Warning: the following may be considered NSFW, particularly if your employer finds avian genitalia inappropriate.
Thanks to the detailed research of Patricia Brennan and the fluent coverage of it by Ed Yong and Carl Zimmer, a lot of people have not only heard of the impressive duck penis, they’ve seen it in all its explosive glory (if you don’t know what I’m talking about, take a moment to click on the links above — trust me, it’s worth it).
Why do chickens and other birds lack the fancy phalluses of their relatives? Good question. At least, now, we know how… Image from Herrera et al., Fig 1.
But while ducks and their fellow water fowl boast these impressive, large penises, the penes of most birds are nothing to squawk about. Ninety-seven percent — over 10,000 species of birds — have either reduced or non-existant penises that are incapable of penetration. “One of the most puzzling events in evolution is the reduction and loss of the phallus in birds,” explains biologist Marty Cohn in a Cell Press Video Abstract. “It’s remarkable that a group of animals would eliminate a structure that is so important for reproduction.” Given that, like us, birds conceive through internal fertilization, you would think a penis would be essential. How else is the male’s sperm supposed to get all up in the female’s vagina?
An Anopheles gambiae mosquito gorging herself on blood. Photo by Jim Gathany, from the CDC’s Public Health Image Library
By the time you realize what has happened, it’s too late. An Anopheles gambiae mosquito can land on your skin completely unnoticed. While you continue unaware, she stealthily walks over your exposed flesh, searching, probing the surface of your skin with her proboscis until she finds a blood vessel. She then situates her body perfectly at just the right angle, hunches down, and plunges her needle-like mouthparts into your skin. Tiny pumps pull the warm, protein-rich blood into her mouth.
With every millisecond increasing her chances of exposure, she drinks as quickly as she can. Your hand isn’t the only obstacle she faces: even as she sucks, your body senses the wound and attempts to plug the hole by forming a clot. She needs your warm, nutritious blood for her eggs, so she’s not about to let your protective mechanisms interfere. To ensure her meal keeps flowing, she pumps saliva laden with anti-coagulants and vasodilators into the wound — and that’s when it happens. That’s when the Plasmodium falciprum sporozoites that have been waiting patiently in her salivary glands enter your bloodstream. Dozens can hitch a ride in her saliva, but it only takes one to cause malaria. One single, microscopic protozoan is enough to kill you. Continue reading “Eau de Manipulation: Malarial Mosquitoes More Attracted To Human Scent”
Our voices communicate information far beyond what we say with our words. Like most animals, the sounds we produce have the potential to convey how healthy we are, what mood we’re in, even our general size. Some of these traits are important cues for potential mates, so much so that the sound of your voice can actually affect how good looking you appear to others. Which, really, brings up one darn good question: what makes a voice sound sexy?
Labroides dimidiatus feeding off a plexiglas plate in the lab at the Lizard Island Research Station. Photo courtesy of Simon Gingins
On the surface, cleaner wrasses seem like real nice fish. They set up their little cleaning stations on patches of reef, offering to eat any external parasites that other fish might have picked up. It’s a pretty sweet deal for both sides — the cleaners get a tasty meal, while the other fish get rid of pests. But not all of these do-gooders deserve their squeaky clean reputation. Every once in a while, a cleaner wrasse will take advantage of the situation and take a bite out of the tasty mucus coating of its client instead of eating parasites like it’s supposed to. This cheating behavior has fascinated scientists, who want to uncover what drives the cleaners to cheat, and what keeps them in line.
“They are a very good system to study cooperation between unrelated individuals,” explains Simon Gingins, who is studying the cooperation between cleaners and their clients for his PhD. Cleaner fish are dependent on their clients to eat, as they’re not fast enough to take bites out of fish that don’t sit and wait. “Their cooperative behavior is central to their life: most of what they do everyday is to interact with other fish species to obtain their food.”
The white cheeks & black chest bar of a great tit [photo (c) David Jirovsky, provided by BioMed Central]
As anyone in Europe knows, pairs of great tits aren’t hard to find. They’re really everywhere, if you keep an eye out for them — great tits can be found from the northern coast of Africa all the way to western central Russia, and in between. Bouncing around without a care in the world, great tits are one of the most popular and well known birds in the world. Yes, I’m talking about the birds, guys. The pretty, charismatic, if not slightly murderous birds.
Great tits have become a wonderful research model for scientists, as their widespread distribution and general lack of fear of people makes them easy study subjects. There are literally thousands of published papers looking at their ecology, behavior, genetics, and evolution. But while scientists have been studying these colorful, engaging birds for about a century, there’s still a lot to discover. Just last month, scientists from Palacky University in the Czech Republic learned something new, and incredible, about female tits: the prettier the mother, the healthier the offspring. Continue reading “Pretty great tits make better mothers”
I imagine that adjusting to life around humans, with all our buildings and fast-moving transport mechanisms, is tough for a bird. It’s estimated that some 80 million birds are killed in motor vehicle collisions every year, and with an ever-growing population of people driving around and paving roads in more remote areas, things must be getting harder and harder for the animals we share our world with. But, the American Cliff Swallow (Petrochelidon pyrrhonota) isn’t one to let people ruin the neighborhood. More and more, their huge nesting populations can be found in man-made structures like bridges and overpasses, and have even become cultural fixtures in areas like California. Their new nesting sites allow them to survive even as their former habitat disappears, but it comes at a cost: by living near roadways, the birds are more at risk than ever of being on the wrong end of an oncoming vehicle.
A scanning electron microscope image of an American house dust mite.
Our world is quite literally lousy with parasites. We are hosts to hundreds of them, and they are so common that in some ecosystems, the total mass of them can outweigh top predators by 20 fold. Even parasites have parasites. It’s such a good strategy that over 40% of all known species are parasitic. They steal genes from their hosts, take over other animals’ bodies, and generally screw with their hosts’ heads. But there’s one thing that we believed they couldn’t do: stop being parasites. Once the genetic machinery set the lifestyle choice in motion, there’s supposed to be no going back to living freely. Once a parasite, always a parasite.
Take a moment to look at yourself in the mirror. I want you to really examine your features—the curves, lines and shapes that make up your face. How broad is your chin? Narrow, or wide? How big is your mouth in comparison? Or your nose? Do you have strong, prominent eyebrows? How close are they together?Just look at this face. Do you trust me? A new study in PLoS ONE says you might, even though you don't know why.
Or, more simply, what color are your eyes?
In a study published today in PLoS ONE, researchers from from Charles University in the Czech Republic had 238 participants rate the faces of 80 students for trustworthiness, attractiveness, and dominance. Not surprisingly, they found that the three measures correlated well with each other, with faces rating high on one scale rating high on the other two. Female faces were generally more trustworthy than male ones. But that’s wasn’t all. A much more peculiar correlation was discovered as they looked at the data: brown-eyed faces were deemed more trustworthy than blue-eyed ones.
It didn’t matter if the judge was male or female, blue-eyed or brown-eyed. Even accounting for attractiveness and dominance, the result was the same: brown-eyed people’s faces were rated more trustworthy. There was some evidence of in-group bias, with blue-eyed female faces receiving lower ratings from brown-eyed women than from blue or green-eyed ones, but this difference didn’t drive the phenomenon. All the participants, no matter what eye color they had or how good-looking they thought the face was agreed that brown-eyed people just appear to look more reliable.
The real question is why? Is there a cultural bias towards brown eyes? Or does eye color really correlate somehow with personality traits like accountability and honesty? Does eye color really matter that much?
To find out, the scientists used computer manipulation to take the same faces but change their eye colors. Without changing traits other than hue of the iris, the researchers swapped the eye colors of the test faces from blue to brown and vice versa. This time, the opposite effect was found. Despite the strange correlation to eye color, the team found that eye color didn’t affect a photo’s trustworthiness rating. So it isn’t the eye color itself that really matters—something else about brown-eyed faces makes them seem more dependable.
To get at what’s really going on, the researchers took the faces and analyzed their shape. They looked at the distances between 72 facial landmarks, creating a grid-like representation of each face. For men, the answer was clear: differences in face shape explained the appeal of brown eyes.
Shape changes associated with eye color and perceived trustworthiness, from the grid-based facial shape analysis done by the researchers. Note the similarities between the shapes of brown-eyed faces and trustworthy ones.
“Brown-eyed individuals tend to be perceived as more trustworthy than blue-eyed ones,” explain the authors. “But it is not brown eyes that cause this perception. It is the facial morphology linked to brown eyes.”
Brown-eyed men, on average, have bigger mouths, broader chins, bigger noses, and more prominent eyebrows positioned closer to each other, while their blue-eyed brethren are characterized by more angular and prominent lower faces, longer chins, narrower mouths with downward pointing corners, smaller eyes, and more distant eyebrows. The differences associated with trustworthiness are also how our faces naturally express happiness—an upturned mouth, for example—which may explain why we trust people who innately have these traits.
Although the trend was the same for female faces, researchers didn’t find the same correlation between trustworthiness and face shape in women. This result is puzzling, but female faces were overall much less variable than male faces, so it’s possible the statistical analyses used to test for correlation were hampered by this. Or, it’s possible that something else is in play when it comes to the trustworthiness of female faces. The researchers hope that further research can shed light on this conundrum.
Given the importance of trust in human interactions, from friendships to business partnerships or even romance, these findings pose some interesting evolutionary questions. Why would certain face shapes seem more dangerous? Why would blue-eyed face shapes persist, even when they are not deemed as trustworthy? Are our behaviors linked to our bodies in ways we have yet to understand? There are no easy answers. Face shape and other morphological traits are partially based in genetics, but also partially to environmental factors like hormone levels in the womb during development. In seeking to understand how we perceive trust, we can learn more about the interplay between physiology and behavior as well as our own evolutionary history.
Citation: Kleisner K., Priplatova L., Frost P. & Flegr J. (2013). Trustworthy-Looking Face Meets Brown Eyes., PLoS ONE, 8 (1) e53285. DOI: 10.1371/journal.pone.0053285
Einstein once said that the definition of insanity is doing the same thing over and over while expecting different results. Yet as scientists, we are taught to fundamentally question this assumption. We replicate and repeat with the express purpose of determining if a result is reproducible or merely the product of random chance. As social and emotional creatures, we do the same thing. We like to believe in second chances. We tell ourselves that stochastic circumstances are to blame when things don’t go the way we imagined, so when presented with the opportunity to try again, we often do. Or, at least, I do. But no matter how logical an argument I can make for do-overs, Einstein was right.
In retrospect, I feel like a fool. As I sit at the edge of my bed fumbling with my guitar, I can’t help but blame myself. Why did I choose time and again to trust a person whose actions have always betrayed it? Blinded by love, I had a slew of reasons, a variety of parameters I could change that I thought might affect the outcome. But now, with 20-20 hindsight, I cannot find any. I should have known better, I chide myself. I failed the scientist in me.
Yet still at the slightest mention of him, I flush with anger, jealousy and regret, and heart pounding, I fantasize about retaliation and justice. Evolutionary psychologists would tell me that the physiological experience of betrayal stems from the fact that humans, at our core, are a social species. Personal bonds were vital to our ancestors, and thus natural selection has reinforced emotional mechanisms that evaluate the connections we form with others. In a dangerous world, our ancestors had to know whom they could trust with their lives. Anyone who threatened the relationships we have with one another didn’t just wound pride or break hearts, they threatened our predacessors very survival. The reaction is strong and visceral: stress hormones spike, leading to twisting pain in our gut and heightened sensitivity. But at the same time, areas of our brain involved in deception detection activate. While we feel the rush of cortisol and adrenaline clouding our thinking, brain regions like the anterior insula process our physical and emotional state to make judgements of trustworthiness to inform future interactions.
If only my previous judgements had been more permanent. A friend of mine likes to say “monkeys learn,” but clearly, I didn’t the first time. Though the rest of our evolutionary lineage seems to be quick to categorize friends from foes, I could not.
What’s done is done, though, and I am left to collect the pieces of my heart that they shattered so effortlessly. While I might not have learned my lesson as quickly as I should have, I have learned it now. I know that this time is different. There will be no more replicates, no more re-runs with the hope of a different result. There are no variables I can change to get what I want. The data are clear, and it’s time to stop trying to bias them toward the end I prefer. All that is left is to document what happened, so like a good scientist, I write and record my final results.
Thursday 26th July saw the launch of SciLogs.com, a new English language science blog network. SciLogs.com, the brand-new home for Nature Network bloggers, forms part of the SciLogs international collection of blogs which already exist in German, Spanish and Dutch. To celebrate this addition to the NPG science blogging family, some of the NPG blogs are publishing posts focusing on “Beginnings”.
In the beginning, the earth was without form, and void; and darkness was upon the face of the deep, as a giant cloud of gas and dust collapsed to form our solar system. The planets were forged as the nebula spun, jolted into motion by a nearby supernova, and in the center, the most rapid compression of particles ignited to become our sun. Around 4.5 billion years ago, a molten earth began to cool. Violent collisions with comets and asteroids brought the fluid of life – water – and the clouds and oceans began to take shape. It wasn’t until a billion years later that the first life was brought forth, filling the atmosphere with oxygen.
Over the next few billion years, single-celled organisms fused and became multicellular; body plans diversified and radiated, exploding into an array of invertebrates. Yet all this abundance and life was restricted to the seas, and a vast and bountiful land sat unused. Around 530 million years ago, there is evidence that centipede-like animals began to explore the world above water. Somewhere around 430 million years ago, plants and colonized the bare earth, creating a land rich in food and resources, while fish evolved from ancestral vertebrates in the sea. It was another 30 million years before those prehistoric fish crawled out of the water and began the evolutionary lineage we sit atop today. To understand life as we know it, we have to look back at where we came from, and understand how our ancestors braved a brand new world above the waves.
It was a small step for fish, but a giant leap for animalkind. Though, looking at modern fish species, it’s not so hard to envision the slow adaptation to life out of the sea. Just the other day, I was feeding my pet scorpionfish Stumpy, and he surprised me with this slow, deliberate crawl towards his food:
A number of fish exhibit traits which are not unlike those of the first tetrapods: the four-limbed vertebrates that first braved life on land, direct descendants of ancient fish. Many of Stumpy’s relatives, including the gurnards, are known for their “walking” behaviors. Similarly, mudskippers have adapted anatomically and behaviorally to survive on land. Not only can they use their fins to skip from place to place, they can breathe through their skin like amphibians do, allowing them to survive when they leave their shallow pools. Walking catfishes have modified their respiratory system so much that they can survive days out of water. But all of these are only glimpses at how the first tetrapods began, as none of these animals has fully adapted to life on land. To understand how tetrapods achieved such a feat, we must first understand the barriers that lay between their life under the sea and the land above that awaited them.
Living in air instead of water is fraught with difficulties. Locomotion is one problem, though as evolution in a number of lineages has shown, not as big a problem as you might think. Still, while mudskippers and catfish seem to walk with ease, the same cannot be said of our ancestors. Some of the earliest tetrapods, like Ichthyostega were quite cumbersome on land, and likely spent most of their time in the comfort of water. These first tetrapods came from an ancient lineages of fishes called the Sarcopterygii or Lobe-Finned Fish, of which only a few survive today. As the name implies, these animals have meaty, paddle-like fins instead of the flimsy rays of most modern day fish species. These lobe fins, covered with flesh, were ripe for adapting into limbs.
But these early tetrapods had to develop more than a new way to walk – their entire skeletons had to change to support more weight, as water supports mass in a way that air simply doesn’t. Each vertebrae had to become stronger for support. Ribs and vertebrae changed shape and evolved for extra support and to better distribute weight. Skulls disconnected, and necks evolved to allow better mobility of the head and to absorb the shock of walking. Bones were lost and shifted, streamlining the limbs and creating the five-digit pattern that is still reflected in our own hands and feet. Joints articulated for movement, and rotated forward to allow four-legged crawling. Overall, it took a long 30 million years or so to develop a body plan fit for walking on land.
At the same time, these cumbersome wanna-be land dwellers faced another obstacle: the air itself. With gills adept at drawing oxygen from water, early tetrapods were ill-equipped to breathing air. While many think that early tetrapods transformed their gills into lungs, this actually isn’t true – instead, it was the fish’s digestive system that adapted to form lungs. The first tetrapods to leave the water breathed by swallowing air and absorbing oxygen in their gut. Over time, a special pocket formed, allowing for better gas exchange. In many fish, a similar structure – called a swim bladder – exists which allows them to adjust buoyancy in the water, and thus many have hypothesized that tetrapod lungs are co-opted swim bladders. In fact, exactly when tetrapods developed lungs is unclear. While the only surviving relatives to early tetrapods – the lungfishes – also possess lungs (if their name didn’t give that away), many fossil tetrapods don’t seem to have them, suggesting that lungfish independently evolved their ability to breathe air. What we do know is that it wasn’t until around 360 million years ago that tetrapods truly breathed like their modern descendants.
The other trouble with air is that it tends to make things dry. You may have heard the statistic that our bodies are 98% water, but, as well-evolved land organisms, we have highly evolved structures which ensure that all that water doesn’t simply evaporate. The early tetrapods needed to develop these on their own. At first, like the amphibians that would arise from them, many tetrapods likely stuck to moist habitats to avoid water loss. But eventually, to conquer dry lands and deserts, animals had to find another way to keep themselves from drying out. It’s likely that many of the early tetrapods began experimenting with ways to waterproof their skin. Even more important was the issue of dry eggs. Amphibians solve the dryness issue by laying their eggs in water, but the tetrapods which conquered land didn’t have that luxury.
The solution to land’s dry nature was to encase eggs in a number of membrane layers, in what is now known as an amniote egg. Even our own children reflect this, as human babies still grow in an amniotic sac that surrounds the fetus, even though we no longer lay eggs. This crucial adaptation allowed animals to cut ties with watery habitats, and distinguishes the major lineage of tetrapods, including reptiles, birds and mammals, from amphibians.
These crucial adaptations to tetrapod skeletons and anatomy allowed them to conquer the world above the waves. Without their evolutionary ingenuity, a diverse set of animals, including all mammals, would not be where they are today. Yet still we barely understand the ecological settings that drove these early animals out of the sea. Did dry land offer an endless bounty of food not to be passed up? Perhaps, but there is evidence that our ancestors braved the dry world very early on, even before most terrestrial plants or insects, so it’s possible earth was barren. Were they escaping competition and predation in the deep? Or was land important for some yet undetermined reason? We may never know. But as we reflect upon our beginnings, we have to give credit to the daring animals that began the diverse evolutionary lineage we are a part of. While we may never understand why they left the water, we are thankful that they did.
