Coco plums

Coco plums, originally uploaded by allspice1.

It's a hedge, it's a tree, it's a delicious edible fruit! It's a Coco Plum! Next to Palm and Pine it is also probably one of the most over-used obligatory plant-name/business-monikers in the tropics. Seriously, there's a resort in Belize, there's a Beach and Tennis Club in Key West, and an appliance store in Vermont (?) that all get higher google ranking than the wikipedia article about the plant.

But it shouldn't be so. It's a very nice plant, Chrysoblanus icaco. All over south Florida, every well-groomed native planting and every scrubby wetland ecosystem is bursting with this attractive, round-leaved native plant.

It has two varieties- an upland and a coastal type. In the picture above you can see the fruit of the upland type. This coco plum can become a bushy tree up to 10 feet tall, bearing dusky purple fruits and dark red growth tips. The coastal type, on the other hand, grows shorter, maybe three feet tall, its new growth blushing only slightly, and its fruits a soft white to pinkish-purple as below.



As my parents and I strolled through a coco plum corridor in Apoxee Park, I squeezed the soft white and pink fruits, wondering how they would taste, but uncertain if their attractive, smooth skin hid poison beneath. My grandmother came to visit us for Thanksgiving and encouraged me to taste the upland variety on another hike. The dark purple fruits turned out to be mostly seed, with a thin layer of white bread-like pulp, dry but sweet. It retreated from my bite, mashed into a shiny white mold of my front teeth. The dark eggplant skin was thick and a little rubbery. I found myself disappointed that I couldn't find more juice in them.

Powering the Cell: Mitochondria

Yay cell biology!

Leviticus

Spur-throated Grasshopper, originally uploaded by OakleyOriginals.

Leviticus 11 is a chapter of Hebrew law dealing with what is and is not permissible to eat as meat. God prohibits eating of pigs, shellfish, birds of prey, lizards, etc. These animals do not fit the cleanness requirements of God's law, and so Israel is not to consume them. Insects are on the list too (vs. 20):

"All flying insects that walk on all fours are to be detestable to you."

Putting aside for a moment the anatomical inaccuracy of saying that insects "walk on all fours" (who really says "walks on all sixes" anyway?), the message is clear: don't eat bugs. But then there's an exception (vs. 21-23):

"There are, however, some winged creatures that walk on all fours that you may eat: those that have jointed legs for hopping on the ground. Of these you may eat any kind of locust, katydid, cricket or grasshopper. But all other winged creatures that have four legs you are to detest."

The Orthoptera are on the menu! The order Orthoptera includes grasshoppers, locusts, crickets, and katydids. Leviticus gives us the easiest sight ID characteristic for this order: jumping legs. If you want to be fancy you can call them "saltatorial" legs. Check out this handsome fellow in the photo above. Nice saltatorial legs, eh?

So, why are Orthopterans invited to dinner, but nobody else from Insecta? This is a difficult question. Some say that they are hygienic, less likely to carry parasites than other insects. They are good, meaty insects too, nutritious. Some say that they aren't as close to the ground because they hop, and so they are cleaner. Others say that they are clean because they are exclusively herbivorous. Others remember that locusts are a major agricultural pest problem in the near east, and in some years the locust swarms would blot out the sun and consume every fruit, leaf, and stick in their path, leaving only the locusts themselves to be consumed by the devastated farmers.

Personally, I like thinking of the Orthoptera as the skilled musicians of the insect world. A vast majority of the Orthoptera chirp, sing, drum, or rattle to call their mates. Few other insects make such pleasing music. Perhaps the singers are invited to dinner to remind the Israelites about their role as praisers of God, commanded to make a joyful noise to him who gives life to all the creatures that swarm on the ground.

Hippoboscidae

Jelenja uš, originally uploaded by natalija2006.

I went for a hike along the Allegheny Front Trail this Sunday and I got lost. Not really badly lost, just frustrated lost. The-directions-say-ignore-trail-so-I-ignore-trail-here-right? lost. As I was bushwhacking my way back to the trail from one of my unfortunate detours, I felt a slight pinch at my neck. My hand found a little critter sucking on my delicious blood- a deer ked.

Deer keds belong to the family Hippoboscidae, a very special family of parasitic flies. They have stout dark hairs on their bodies and long legs that curl themselves around your finger. Their wings are fine and diaphanous. What is most shocking about Hippoboscids is just how flat they are. I tried to squish the little blood-thief that I found on my neck, but he just wouldn't squish. I couldn't make him any flatter than he already was.

Deer keds typically spend their early life flying around looking for a nice, juicy host deer to suck on. Once they find one, they use their prehensile feet to nestle themselves into the deer's fur. Their wings aren't necessary anymore, so they break them off and settle down. You can see one wing gone in the picture of the Hippoboscid above - perhaps he fell off while he was still trying to get comfortable on his chosen deer. Deer keds find love on their deer host, and little deer keds are birthed shortly thereafter.

The female deer ked does not lay eggs like most insects. Instead she nurtures a single larva at a time in her abdomen, waiting until it is nearly full-grown before she releases it. Deer ked reproduction is not unlike our own in this respect. They have an organ that can only be described as a "uterus," and glands that can only be described as "milk" glands, with which they feed the larva until it is big enough to pupate. The mother deer ked then releases the larva and it drops to the ground where it immediately begins the transformation into an adult by pupating. No activity is apparent during the pupal stage. The little brown capsule of the puparium, however, hides profound changes. In the puparium, the deer ked goes from a legless, eyeless, featureless white bag of goo to a hairy, strong flier with excellent eyesight and a vampiric drive. Eventually the adult deer ked emerges from its protective puparium and flies off to find its own nice, juicy deer.

The life cycle of the deer ked reminds me a lot of our own. We are cared for by our mothers for years, then released to the world that sometimes expects us to immediately begin functioning as an adult. But all of us need a period of pupation. Time to change, to grow, to transition from the old way of life to the new way. In some way, every period of our life is probably a time to pupate and prepare for the next phase.

Reflex bleeding

Today I spent most of the day at a friend's wedding. It was a rare sunny, warm October day, and the beetles were swarming. Harmonia axyridis, to be exact: ladybugs from Asia, hit-men imported to take care of aphids and scale insects plaguing many crops here in the US. Unfortunately, these efficient aphid-killers proved to be real goons-- indiscriminately killing their own ladybird-kind and other beneficial insects. In addition, H. axyridis likes to overwinter in our houses, amassing in hoards under eaves and in crevices. They also bite. They're not nice bugs.

One of the other delightful tricks of H. axyridis (and other ladybeetles) is something called reflex bleeding. When something scary happens to the ladybeetle, such as when a lovely girl in white sits upon a little Harmonia beetle hidden in the folds of her voluminous dress, the squeezed beetle panics. The beetle tears open specialized weak spots in its cuticle, allowing its yellow-orange hemolymph (blood) to bubble out in a little droplet. This defensive secretion, in addition to making an unsightly orange stain on a white dress, will release a bitter chemical and a noxious odor.

Sometimes I too bleed uncontrollably. A little thing can set me off and before I know it I'm pouring out bitter chemicals and a noxious odor. It can't be helped. Is the burst of ugly emotions that I experience --like the ladybeetle's reflex bleeding-- meant to protect me from being eaten by an even uglier fate?

Photo by Flickr user Ombrosoparacloucycle, licensed for re-use under a Creative Commons license.

Roach reflexes

I've told you about the spectacle that is the Great Insect Fair Cockroach Races. Roaches are impressive runners. Apparently the fastest roach ever recorded sprinted at an amazing 3.4 miles per hour, which, when you're only 2 inches long, is lickety-split.

Perhaps you have had the surreal experience of being sure that you have stamped on an offending cockroach, only to find that he has Houdini'd his way out from under your shoe and is now across the room and disappearing under your fridge. How is it- you ask yourself- that roach-kind has invented teleportation?

Roaches, it turns out, have mastered the art of escape not with magic, but with fast reflexes.

Cockroaches are characterized by the presence of two appendages called cerci (SIR-see, singular cercus) on their last abdominal segment (read: butt). In many species, the cerci are covered with delicate sensory hairs for chemoreception or mechanoreception and act kind of like antennae for the rear end of the insect. The cerci of cockroaches are exceptionally sensitive. They are sensitive enough to pick up the tiny air currents created by your foot sweeping toward them threateningly. The sensitive cerci send a signal up the ventral nerve chord directly to the nerve center of the thorax controlling the roach's legs. Only three neurons stand between the cerci and the legs. Accordingly, the roach can react in less than 70 milliseconds. A blink of an eye is 300-400 milliseconds.

It is grace, is it not, that God gives cockroaches this kind of speed? They are universally hated and feared, constantly persecuted by stomping feet or chemical warfare. But at least the cockroach has been given the reflexes to escape from impending doom with near-clairvoyant speed.

Jet-propulsion

In a previous post I talked about how totally awesome and totally impossible it would be to be born with rocket-thrusters. As personally disappointing as this is, I take joy in the fact that many other animals are blessed with magnificently bizarre methods of locomotion.

Dragonfly larvae, for example. They are rather ugly brown critters that swim around in shallow ponds, catching small invertebrates and fish with an extensible bear-trap jaw, biding their time until they can emerge as adult dragonflies and take up their rightful place among the high-speed insect jewels in the sky.

Dragonfly larvae do not have paddle-like appendages for swimming under the water. They are not helpless, however, against predators. God, in his wisdom, has given them jet-propulsion. When chased, a dragonfly larva will suck water into its anus like a turkey-baster and then blast it out, propelling itself through the water with surprising speed. Yes, dragonfly larvae are equipped with their very own rectal rocket-thrusters.

If that wasn't awesome enough for you, the gills of dragonfly larvae are also housed within the rectum. Picture, for a moment, what a different life it would be to use your rectum for both jet-propulsion and breathing.

And now you know why I feel my heart rise into my throat when I study insects. There is something ludicrous everywhere you look.

Cockroach races

The Great Insect Fair was last weekend. As I do every year, I stood at the starting gate of the cockroach races and prayed that the cockroaches wouldn't escape as small children, their hands barely grasping the roach tubs, tried to pour their cockroaches into pvc-pipe tracks. Cockroaches, being non-liquid, typically do not pour well. And if you take your eyes off of them for a second, they will happily scurry out of the container and onto the child, causing shrieks and severe trauma. Then I would set out running after the fugitive, who, realizing I was behind him, would tuck himself under some child's foot or run between some mother's legs, sending a ripple of excitement out from the cockroach racing table. Executing a graceful volleyball dive, I would smack my hand on the cockroach's greasy forewings and pinch up the cockroach with a ferocity that startled cockroach-lovers. Captured again, the cockroaches looked sullen, but unharmed.

When mindful children and volunteers managed to dump the cockroaches into the race-track successfully, roach performance was mixed at best. At times the roaches performed like trained greyhounds, streaking through the pvc tunnel in 2 seconds or less. Other times, the roaches found the tunnel an ideal space for grooming or contemplation. As you might expect, they all run pretty fast when they get a whiff of freedom.

The cockroach races have a profound effect on the psyche of observers. People who would find themselves standing on a chair if a cockroach walked across their kitchen floor are picking their favorites to win, cheering like they had money riding on it. They feel kinship with the roach, like it is their own pet. Perhaps there is something delightful about watching any animal run. But as soon as the roach is running outside of the track, people instantaneously revert to their natural human hate reflex and cannot understand why people like me are willing to touch roaches with my bare hands.

By the end of the day my hands smell strongly of cockroaches, my voice is hoarse, and my feet are sore from standing. I go home and take a long shower and breathe in deeply the lack of anxiety as I throw my own cockroaches a few bits of fruit.

Limits of Adaptationism #3: What your momma gave you

Existing genetic variation

Natural selection can only work on existing genetic variation. There is a gene pool, and out of it survivors are selected to reproduce for the next generation's gene pool, but no one who isn't already in the pool can be invited in.

In other words, on your birthday, your momma gave you some genes - dimples, a rear end the size of Milwaukee, maybe a mustache. Bummer- you really wanted rocket thrusters. But your momma could only give you genes that she already has, likewise your daddy couldn't pull rocket thrusters out of the air to give to you.

Some things, like rocket thrusters, would be totally sweet to have, but let's face it- you're not going to get them anytime soon. Fish might really wish that they had lungs in addition to gills, but they're not going to get them anytime soon. So it's foolish to ask "why don't fish have lungs?" or "why can't people fly?"

Adaptationism would cause us to answer these questions by looking for reasons why it wouldn't be advantageous to have rocket thrusters. But clearly, personal rocket-assisted flight would be advantageous. Going back to the insect antennae- we might expect that having foldable, elbowed antennae would be advantageous to any insect. But not everyone's got the genetic wherewithal to make elbowed antennae. The reason why a certain insect has a certain kind of antennae might not be related to what is most advantageous for that insect, but rather, what that insect's momma gave them.

Limits of Adaptationism #2: Genetic constraints

Linked Genes: Pleitropy and Epistasis

Genetics is seldom a straight path from gene to protein to mustache. At every step, there can be modification and multiple effects. Pleitropy is when a single gene has an effect on multiple traits. For our mustache example, a gene regulating secondary sexual characteristics (the changes in men and women's bodies that occur during the advent of adolescence, such as facial hair) can have an effect on hair produced all over the body. Generally, the more hirsute a person is, the more likely they are to have a mustache. Since there is no actual mustache-gene, and since hairlessness isn't necessarily selected for, we will see mustaches as long as there is positive selection for hair.

Epistasis is when the expression of one gene effects the expression of another gene. For example say there is a gene at the "hipster-ness" locus that has two alleles, "hipster" and "non-hipster." When an individual has the "hipster" allele, the expression of this gene will turn on the expression of other genes such as the genes for mustaches, non-prescription thick-rimmed glasses, androgynous hair styles, and appreciation of terrible indie-rock. Any one of those downstream traits may be driving the selection for the hipster allele. Even if the mustache is selected against, it is regulated by another gene that may be positively selected for some inscrutable reason.

In both of these examples when we ask "what for?" we cannot give a satisfactory answer, because the expression of a mustache isn't the real unit of selection. The mustache is linked to other traits that are undergoing selection and influencing the expression of mustaches, despite their unpopularity.

Limits of Adaptationism #1: Founder Effects

This is the first in our series examining the limits of adaptationism, where we will examine why teleological questions (asking "what for?") don't necessarily get us the right answers in biology.

Take for example a man with an elaborate mustache. What is a mustache for? We could come up with all kinds of wild functional explanations for why mustaches exist, but none of them truly convincing. We know that men without mustaches live very normal, if not happier lives, than men with mustaches. In this era of human biology, mustaches are selected against, and the men who grow mustaches are cursed by the necessity of shaving them if they want women-folk to like them. In localized hipster populations, this trend can be reversed, but let's just say for the sake of argument, that all women feel more or less like I do.

So the reason for mustaches isn't really clear. Adaptationism would assert that since it takes energy to produce and maintain a sweet 'stache, it must serve some purpose for the adult male human, otherwise it would have been lost from the population and men would be largely mustache-less. But what if adaptationism has led us down a rabbit-trail looking for reasons where they may not exist?

An alternative explanation for why mustaches exist may be a genetic constraint on natural selection known as the founder effect or legacy effect. Basically, you can't throw out all your starting material and start over when starting a new population. The population always has founders. Perhaps the founders of the male human population had facial hair on their upper lip. Perhaps this was because they were bigfoot or wookie-like creatures with a lot of fur anyway. Selection against large amounts of body hair has occurred over the evolution of male humanity, but because of the founder effect, it's going to take a lot to get rid of those mustache genes.

Similarly, the legacy effect is a constraint placed on selection now due to selection in the past. A couple centuries ago, mustaches were the hotness. Women felt they were manly, and preferentially mated with men who had mustaches over those who did not. Now we have a gene pool full of mustaches, and we can't really get rid of them due to the legacy of the age of mustache-rage.

So, the "what for?" question doesn't help us understand what mustaches are for, unless we ask what mustaches might have been for back in the evolutionary history of hairy men.

If we go back to our insect antennae, we may ask why certain insect taxa seem to have a particular style of antenna. The question may not have a functional answer, because the reason for different styles of antennae is buried far back in the evolutionary history of these bugs. Perhaps the founders of modern butterflies had knobbed antennae, and the founders of modern moths straight or plumose (mustache-like) antennae. The reason why their antennae diverged back in that day may be as simple as genetic drift or it may have had a functional meaning in those days, but today it seems to be the capricious whim of a God who likes knobby antennae.

Photo by Flickr user a4gpa licensed for re-use by Creative Commons license.

Limits of adaptationism

Yesterday we talked about the "why" of insect antennae. Why ask why?

When biologists ask "why" - they are usually asking for a functional "because." The question could be re-phrased as "what for?" This is a very old approach for understanding how biological things work. It assumes that there's a certain order to things, that organisms are a certain way for a reason. God, in his infinite wisdom, made them that way to be suited to their world.

William Paley talks a lot about this. He's the guy who came up with the watchmaker argument for the existence of God. This argument basically states that a watch is complex and contains a mechanism that works in a intricate way to keep time, so when we see a watch, we get a sense that it has purpose and design and therefore a designer. Living things like animals and plants are likewise complex and work in an intricate way to perform their tasks of survival and reproduction. Ergo, living things have design and have a designer. And it follows that the traits expressed by these living things should have a purpose in that design.

But what about traits of living things that seem to have no function? Are they just fanciful inventions of a whimsical God? Whimsy is not something I typically attribute to God. So perhaps there are other explanations. For the next several days we'll examine the limits of adaptationism - why we cannot always ask why and get a straight answer in biology.

Antennation

Insect antennae are sophisticated organs that can perform many functions for insects:

• Olfaction (smell)
• Gustation (taste)
• Mechanoreception (feeling)
• Hygroreception (humidity detection)
• Thermoreception (temperature)

Basically, antennae can do everything but see. They play powerfully in orientation of the insect in space; detecting wind speed and direction, the smell of pheromones in the air leading them to a mate, or the subtle vibration of prey below the bark of a tree. What is interesting to me is that antennae have so many different forms. Termites have simple moniliform antennae like tiny strings of tiny beads. Silkmoth and mosquito males have elaborate bipectinate plumose antennae. My small hive beetles have adorable club-shaped antennae which make them look like Mickey Mouse when they hold their antennae up. The antennae of house flies are two fat dangly bulbs with a single feather mounted at the top of each. The antennae of scarab beetles terminate in a fan-like array of delicate fingers called lamellae that can be spread open or closed tightly like a fist and tucked away into cavities under the insect's head. Dragonflies have nothing but two short bristles for antennae. Dizzying variety is the rule when it comes to antennal form. So why so many types? Does each of them correspond to some special life-style like insect leg types?


Question of the day:

Why are there so many types of insect antennae?

Answer:

Dunno.

No, seriously- we don't know why there are so many types of insect antennae. Generally, where olfaction is important, we find more elaborate or specialized antennae, such as those of male moths. Dragonflies, on the other hand, hunt primarily by sight, and thus may be forgiven for having simple and uninteresting antennae. Evolution seems to have favored divergence in most cases and convergence in a few like the elbowed antennae of weevils and ants. Beyond that, antennae are as diverse as the insects themselves. Family resemblance in the antennae is quite useful for classifying insects, but why scarab beetles have fancy lamellate fingers and small hive beetles small club-shaped antennae is rather a mystery.

Some questions in biology will always be easier to answer with "It's for decoration" or "Because that's how God made him." And perhaps in a sense, this is true- that God has seen fit to elevate diversity over uniformity, and style sometimes seems to trump function. But as we scientists study and search for a function for strange traits and find that they do, indeed, have a function, are we disappointed? On the contrary, when fascinating form and amazing function come together we get a new sort of joy- beyond the joy of beauty and the joy of a well-made machine. It is the joy of something that is, on all accounts, very good - just as the creator said it was.

Anthocyanin Crimson

I have been looking for words to express the red color of anthocyanins in fall leaves. The thesaurus gives me many delightful words for red such as the color of blood, bittersweet, bloodshot, blooming, blush, brick, burgundy, cardinal, carmine, cerise, cherry, chestnut, claret, copper, coral, crimson, dahlia, flaming, florid, flushed, fuchsia, garnet, geranium, glowing, healthy, inflamed, infrared, magenta, maroon, pink, puce, rose, roseate, rosy, rubicund, ruby, ruddy, rufescent, russet, rust, salmon, sanguine, scarlet, titian, vermilion, and wine - some of which (anyone heard of cerise?) are a bit obscure. Whatever you call it, red is definitely one of God's favorite colors, especially around fall.

Anthocyanins (an-though-SIGH-un-ins) are what makes fall leaves red. These pigments are produced in the leaves of deciduous trees as they transition to winter. The leaves will soon be lost, so the trees withdraw their nutrients and store them away as the leaves die off or senesce. Unlike carotenoids, which are present in the leaves throughout the year and are revealed by fading chlorophyll, anthocyanins are produced in the leaves as the leaves are dying.

But it seems illogical to use energy produce new compounds in a leaf that is already on its way out, right? This question has stumped scientists for a long while. They have proposed all kinds of interesting theories for why leaves produce anthocyanins in the fall. One theory that has recently stood out is that anthocyanins are protective compounds that keep the leaves on as long as possible to make sure the tree can suck all the nitrogen out before they fall. Anthocyanins, like carotenoids, are powerful antioxidants and could be protecting the leaves from oxidative stress. In addition, anthocyanins absorb UV and can act like a sunscreen to protect the leaf from light stress (and here I thought that trees couldn't get sunburned).

So the anthocyanin is like a shield detachment sent to cover the retreat of nutrients from the leaves. With anthocyanins, the leaves stay on longer and the tree can store away more nitrogen. But the anthocyanins still cost energy to produce, so trees that grow in nitrogen-rich conditions will be less red because the extra nitrogen that they get isn't worth the investment in the sunscreening anthocyanins. Trees that grow in nitrogen-poor conditions, on the other hand, will glow like red-hot embers as they try to protect as much of their nitrogen as they can.

Fall Colors

Fall is closing in on us rapidly. The past two days have been less sunny, more rainy, and the trees have just begun tinge yellow and red. My friend Katie texted me today and asked "What makes the leaves change colors in the fall?" I pondered how I would answer this in less than 160 characters, then wrote this text:

"The trees are withdrawing nutrients from the leaves before they shed them. When green chlorophyll is broken down you can see other colored pigments!"*

*yes, I am one of those obnoxious people who refuse to abbreviate in text messages. I have a keyboard and goshdarnit, I'm going to use it.

There's a little bit more to it than that, as you might imagine, but not much more. When the day length begins to shorten, the light to weaken, and the temperatures to drop, deciduous trees (trees that shed their leaves in the fall) pass through an important transition to survive the upcoming winter. In the warmer months, leaves are the solar collectors and energy factories of the trees, but in winter, the trees will retreat into a quiescent state of tightly clenched buds and bare stems, and their leaves will be unnecessary to their long winter sleep. Leaves will only make the trees more susceptible to damage in the coming snowfall anyway (see photo here of results of early October snowfall in central Pennsylvania last year). But the leaves represent a lot of energetic investment on the part of the plant, particularly nitrogen, which the tree will need to survive the winter ahead. So as the trees bundle up for winter they pull nutrients out of the leaves to store up for the winter.



Here's how it happens. In the beginning of the fall, trees will gradually shut off the production of chlorophyll, their green pigment and secret to their photosynthetic magic. The remaining chlorophyll and its accompanying photosystems in the leaf tissue will slowly be digested and the nitrogen-rich pieces sucked back into the trunk and roots of the tree. (Imagine the roots of a tree are a basement for sealing up canned goods to be eaten over the winter.) The vibrant green of chlorophyll fades from the leaf to reveal the bright yellows and oranges of carotenoid pigments, accessory pigments that harvest light much like chlorophyll but at a different wavelength. Carotenoids also protect the delicate chlorophyll from UV and oxidative damage and thus are really good for you too in things like carrots (something your mom always told you but you never really wanted to listen to).

Carotenoids are also highly attractive and earn sleepy little wooded hillsides seasonal fame for their spectacular colors every autumn. But now I really digress. Anyway, the bright carotenoids have been there in the leaf all along, helping with photosynthesis and protecting chlorophyll. These pigments are just more stable than chlorophyll, and will persist longer in the leaf after resources have been withdrawn in the fall.

Now, that's yellow and orange leaves explained. Check. But what about red? If you were anything like me in my first fall in the Northeast, you probably searched the forest floor for the brightest, most cheery red-colored leaf you could find, held it tightly in your little gloved hand and marveled at just how very red that leaf shined against the grey days ahead.

Red leaves are more complicated. Maybe we can talk about them tomorrow.

Photo by Flickr user mmwm, licensed for non-commercial use by Creative Commons License.

Water Activity

Today I measured water activity in my pollen substrates. I spent about half an hour with the AquaLab CX-2 in a food science lab near the Creamery, putting stuff into little plastic cups, loading them into the smooth black steel drawer where they fit snugly into a round opening, sliding the drawer closed and turning the instrument to "read," then waiting approximately 4 minutes per sample for the insistent beeping to notify me that my water activity measurement was finally ready.

"As you can see, taking the measurement is a trivial process," said the food scientist in a white lab coat. But the measurement of water activity is quite far from trivial when you consider its implications.

Water activity is a measurement of how much water is "available" in a substance. In technical terms, it's the partial pressure of water vapor in the headspace of a given substance- but let's talk about water "availability." What would this water be available for exactly?

I like to think of water activity a measurement of grooviness. Imagine your material is having a rave. There are lots of substances in attendance: sugars, lipids, proteins, inorganic compounds, organic compounds, water. Naturally, water is the life of the party and everyone wants to dance with it. In some materials, all the water is already locked into dancing with someone else at the party- some sugar or some random alcohol group or what have you. In other materials, someone forgot to invite the water so the party is lame and dry and no one is dancing with anyone. In materials like my pollen dough, the water is there, but only some of it is dancing with other attendees. So the water activity is measuring how much water present in the material is hanging around looking for someone to dance with. This water has a tendency to vaporize and hang out in the headspace or the air around the party, where it can be measured by the AquaLab CX-2 if you have 4 minutes to wait.

Water activity increases with water content, but also varies depending on the composition of the medium (whoever else it has to dance with), so the relationship between water activity and water content is seldom linear. Microbes like my yeast love water and will gladly cut a rug with that unoccupied water and have a grand old time. If there isn't enough water ready to dance, they'll leave the party. In fact, each microbial species has a threshold for water activity, below which they cannot grow. So this is why we measure water activity; it measures how much water is available -or ready to dance with microbes- while water content will only tell you how much water is there at the party.

My yeast seems to need a really groovy party to be happy. So far I have failed to see growth on pollen substrates with an A_w (fancy abbreviation for water activity) as much as 0.77, which should be close to the same as that of bee bread in the hive.

American Goldfinch

Today I have seen a handsome American Goldfinch (Carduelis tristis (L)) on my balcony feeder for the first time. He surprised me when I first saw him, small and unassuming in shape but bright big-bird yellow with black wings crossing his back and clashing with his yellow like crime scene tape. He's been visiting it frequently all day as I watch from the couch, alternately falling asleep, working, and wasting my afternoon. My Audubon guide says that American Goldfinches wait to pair up until late in the summer when tasty seeds tend to be more plentiful. Other species with broader diets are already busy parents, laying eggs and rearing multiple broods of chicks while the Goldfinches are still flocking around in big irresponsible groups.

This makes me smile. The goldfinches have their appointed time for relationship and parenthood, but it's later than the other birds' time. They flock together like anxious graduate students waiting to see how the seeds will shake out before they settle down and start that family. I wonder if my goldfinch has transitioned into family life or if he's still hanging out with all his yellow friends.

Photo by Flickr user Jason Means licensed for non-commercial use by Creative Commons.

Dissertation dump

I am an articulate person. This is a fact that I believe like I believe that I have brown curly hair and stand 5 feet 9 inches tall. I have always loved writing. I won a prize for a science essay in high school and collected cherished praises from every writing professor. In college, I was an English major before I was wooed away from words by the breathtaking beauty of the insect world. Before bugs, I used to stay up all night working on painfully beautiful critiques of medieval poets. Now I only pull all-nighters for insect collections, posing the shiny exoskeletons of dead insects on tiny black-enameled pins and snipping out labels printed in 2pt font on which you will find only the barest details, unpoetic epitaphs to be read by the tearless eyes of scientists behind magnifying glasses.

I am rapidly approaching the culmination of my PhD-seeking career in Entomology. It's called a dissertation. It's a document containing the justification for my existence for the past 4.5 years. If there were anything which really ought to be written well, this is it.

So why is it that when I mean to write something glowing with competence, clarity, and grace- I get something that sounds like an angry grasshopper bouncing on my keyboard? Choppy, unattractive prose flows from the cursor like a malicious force is confounding any ability to communicate that I once possessed.

Part of the problem is that there's too much there- too much going on at once and no good narrative structure to make it spread out on the page. Every sentence carries the burden every minute of the past 4.5 years like a freight train pulling a thousand cars at full speed into the station. There's no parsing it. It flashes by in a blur. Can I make it slow down just for a minute to write a few sentences? Let's hope so, friends. 'Cause if it's not the light at the end of the tunnel, it might be the train.