Observations – Science Sushi

Darwin’s Degenerates – Evolution’s Finest | Observations

153 years ago on November 24th a naturalist named Charles Darwin published a book with a rather long and cumbersome title. It was called On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life (for its sixth edition in 1872, the title was cut short to simply The Origin of Species, which was found to be much more manageable to say in conversation). It was inspired by an almost five year journey around the world on a ship named for a small, floppy eared canine during which Darwin did his best to catalog and understand geology and the diversity of life he found.

It’s incomprehensible, now, to think of someone writing a single volume that could equally change science as we know it. The two simple ideas that Darwin fleshed out in his first publication were earth shattering at the time. He has since been called both a genius and a heretic for these two theories – both titles equally deserved. But whatever you call him, his vision has changed the world irrevocably. Today, on what would have been his 203 birthday, we celebrate the life and scientific contributions of this man. In honor of the occasion, I am reposting my first Darwin Day post ever, from way back in 2009. Enjoy!

If I ask you what group of organisms is an exhibition of evolution at its finest, what would you say? Most people, I think, would say human beings, or at least apex predators. After all, we have staggering intellect compared to our prey items and clearly dominate the planet, eat what we will, etc. Not only that, we’re insanely complex. Ask some scientists, and they might give you any number of answers. Cockroaches are likely to exist long after we do, as are rodents, so maybe they get the title. Or, being scientists, they might be biased to whatever organism they study. Maybe algae and plants, as the sustenance for all other life. But all of you, in my humble opinion, are wrong. That is, unless you choose parasites.

It’s ok if you don’t believe me yet. Darwin wouldn’t have, either. He and his contemporaries viewed parasites as degenerates who, at best, violated the progressive nature of evolution. Even in The Origin of Species, Darwin refers to parasites as regressive instead of progressive. But truly, no group of species is a better choice for evolution’s finest.

An ant being attacked by a parasitoid phorid fly. Photo Credit: Bernardo Segura

First off, let’s talk numbers. Parasitism is the most popular lifestyle on earth – over 40% of all known species are parasitic, and the number of parasitic species rises daily¹. Sure, you might say, but they tend to be small. In that case, let’s talk biomass – weight, just to be clear. One group of parasites, the flukes, have been found to be equal in weight to fish in estuarine habitats, and three to nine times the weight of the top predators, the birds – estimates which are thought to be conservative for the earth as a whole². Though they’re largely ignored when we study food webs, they’ve been estimated to be involved in over 75% of inter-species interactions¹. Clearly, by the numbers, they are the most prolific and successful organisms on earth.

But even that is not why I would argue they are evolution’s finest. They, more than any other group out there, both exhibit extreme evolutionary adaptations and spur them onward in other species.

No matter how complex or how impressive any other species may be, it has parasites. We do – lots, actually. Every species we might hold as a masterpiece of evolutionary complexity cannot out maneuver their parasites. Not one. Even parasites, marvelous as some are, have parasites – like a crazy russian doll. They have evolved amazing abilities to survive host defense systems, manipulate host behavior and boost heir own reproductive success. They’ve even been implicated in major cultural differences in people. It turns out that a rat parasite, Toxoplasma gondii, needs to be eaten by a cat to complete its lifestyle. Somehow it developed a trick to make rats unafraid of cat smells. When it accidentally ends up in people, it does the same kind of mind-altering, making people more guilty and insecure, even more frugal, mild-tempered, and complacent³. Other parasites do far more intricate manipulations of behavior, turning males into females, creating walking zombies, even forcing suicide. If parasites can not only break into and survive the most complex assortments of systems available, even with modern medicine fighting against them, and manipulate those complex organisms to slave to their bidding, how can we not credit them as masters at what they do?

But even more impressively, I would argue, is that no other group has so dramatically impacted how other species have evolved. They don’t just affect their hosts immune systems, either. If you read much into evolutionary theory, you realize it’s riddled with parasites. Why are some birds very colorful? Oh, because if they’ve got a lot of parasites they can’t be, so it’s a signal of a healthy male⁴. Why are we attracted to certain people? Because their immune genes are different from ours, giving our children the best chance to fight off the next generation of parasites. Almost everywhere you look, evolutionary changes are spurred on by parasites. It’s even suggested that sex itself evolved as a response to parasites. It’s a way of better shuffling our genes so that we have better odds at fighting off parasites.

Even we, as “ideal” or “complex” as we are, owe much to parasites. Some even argue that we are worse off without them. The argument, as it goes, is that our immune system evolved in the presence of unkillable parasites, particularly the parasitic worms. These worms, or Helminths as they are called as a group, were too costly to try and eradicate. Attacking foreign invaders, after all, is energetically expensive, and always runs the risk of over-activating our immune system, leading to self-inflicted injuries and diseases. So the best strategy, instead, was to have an immune system that functioned optimally against other issues, like the fatal viruses or bacteria, despite the mostly benign worm infections⁵. Since worms secrete anti-inflammatory compounds to fight off our defenses, we were better off with systems that overcompensated for that. Now, since we have drugs which kill them off, our immune system is out of balance. Many cite the rising rates of auto-immune and inflammatory diseases like allergies, arthritis, irritable bowel, type 1 diabetes, and even cancer in developed nations as evidence that ridding ourselves of helminths has damaged our health⁶. They’re backed up with multiple studies that show unexpected results, like that mice genetically predisposed to diabetes never develop it if infected with flukes at an early enough age.⁷

Parasites are uniquely capable of out-evolving their hosts and adapting to whatever changes go on in them. Simply put, they evolve better. They change their genes faster and keep up with a barrage of host defense systems, often like it’s effortless, spurring onward dramatic changes in other species. If Darwin had only known how amazingly complex the barriers these creatures have to overcome and the extent to which they have affected the species he’d encountered on his travels, he would not have labeled them “degenerates”.

As far as evolution is concerned, no group of species demonstrates it, causes it, and is so capable of it as the parasites. While disgusting or even cruel, they are truly evolutionary masterpieces. So while you may find them vile or detestable, you have to admit they’re good at it. Can you really argue that some other group is more deserving of the title of Evolution’s Finest?

Cited:
1. A. Dobson, K. D. Lafferty, A. M. Kuris, R. F. Hechinger, W. Jetz (2008). Colloquium Paper: Homage to Linnaeus: How many parasites? How many hosts? Proceedings of the National Academy of Sciences, 105 (Supplement_1), 11482-11489 DOI: 10.1073/pnas.0803232105
2. Armand M. Kuris, Ryan F. Hechinger, Jenny C. Shaw, Kathleen L. Whitney, Leopoldina Aguirre-Macedo, Charlie A. Boch, Andrew P. Dobson, Eleca J. Dunham, Brian L. Fredensborg, Todd C. Huspeni, Julio Lorda, Luzviminda Mababa, Frank T. Mancini, Adrienne B. Mora, Maria Pickering, Nadia L. Talhouk, Mark E. Torchin, Kevin D. Lafferty (2008). Ecosystem energetic implications of parasite and free-living biomass in three estuaries Nature, 454 (7203), 515-518 DOI: 10.1038/nature06970
3. Kevin D. Lafferty (2006). Can the common brain parasite, Toxoplasma gondii, influence human culture? Proceedings of the Royal Society B: Biological Sciences, 273 (1602), 2749-2755 DOI: 10.1098/rspb.2006.3641
4. Jesús Martínez-Padilla, François Mougeot, Lorenzo Pérez-Rodríguez, Gary R. Bortolotti (2007). Nematode parasites reduce carotenoid-based signalling in male red grouse Biology Letters, 3 (2), 161-164 DOI: 10.1098/rsbl.2006.0593
5. Joseph A. Jackson, Ida M. Friberg, Susan Little, Janette E. Bradley (2009). Review series on helminths, immune modulation and the hygiene hypothesis: Immunity against helminths and immunological phenomena in modern human populations: coevolutionary legacies? Immunology, 126 (1), 18-27 DOI: 10.1111/j.1365-2567.2008.03010.x
6. Joel V. Weinstock, David E. Elliott (2009). Helminths and the IBD hygiene hypothesis Inflammatory Bowel Diseases, 15 (1), 128-133 DOI: 10.1002/ibd.20633
7. Anne Cooke (2009). Review series on helminths, immune modulation and the hygiene hypothesis: How might infection modulate the onset of type 1 diabetes? Immunology, 126 (1), 12-17 DOI: 10.1111/j.1365-2567.2008.03009.x

Evolution: A Game of Chance | Observations

One of the toughest concepts to grasp about evolution is its lack of direction. Take the classic image of the evolution of man, from knuckle-walking ape to strong, smart hunter:

We view this as the natural progression of life. Truth is, there was no guarantee that some big brained primates in Africa would end up like we are now. It wasn’t inevitable that we grew taller, less hairy, and smarter than our relatives. And it certainly wasn’t guaranteed that single celled bacteria-like critters ended up joining forces into multicellular organisms, eventually leading to big brained primates!

Evolution isn’t predictable, and randomness is key in determining how things change. But that’s not the same as saying life evolves by chance. That’s because while the cause of evolution is random (mutations in our genes) the processes of evolution (selection) is not. It’s kind of like playing poker – the hand you receive is random, but the odds of you winning with it aren’t. And like poker, it’s about much more than just what you’re dealt. Outside factors – your friend’s ability to bluff you in your poker game, or changing environmental conditions in the game of life – also come into play. So while evolution isn’t random, it is a game of chance, and given how many species go extinct, it’s one where the house almost always wins.

Of course chance is important in evolution. Evolution occurs because nothing is perfect, not even the enzymes which replicate our DNA. All cells proliferate and divide, and to do so, they have to duplicate their genetic information each time. The enzymes which do this do their best to proof-read and ensure that they’re faithful to the original code, but they make mistakes. They put in a guanine instead of an adenine or a thymine, and suddenly, the gene is changed. Most of these changes are silent, and don’t affect the final protein that each gene encodes. But every once in awhile these changes have a bigger impact, subbing in different amino acids whose chemical properties alter the protein (usually for the worse, but not always).Or our cells make bigger mistakes – extra copies of entire genes or chromosomes, etc.

These genetic changes don’t anticipate an individual’s needs in any way. Giraffes didn’t “evolve” longer necks because they wanted to reach higher leaves. We didn’t “evolve” bigger brains to be better problem solvers, social creatures, or hunters. The changes themselves are random*. The mechanisms which influence their frequency in a population, however, aren’t. When a change allows you (a mutated animal) to survive and reproduce more than your peers, it’s likely to stay and spread through the population. This is selection, the mechanism that drives evolution. This can mean either natural selection (because it makes you run faster or do something to survive in your environment) or sexual selection (because even if it makes you less likely to survive, the chicks dig it). Either way the selection isn’t random: there’s a reason you got busier than your best friend and produced more offspring. But the mutation occurring in the first place – now that was luck of the draw.

Mistakes made by genetic machinery can lead to huge differences in organisms. Take flowering plants, for example. Flowering plants have a single gene that makes male and female parts of the flower. But in many species, this gene was accidentally duplicated about 120 million years ago. This gene has mutated and undergone selection, and has ended up modified in different species in very different ways. In rockcress (Arabidopsis), the extra copy now causes seed pods to shatter open. But it’s in snap dragons that we see how the smallest changes can have huge consequences. They, too, have two copies of the gene to make reproductive organs. But in these flowers, each copy fairly exclusively makes either male or female parts. This kind of male/female separation is the first step towards the sexes split into individual organisms, like we do. Why? It turns out that mutations causing the addition of a single amino acid in the final protein makes it so that one copy of the gene can only make male bits. That’s it. A single amino acid makes a gene male-only instead of both male and female.

Or, take something as specialized as flight. We like to think that flight evolved because some animals realized (in some sense of the word) the incredible advantage it would be to take to the air. But when you look at the evolution of flight, instead, it seems it evolved, in a sense, by accident. Take the masters of flight – birds – for example.

There are a few key alterations to bird bodies that make it so they can fly. The most obvious, of course, are their feathers. While feathers appear to be so ideally designed for flight, we are able to look back and realize that feathers didn’t start out that way. Through amazing fossil finds, we’re able to glimpse at how feathers arose, and it’s clear that at first, they were used for anything but airborne travel. These protofeathers were little more than hollow filaments, perhaps more akin to hairs, that may have been used in a similar fashion. More mutations occurred, and these filaments began to branch, join together. Indeed, as we might expect for a structure that is undergoing selection and change, there are dinosaurs with feather-like coverings of all kinds, showing that there was a lot of genetic experimentation and variety when it came to early feathers. Not all of these protofeathers were selected for, though, and in the end only one of these many forms ended up looking like the modern feather, thus giving a unique group of animals the chance to fly.

There’s a lot of variety in what scientists think these early feathers were used for, too. Modern birds use feathers for a variety of functions, including mate selection, thermoregulation and camouflage, all of which have been implicated in the evolution of feathers. There was no plan from the beginning, nor did feathers arise overnight to suddenly allow dinosaurs to fly. Instead, accumulations of mutations led to a structure that happened to give birds the chance to take to the air, even though that wasn’t its original use.

The same is true for flying insects. Back in the 19^th century, when evolution was fledging as a science, St. George Jackson Mivart asked “What use is half a wing?” At the time he intended to humiliate the idea that wings could have developed without a creator. But studies on insects have shown that half a wing is actually quite useful, particularly for aquatic insects like stoneflies (close relatives of mayflies). Scientists experimentally chopped down the wings of stoneflies to see what happened, and it turned out that though they couldn’t fly, they could sail across the water much more quickly while using less energy to do so. Indeed, early insect wings may have functioned in gliding, only later allowing the creatures to take to the air. Birds can use half a wing, too – undeveloped wings help chicks run up steeper hills – so half a wing is quite a useful thing.

But what’s really key is that if you rewound time and took one of the ancestors of modern birds, a dino with proto-feathers, or a half-winged insect and placed it in the same environment with the same ecological pressures, its decedents wouldn’t necessarily fly.

That’s because if you do replay evolution, you never know what will happen. Recently, scientists have shown this experimentally in the lab with E. coli bacteria. They took a strain of E. coli and separated it into 12 identical petri dishes containing a novel food source that the bacteria could not digest, thus starting with 12 identical colonies in an environment with strong selective pressure. They grew them for some 50,000 generations. Every 500 generations, they froze some of the bacteria. Some 31,500 generations later, one of the twelve colonies developed the ability to feed off of the new nutrient, showing that despite the fact that all of them started the same, were maintained in the same conditions and exposed to the exact same pressures, developing the ability to metabolize the new nutrient was not a guarantee. But even more shocking was that when they replayed that colony’s history, they found that it didn’t always develop the ability, either. In fact, when replayed anywhere from the first to the 19,999th generation, no luck. Some change occurring in the 20,000 generation or so – a good 11,500 generations before they were able to metabolize the new nutrient – had to be in place for the colony to gain its advantageous ability later on.

There’s two reasons for this. The first is that the mutations themselves are random, and the odds of the same mutations occurring in the same order are slim. But there’s another reason we can’t predict evolution: genetic alterations don’t have to be ‘good’ (from a selection standpoint) to stick around, because selection isn’t the only evolutionary mechanism in play. Yes, selection is a big one, but there can be changes in the frequency of a given mutation in a population without selection, too. Genetic drift occurs when events change the gene frequencies in a population for no reason whatsoever. A massive hurricane just happens to wipe out the vast majority of a kind of lizard, for example, leaving the one weird colored male to mate with all the girls. Later, that color may end up being a good thing and allowing the lizards to blend in a new habitat, or it may make them more vulnerable to predators. Genetic drift doesn’t care one bit.

Every mutation is a gamble. Even the smallest mutations – a change of a single nucleotide, called a point mutation – matter. They can lead to terrible diseases in people like sickle cell anemia and cystic fibrosis. Of course, point mutations also lead to antibiotic resistance in bacteria.

What does the role of chance mean for our species? Well, it has to do with how well we can adapt to the changing world. Since we can’t force our bodies to mutate beneficial adaptations (no matter what Marvel tells you), we rely on chance to help our species continue to evolve. And believe me, we as a species need to continue to evolve. Our bodies store fat because in the past, food was sporadic, and storing fat was the best solution to surviving periods of starvation. But now that trait has led to an epidemic of obesity, and related diseases like diabetes. As diseases evolve, too, our treatments fail, leaving us vulnerable to mass casualties on the scale of the bubonic plague. We may very well be on the cusp of the end of the age of man, if random mutations can’t solve the problems presented by our rapidly changing environment. What is the likelihood that man will continue to dominate, proliferate, and stick around when other species go extinct? Well, like any game of chance, you have to look at the odds:

99.99% of all the species that have ever existed are now extinct.

But then again – maybe our species is feeling lucky.

* If you want to get into more detail, actually, mutations aren’t completely random. They, too, are governed by natural laws – our machinery is more likely to sub an adenine for a guanine than for a thymine, for example. Certain sections are more likely to be invaded by transposons… etc. But from the viewpoint of selection, these changes are random – as in, a mutation’s potential selective advantage or disadvantage has no effect on how likely it is to occur.

Originally posted Nov 1st, 2010.

References:

Airoldi, C., Bergonzi, S., & Davies, B. (2010). Single amino acid change alters the ability to specify male or female organ identity Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1009050107

XU Xing, & GUO Yu (2009). THE ORIGIN AND EARLY EVOLUTION OF FEATHERS: INSIGHTS

FROM RECENT PALEONTOLOGICAL AND NEONTOLOGICAL DATA Verbrata PalAsiatica, 47 (4), 311-329

Perrichot, V., Marion, L., Neraudeau, D., Vullo, R., & Tafforeau, P. (2008). The early evolution of feathers: fossil evidence from Cretaceous amber of France Proceedings of the Royal Society B: Biological Sciences, 275 (1639), 1197-1202 DOI: 10.1098/rspb.2008.0003

Marden, J., & Kramer, M. (1994). Surface-Skimming Stoneflies: A Possible Intermediate Stage in Insect Flight Evolution Science, 266 (5184), 427-430 DOI: 10.1126/science.266.5184.427

DIAL, K., RANDALL, R., & DIAL, T. (2006). What Use Is Half a Wing in the Ecology and Evolution of Birds? BioScience, 56 (5) DOI: 10.1641/0006-3568(2006)056[0437:WUIHAW]2.0.CO;2

Blount, Z., Borland, C., & Lenski, R. (2008). Inaugural Article: Historical contingency and the evolution of a key innovation in an experimental population of Escherichia coli Proceedings of the National Academy of Sciences, 105 (23), 7899-7906 DOI: 10.1073/pnas.0803151105

Evolution: Watching Speciation Occur | Observations

This is a repost from April 24^th, 2010. Watching Speciation Occur is the second in my Evolution series which started with The Curious Case of Dogs

We saw that the littlest differences can lead to dramatic variations when we looked at the wide variety in dogs. But despite their differences, all breeds of dogs are still the same species as each other and their ancestor. How do species split? What causes speciation? And what evidence do we have that speciation has ever occurred?

Critics of evolution often fall back on the maxim that no one has ever seen one species split into two. While that’s clearly a straw man, because most speciation takes far longer than our lifespan to occur, it’s also not true. We have seen species split, and we continue to see species diverging every day.

For example, there were the two new species of American goatsbeards (or salsifies, genus Tragopogon) that sprung into existence in the past century. In the early 1900s, three species of these wildflowers – the western salsify (T. dubius), the meadow salsify (T. pratensis), and the oyster plant (T. porrifolius) – were introduced to the United States from Europe. As their populations expanded, the species interacted, often producing sterile hybrids. But by the 1950s, scientists realized that there were two new variations of goatsbeard growing. While they looked like hybrids, they weren’t sterile. They were perfectly capable of reproducing with their own kind but not with any of the original three species – the classic definition of a new species.

How did this happen? It turns out that the parental plants made mistakes when they created their gametes (analogous to our sperm and eggs). Instead of making gametes with only one copy of each chromosome, they created ones with two or more, a state called polyploidy. Two polyploid gametes from different species, each with double the genetic information they were supposed to have, fused, and created a tetraploid: an creature with 4 sets of chromosomes. Because of the difference in chromosome number, the tetrapoid couldn’t mate with either of its parent species, but it wasn’t prevented from reproducing with fellow accidents.

This process, known as Hybrid Speciation, has been documented a number of times in different plants. But plants aren’t the only ones speciating through hybridization: Heliconius butterflies, too, have split in a similar way.

It doesn’t take a mass of mutations accumulating over generations to create a different species – all it takes is some event that reproductively isolates one group of individuals from another. This can happen very rapidly, in cases like these of polyploidy. A single mutation can be enough. Or it can happen at a much, much slower pace. This is the speciation that evolution is known for – the gradual changes over time that separate species.

But just because we can’t see all speciation events from start to finish doesn’t mean we can’t see species splitting. If the theory of evolution is true, we would expect to find species in various stages of separation all over the globe. There would be ones that have just begun to split, showing reproductive isolation, and those that might still look like one species but haven’t interbred for thousands of years. Indeed, that is exactly what we find.

The apple maggot fly, Rhagoletis pomonella is a prime example of a species just beginning to diverge. These flies are native to the United States, and up until the discovery of the Americas by Europeans, fed solely on hawthorns. But with the arrival of new people came a new potential food source to its habitat: apples. At first, the flies ignored the tasty treats. But over time, some flies realized they could eat the apples, too, and began switching trees. While alone this doesn’t explain why the flies would speciate, a curious quirk of their biology does: apple maggot flies mate on the tree they’re born on. As a few flies jumped trees, they cut themselves off from the rest of their species, even though they were but a few feet away. When geneticists took a closer look in the late 20th century, they found that the two types – those that feed on apples and those that feed on hawthorns – have different allele frequencies. Indeed, right under our noses, Rhagoletis pomonella began the long journey of speciation.

As we would expect, other animals are much further along in the process – although we don’t always realize it until we look at their genes.

Orcas (Orcinus orca), better known as killer whales, all look fairly similar. They’re big dolphins with black and white patches that hunt in packs and perform neat tricks at Sea World. But for several decades now, marine mammalogists have thought that there was more to the story. Behavioral studies have revealed that different groups of orcas have different behavioral traits. They feed on different animals, act differently, and even talk differently. But without a way to follow the whales underwater to see who they mate with, the scientists couldn’t be sure if the different whale cultures were simply quirks passed on from generation to generation or a hint at much more.

Now, geneticists have done what the behavioral researchers could not. They looked at how the whales breed. When they looked at the entire mitochondrial genome from 139 different whales throughout the globe, they found dramatic differences. These data suggested there are indeed at least three different species of killer whale. Phylogenetic analysis indicated that the different species of orca have been separated for 150,000 to 700,000 years.

Why did the orcas split? The truth is, we don’t know. Perhaps it was a side effect of modifications for hunting different prey sources, or perhaps there was some kind of physical barrier between populations that has since disappeared. All we know is that while we were busy painting cave walls, something caused groups of orcas to split, creating multiple species.

There are many different reasons why species diverge. The easiest, and most obvious, is some kind of physical barrier – a phenomenon called Allopatric Speciation. If you look at fish species in the Gulf of Mexico and off the coast of California, you’ll find there are a lot of similarities between them. Indeed, some of the species look almost identical. Scientists have looked at their genes, and species on either side of that thin land bridge are more closely related to each other than they are to other species, even ones in their area. What happened is that a long time ago, the continents of North and South America were separated, and the oceans were connected. When the two land masses merged, populations of species were isolated on either side. Over time, these fish have diverged enough to be separate species.

Species can split without such clear boundaries, too. When species diverge like the apple maggot flies – without a complete, physical barrier – it’s called Sympatric Speciation. Sympatric speciation can occur for all kinds of reasons. All it takes is something that makes one group have less sex with another.

For one species of Monarch flycatchers (Monarcha castaneiventris), it was all about looks. These little insectivores live on Solomon Islands, east of Papua New Guinea. At some point, a small group of them developed a single amino acid mutation in the gene for a protein called melanin, which dictates the bird’s color pattern. Some flycatchers are all black, while others have chestnut colored bellies. Even though the two groups are perfectly capable of producing viable offspring, they don’t mix in the wild. Researchers found that the birds already see the other group as a different species. The males, which are fiercely territorial, don’t react when a differently colored male enters their turf. Like the apple maggot flies, the flycatchers are no longer interbreeding, and have thus taken the first step towards becoming two different species.

These might seem like little changes, but remember, as we learned with dogs, little changes can add up. Because they’re not interbreeding, these different groups will accumulate even more differences over time. As they do, they will start to look less and less alike. The resultant animals will be like the species we clearly see today. Perhaps some will adapt to a lifestyle entirely different from their sister species – the orcas, for example, may diverge dramatically as small changes allow them to be better suited to their unique prey types. Others may stay fairly similar, even hard to tell apart, like various species of squirrels are today.

The point is that all kinds of creatures, from the smallest insects to the largest mammals, are undergoing speciation right now. We have watched species split, and we continue to see them diverge. Speciation is occurring all around us. Evolution didn’t just happen in the past; it’s happening right now, and will continue on long after we stop looking for it.

Soltis, D., & Soltis, P. (1989). Allopolyploid Speciation in Tragopogon: Insights from Chloroplast DNA American Journal of Botany, 76 (8) DOI: 10.2307/2444824
McPheron, B., Smith, D., & Berlocher, S. (1988). Genetic differences between host races of Rhagoletis pomonella Nature, 336 (6194), 64-66 DOI: 10.1038/336064a0
Uy, J., Moyle, R., Filardi, C., & Cheviron, Z. (2009). Difference in Plumage Color Used in Species Recognition between Incipient Species Is Linked to a Single Amino Acid Substitution in the Melanocortin?1 Receptor The American Naturalist, 174 (2), 244-254 DOI: 10.1086/600084
Phillip A Morin1, Frederick I Archer, Andrew D Foote, Julie Vilstrup, Eric E Allen, Paul Wade, John Durban, Kim Parsons, Robert Pitman, Lewyn Li, Pascal Bouffard, Sandra C Abel Nielsen, Morten Rasmussen, Eske Willerslev, M. Thomas P Gilbert, & Timothy Harkins (2010). Complete mitochondrial genome phylogeographic analysis of killer whales (Orcinus orca) indicates multiple species Genome Research

Image Credits:

Salsify plate showing two new species from the New Zealand Plant Radiation Network (taken from Ownbey, 1950 in which the species were described)

Flycatchers image by Robert Boyle, as featured on Science Now

Evolution: The Curious Case of Dogs | Observations

This is the first in a series of post of mine about Evolution that I started posting in January of 2010. I’ll be reposting the series over the next two months, culminating in a brand new post for the set in Jan 2012! I’m excited. You know you’re excited. Enjoy!

Man’s best friend is much more than a household companion – for centuries, artificial selection in dogs has made them prime examples of the possibilities of evolution. A century and a half ago, Charles Darwin recognized how the incredibly diverse dogs supported his revolutionary theory in his famous book On The Origin Of Species. At the time, he believed that dogs varied so much that they must have been domesticated from multiple canine species. Even still, he speculated that:

if… it could be shown that the greyhound, bloodhound, terrier, spaniel and bull-dog, which we all know propagate their kind truly, were the offspring of any single species, then such facts would have great weight in making us doubt about the immutability of the many closely allied natural species

If only Darwin knew what we know now, that indeed, all dogs did descend from one species!

While humans have been breeding dogs for over ten thousand years, it was until recently that strict standards and the emphasis on “purebreds” has led to over 400 different breeds that are some of the best examples of the power of selection. Those that doubt whether small variations in traits can lead to large levels of diversity clearly haven’t compared a Pug to a Great Dane – I mean, just look at them compared to their ancestor:

We’ve turned a fine-tuned hunting animal, the wolf, into a wide variety of creatures, from the wolf-looking shepherds to the bizarre toy breeds. Before domestication, dog’s life was tough. But when people pulled specific wolves out of their packs and began breeding them, we changed everything. There were some traits that made this easy – the social structure of wolves, for example, made them predisposed to belonging to a community. Still, we opened up a number of genetic traits and allowed them to express variety that would have been fatal in the wild. We not only allowed these traits to persist, we encouraged them. We picked dogs that were less aggressive or looked unique. And in doing so, we spurred on rapid diversification and evolution in an unbelievable way.

Take their skulls, for example. Like other members of the order Carnivora, dog’s skulls have a few distinctive characteristics: relatively large brains and a larger-than-normal structure called a zygomatic arch which allows for bite power and chewing. But years of hand-picked puppies has led to an amazing amount of skull diversity in dogs. A study recently compared the positions of 50 recognizable points on the skulls of dogs and compared them to each other and other members of the order Carnivora. They found that there was as much variety in the shape of the skulls of dogs as in the entire rest of the order, and the extremes were further apart. What does that mean, exactly? It means that the differences between the skulls of that Pug and Great Dane I mentioned before (on R) are greater than the differences between the skulls of a weasel and a walrus. Much of this variation is outside the range of the rest of the order, meaning dogs’ skull shapes are entirely unique. In just a few centuries, our choices have created unbelievable variety in the heads of dogs – more than 60 million years has created in the rest of the carnivores.

The amazing diversity of dogs is a testimonial to the possibilities of selection. And it’s not just their skulls that vary. A joint venture between the University of Washington and the Veterinary School at UC Davis mapped the variation in the genomes of a mere 10 different breeds of dogs. They found that at least 155 different regions of the dog’s genome show evidence of strong artificial selection. Each region contained, on average, 11 genes, so it’s harder to identify exactly what about each area was under the most selection, though there were clues. About 2/3 of these areas contain genes that were uniquely modified in only one or two breeds, suggesting they contain genes that are highly breed-restricted like the skin wrinkling in the Shar-Pei. Another 16 had variations in 5 or more breeds, suggesting they encode for traits that are altered in every breed, like coat and size.

While we usually think of evolution as a slow and gradual process, dogs reveal that incredible amounts of diversity can arise very quickly, especially when selective pressures are very, very strong. It’s not hard to see how selection could lead to the differentiation of species – just look at the breeds of dogs that exist today. There’s a reason that you don’t see many Chihuahua/Saint Bernard mixes: while it’s entirely possible for their genetics to mix, it’s just physically difficult for these two breeds to actually do it. Just imagine what a poor Chihuahua female would have to endure to give birth to such a mix, or how hard it would be for male Chihuahua to mount a female Saint Bernard. Indeed, dogs are well on their way to speciation.

Of course, it’s at this point that I have to mention that while I have talked about “dogs” this entire time, they’re not actually a different species. Wolves are Canis lupus, while dogs are merely a subspecies of wolves, Canis lupus familiaris. Despite centuries of selective breeding and the vast array of physical differences, dogs are still able to breed with their ancestors.

When you take away the selective breeding done by humans, a number of these unique traits disappear. But feral dogs don’t just become wolves again – their behaviors and even looks depend greatly on the ecological pressures that surround them. Our centuries of selective breeding have opened a wide variety of traits, both physical and behavioral, that may help a stray dog survive and breed.

A good example of what happens to dogs when people are taken out of the picture can be found in Russia’s capital city. Feral dogs have been running around Moscow for at least 150 years. These aren’t just lost pets that band together – these dogs been on their own for awhile, and indeed, any poor, abandoned domesticated canine will meet an unfortunate fate at the hands of these territorial streetwalkers. Moscow’s dogs have lost traits like spotted coloration, wagging tails and friendliness that distinguish domesticated dogs from wolves – but they haven’t become them. The struggle to survive is tough for a stray, and only an estimated 3% ever breed. This strong selective pressure has led them to evolve into four distinct behavioral types, according to biologist Andrei Poyarkov who has studied the dogs for the past 30 years. There are guard dogs, who follow around security personnel, treating them as the alpha leaders of their packs. Others, called scavengers, have evolved completely different behaviors, preferring to roam the city for garbage instead of interacting with people. The most wolf-like dogs are referred to as wild dogs, and they hunt whatever they can find including cats and mice.

But the last group of Moscow’s dogs is by far the most amazing. They are the beggars, for obvious reasons. In these packs, the alpha isn’t the best hunter or strongest, it’s the smartest. The most impressive beggars, however, get their own title: ‘metro dogs’. They rely on scraps of food from the daily commuters who travel the public transportation system. To do so, the dogs have learned to navigate the subway. They know stops by name, and integrate a number of specific stations into their territories.

This dramatic shift from the survival of the fittest to the survival of the smartest has changed how Moscow’s dogs interact with humans and with each other. Beggars are rarely hit by cars, as they have learned to cross the streets when people do. They’ve even been seen waiting for a green light when no pedestrians are crossing, suggesting that they have actually learned to recognize the green walking man image of the crosswalk signal. Also, there are fewer “pack wars” that once were commonplace between Moscow’s stray canines, some of which used to last for months. However, they remain vigilant against the wild dogs and wolves that live on the outskirts of the city – rarely, if ever, are they permitted into Moscow. When politicians thought to remove the dogs, their use as a buffer against these animals was cited as a strong reason not to disturb them.

Moscow’s exemplary dogs show how different traits help dogs adapt to different ecological niches – whether it be brute strength for hunting in the truly feral wild dogs or intelligence in the almost-domesticated beggars. Some wonder if the strong selection for intellect will make Moscow’s metro dogs into another species all together, if left to their own devices.

Dogs make it easy to understand and demonstrate the core principles of evolution – variation and selection – and how they can make such a dramatic impact on an animal. It’s no wonder that Darwin took cues from domesticated animals when formulating his theory of evolution. However, there’s still a lot to learn about the processes that have shaped our best friends, and what future lies for them. How much time will it take to completely separate dogs from wolves, into their own species? What areas of the genome are key to doing so? In studying dogs and wolves, we may gain insight into how speciation occurs and when a threshold of change is met for it to do so. Seeing how much change has occurred already makes you wonder what surprises our canine companions still have in store for us as they, and we, continue to evolve together over the next ten thousand years.

Citations:

Drake, A., & Klingenberg, C. (2010). Large Scale Diversification of Skull Shape in Domestic Dogs: Disparity and Modularity The American Naturalist DOI: 10.1086/650372

Akey, J., Ruhe, A., Akey, D., Wong, A., Connelly, C., Madeoy, J., Nicholas, T., & Neff, M. (2010). Tracking footprints of artificial selection in the dog genome Proceedings of the National Academy of Sciences, 107 (3), 1160-1165 DOI: 10.1073/pnas.0909918107

Poyarkov, A.D., Vereshchagin, A.O., Goryachev, G.S., et al., Census and Population Parameters of Stray Dogs in Moscow, Zhivotnye v gorode: Mat-ly nauchno-prakt. konf. (Proc. Scientific and Practical Conf. Animals in the City ), Moscow, 2000, pp. 84 87.

Vereshchagin, A.O., Poyarkov, A.D., Rusov, P.V., et al., Census of Free-Ranging and Stray Animals (Dogs) in the Coty of Moscow in 2006, Problemy issledovanii domashnei sobaki: Mat-ly soveshch (Proc. Conf. on Problems in Studies on the Domestic Dog), Moscow, 2006, pp. 95 114.

Observations: Why do women cry? Obviously, it’s so they don’t get laid.

This week, a paper came out looking at testosterone levels in fathers. A whirlwind of poor journalism followed, which was beautifully smacked down by William Saletan over at Slate (aslo: see this great post on the topic by our very own Kate Clancy). But it reminded me of a similar kerfluffle that occurred this past January over a paper on the effects of sniffing tears. This was my post from Jan 8^th on that paper and the media surrounding it, which just so happens to look at the meaning of lowered testosterone levels in terms of evolution.

I don’t think Brian Alexander is a bad guy or a misogynist. He writes the Sexploration column for MSNBC, so sure, his job is all about selling sex stories to the public. He even wrote a book about American sexuality. But I don’t personally think he has a burning hatred for women, or views them as objects placed on this Earth for the sexual satisfaction of men. However, I very easily could, given how he chose to report on a recent study published in Science about men’s physiological responses to the chemicals present in women’s tears.

The headline alone was enough to make me gag — “Stop the waterworks, ladies. Crying chicks aren’t sexy.” The sarcastic bitch in me just couldn’t help but think Why THANK YOU Brian! I’ve been going about this all wrong. When I want to get some from my honey, I focus all my thoughts on my dead dog or my great grandma and cry as hard as I can. No WONDER it isn’t working!

I didn’t even want to read the rest of the article.

But I did.

It doesn’t get better.

Alexander’s reporting of the actual science was quick and simplistic, and couched in sexist commentary (like how powerful women’s tears are as manipulative devices). And to finish things off, he clearly states what he found to be the most important find of the study:

“Bottom line, ladies? If you’re looking for arousal, don’t turn on the waterworks.”

It’s no wonder that the general public sometimes questions whether science is important. If that was truly the aim of this paper, I’d be concerned, too!

Of course, Brian Alexander missed the point. This paper wasn’t published as a part of a women’s how-to guide for getting laid. Instead, the authors sought to determine if the chemicals present in human tears might serve as chemosignals like they do for other animals — and they got some pretty interesting results.

In many species, chemical signals run rampant. Scents, pheromones, and other chemical cues are deliberately and unconsciously given off to tell other individuals anything from “Back Off – MY Tree!” to “Hop on and ride me, baby!” But despite how common they are in the rest of the animal kingdom, the function of chemical signals in humans is hotly debated. Years of searching has yet to find human pheromones (no matter what those websites tell you), and while scent seems to play a role in communication in people, there is still relatively little knowledge as to what chemicals and why.

Given that tears are known to serve as sexual signals in mice, it isn’t strange at all that Noam Sobel and his team chose to look at the physiological responses to tears. The Israeli team designed an impressive and unbiased set of experiments to determine if the tears produced by women when sad elicit physiological responses in men separate of the visual or auditory stimuli of a woman crying.

To find out if tears alone acted as chemosignals, the scientists collected tears from women watching tear-jerkers, and as a control, compared their effects to saline rolled down women’s cheeks. Men sniffed the solutions without any knowledge as to what they were during a series of different experiments. In the first, men with a tear-soaked pad under their nose were asked to rate the sexual attractiveness and mood of female faces. While the smell of saline had no effect, men inhaling Eau de Tears consistently rated women’s faces as less attractive, though this had no impact on whether they found the faces happy or sad.

For the second experiment, men sniffed tears before watching a sad movie. While doing so didn’t affect their mood, the smell of tears did elicit a physiological response: men’s faces became more conductive to electricity, which happens when we sweat and is indicative of a psychological reaction. Furthermore, the men self-reported less sexual arousal, which was reflected in their bodies as a 13% drop in saliva testosterone levels.

But to really get to the meat of it, the team threw their male test subjects into an fMRI machine and scanned their brains for activity while sniffing tears. Researchers saw much less activity in the hypothalamus and the fusiform gyrus, both of which are thought to be involved in sexual arousal. All three experiments lead to the same conclusion: the chemicals in women’s emotional tears reduce male sex drive.

The real question, though, is why? Why do men’s testosterone levels tank at the smell of a woman’s tears? The overwhelming answer given by mainstream media (as Rheanna pointed out) is that tears just aren’t sexy. When women cry, so the journalists say, it’s a chemical signal that they don’t want to have sex. Because evolution is all and only about sex… right?

Sorry to burst their bubble, but even when it comes to evolution, it’s not all about sex. Selection also favors survival — because, you know, you can’t have sex when you’re dead*. Thus women’s tears are not necessarily evolutionarily intended to turn guys off. For example, Ed Yong brings up the hypothesis that tears might be used to downplay aggression. Think about it: we cry when we’re sad or physically in pain. In both cases, we’re more vulnerable. Getting others, especially angry men, to be less aggressive towards us in that moment could certainly be a benefit to survival.

Really, the idea that tears are intentionally used as a turn off is a hard sell to an evolutionary biologist. What benefit do women get from not having sex when crying? Does it somehow make them have healthier or more babies? Not for any reason I can think of.

There is, instead, an even more intriguing explanation, one that makes a whole lot more sense. Many who wrote about this paper (including Brian Alexander) mentioned that tears are known to contain a variety of compounds, including prolactin, the hormone which is responsible for making a guy cool his jets after he gets off. But prolactin does much more than ensure a guy stops going at it — it’s a hugely important hormone for nurturing behaviors. In fact, the connection between reduced testosterone and nurturing/bonding behaviors may be the real reason as to why men’s testosterone levels dip upon sniffing tears.

Numerous studies have shown that parental and nurturing behaviors are mediated by prolactin while inhibited by testosterone. For example, research has shown that prolactin levels positively and testosterone levels negatively correlate with a father’s impulse to respond to a baby’s cry. Furthermore, men’s prolactin levels spike and testosterone levels drop in the weeks before their partner gives birth.

It goes beyond babies, too. Decreased testosterone and increased prolactin are strongly implicated in establishing and maintaining relationships. Monogamous men have significantly lower testosterone levels and higher prolactin levels than their single brethren. Furthermore, studies have directly shown that artificially increasing testosterone in a double-blind, placebo-controlled setting makes men less generous to strangers and reduces a person’s empathy for others.

Perhaps prolactin or other chemical signals in tears are directly targeting and activating the nurturing pathway in men’s brains. Being taken care of or protected when in emotional or physical pain would definitely benefit an individual’s survival. Personally, I would like to see this study of tears replicated to determine women’s responses to the scent as well as men’s reactions when using men’s and children’s tears, as well as looking at the levels of prolactin, oxytocin, and other well-established bonding and empathetic hormones. My bet is the response isn’t limited to men, and isn’t limited to emotional secretions from women.

While Brian Alexander and the rest of the sensationalists seem to suggest the signal is “I’m not in the mood,” its likely that the message has nothing to do with having or not having sex. Women aren’t saying “back off” — they’re saying “help me.”

Why do I care so much? It’s not just that they got it wrong. It’s that their interpretation of research isn’t labeled as opinion. It’s that the vast majority of people who have any interest in science news are going to read inaccurate (if not downright insulting) news articles and think studies like this one are either misogynistic or frivolous. It’s that journalists like Brian Alexander undermine good science for the sake of attention grabbing headlines. And as a scientist and a writer, it’s a double insult.

Gelstein, S., Yeshurun, Y., Rozenkrantz, L., Shushan, S., Frumin, I., Roth, Y., & Sobel, N. (2011). Human Tears Contain a Chemosignal Science DOI: 10.1126/science.1198331

* I can hear the comments now, you sickos, so let me clarify: you can’t have baby-producing sex when you’re dead.

Also, thanks to Kira Krend for the thoughtful and hilarious discussion on this topic!

Other References:

Haga S, Hattori T, Sato T, Sato K, Matsuda S, Kobayakawa R, Sakano H, Yoshihara Y, Kikusui T, & Touhara K (2010). The male mouse pheromone ESP1 enhances female sexual receptive behaviour through a specific vomeronasal receptor. Nature, 466 (7302), 118-22 PMID: 20596023
Fleming, A. (2002). Testosterone and Prolactin Are Associated with Emotional Responses to Infant Cries in New Fathers Hormones and Behavior, 42 (4), 399-413 DOI: 10.1006/hbeh.2002.1840
Storey AE, Walsh CJ, Quinton RL, & Wynne-Edwards KE (2000). Hormonal correlates of paternal responsiveness in new and expectant fathers. Evolution and human behavior : official journal of the Human Behavior and Evolution Society, 21 (2), 79-95 PMID: 10785345
Burnham, T. (2003). Men in committed, romantic relationships have lower testosterone Hormones and Behavior, 44 (2), 119-122 DOI: 10.1016/S0018-506X(03)00125-9
Zak, P., Kurzban, R., Ahmadi, S., Swerdloff, R., Park, J., Efremidze, L., Redwine, K., Morgan, K., & Matzner, W. (2009). Testosterone Administration Decreases Generosity in the Ultimatum Game PLoS ONE, 4 (12) DOI: 10.1371/journal.pone.0008330
HERMANS, E., PUTMAN, P., & VANHONK, J. (2006). Testosterone administration reduces empathetic behavior: A facial mimicry study Psychoneuroendocrinology, 31 (7), 859-866 DOI: 10.1016/j.psyneuen.2006.04.002

Tuna | Observations

Every once in a while, you write something you really, really like. You write something you like so much, you wish you could write it again, over and over. Well, I happen to have a few of these posts that I have written previous to my move here, and I want to share them with you. They’ll be labelled as “Observations,” indicating they were originally posted on my old blog, Observations of a Nerd. Enjoy!

mouse — Mouse, my adorable cousin, showing off a bubble

“Christie! Christie!” My four-year old cousin tugs eagerly on my jacket. “I wanna see the fishes.”

“Ok, Tuna, we can go see the fish.”

My little cousin loves the word ‘tuna’. She says it all the time. Tuna, tuna, tuna. Everything is a tuna-face or a tuna-head. She doesn’t even like tuna (she doesn’t eat it), but she loves the sound of the word rolling off her tongue. Finally, her nanny threatened that if she kept saying ‘tuna,’ we’d have to start calling her it. My ever so adorable cousin’s response was, of course, “TUNA!” So now that’s her nickname. She’s Tuna.

I’m waiting in line with her and her sister at the Rainforest Cafe in the Burlington Mall. They love the Rainforest Cafe. There’s a giant mechanical alligator out front that they can’t seem to get enough of. Mouse (as I now call Tuna’s older sister) is convinced that it’s real. Who am I to burst her bubble?

But now, in line, their eyes are instead drawn to the entrance arch of fish tanks. As a marine biologist, I feel obligated to tell them about the fish.

“You see that one? That’s a butterflyfish. And that one — that’s a grouper. Oh! And that little colorful one there — that’s the Hawaii State Fish. It’s name in Hawaiian is Humuhumunukunukuapua’a. Can you say Humuhumunukunukuapua’a?”

My two cousins look at me like I’m insane. I guess they’re a little young to try and learn Hawaiian fish names.

“Christie! Christie!” Tuna grabs my jacket again. “Are there any tuna?”

“Tuna. Tuna. TUNA!” Mouse grins at her sister, and the two burst into giggles.

Their attention quickly drifts to shooting back and forth funny words like Tuna and Pizza, and instead I am left with my little cousin’s innocent question derailing my thoughts.

Tuna. One of my favorite fish. Large, majestic creatures built for speed and strength. Even a rudimentary understanding of how perfectly suited they are as open ocean predators leaves one in awe of evolution’s handiwork. A sleek, streamlined design, with specialized circulation and muscles to provide warmth and power even in cold water — they are truly incredible fish.

There are many kinds of tuna: Albacore, Bigeye, Blackfin, Bluefin, Karasick, Longtail Skipjack and Yellowtail. Even within a ‘kind’ like Bluefin there is Northern Bluefin, Southern Bluefin, and Pacific Bluefin.

They’re all similar in that they’re unbelievably delicious.

I remember the last time I ate tuna. I would love to say it was a long time ago, but it wasn’t. I slipped into the take-out sushi place as quietly as possible, but the little bells attached to the door handle announced my entrance.

“Wat can get fo you?” the nice man behind the counter asked.

“I’ll have the Spicy Ahi Maki, please.” Once my treat was handed over, I made quick work of the bright red fish smothered in my favorite chili mayo. The soft, tender flesh melted in my mouth, tasting of decadence. Within a matter of minutes it was all over.

As soon as I walked out the door, though, it hit me. The guilt. You should know better, I chided myself. The tuna fisheries, by and large, are a disgrace. Many are overfished and on the verge of collapse. Take the Mediterranean Bluefin tuna fishery, the largest fishery for Bluefin in the world, for example. Tuna are caught young in massive numbers and corralled in cages offshore where they’re fattened for the sushi and sashimi market. If the Mediterranean Bluefin tuna fishery is not closed now, some scientists project that the tuna in that part of the world will be functionally extinct in just two years.

Of course, I know that the tuna I ate wasn’t likely to be Bluefin. It wasn’t Albacore, either, as Albacore is the tuna you get in cans, not the kind served in sushi bars (though it can be found under the name “Shiromaguro” if they have it). While the Japanese are much pickier about their labeling, giving each species a different name, in the states, Ahi or Maguro can refer to just about any tuna species, though most often it refers to Bigeye, Yellowfin or sometimes Skipjack. It’s only if you get Toro, the fatty tuna that will cost you an arm and a leg, that you’re likely to be eating Bluefin.

But ordering tuna in a restaurant is a bit like playing ecological Russian Roulette. Rarely do restaurants know or care where their fish comes from, only that they got it at a decent price. Even if they think they know and think they care, they’re often wrong. A recent study which genetically tested ordered tuna in restaurants found you may be served anything from the critically endangered Southern Bluefin to Escolar, a disgusting fish known to cause illness when eaten. Most (79%) of the menus did not say what species was served, and when asked, almost a third said the wrong species while another 9% had no idea.

The problem, of course, is that it matters which species you eat. All Bluefin fisheries are unsustainable, and eating them ensures their doom. Meanwhile, Yellowtail and Bigeye, though better off, are approaching the same fate — though if caught with pole and line (the slower and more expensive way to fish), they could be sustainable. Only Albacore and Skipjack have healthy and well managed stocks right now, though if we lean more on them to make up for losses in the other three major fisheries, it’s likely they, too, will be in trouble. Despite warning after warning, government agencies all over continue to keep quotas for most species well above sustainable levels.

As if that’s not bad enough, members at the recent CITES meeting rejected legislation that would have limited the trade of tuna between countries. It seems that the politicians just don’t care enough, and it’s up to the public to make it clear that driving these species to extinction is not something we’re willing to stand for. To do that, we have to stop supporting the market… to stop going out to little take out sushi places and getting the Spicy Ahi Maki.

I tried to console myself that, living in Hawaii, it’s possible that the tuna I just ate was Skipjack, pole-caught locally… but I know better. Pole-caught fish are more expensive, and it’s not likely the cheap take-out sushi place is splurging for the local variety just for kicks, especially if they aren’t advertising the fact. No, that delicious meat was likely Yellowfin or Bigeye purse-seined or long-lined in some foreign country and shipped, frozen, to Honolulu to be eaten by cheap people like me.

The feeling that washed over me in that instant was not unlike the feeling you get when you drunkenly sleep with your ex a month or so after the breakup. Sure, it seems like a good idea at the time, and for a brief moment you feel pure pleasure. But you wake up the next morning coated with filth and regret. The truth is, you’ve only made things worse. You glare at yourself in the mirror, pissed that you were so stupid. But the worst part is the unshakeable feeling that lingers for days. You feel… well, there’s really no nice word for it. You feel like a slut.

That’s what you are, you know my conscience spits at me. You’re a tuna slut.

“Christie! Christie!” My cousin’s pleas snap me back.

“What is it Tuna?”

“You’re a toushie-face!” They erupt into laughter. The two are completely out of control. With the artful skill only an older cousin can have, I draw their attention back to the fish, explaining the different types and little facts about how they live. They’re mesmerized. Soon enough we’ve been seated, ordered our food, and had a nice lunch surrounded by the chaotic jungle of the Rainforest Cafe.

Later that evening, the girls kiss and hug me goodnight. “Goodnight Mouse, Goodnight Tuna,” I whisper to each. As they head upstairs with their parents to bed, I sip a glass of my uncle’s homemade red wine and can’t help but think about the plight of tuna.

A fish so beloved by so many like myself, yet its very survival is threatened by that adoration. The trouble is that it’s just hard to give up something we love so much. If I — a marine biologist armed to the teeth with the knowledge of exactly how bad the problem is — still cannot restrain myself from indulging, it seems hopeless to expect that the world will. If we continue to fish for bluefin and other tuna like we do now, there is no ambiguity about the result. They will disappear. Probably within my lifetime, maybe even sooner. And before they disappear, they’ll become so hard to find that a slice of sashimi will be as expensive as Beluga caviar is now.

It’s possible that regulating agencies will come to their senses and limit the catch, thus allowing tuna species to rebound before they’re completely gone — but they sure as all hell don’t seem inclined to. Some have had the idea of rolling moratoriums, where certain fishing locations are banned for several years, then others the next few years, to allow wild populations time to recover. Or maybe they could instate tuna credits, allowing fish-hungry nations like Japan to eat their fill while others abstain. There are a lot of ways politicians could help prevent overfishing — none of which, of course, they seem to want to do.

It’s also possible that we’ll find a way to farm tuna, taking the pressure off of falling wild stocks. As it stands now, many species of tuna are caught young and kept in pens until they’re big and fat enough to be slaughtered. But this isn’t really farming in the truest sense because they still have to be wild-caught first. Tuna species, particularly the plummeting Bluefin, have proven to be extremely difficult to aquaculture. They take 12 years to mature, and apparently, don’t find large aquariums or offshore corrals very romantic, so they don’t produce the next generation in captivity. Some have had luck using drugs to trick them into producing eggs, but the method was expensive and labor intensive, and it has yet to be seen if the young produced are healthy. While this does produce hope, it’s limited, and it’s hard to see commercial aquaculture technology rising fast enough to the occasion to save these species.

I can’t help but wonder if, in fifteen or twenty years, I’ll even be able to order maguro if I take my cousin out to a nice sushi restaurant so she can try the fish she’s nicknamed after.

Even if I can, I hope that when I suggest it, she glares, then sighs like she’s sick of explaining this kind of thing to ignorant people like me. Her generation will have learned from our mistakes. They will do better. She will remind me that tuna are rare and beautiful fish; that they’re aren’t that many left, and if we keep ordering tuna and continuing the demand for their meat, they will disappear altogether.

And, she’ll likely say, I’m a grown woman now — so stop calling me Tuna.

For more information about sustainable seafood choices, take a look at the Monterrey Bay Aquarium’s Seafood Watch List for your area. In particular, you can help protect the wild tuna by ordering other, more sustainable sushi. For examples, check out SustainableSushi.Net.

Learn more about the plight of the tuna and what you can do to help at SaveTheBluefinTuna.Com.