Tag Archives: sex

You Don’t Know What You’ve Got

Every day my mind is blown by live broadcasts of astounding, weird creatures from our deepest oceans. I’ve posted a taste of this live stream video and photography extravaganza.

In the past, it’s been almost impossible to study life in the deepest oceans. Why? Because it’s freakin’ freezing (sometimes just above zero degrees centigrade (C) or 32oF by your U.S. thermometer), or boiling hot (60 to 464 °C), and the hydrostatic pressure is enormous, almost beyond comprehension. A fish, worm, or crab living down at the bottom of the sea is experiencing literally tons of pressure per square inch, like the weight of an elephant or an SUV compared to the 14.5 pounds per square inch you are probably experiencing right now. And yet, as we speak, heroic explorers are sending live stream video directly to you. And WOW! What they are seeing is beautiful and bizarre!

My colleague from the Lehigh University Department of Biological Sciences, Santiago Herrera, is the lead biologist on an expedition to the American Samoas to some of the deepest parts of the ocean, 3,000-5,000 meters, that is, about 2 miles under the sea. He’s now aboard the Okeanos Explorer, an impressive vessel equipped with high-tech lights, cameras, robot arms and scoops, and lasers that are sent to the sea floor and manipulated by the crew with precision. They broadcast live every day from their American Samoa Expedition.

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NOAA Ship Okeanos Explorer docked at the pier at the Port of Pago Pago in American Samoa. Significant outreach was conducted prior to commencing the expedition. Interviews were conducted with media, and ship tours were held for local elementary through college students, local partners, and government and agency representatives. Image courtesy of the NOAA Office of Ocean Exploration and Research, 2017 American Samoa.

Alien life on Our Own Plant

Just this week, the Okeanos Explorer crew sent these videos of Dr. Seuss-like creatures that you might think were discovered in outer space. What’s incredible is that these creatures’ habitat is actually the most common habitat on our planet. Santiago tells us that most of our planet consists of deep oceans (about 72%), and yet we know very little about what lives there.

Sex and Food Under the Sea

The other day, as I watched the Okeanos team zoom in on some rare sponges, sea anemones, and a type of deep water clam never-before-seen alive, Santiago explained that another extreme feature of the deep sea environment is very low fuel and nutrient availability. Most animals down there depend on a small, slow trickle of organic matter that floats down from shallow parts of the ocean. The link between food and sex holds up in these alien environments. Deep sea creatures must conserve energy and nutrients by maturing very slowly. In comparison to the willy nilly reproduction that’s going on up here, deep sea creatures engage in the energetically-expensive process of reproduction only rarely.

There are many other fascinating adaptations to the extreme deep sea environment. Cell walls and nuclear membranes of deep sea creatures are made to withstand enormous hydrostatic pressure, and therefore, if they are brought up from their deep sea habitat into lower pressures, they literally fall to bits. Many of these creatures are a deep red color, owing to high levels of hemoglobin. Hemoglobin is the thing in your red blood cells that makes them red, and the thing that transports oxygen to your various organs. Extra hemoglobin helps deep sea organisms survive in their low-oxygen environment. So, in the Okeanos Explorer videos, you will often see bright red shrimp, psychedelic ctenophores (comb jellies), and fiery-colored fish in the deepest waters. Here are some screen shots from their gorgeous website.

Kiss it Goodbye

Now that you’re amazed by and bonded to these fascinating friends, let me crush your soul. Climate change will have a devastating impact on our deep sea organisms, and this is related to the food-sex connection and the reality of trickle-down economics. The slow trickle of energy-yielding food to the lower depths has led to the evolution of animals that are now adapted to living on very little food and oxygen. They have survived and spread their traits to each generation because they have an innate tendency to grow and mature very slowly, and reproduce infrequently. Their habitat has been very stable for long periods of time, and once disturbed, they don’t appear to have innate mechanisms to make a comeback. Their rates of reproduction are too slow, and when they experience changes in the acidity, levels of oxygen, or temperature, their populations might not  recover. Climate change, global warming, whatever you want to call it, will cause these devastating changes that disturb the deep sea conditions. Scientists from Scripps Institute of Oceanography have published a study indicating that the food supply to some areas of the earth’s deep oceans will decline by up to one half by the year 2100.

It doesn’t appear that we can count on the United States to delay the onset of climate change. Think about it. Why do we need the governments to make us install solar, purchase electric vehicles, and recycle? When you are planning your own survival and that of your children and grandchildren, think of these deep sea organisms, and our native American friends at Standing Rock, and let them inspire you.

Please let me leave you with something better than a sad Joni Mitchell lyric (“You don’t know what you’ve got til it’s gone”). Keep learning, dig, dig, dig deeper than your initial shallow understanding. Acquiring knowledge is not elitist; it’s freedom and it’s fun. In the words of the B52s, There Goes a Sea Robin!

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Bad Birds Make Good Birds Feel So Good: It’s In the Genes

Donna Maney's lab found that the more aggressive white-striped morph has a change in the gene for estrogen receptor-alpha that makes expression of this gene more efficient in brain areas important for monogamy, aggression, and parental care.

Donna Maney’s lab found that the more aggressive white-striped morph has a change in the gene for estrogen receptor-alpha that makes expression of this gene more efficient in brain areas important for aggression and parental care.

Donna Maney and colleagues report that

the evolution of complex mating strategies are linked to changes in the gene for the estrogen receptor. Changes in one gene can predispose birds toward a “parental investment strategy” (low levels of competition, high levels of parental care) or a “mating strategy” (high levels of competition, low levels of parental care and exta-pair matings).

That in itself is remarkable, but there is another twist. The birds with the genetic change linked to more aggression and less parental behavior almost invariably mate with birds carrying the other genetic arrangement! We knew that both strategies have their advantages, but now it appears that

the two strategies might be complementary when they occur together in the same couple. One member of the pair is more aggressive and territorial, while the other tends to the nest. In pairs where the male takes on more parental duty, the female is likely to be the one who is more aggressive.

Genes and Behavior

Most people agree that our genes affect some behaviors. Think of Huntington’s disease, in which the devastating loss of motor function, memory, and impulse control are linked to a single gene, HTT. Think about the behavior of different dog breeds. The border collie’s intensity differs from the laid-back demeanor of the Labrador, and both of these tendencies differ from those of the happy yappy terrier. There is no doubt that these behavioral differences came about by selective breeding for specific traits, and that the basis for selective breeding is the heritability of those traits. Heritable traits, those that can be inherited, are affected by genes. No problem, but what about complex social behaviors?

Genes, Hormones, Monogamy, and Parental Care

We know that species differ in their mating strategies. Some species tend toward monogamy in that they show a strong preference for mating with a familiar partner, the parent of their own offspring. In these species, fathers tend to share the parental care of their own offspring, and these behaviors are often incompatible with high levels of aggressive competition. Other species tend toward promiscuity (multiple mating partners and no pair-bonds) and in these species, females tend to bear the burden of offspring care. We know quite a bit about hormonal control of these behaviors in certain species. Hormones are secreted from endocrine glands, and they act by binding to receptors. Hormone-receptor binding stimulates or inhibits the neural circuits that control behavior. In male prairie voles and marmoset monkeys, monogamy is linked to a number of hormones, two of which are oxytocin and vasopressin. Promiscuous species differ from monogamous species in the distribution of these receptors in the brain. One specific gene encodes the vasopressin V1A receptor, and monogamy in male voles is linked to the distribution of brain V1A receptors, which in turn is a consequence of the gene for this receptor. One form of the gene (a polymorphism) is linked with monogamy. How strong is the link between hormone receptor distribution and monogamy? In terms of their vasopressin and oxytocin receptors, monogamous marmoset monkeys look more like monogamous prairie voles than they look like promiscuous species of monkeys! Hormonal influences on monogamy and parental behaviors in birds and mammals are well accepted, and this line of research has provided insights into child neglect and abuse, postpartum depression, and autism.

 

Donna Maney and her students study song birds that are monogamous, but can be divided into two types, “dads or cads.” They study hormonally-mediated aggressive song and parental behavior in wild birds that form pair bonds with different levels of exclusivity. In biology, we say these species are “monogamous,” but this does not mean they don’t have sex with more than one partner.  In these song birds, they all form pair bonds, but high levels of aggression and territoriality and low levels of offspring care are correlated with more “philandering,” that is, mating with multiple partners. In male birds, sex and aggressive behaviors are linked to hormones like testosterone from the testes and estradiol made from testosterone in the brain. As you will see, this model system affords unique advantages.

Two Morphs of White-throated Sparrow (Dads or Cads)

To link the evolution of behavior to specific genes, we need a snapshot of evolution in action, that is, we need two groups emerging within one population. Maney chose to study two different wild morphs within one population of white-throated sparrows (Zonotrichia albicollis). The morphs differ in their degree of aggressive song and parental care, as well as their propensity for multiple mating partners. As pictured at the top of this post, the tan-striped morph shows more parental behavior, more exclusive pair bonds, and less aggressive song, whereas the white-striped morph forms pair bonds, but also copulates freely with other birds. The white-striped males are less parental. Aggression can be easily measured by recording the species-typical song in response to that of an intruding male. Videos of the aggressive songs and display can be seen in the video here.

The two morphs also differ at chromosome 2, or ZAL2. Sparrows of the white-striped, aggressive morph all have at least one copy of a rearranged chromosome 2, ZAL2m, whereas the tan-striped sparrows never have this inverted chromosome. Donna Maney set out to study gene differences on this inverted chromosome that might explain differences in complex social behavior.

What’s Estrogen Got To Do With It?

In both morphs, the onset of aggressive, territorial song is correlated with increases in testosterone secreted from the testes during the breeding season (spring). Thus, you might suspect that the white-striped morph is more aggressive due to higher levels of testosterone. You would be wrong. When testosterone levels are equalized, the behavioral differences persist. There is something else going on. In the brains of sparrows and many song bird species, testosterone is converted to estradiol. Aggressive song is blocked by treatments that prevent conversion of testosterone to estradiol or by treatments that block estradiol binding to the estrogen receptor-alpha (ER-alpha) (reviewed by Kiran Soma). Receptors for estradiol, in particular ER-alpha, are located in brain areas involved in aggression, including the medial amygdala. Parental behavior is related to ER-alpha in other brain areas, including the medial preoptic area. The differences between the morphs might be related to differences in ER-alpha in the amygdala and preoptic area.

Just to remind you, Maney and colleagues knew that wild males of the more aggressive, white-striped morphs all have at least one copy of a rearranged copy of chromosome 2 (the rearranged chromosome is called ZAL2m). It turns out, the gene for ER-alpha, called ESR1, is located on this chromosome. Yes. Maney and her colleagues hypothesized that the rearrangement in the chromosome led to a change in ESR1 that led to elevated sensitivity to estradiol, and hence, higher levels of aggression and less parental behavior.

Indeed, Horton et al. found that the white-striped sparrows’ aggression was associated with a more efficient transcription of the gene, ESR1. That is, when the DNA is transcribed to messenger RNA, it occurred at a greater rate in the more aggressive, less parental, white-striped birds. More transcription might led to more translation, and hence more ER-alpha.  This would be expected to render the white-striped birds more sensitive to estradiol’s effects on behavior.

Furthermore, Horton et al., found that in the white-throated morphs, territorial singing and ESR1 expression were higher in a region of the medial amygdala associated with aggression.  Similarly, levels of nest provisioning were predicted by the level of ESR1 expression in the medial preoptic area. Thus, Maney’s group 1) linked a genetic change to a change in behavior, 2) linked a genetic change to a change in efficiency of gene transcription, 3) linked a change in gene expression in a particular brain area to a change in a particular behavior.

Together, these results are consistent with the idea that a genetic change in the gene for the estrogen receptor-alpha has led to the evolution of two different morphs of sparrow that differ in complex social behaviors. These experiments were done using wild birds from natural environments, not just laboratory animals. This and other work on this species was blogged by the awesome, Grrlscientist, at the Guardian. To the best of my knowledge, the Horton et al. article is the first such report in any vertebrate species.

It Takes All Kinds of Birds

Depending on your personal bias, you probably jump to the conclusion that one morph is better than the other, and one morph will win out. Exclusive pair bonds and low levels of aggression might result in more offspring if the offspring receive more parental care. The investment in parental care leads to a pay off in terms of number of reproductively successful offspring.  On the other hand, aggressive, less parental birds can win larger territories and a greater abundance of resources (food and shelter). As this blog documents, the more energy, the greater the reproductive success. Read our latest review for more info on energy and reproduction. I wonder whether the frequency of the different morphs would change depending on the availability of energy in the environment. In any case, this means that in the white-stripe, “Don Draper-like” morph, greater investment in competition for resources might lead to more matings, greater fertility, and higher levels of long-term reproductive success. Maney tells us that these two morphs are not in competition, and probably not about to evolve into two separate species.

In reality, almost all white-throated sparrow breeding pairs consist of one individual with and one without the inverted ZAL2m chromosome. The females also differ in their level of parental investment. In other words, the tan-striped morph invariably mates with the white-striped morph, and the tan-striped male or tan-striped female takes up the slack at the nest. This increases the frequency of heterozygous individuals, and maintains the inverted chromosome ZAL2m in the population. Presumably, there is an evolutionary advantage to both the original version of chromosome 2 and the inverted chromosome ZAL2m, perhaps related to differential parental investment. It’s fascinating that the tan-striped males tend to mate with the more aggressive and territorial females and pick up the slack in the parenting department.

Maney and colleagues and their elegant experiments have shown that in white-throated sparrows, rearrangement of a specific gene, ESR1, is one of the genetic changes that underlies the emergence of two different, complementary life-history strategies.

Human Beings

In birds, voles, and monkeys, the behaviors are measured with precision, and these animals can’t deny, lie about, or exaggerate their sex behaviors. A number of studies have associated human monogamous/promiscuous and parental/nonparental tendencies with genetic polymorphisms, but it’s reasonable to wonder whether monogamy can be studied with any precision in people with such complicated sexuality. When it comes to sex, people are inhibited, shy, disingenuous, priggish, or boastful, rather than factual. Questions about human sexuality might have to wait until sex researchers get a hold of the data compiled by the NSA (that is, data compiled when the agents aren’t spying on their own love interests). Ah, yes. Therein lies a clue.

Well, if humans share anything in common with white-throated sparrows, it would surely be reflected in our musical archives…

 

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When I’m Sixty Five

Special dedication to

Jacques Balthazart!

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Pictured, a Valentine, a birthday greeting, a bottle of wine, and a Jupiler

Jacques Balthazart is a true leader in behavioral neuroendocrinology, the study of how hormones affect the brain and behavior. His retirement demanded a fitting tribute, but there was a problem. When it comes to international conference organizers, nobody does it better than Jacquesyoung jacques Balthazart. So, who would throw this party? No worries. The Belgian government’s policy requiring mandatory retirement at age 65 turned out to be the catalyst for a nonpareil scientific meeting (throughout this blog, all words underlined are links). It also turned out to be an outrageous birthday party and a creative plan to continue research on his own terms. Last week, the combination of foundational research, cutting-edge science, Belgian beer, and collegiality led to the conference’s new nom de plume: The International Conference Honoring Brilliant Balthazart (ICHBB).

Jacques is shown above and to the right just moments before the party, and below, just a few days into the party.

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Photo by GianCarlo Panzica of Jacques Balthazart, 65,  in a gift hat symbolizing his dual loyalty to Belgium and the U.S.
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ICHBB Conference photos by GianCarlos Panzika

After all, when you are the premier conference organizer, entertainer, and hub of your scientific community, it makes sense that you should plan, host, and orchestrate your own birthday retirement party!

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“Team Jacques” adapted from a funny photo by Julie Bakker

The first ICHBB was named the International Conference on Hormones Brain and Behavior and held in Bielfeld, Germany in 1982. It was conceived and developed from Jacques’ isolation as one of the few behavioral endocrinologists in Belgium. His uncontrollable desire for scientific interaction led him to invite about 40 premier behavioral endocrinologists from around the world to Bielfeld. To his surprise, they all showed up; it was an unqualified success; and everyone wanted to do it again and again. And again. In subsequent years, Jacques personally nursed the ICHBB in his home town of Liege (in 1984, 1989, and 2014) and affectionately nurtured the conference when it was hosted by others in France, Italy, and Spain.

liege buttfly bushes  2 I learned some things about Jacques’ life that I hope will be shared, remembered, and handed down to our academic offspring! First, necessity is the mother of invention in that some of Jacques’ biggest contributions to science come from his ability to embrace his authentic small-town lifestyle while uniting the world of behavioral neuroendocrinology. He was born, raised, educated, bred, and “retired” in Liege, Belgium, far less a tourist destination than a very pleasant place to grow up, and Jacques truly loves Liege. Many Americans have never even heard of Belgium, let alone, Liege, but one thing is very clear. Liege is “on the map” in the minds of behavioral endocrinologists. This just shows that there is no point in whining about where you work. I know behavioral endocrinologists at big U.S. medical schools, at Yale, or in big universities like UC-Berkeley who feel more isolated than Jacques.

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Scenes from Liege

 

 

 

 

 

 

 

 

 

 

 

 

 

This idea was confirmed by plenary speaker, Kathy Olsen, former deputy director of the National Science Foundation, chief scientist for NASA, and associate director and deputy director of science in the executive offices of the President of the United States of America. According to Kathy, there is no one else to blame for putting Liege on the map other than Jacques Balthazart.

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Kathy Olsen (right) shown with Vicki Luine and Yasuo Sakuma (left)

In terms of hormones and behavior, Jacques brought the world to Liege. I was surprised to learn that the man we know as the hub of our global science community is very much a local family man. Jacques’ father was a local architect, and his mother worked as a full-time homemaker and mother of two children. Jacques was educated from primary school on up through college in his home town of Liege. It was at the University of Liege that he fell in love with one of his biology professors, the beautiful and enviably fit, Claire (apparently she still runs 10K a day!). In addition to having a successful career in biology, Claire is a super friendly, social, community-oriented woman-about-town. Jacques, on the other hand, is not nearly as involved with his local friends and relatives. Though Claire chides Jacques for not remembering neighbors who have known Jacques his whole life, Jacques, ironically, is the social glue holding together a giant global network of scholars and friends, many of whom traveled far and wide to celebrate Jacques’ birthday. In one of Jacques’ presentations this week, he showed a world map dotted in every continent with markers showing where he has friends who will meet him at the airport.

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Lauren Riters and family (left) and Nicole Cameron with a lot of French stripes (right)

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Nicole, Lauren, Lauren’s son, Nancy Forger and Geert DeVries (left) and cannibals on the menu (below)

A Bad Bromance

Everyone in behavioral endocrinology knows that Jacques Balthazart has co-authored numerous landmark articles with Greg Ball, begging the question “How did this fertile collaboration begin?” During the various tributes at the conference, we learned that in 1983, Greg Ball was a graduate student at the Institute for Animal Behavior at Rutgers-Newark, where Jacques Balthazart was a distinguished visitor. Jacques, however, was not impressed with that Greg Ball character!

Jacques recalls Greg as a “lazy, long-haired hippie hanging around drinking coffee and pontificating in the break room all day long in a booming voice that could be heard all over the department.” As they say, first impressions are the best. Well, except the lazy part, because Greg’s and Jacques’ publications together number at least 400, and somewhere between 110-115 of those articles are co-authored by Ball and Balthazart or Balthazart and Ball.

The Ball and Balthazart Bromance was finally consummated (scientifically) a few years later in Germany. Greg Ball, then a postdoc with John Wingfield, was invited to speak at the conference. Greg was put up in a small dormatory-like room with a single bathroom shared by the adjacent room. Greg was brushing his teeth when his new next door neighbor, Jacques Balthazart, burst into the bathroom. “Well, well, well, we meet again!” Only this time, the Greg-Jacques Belgian beer bromance began in earnest (Wait? Who’s Ernest?) From the time of that meeting, Jacques Balthazart and Greg Ball became fast friends and insanely productive collaborators.

Incidentally, you can trace the academic family trees of these characters and that of your own mentor at Neurotree.org. Greg Ball’s tree is probably the most interesting, reaching straight back to Niko Tinbergen and Konrad Lorenz.

Peg McCarthy, Greg Ball’s beloved spousal unit, in her plenary lecture, explained that Jacques was a daunting obstacle blocking Greg’s affections for Peg in the initial stages of their courtship. At first, it was clear to Peg that Jacques would always be Greg’s “first wife.” It seemed she could never compete with Jacques. Luckily, Jacques came to adore Peg, and now warmly accepts Peg as a sisterwife. Suffice to say, that if all sisterwives were like Jacques and Peg, we would all be Mormons.

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Greg Ball and Peg McCarthy (left) and a nicer pic of Peg with me and Colin Saldanha

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   Celebrating Belgium Moving Up In the World Cup 2014

To Sir Jacques With Love

The entire meeting was infused with enormous gratitude and affection from Jacques’ present and former students, postdocs, collaborators, family, and friends. Greg Ball gave a “What I learned from Jacques” speech that I wish all graduate students could hear. The highlights included

1) PUBLISH all of your data immediately. You never know when or how your results will be useful to other scientists, and none of it will matter if it is not published.

2) Time is precious, so, collect data, and write without fail, regardless of how late you stayed up the night before. No excuses. As Jacques would say, you have one 33 cl (Jupiler) at lunch and then bike back to work!

3) Be brave about methods. If it’s been done, you can do it.

4) Good ideas come from many sources, so, go to meetings and host your own.

5) Good colleagues can be good friends.

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Jacques and Jeff Blaustein are not at all faking interest in my poster presentation. Photo taken by Vicki Luine.

In any case, there were so many excellent talks and posters at the meeting, demonstrating that Jacques will live on through his scholarship and mentoring as long as human civilization survives. Happily we learned that Jacques will continue working at the University of Liege, without the unpleasant duties of his old position, but instead intensifying focus on the research that he loves. This is one of the benefits of launching the careers of young, outstanding scientists and scholars. Shown below are ICHBB attendees who came to honor Jacques: Dave Grattan, Colin Saldanha, Kiran Soma, Jim Pfaus (with son, Josh), Thierry Charlier, Chuck Roselli and many others in the group photos.

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Enjoy the next phase, Jacques! Your work is alive and well in all of our research programs. See you soon.

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The above photo of Jacques and the preceding six were taken by GianCarlo Panzica.

There will be more pictures available through the website for the ICHBB. Meanwhile, you will find some links to seminal Balthazart discoveries here and here.

And finally, here’s a funky version of what I’m sure Jacques’ mentees are thinking…

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Should I Stay or Should I Go?

Crawling C. elegans hermaphrodite worm

Crawling C. elegans hermaphrodite worm (Photo credit: Wikipedia)

             Should I stay or should I go? Well, how much food do you have? In some organisms, sexual desire is expressed by leaving, that is, by bidding adieu to a delicious pile of food and wandering off in search of a mate. But not just any mate, a mate with food! Lipton et al., at  Albert Einstein College of Medicine, use the “leaving assay” to measure male sexual desire. Their subject is the elegant, rod-like worm, Caenorhabditis elegans.*  They start by placing males on their preferred food source; then they measure how often males exit in search of mating partners. You can see the trails they leave in the substrate in this video of C. elegans appropriating Harlem art and culture.

              How do the researchers know “leaving” is a sex behavior? Context. Leaving a food source occurs only in a sexual context, and the leaving assay is being used to tease apart the threads that control the appetites for food and sex.

            First, a quick lesson in the fascinating sexuality of C. elegans. Males are not interested in other males, but they search intensely for a mating partner of the other sex. Note that I said “other sex” not “opposite sex.” There are no female C. elegans.  Males of this species mate enthusiastically with hermaphrodites. Hermaphrodites can, of course, self-fertilize, but sexual unions between males and hermaphrodites are far more fruitful than selfing. For hermaphrodites, mating with a male will produce more offspring, and for males, hermaphrodites are the only crying game in town.

            In the leaving assay, C. elegans males are placed on a preferred food source with or without hermaphrodites. Sexually mature males tend to linger when dining with hermaphrodites but leave readily when no hermaphrodites are present at the food source. They wander off searching for mates. The predilection is specific to sexually mature C. elegans, not to juveniles or males that have had their gonads removed.  It’s the gonads that put the lust in wanderlust. As sexy males’ bodies move through the substrate, they leave their snakey imprint, a permanent record of their search for the ideal dining experience. What is the ideal? A cozy little bistro with not only delicious cuisine but hermaphrodite companionship. What’s more, the hermaphrodites alone are not enough. Males prefer to stay and mate with hermaphrodites, but only hermaphrodites positioned at an abundant food source.

            The leaving assay in C. elegans is being used to tease apart the intricate threads that control the appetites for food and sex. Like our own appetites, those of C. elegans are sensitive to prior experience. Males that have been previously food-deprived have a longer latency to leave a food source. Hungry males will stay longer on a lonely, hermaphrodite-free food source before finally wandering off in search of a companion. The longer the food deprivation, the longer the males delay their wanderlust. These changes in the hunger for food and desire for sex may be mediated by some of the same hormones at work in our own species. Other researchers have shown that when members of C. elegans eat food, there is an increase in the secretion of serotonin. You’ve heard of it. Drugs prescribed for human depression target serotonin action. Prozac, for example, increases serotonin levels by blocking the reuptake of serotonin by the cells that secreted it in the first place. We have long known that depletion of serotonin is associated with anxiety and depression, and more recently it has been suggested that overeating foods that promote serotonin synthesis is a form of self-medication. Getting back to C. elegans, Lipton et al., found that mutations in the genes that encode serotonin receptors render the males insensitive to serotonin action. Mutant males that are insensitive to serotonin act like food-deprived males in that they fail to leave a food source in search of mating partners. There’s more. Mutations or other manipulations that inhibit gonadal function also act like food deprivation, i.e., they prevent wanderlust. Mutation of the fog-1 gene transformed males to females, that is, fog-1 mutants produced oocytes instead of sperm. Those males so transformed did not show the leaving behavior, but instead remained on food! This suggest that the chemical pathways that determine whether a young nematode develops into an adult male or a hermaphrodite also determine the leaving response to a food source.

            As I have noted in recent a review article (Schneider et al., 2012), most of the chemical messengers that increase the hunger for food inhibit sexual desire and ability. The reverse is also true. Chemical messengers that inhibit eating tend to increase sexual desire and ability.  The sheer number of these chemical messengers is mind boggling. The thought of unraveling the complexity of motivated behavior in vertebrates is overwhelming. On the other hand, the nervous system of C. elegans, a nematode worm, is comprised of only a few hundred neurons. The fact that they show quantifiable, goal-oriented decisions regarding food and sex is remarkable.

            Most investigators study food intake in animals (usually rats or mice) that are singly-housed and have little or no opportunity to move, let alone interact with potential mating partners. Most investigators that study reproduction do not observe their experimental subjects in the presence of food. The entire pharmaceutical-industrial complex is driven by theories derived from studying animals in these artificial environments. The knee-jerk assumption in obesity research is that chemical messengers like serotonin, leptin, and others function to keep body weight within some fashionable and “healthy” limit, and that this system has failed in over 60% of the population.  The work of Lipton is more in line with the idea that these chemical messengers function to orchestrate the appetites for food and sex in environments where energy availability fluctuates. For testing this idea, what system could be more elegant than that of C. elegans?

*its name is actually Greek and Latin for “recent, rod-like, elegant”

This is my favorite

C. elegans parody of that awful Harlem Shake video.

Lipton, J. Kleemann, G., Ghosh, R. Lints, R., Emmons, S. W. Journal of Neuroscience, 24 (34) pp. 7427, 2004.

Schneider J. E., Klingerman C. M. and Abdulhay A. (2012) Sense and nonsense in metabolic control of reproduction. Front. Endocrin. 3:26. doi: 10.3389/fendo.2012.00026.

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