By Alexandra DeCandia
Humans have a talent for disrupting natural processes. Through the overharvest of species and inundation of landscapes with highways and suburbs, we’ve continuously rendered wild populations small and fragmented. Compared to larger, outbred populations, these communities exhibit higher rates of inbreeding. If their circumstances do not improve, inbreeding depression, or reduced reproductive fitness, may lock these populations in “extinction vortices,” whereby genetic and demographic declines work synergistically towards ultimate extinction.
Luckily, it is possible to escape this vortex. “Genetic rescue,” a more positive example of human disruption, has been proposed as means of mitigating inbreeding depression. It occurs when immigrants into a small population drastically improve overall fitness beyond theoretical predictions. These immigrants inject genetic diversity into ailing populations and thereby reduce their genetic load by disrupting homozygous deleterious alleles. This then enables rapid population expansion and overall improved fitness.
As a management strategy, genetic rescue can be achieved in two ways: (1) facilitating natural gene flow through improved connectivity between fragmented populations, and (2) artificially translocating immigrants into an inbred population. The management of Mexican wolves presents an example of the first strategy. Mexican wolves (Canis lupus baileyi) are the most genetically distinct descendants of the North American gray wolf. Due to habitat loss and human hunting throughout the 19th and 20th centuries, these once abundant carnivores were reduced to seven captive individuals by the mid-20th century. Unsurprisingly, signs of inbreeding depression appeared in reintroduced populations as a result of founder effects and geographic isolation. To prevent further declines, conservation geneticists combined population viability analysis with topographic data to propose a series of corridors between the introduced populations. Increased connectivity, when combined with Mexican wolves’ dispersal capabilities, now facilitates natural gene flow between populations.
Alternatively, the second management strategy, translocation, artificially transports foreign gametes or individuals into inbred populations. Source populations for these organisms include other wild populations (e.g. California bighorn sheep), captive populations (e.g. Houbara bustard), and wild populations of different subspecies (e.g. Florida panther). Genetically distinct, translocated individuals deposit variation from their source populations into those suffering from inbreeding depression. Occasionally, translocations even possess specific genotypic aims. In the case of the American chestnut (Castanea dentata), for example, conservation geneticists sought to imbue the once widespread species with genetic resistance to blight fungus. Through hybridization with the Chinese chestnut (C. mollissima) and repeated backcrossing with resistant American chestnuts, the species was able to maintain unique morphologies alongside appropriated fungal-resistance.
While successful in the aforementioned cases, genetic rescue should not be considered a panacea for all species suffering from heavy genetic loads. As genetic management of wild populations remains relatively novel, few studies document its long-term effects. In some cases, the intentional hybridization of divergent populations can render hybrids and their offspring maladapted to a particular environment, a phenomenon termed outbreeding depression. These fitness reductions may even increase pathogen susceptibility, as was documented in an experimental crossing of two genetically distinct populations of largemouth bass (Micropterus salmoides). As a result, the decision to implement genetic rescue through connectivity or translocation becomes a cost-benefit analysis of the relative risks associated with inbreeding and outbreeding depression. What’s more, if the ultimate causes of a population’s decline are not removed, no number of translocations will be able to sustain the species in perpetuity.
Despite these limitations, however, genetic rescue has proven a viable management strategy for highly inbred populations. Without it, the world would no longer have greater prairie chickens, Swedish adders, black-footed ferrets, freshwater mussels, South Island robins, golden lion tamarins, and a plethora of other species. Through improving connectivity and managing translocations of captive and wild individuals, humans are attempting to undo some of the damage we have inflicted upon the natural world. We are doing our part to aid in the escape from extinction vortices.
By Julia Zeh
Edited by Aishwarya Raja
On August 15th, 1934, William Beebe (pronounced “Beebee”, not “Beeb”) and Otis Barton went where no humans had ever gone before. Although they did not leave the confines of the Earth’s atmosphere, they did travel to a world which, until then, had been unknown to man. This past summer marked the 80th anniversary of the pair’s journey 3,028 feet below the surface of the ocean into the home of a multitude of alien species.
To give a little background, Otis Barton was an engineer pursuing a postgraduate degree at Columbia University when he came up with the idea for the bathysphere, a large metal sphere in which he and Beebe would later explore the deep sea. William Beebe was a naturalist for the Wildlife Conservation Society, had been a founding ornithologist at the Bronx Zoo, and had also attended Columbia University.
When they were kids, Barton and Beebe had created their own diving helmets to explore shallow waters. Interestingly enough, both would eventually grow up to live out their dreams of exploring deeper waters. Barton designed the bathysphere and brought it to Beebe in the hopes of finding a partner for his ocean exploration project. His first meeting with Beebe was so successful that his design for the bathysphere went on to be manufactured. Eventually, the two would squeeze into this dark, metal sphere only four feet in diameter and make history together.
Starting in 1930, the pair began diving off the coast of Nonsuch Island, Bermuda, and would continue diving for the next four years. In the summer of 1934, Beebe and Barton made a dive that would make history. The pair dove to a world record-breaking 3,028 feet, a record that would stand for 15 years until Barton would dive deeper with his own improvements on the original bathysphere.
During this incredible dive, Beebe transmitted his observations via radio to scientists above the surface. These scientists recorded everything Beebe said and sketched the various organisms he described. Beebe and Barton had entered an entirely new world with animals that no one had ever seen before. Outside the portholes of the bathysphere, they witnessed firsthand bioluminescent animals that glowed in the dark. In a paper written in 1932, Beebe described the illumination, the temperature, the pressure, and the animal life at these great depths. He devoted a great deal of his time and writing to identifying fish species he observed during his dives. In particular, Beebe became so accustomed to the different flashes of light that he could associate them with specific fish species. His team also spent time trawling and recording data. Fish from their nets were described in Beebe’s paper and were another important aspect of his identifications of various deep sea fish.
The surprisingly small hunk of metal that took Beebe and Barton down to the mysterious depths of the ocean now finds its home at the New York Aquarium, where thousands of people walk by it every day. Though it looks unimpressive among the walruses and brightly colored fish, the bathysphere marks an important development in scientific history, bringing knowledge of the deep to humans on the surface.
Author Tiago Palmisano
Editor Aishwarya Raja
“Sleep is a waste of time.” It’s an opinion that, as a college student, I’ve been forced to occasionally consider when it’s midnight and a looming pile of work clashes with the possibility of a good night’s rest. And unfortunately, sleep deprivation is not limited to the overloaded college student; many urbanites find that their busy schedules require them to burn the midnight oil, and maybe even the 4 AM oil. Sleep is easily ignored when it gets in the way of studying for a difficult test, going out with friends, or clocking in an extra shift at work. But consistent sleep loss carries some significant and often underestimated biological consequences.
To understand why sleep loss is damaging, it is necessary to know how the body regulates sleep cycles. The first way your body tells you to get to bed is through sleep-dependent homeostatic regulation. The mechanism is simple – when we are awake, our body releases a neurotransmitter called adenosine. The longer we are awake, the more adenosine piles up in our brain, and at a certain level this excess of adenosine causes decreased alertness and increased tiring. The second way is via our circadian rhythm, which is dependent on signals from the environment called zeitgebers, such as a lack of sunlight or cold temperature. When the hypothalamus in our brain senses a zeitgeber, it sends a signal to the pineal gland to release the neurotransmitter melatonin, which also decreases alertness and makes us sleepy.
Therefore, these two physiological systems make us tired at night, and when we have been awake for a long time. It makes sense, then, that at midnight after a long day we are extremely tired; homeostatic regulation and circadian rhythm are in full effect. Now I know what you’re going to say, “Of course I get tired at midnight, but I can just use coffee and Red Bull to increase my alertness and stay up with ease.”
Using caffeine, the energizing component of coffee and energy drinks, to fight off sleepiness is certainly a common and efficient tactic. However, decreased alertness is not the only effect of sleep deprivation. Evidence suggests that losing sleep also impairs higher-level cognitive skills, such as forming memories. When we absorb new information, a part of the brain known as the hippocampus decides if the information is worth storing. If it is, then the information is stored in the long-term memory. Studies have demonstrated that even a single night of sleep deprivation impairs the neural circuitry in the hippocampus, and prevents it from properly committing information to the long-term memory. So when you stay up late cramming for that difficult test, your brain will be less able to retain details, and when you attempt to recall them the next day, you’ll be left searching.
Furthermore, certain skills such as reasoning and memory formation are not stimulated by caffeine. Coffee and Red Bull will make you more alert, but no matter how much caffeine you ingest, your ability to remember details will decrease if you neglect to sleep. Studies have consistently linked sleep loss to a lower average GPA. The consequences of sleep deprivation, though, cut much deeper than an underperforming memory. Research has indicated that disrupting homeostatic regulation and circadian rhythm (or messing with the balance of adenosine and melatonin) may significantly impair the immune system. As a result, long-term sleep deprivation increases the risk of heart disease, stroke, type-2 diabetes and even certain types of cancer. In fact, the World Health Organization lists overnight work as a probable carcinogen.
Messing with the body’s natural sleep cycles is extremely risky. Trying to exchange sleep for studying, socializing, or working is like walking on the edge of a cliff. The potential consequences are too damaging to ignore. But realistically, most people will not choose to ignore the responsibilities of a busy schedule. Therefore, it is critical to learn to balance your body’s physiology while finding enough time to be productive.
A relatively healthy method of getting through a period where a full night’s sleep isn’t an option is to combine occasional two-hour naps with caffeine. The short naps allow for a partial correction of the chemical imbalances associated with sleep loss, and the caffeine prevents the low levels of alertness that most people experience immediately after a nap. Furthermore, consistent exercise has been shown to increase sleep quality and prevent tiredness when the body is awake, allowing sleep to be more effective.
Two years of college have taught me that a healthy sleep cycle can’t be ignored. You depend on your body for nearly everything, and you should hold a responsible attitude towards sleep. So if you must trade in some rest for that busy schedule, make sure to use naps, caffeine, and exercise wisely. And if you can, try not to always burn the midnight oil. Sleep isn’t a waste of time.
By Ian MacArthur
Revolutions in one field of science often revolutionize other scientific fields. Breakthroughs in nuclear physics in the 1940’s later allowed organic chemistry to thrive with improved chemical detection methods and gave rise to biological imaging technologies. Recent developments in nanotechnology are now set to drastically enhance our understanding of biology and medicine.
The lab of Dr. Michael Strano, professor of chemical engineering at MIT, is studying the use of carbon nanotubes as biological sensors. The team has devised a nanotube-based sensor that can function in living creatures for more than a year. Specifically, the sensor can be used to monitor physiological levels of nitric oxide (NO), an important molecule involved in intercellular communication. The development of the first long term nano-sensor is likely to shed unique insight into the role that NO plays in cell signaling, immune system function, and cancer.
Carbon nanotubes are hollow, cylindrical structures with a diameter of one nanometer. They are naturally fluorescent, making them an ideal candidate for use as biological sensors. By wrapping the nanotubes in a molecule that is able to bind to the targeted chemical for detection, levels of the targeted chemical can be measured by how the fluorescence of the nanotube is affected by the degree of binding. In the case of nitric oxide, Dr. Strano’s lab discovered that wrapping a nanotube in DNA of a specific sequence would bind the nanotube to NO and alter fluorescence.
The long term sensor was created by embedding carbon nanotubes in a gel polymer found in algae and placing it under the skin of mice. There, the sensor was able to successfully function for 400 straight days, a time-frame that the researchers believe can be extended. Now that the sensor has been demonstrated to be operable over a long period of time, Dr. Strano and his team are beginning to study how this technology can be used to detect blood glucose levels in people who suffer from diabetes. The commonest current method for diabetics to read their blood glucose levels is to prick their fingers multiple times a day. Although electrochemical sensors have been developed as an alternative to finger pricking, the best ones available today are only able to last a week and carry the risk of infection due to having to break skin to insert them. A carbon nanotube sensor like the one being developed in the Strano lab would eliminate both of these problems.
But what are the broader implications of this early success in biological nanotechnology? Surely, this single advancement does not constitute a revolution in itself. However, as the sophistication of nanotechnology increases and its application to biological systems is enhanced, we may see a paradigm shift in the practice of medicine. The potential applications of nanotechnology in medicine are vast, from using nanosensors to detect pathogens in the bloodstream to using nano-sized machines to deliver drug payloads to specific cell receptors.
Although nanotechnology is still a nascent field, the current exponential growth in information technologies means it may grow and advance rapidly. These advances, coupled with new developments in bioinformatics and personalized medicine, may revolutionize medical practice in the coming decades. While we patiently wait for the full potential of these technologies to be realized, we may still marvel in the elegant simplicity of the carbon nanotube sensor.
How Love Works
Part 1 of a series on love.
By Aditya Nair
Every thought, idea, or emotion that you’ve ever had is the result of networked interactions of cells in the brain called neurons. Every time you feel a strong emotion like the apprehension in the pit of your stomach before a biology test, the excitement of a sporting event, and the warmth and joy of being with a significant other can be traced back to a complicated cascade of chemical reactions.
One of these emotions, love, has become a central element of our individual and societal existence. So strong is love’s emotive power that a grossly disproportionate amount of music, art, and literature is devoted to themes of love or affection. One would be hard pressed to find a culture that doesn’t have a song, poem, or book enveloped within its artistic canon. But why is love such a central part of our personal and cultural identities? What exactly is the neuro-biological basis for love?
As with many biological explanations, the answer starts with evolution. At the face of it, love seems like a very silly emotion to evolve. In the struggle for survival, being irrationally attached to something only seems to weigh a creature down. Envision the case of an early hominid that might have escaped a sabre-tooth tiger attack, but instead returned to save his infant daughter and mate. Surely his chances of survival would have been higher had he escaped as quickly as possible instead of returning to his loved ones. If a creature subject to Darwinian evolution had a behavioral Achilles heel, love is surely it.
One way to begin to address this issue is to note that the commonly held conception of “survival of the fittest” requires a certain degree of nuance to be fully accurate. Evolution doesn’t actually select for the fittest animal, but rather for the fittest offspring of an animal. It doesn’t take much thought to demonstrate why this must be the case. A particular animal, for instance an alpha-male gorilla, may be by leaps and bounds the strongest of his fellow gorillas. In the case of natural calamity, starvation, or disease, he is most likely to survive due to his strength and vigor. However, if this individual happens to be infertile, his physical fitness would count for nothing in the eyes of natural selection. He would age much like any other animal and his death would result in him fading into irrelevance from an evolutionary standpoint. However, if he had more kids than his competitors, who in turn had more kids than their competitors, his genes would carry on through posterity and be embraced by natural selection. Of course, if there were a selective pressure that killed animals before they could reproduce, “survival of the fittest” would come into play. But given that a particular animal will reproduce, it’s not precisely “survival of the fittest” that is the concern of evolution. Rather, it’s the less pithy “survival of the genes of the individual most successful at having viable and fertile offspring”.
Over the years, organisms have developed different strategies for maximizing their number of healthy offspring. Trees, for example, produce a tremendous number of offspring (seeds) so that even if an almost negligibe proportion of them survive to produce offspring of their own, the tree’s genes will endure. These organisms invest a relatively small proportion of their valuable energy resources caring for their offspring and instead focus on producing as many offspring as possible. Their offspring tend to become functionally independent earlier on in life, so they are not vulnerable in the absence of child care.
On the other hand, some organisms choose the opposite path. Their strategy is to create only a relatively small number of offspring, but ensure that a larger proportion of them reach viable adulthood. These organisms invest a large proportion of their resources into caring for their offspring. Humans fall into this category. This method of reproduction could begin to explain some aspects of human love.
Humans have big brains. Big brains are the plus sized SUV’s of the evolutionary world: expensive, energy sapping, and difficult to maintain. Developing such a brain is difficult, and takes time. Rather than grow this massive brain in the womb (which would lead to a more difficult birthing process), humans undergo brain development outside of the womb to a greater extent than other organisms and primates. During this development period, humans are largely dependent on their mothers for safety and sustenance. Much of the mother’s time and resources go towards caring for her child for a relatively long period of time. If one is an adult male, developing a strong attachment to the mother may ensure lasting resources and the long-term safety of the child. Likewise, female attachment to the male may be explained by a desire to provide the child with resources that only the male can offer.
Could it be that the fundamentally human emotion of love can be explained by this very practical quirk in evolution? We will continue to explore and analyze the neurobiological considerations in future installments.