Tuesday, 19 May 2015

Why I'm excited about the opah

Last week, a new paper in Science (Wegner et al. 2015) announced that they had discovered whole body endothermy (that is, the ability to generate metabolic heat to keep the temperature of the internal organs above ambient temperature) in a pelagic bony fish. This fact is intrinsically cool, but as a mammalian paleontologist who is interested in the evolution of mammalian physiology, I was immediately intrigued and excited to know more.
Everyone knows that mammals and birds are "warm blooded", that is that they maintain a stable body temperature that is above that of the environment. Usually, they are described this way to distinguish them from lizards, snakes, crocodiles, amphibians and fish, collectively referred to as "cold blooded". But the details of heat physiology are much more complex than this simplistic dichotomy. At the most fundamental level, there are two different, and related axes of variation along which animals can be placed to describe their body temperature physiology.
One axis separates animals that maintain a constant body temperature (known as homeotherms) from animals that do not (known as poikilotherms,  a personal favorite word of mine). The other axis separates endotherms, that is animals that use the heat generated by internal metabolic processes (such as muscle contraction) to warm their internal organs, versus ectotherms, that use environmental sources (most often the sun, but sometimes other sources such as hot springs) to heat themselves.
Now here's what's really fascinating. If you imagine a plot with these two axis, you will find organisms all over it. You will find ectotherms that are excellent homeotherms, and endotherms that are highly poikilothermic (many tropical marsupials fall in this category). What is more, most animals can occupy, depending on the environment they're in and the specifics of their physiology, multiple positions in this space.
Of particular interest to this debate are the many ocean going, highly active predatory fish that have evolved varying degrees of facultative endothermy. These are animals (such as tuna and sharks), that use a specific arrangement of blood vessels called a counter current exchanger to trap the heat generate by muscle activity in their swimming muscles, thus allowing them to keep those muscles at the best temperature for efficient function in cold water. The limitation of this strategy, however, is that eventually the heart cools down, slowing down its pumping rate and starving the muscles of oxygen.
Which is where the opah comes in. It flips the script on what other facultative endotherms do, and places the counter current exchanger in the gills (I urge to go and look at the paper now; the pictures of those gill counter current exchangers are breathtaking). As the gills are in direct contact with water, they are a major site of heat loss. Mammals and birds have similar problem in the respiratory system, and have independently evolved highly vascularised nasal turbinates which also use vascular counter current exchange to trap heat inside the body cavity during exhalation. By placing the counter current exchangers in its gills, the opah (if physicists will forgive me this inaccurate metaphor) traps the cold outside its body (thus brilliantly illustrating Claude Bernard's definition of homeostasis). Furthermore, evidence suggests that the opah may use its pectoral fin muscles purely to generate heat, rather than to aid in locomotion, thus fulfilling the strictest definition of endothermy (that is, the use of metabolic energy purely for the generation of heat). Finally, the opah has developed significant insulation the form of fat, so as to prevent heat loss through the skin. The upshot of all this is that the opah's internal organs, including its heart, remain considerably warmer than the surrounding water.
So it seems pretty clear the opah is probably a homeothermic endotherm, and probably a pretty good one. It is always exciting to see a completely unexpected organism have converged on an evolutionary solution that we thought only another organism had achieved. But what really got me excited was the discussion of why the opah might have evolved this form of life. Namely, facultative endotherms like tuna must eventually leave cold deep waters (which are rich in fish) for sun-warmed surface waters when their hearts cool down. The opah, through its metabolically expensive endothermy, can remain in those waters permanently. Why is this exciting? Because the exploitation of a cold environment is exactly the scenario that has been advanced for the evolution of endothermy in mammals. Namely, it has been suggested that mammalian endothermy allowed triassic mammals to hunt at night, when other, ectothermic amniotes would be sluggish. In the opah, we have validation of the hypothesis that endothermy can evolve so that a thermally constrained niche can be exploited.
Biology training is becoming increasingly narrow, yet also increasingly broad. We study systems in limited model organisms, and then expand the mechanisms across groups without consideration of the ecological, and evolutionary specificities that have made these organisms what they are. But if our evolutionary scenarios make sense, then we should expect them to be repeated: the biological equivalent of the old maxim that the same causes produce the same effects. In the opah, we find, unexpectedly, confirmation of our hypotheses on the ecological situations that underpin the evolution of endothermy. In the study of the opah's evolution, we may gain insight into the variety of thermoregulatory solutions that accompany such trends. Comparative physiology, broadly studied and understood, is full of unsuspected explanatory power.

Monday, 4 May 2015

Lines: on the experience of Baltimore

This is not a post about current events. I am not the voice you should be listening to for that. There are many excellent authors and social media activists of color (I suggest Sean Reed, Shaun King and DNLee as excellent places to start) who can provide a better view on the struggles that urban people of color face in the US and in academia.

This is a post about experiencing Baltimore the way most white academics will experience it: as an outsider dropping into one of the city's elite universities. It is a post about understanding how the social and geographic spaces of the city are structured to make you see only a tiny part of it, and to make you believe that part is most of the city. It is a post about how the stories about the rest of the city are controlled. It is a post about complicity in a system that wants to maintain the narrative that the salvation of Baltimore has to come in spite of the people that live there, not because of them. It is a post about the difficult feelings that those of us who came to love this most unloved of cities carry with us about that place, and about our place in it.
It is a post that does not always present me in the best light. It is a post that does not present Baltimore's elite universities in the best light. But if this week's events have shown anything, it is that we cannot, should not, accept narratives about Baltimore's institutions that paint them in a good light. Because what is left out of those paintings is odious. 

I moved to Baltimore to do my PhD at Johns Hopkins Medical School in 2007. Before I have even left the UK, I was being warned about the city. "Have you seen the Wire?" was to become a refrain I would hear continuously over the next five years. When flat hunting, (as I wouldn't have a car), I limited my search to place within walking distance of the Hopkins shuttle route. But even then, there were caveats: "not North Avenue", "Don't live near the medical school". I was being taught the rudiments of the geography of Hopkins Baltimore.
When I got to my little apartment in Mount Vernon, next to a hip sushi restaurant and on the same block as the city's two main gay bars, I found I could see the medical school from my apartment. The first day I headed to work, I couldn't figure out where to get the shuttle. So I walked to campus. Down monument street. Under I 83 (through a fenced in parking lot, as there was no path). Past what I would later learn was the infamous Downtown Baltimore Supermax. Past abandoned buildings, school playing fields, housing projects, emergency clinics and bailbondsmen. Towards Hopkins medical school. I was uncomfortable. My years of living in London told me this wasn't an entirely safe neighborhood. And, to be honest, I had never encountered that level of dilapidation and poverty in London. But I made it to work. I found my department. And I was instantly told not to tell anyone I had walked to work, or they would freak out. And certainly never to do it again. You'd have thought I had walked through a mine field.
As the semester wore on, I began to notice other lines. Such as that no one at Hopkins knew how the city buses worked. We all used the Hopkins shuttles and went only were they went. Or we drove. I began to notice that the people behind the reception desks, or the people cleaning the office, pushing the carts, doing security, were black. And the people in the offices white. I began to wonder about riding a shuttle emblazoned with the Hopkins logo through deprived East Baltimore towards the Campus. I noticed that the words Kennedy and Krieger were lit up at night on the tallest building on campus, in the middle of the poorly lit streets of east Baltimore. I noticed, when I finally took a city bus to the party district of Fells Point, that everyone on the streets was black until you got to three blocks from the waterfront. Then suddenly, lily white.

The narratives that students and faculty told about Baltimore were stories of fear. There is almost a hazing of new arrivals. You're told where not to walk, where not to go. You're told where is not safe after dark. You're told of all the muggings and the murders (even if, when you finally look up the statistics, you realise that affluent whites are not at all the victims of Baltimore's crime problem). And it seeps into your skin.

When my mother came to visit, I got her a map. I drew lines on it, delineating a small area from Mount Vernon to the inner harbor. "Don't go north of here (north avenue), South of here (Federal hill), West of here (Lexington market), East of here (I 83)". I had learnt the geography of Baltimore quite well. Better, in fact, than I knew

A few months after I arrived, I missed the bus again. I tried once more to walk to work. Nothing had happened to me in all my time in the city. But as I reached I 83, my anxiety reached epic levels. I began to  have difficulty putting one foot in front of the other. Every inch of my being screamed for me to turn back, and head to the safety of the shuttle. I did.

That moment was a turning point. I realized that if I was going to live in the city, I had to fight the narrative I was being given. I moved closer to campus, and got to know the nice bits of East Baltimore better. But there were still lines. I never went North of Campus. I never went West of MLK.

A few years into my graduate program, I stood on the roof of one of the Hopkins parking lots and looked north. When I had gotten to Baltimore, the abandoned housing had reached up to that building. Now there were two blocks of bare ground in every direction. New lines being drawn in the cities divided geography.

I grew to love Baltimore. I met my husband and some of my best friends there. But in five years living in that city, three of which were within a bock of the Caroline Street projects, and two local schools, I never made friends with any of the city's African American residents. The bars and restaurants and cultural institutions that I love so much catered to that semi transient, mostly white, population that moved there for school or work, and left when they had kids.

And here's the thing: the city that people like us lived in is nothing like the city that most of Baltimore's population live in. Yet ours is deemed "economically important". And I know full well that that economic importance is used to justify the police activities in Baltimore. After all, how will Hopkins and UMD attract top talent to a city without a couple of craft cocktail bars?

And we can't accept that. My lifestyle in Baltimore ought not, must not be used to justify the violent oppression of those whom the city has ignored and mistreated. Fixing Baltimore must primarily fix the city for the majority of its population. Those of us who've lived there must recognise that, and put our experience of Baltimore aside. When we tell people about how hip and cool Fells Point and Canton are, when we talk about all the festivals, when we discuss the city as though the tiny portion of it we know is all the city, we are complicit in a narrative that wants to erase the reality of the city for most of its population. And that erasure, as we have seen, is more than rhetorical.