, 2012 Savino, 2008
Weyerman, 2006
LeptinRegulation of energy conversion and infant
BMI, appetite regulation
Savino, 2008 Savino, 2012a Savino 2012b Palou, 2009
Weyermann, 2006
GhrelinRegulation of energy conversion and infant
BMI
Savino, 2008 Savino, 2012 Dundar 2010
Oligosaccharides & glycans
HMOSPrebiotic, stimulating beneficial
colonization and reducing colonization with
pathogens reduced inflammation
Newburg, 2005 Morrow, 2005 DeLeoz, 2012 Marcoba, 2012
Kunz, 2012 Ruhaak, 2012 Bode, 2012
GangliosidesBrain development anti-infectiousWang B, 2012
GlycosaminoglycansAnti-infectiousCoppa, 2012 Coppa 2011
Mucins
MUC1Block infection by viruses and bacteriaRuvoen-Clouet, 2006 Liu, 2012 Sando, 2009 Saeland, 2009
Yolken, 1992
MUC4Block infection by viruses and bacteriaRuvoen-Clouet, 2006 Liu, 2012 Chaturvedi, 2008

Marine Biology > Find My Plankton Baby Picture

The ocean teems with life, from the blue whale to the pygmy seahorse to brain coral. But did you know that the ocean is also home to plankton ? These marine organisms drift with ocean currents. And many of them are too small for humans to see. There are two kinds of plankton: phytoplankton and zooplankton.

Phytoplankton are microscopic organisms that use sunlight to grow and make food. They also produce most of the oxygen we breathe. Phytoplankton are just as important to life on Earth as rainforests!

Zooplankton are tiny marine animals that can't swim strongly against the ocean current. Some are permanent drifters in the sea. Others are actually larvae : baby forms of larger marine animals. As these ocean babies grow up, some gain the ability to swim. Some become able to propel themselves through water. And some eventually settle out to live on or near the ocean bottom. The adults they become no longer drift with the currents. So, they are no longer considered plankton.

These marine adults can look very different from the larvae they once were. Can you find their plankton baby pictures?


Liver Flukes

Liver flukes are parasites that can infect humans and cause liver and bile duct disease. There are two families of liver flukes that cause disease in humans: Opisthorchiidae (which includes species of Clonorchis and Opisthorchis) and Fasciolidae (which includes species of Fasciola). These two families of liver flukes differ in their geographic distribution, life cycle, and long-term outcome after clinical infection.

Clonorchis is a liver fluke parasite that humans can get by eating raw or undercooked fish, crabs, or crayfish from areas where the parasite is found. Found across parts of Asia, Clonorchis is also known as the Chinese or oriental liver fluke. Liver flukes infect the liver, gallbladder, and bile duct in humans. While most infected persons do not show any symptoms, infections that last a long time can result in severe symptoms and serious illness. Untreated, infections may persist for up to 25&ndash30 years, the lifespan of the parasite.

Opisthorchis species are liver fluke parasites that humans can get by eating raw or undercooked fish, crabs, or crayfish from areas in Asia and Europe where the parasite is found, including Thailand, Laos, Cambodia, Vietnam, Germany, Italy, Belarus, Russia, Kazakhstan, and Ukraine. Liver flukes infect the liver, gallbladder, and bile duct in humans. While most infected persons do not show any symptoms, infections that last a long time can result in severe symptoms and serious illness. Untreated, infections may persist for up to 25&ndash30 years, the lifespan of the parasite. Typical symptoms include indigestion, abdominal pain, diarrhea, or constipation. In severe cases, abdominal pain, nausea, and diarrhea can occur.

Fascioliasis is a parasitic infection typically caused by Fasciola hepatica, which is also known as &ldquothe common liver fluke&rdquo or &ldquothe sheep liver fluke.&rdquo A related parasite, Fasciola gigantica, also can infect people. Fascioliasis is found in all continents except Antarctica, in over 70 countries, especially where there are sheep or cattle. People usually become infected by eating raw watercress or other water plants contaminated with immature parasite larvae. The young worms move through the intestinal wall, the abdominal cavity, and the liver tissue, into the bile ducts, where they develop into mature adult flukes that produce eggs. The pathology typically is most pronounced in the bile ducts and liver. Fasciola infection is both treatable and preventable.


Watch the video: Γιατρός κάνει εμβόλια σε μωρά με τον πιο γλυκό τρόπο (December 2022).