Hard boiled selection?

On Thursday June 18th I walked from my office to a corn field on the Saint Michael's College campus. Along the way I nearly tripped over two painted turtles in the middle of the gravel road used to truck food waste to our compost facilities.  After perhaps pointlessly returning the first one to the nearest pond I recognized that the second one was digging a hole to lay eggs.

When I got as far as the corn field I found a third turtle backed up to a freshly covered hole where I presume she had deposited her eggs.  No eggs were visible and I was not about to dig to confirm my hunch.  In my days as a summer camp nature study instructor I learned that unlike bird eggs that actually require turning, turtle eggs should not be turned over during incubation.  Developing turtles attach to the inside surface of their eggs and turning can harm the growing embryo.

I did confirm that the cornfield was quite attractive turtle nesting habitat.  As I skirted the edge of the plowed and planted field I encountered no fewer than 17 turtle nests.  With the exception of the nest that was being completed, each and every nest that I found had been plundered and generally only egg shells remained.  I found intact eggs that had been dug up from just one nest but I suspect that digging up alone may have been sufficient to destroy the developing turtles.

With brief research I learned that it is not unusual for more than 90% of painted turtle nests to be plundered.  Racoons and skunks are frequent predators of turtle nests.  At first blush one might consider that all of this nest plundering would damage the turtle population.   However, turtles can reproduce each year for between ten and twenty years so there are multiple opportunities for each female to contribute to the next generation.

It is worth noting that I have no real way of knowing how many intact nests I walked past.  It seems that these turtles all lay their eggs in a relatively short time window.  This strategy is sometimes called "predator dilution".  If there is a large number of simultaneously available nests, then the chances of one particular nest being plundered is reduced.  There would therefore be selective pressure on turtles to nest at the same time as their neighbors.  Genes that favored solo nesting would be rapidly eliminated because each solo nest would be the only available target for predators.

Supporting the predator dilution hypothesis would require some field work and experimentation.  I'd first need to confirm clutch synchrony in the population; seems a worthy excuse for a regular walk to the cornfield.  An experiment to confirm that clutch synchrony was protective of the nests would be easy to design if not to implement.  I have no desire to in any way interfere with nesting turtles, but an experiment with an inexpensive substitute might do the trick.  My fake turtle nests might consist of shallow nests dug along the corn field and seeded with chicken eggs.  If predators are being satiated by availability of eggs, then I'd expect proportionally fewer eaten eggs where I placed 20 nests and proportionally more consumed eggs where I placed just 1 or 2 nests.

As with any good experiment, we should entertain alternative hypotheses.  In this case, it may be that the availability of multiple nests of eggs may attract multiple predators on a feeding binge.  One version of this hypothesis is called "local enhancement".  Hungry predators are drawn to rich food sources by the presence of other predators actively feeding.  It's far easier for a vulture to spot a flock of feeding vultures than to spot a carcass from the sky.  The same may well be true for fake turtle nests.

I'd need to replicate the experiment, collect, and analyze the data.  This how scientists know what we know: experimentation, replication, and data analysis.  This particular piece of science will remain a thought experiment for now.  But one never knows; there may just be a Saint Michael's College student in need of a viable project and this may be just the thing.  At least I'll gather the data on clutch synchrony next year and perhaps be a little fitter as a result.

All images for this post were taken on using a cell phone camera.

An asteroid strike, dinosaur extinction, and a bench-top fossil dig.

I teach a weekly hands-on laboratory as part of my evolution course each Spring at Saint Michael's College in Vermont. Fossils are essential components of the evolutionary biologist's toolbox and I wanted an engaging way to look at fossils that would generate quantitative data for student lab reports.  I'm lucky to to have access to the college's modest fossil collection.  The collection includes some fascinating examples but does not lend itself to a particularly quantitative laboratory exercise.

Show-and-tell with fossils has it's place but I had a more comparative laboratory in mind.  I wanted students to experience the sense of discovery of a fossil dig, generate quantitative data, and have a comparative question to answer using real data.  Microfossils turned out to be the answer!

Where ever marine sediments accumulate, the hard parts of microscopic organisms also accumulate.  These microfossils tend to be drawn from diverse and unrelated groups but are studied as a single category because they are all small, and are extracted from mixed sediments using the same techniques.

There certainly are abundant marine sediments right under our campus in the Champlain Valley, but they are from a limited number of time periods.  My interest in working in sediments of diverse ages brought me to one of my favorite sources of specimens: Ebay!  A fossil dealer in England offered a collection of pre-sifted fossiliferous sediments in labeled vials.  The samples come from sediments spanning a more than 200 million years of deposition.

I purchased vials that came from before and after the KT boundary that marks the time in Earth's history when the dinosaurs disappeared in a geological blink of the eye.  While various hypotheses regarding dinosaur extinction have been tested, an asteroid strike near the Yucatan Peninsula in Mexico is supported by the overwhelming force of evidence.

Dinosaurs capture the imagination and the headlines, but most other groups of organisms on the planet suffered severe declines at the time the non-avian dinosaurs vanished.  Conveniently, microfossils are drawn from several groups of organisms and so we can reasonably expect a reduction in the number of species found in microfossil samples following the KT boundary.

My students picked through the small vials of sand to isolate and count microfossils using techniques developed by Charlie Drewes. They then counted the number of distinct types of fossil in each sample and measured a diversity index.  After repeating this procedure for each vial, they ran statistical analyses to determine whether there was, as predicted, a fall in the number of species and diversity detected following the KT boundary.

I'm happy to say that the new laboratory was a success and will become part of the regularly scheduled labs in the Evolution course.

Image source: http://commons.wikimedia.org/wiki/File:Mikrofossils_hg.jpg

Artificial selection: simulating rapid evolution on a spreadsheet.

I was rereading Richard Dawkins' The Blind Watchmaker recently and became interested in one of the analogies he used to illustrate natural selection and artificial selection.  The analogy he presented was that of a monkey poking at keys on a typewriter.The chances of the monkey producing a particular phrase are vanishingly small and the time needed to repeat the process until the correct phrase was randomly typed would exceed the lifetime of the monkey and indeed several generations of monkeys.

I have access to neither a monkey nor a typewriter so I settled upon MS Excel instead.  I instructed Excel to randomly plop letters in each of 8 cells to see if I could match an 8-letter word: "CharlesD".  Not surprisingly, I never found a match despite running several thousand iterations of my experiment.  It illustrates beautifully the idea that random evolution could never work.  Expecting several random mutations to spontaneously generate an organism with traits that fitted it for a particular set of environmental conditions is similarly unlikely.

But evolution is far from a random process.  Certainly mutations can be random, but the survival and reproduction of the resulting mutants is certainly non random. If several mutants are about average, better, or worse at catching prey and therefore surviving and reproducing, then those better suited to predation will survive, reproduce, and pass those superior mutant genes in greater numbers to the next generation.  This is the process of natural selection as outlined by Darwin and Wallace in the 19th century.

Artificial selection is rather like natural selection on steroids.  A plant or animal breeder can artificially select some desirable trait over several generations.  Each time a particular plant or animal better matches that trait, it will be selected as breeding stock.  This brought me to a second simulation. Again MS Excel plopped random letters in cells in a spreadsheet row, but checked the letters against the target phrase "CharlesD".  Any letters that matched the target phrase were placed in the next row and new random letters or 'mutations' were placed in other the remaining slots.  Every time a letter matched one from the target phrase, it was retained and passed onto the next row or 'generation'.

I found that in this simulation the phrase evolves to match the target phrase in a short number of repetitions; often fewer than 100 generations.  One such simulation is presented below.  The letters plopped into the phrase are just as random as the mutant letters in the first simulation I mentioned above.  The crucial difference is that the target letters are retained in successive generations as would be the case if a cattle breeder selected for higher butterfat content of milk over generations.

Try it using your own phrase in this simple MS Excel sheet.

An example that converged on the target in 30 generations:

	Target phrase:	C	H	A	R	L	E	S	D
generation
1		H	D	A	V	R	X	P	U
2		T	K	A	L	G	L	U	N
3		G	I	A	P	P	X	B	P
4		W	S	A	W	S	U	O	J
5		I	W	A	R	X	V	O	C
6		Q	R	A	R	K	V	O	Z
7		P	W	A	R	G	X	M	L
8		C	J	A	R	U	I	G	P
9		C	P	A	R	A	E	T	A
10		C	W	A	R	I	E	M	F
11		C	H	A	R	Y	E	T	Y
12		C	H	A	R	I	E	F	I
13		C	H	A	R	Q	E	L	B
14		C	H	A	R	Q	E	D	E
15		C	H	A	R	E	E	L	W
16		C	H	A	R	J	E	Y	J
17		C	H	A	R	X	E	S	D
18		C	H	A	R	Z	E	S	D
19		C	H	A	R	Z	E	S	D
20		C	H	A	R	I	E	S	D
21		C	H	A	R	E	E	S	D
22		C	H	A	R	J	E	S	D
23		C	H	A	R	H	E	S	D
24		C	H	A	R	O	E	S	D
25		C	H	A	R	Z	E	S	D
26		C	H	A	R	M	E	S	D
27		C	H	A	R	M	E	S	D
28		C	H	A	R	P	E	S	D
29		C	H	A	R	U	E	S	D
30		C	H	A	R	L	E	S	D

Like a bat out of.....my house

My children are truly wonderful young people and not particularly given to shrieks of panic.  So when all three screamed in unison this evening I took it seriously.  The cause of the hysteria was a large bat flying around the living room.  I had been working on the driveway and closed the garage doors when I was finished.  Evidently, the bat had flown through the garage and up from the basement into the house...where my children were waiting.

I suppose I could have called animal control and had them show up when they could.  They might search the house or use their knowledge and experience to come up with a solution? More likely they'd polietly tell me to grow up and open the doors.  Instead I decided to deal with the problem myself based on the potentially flawed logic that a reasonably well informed biologist could take care of a biological problem.  So I gathered my children in a bat-free room, closed the door and set to work.

The bat had come to rest in curtains and when I approached to open the windows he or she took off...like a bat out of...curtains?  As the bat flew in rapid circles I grabbed a tall narrow trash can and a lid.  I turned on all of the lights in the house to more easily track the bat, it's shadow, or reflection from room to room.  A second landing in a different curtain lead to a failed attempted capture.  After flying around the living room for at least 10 minutes he started to explore the rest of the house and found his way upstairs.  I closed as many bedroom doors as I could to narrow the options for both of us.

As I approached the only remaining bedroom door, the scared and exhausted bat came to rest on the top of the door frame - perfect!  Somewhere back in my lizard brain I remembered that bats need to drop to take flight so a container underneath seemed like a reasonable solution.  I brought the trashcan up underneath the bat and as soon as the rim made contact with the door frame the bat obligingly dropped in an attempt to fly once more.  I popped the lid on top.  As efficiently as I could, I brought can/lid/bat down stairs and out the front door.  I dumped the worn out bat on the grass near a tree and gave him all the space he could wish for.

So what take-home message should there be?  It's worth remembering that bats like any scared animal can bite and they do carry rabies.  Bat populations are dwindling in parts of the United States and Canada because of white-nose syndrome.  Avoiding direct contact by trying to kill a bat is good; releasing a live bat to consume lots of insect pests is good also.  The Humane Society offers advice on dealing with trapped bats. One piece that differed from my approach was to tilt the container towards a tree trunk so that the bat can climb high enough to drop and fly....good advice for the next time.  They also recommend thick gloves.  And if you are bitten??  Get medical treatment as soon as possible; untreated rabies is fatal.

Bat image is from Wikimedia Commons.

Burn baby burn

Fire in Camp Johnson; photograph courtesy of Peter Hope

Before proctoring my Evolution lab today I caught a whiff of the sweet smoky smell of burning leaves.  If I lived in a California wild-fire zone I might have worried.  Even in Vermont the smell might be cause for concern; we have had 9 days without rain and a pleasant week of sunshine.  The National Weather Service has advised against lighting fires and indeed there was a localized forest fire during the past few days.  My lack of concern is based upon some insider knowledge.  My colleague Peter Hope has been conspiring or should I say collaborating with a consultant, the military, and conservation biologists to burn some patches of sandplain forest for some time now and I knew that today was the big day.

Sandplain forests grew in much of Chittenden County Vermont before the area that is now the Saint Michael's College campus was cleared for farming by European settlers. The sandplains formed when rivers including the Winooski deposited sand and built deltas in Lake Vermont, and then the Champlain Sea.  As glaciers receded they dropped materials to the south forming a terminal morain that functioned like a dam containing the meltwaters from the glaciers forming what geologists call Lake Vermont.  A layer of finely ground 'rock flour' that settled from the melt water can still be found beneath what is now Lake Champlain.  The weight of glacial ice that was literally miles in thickness depressed the earth's crust in Vermont below sea level.  When the glaciers melted back as far as where the Saint Lawrence River mouth is today, sea water flowed in forming the Champlain Sea.  Eventually post-glacial rebound brought the Champlain Valley above sea level and the deltas were lifted above the water level.  Modern-day Lake Champlain is roughly 100 feet above sea level.

Because of the very sandy soil in these old deltas, the forests tend to be adapted to well-drained dry soils and would be expected to periodically burn following lightening strikes.  The pitch pine is a tree species example that is one step beyond fire tolerant and is actually fire dependent.  Pitch pine cones open only after fire and the seed can only grow when the organic matter layer on top of the soil is burned back to bare sand.  In the Gil Brook Natural area where fire is suppressed, we can see that the pitch pines are gradually dying out and being replaced by white pines.  Coincidentally, a patch of Gil Brook accidentally burned this week and it will indeed be interesting to see how this affects the vegetation there.

The planned burn in the sandplain forest in Camp Johnson this week was designed to burn off most of the organic layer and facilitate growth of the natural vegetation including pitch pines.  The 2013 burns are just the latest in a series of burns implemented to preserve the sandplain forest and perpetuate the heath-like vegetation that would have dominated this region before European settlement.

For a number of years, Saint Michael's College students enrolled in General Biology have sampled insects, trees, and plants in both Gil Brook and Camp Johnson.  These efforts were complimented by intensive sampling by students under the direction of Valerie Banschbach and Peter Hope last summer in the areas slated to be burned.  Post burn sampling will happen this summer and the Fall General Biology class will be the first set of students to sample from recently burned forest plots.  It's a lot of fun to work with students on real research questions during the course of regular classes!

Your child's first microscope (or a gift for your grade-school teacher)

This post can be summarized thus: Buy a used dissecting scope on Ebay.

Parents and grandparents love to purchase microscopes for their favorite children.  My parents did; and I did the same for my kids.  Perhaps we are motivated by the idea that we can stimulate interest in science?  Personally I like the motivation but not the potential result of a poor purchase choice.

Toy manufacturers market cheap plastic compound microscopes with poorly mounted optics and underpowered battery-operated light sources.  I think that these toys are truly junk and likely to lead to frustration rather than deep fascination for science.

Looking past the quality issue, the more fundamental issue is the choice of microscope type.  Compound microscopes magnify 100 or more times and are great for looking at the scales on a fly's wing mounted on a glass slide.  Light shines through the specimen and the more you magnify, the more light you need to see anything.  The maximum magnification on some of these scopes is often non functional as a result.  Only thin specimens or slices of specimens through which light can be transmitted will work.  I suspect that many kids starting out would rather look at the whole fly.  And by the way, could we skip the whole glass slide part?

This is where dissecting (AKA stereo or stereoscopic) microscopes come in.  A child or college professor can pop an insect, coin, or fossil onto a dish or piece of paper under a dissecting scope without slide mounting and get a good look in seconds.  Because they typically magnify in the 10 to 40 X range, you see the whole organism and can get by with room light or with a flashlight.  Chunky specimens like fingers and coins are fine because stereo scopes make use of reflected light.  My five-year-old daughter had no difficulty examining insects, twigs, and rocks using an old dissecting scope and natural light on a picnic table at a camp out last spring.  In fact she spend close to 2 hours hauling her spectacular finds out from rotting logs and proudly sharing the view with anyone and everyone near by.

Other big advantages of dissecting scopes include large depth of focus and deep working distance.  In other words, more parts of thick specimens will be in focus at one time than under a compound scope; and there is more room to place specimens between the lenses and the stage.  And I did mean 'lenses'; there are two aimed at slightly different angles resulting in a 3D view of your specimens.

So what might you purchase?  Some very nice stereo microscopes made in the 50s, 60s, and 70s by American Optical were in use in schools and colleges across the country and in many cases still are.  Many have found their way into the used market and are plentiful on Ebay.  Search for "American Optical forty" (photographed above) and expect to pay between $50 and $150.  My search revealed 8 today, and the number is low because I purchased 8 last week for an outreach program.  These scopes are heavy, stable, and durable.  They come with built-in lights and two levels of magnification.

Tweezers from your nearest pharmacy make great forceps (and with your new scope you can more readily and gently remove splinters).  Plastic lids from jars are a great substitute for Petri dishes and will protect your microscope from scratches.  Medicine droppers are worth having and usually come 2 on a card for under $4.  Need a plankton net?  Use a nylon stocking and a coat hanger.  Drop a baby food jar down into the foot and secure it with rubber bands around the neck.

If you find that your budding scientist is spending a lot of time on the microscope and getting serious about things, you could consider trading up......

You've got a lot a gall....

Wouldn't it be great if a teacher and students could study a plant, its herbivore, and the predators of the herbivore?  Ideally you'd want to study these three trophic layers of the system in a single class session, or perhaps two.  Of course, as an educator, you'd want all of this to happen very cheaply, or better yet, for free.

Warren G. Abrahamson, his colleagues, and a host of students have been working with just such a system for many years.  They have generously provided all of the tools necessary for teachers to share this system with their students.

Goldenrod species are found in most places in the United States and in many locations they are unwitting hosts to the goldenrod gall fly.  Female flies lay eggs into the growing tip of the goldenrod.  Chemicals released by the hatchling larva cause the plant to form a corky spherical gall about the diameter of a quarter coin.  The larva spends about 50 weeks in the gall feeding on plant tissue, growing, and pupating, before emerging as an adult to complete the life cycle.

Students in my evolution class collect a sample of about 250 galls during the first week of class in mid January.  For two years in a row now we have completed the task without the need for snowshoes.  We number and then measure the diameter of each gall using a plastic artist's templates designed for drawing circles of increasing diameters.  Next we carefully split the galls using pruning shears and use Dr. Abrahamson's online key to determine the outcome of the gall fly's efforts. I would say that the pruning shears are perhaps the most important tool for success with this research project; asking 20 students to cut hard spherical objects using knives might be a recipe for disaster.  As much as I respect and admire the work of the Saint Michael's College Rescue Crew, I'd rather not set myself up to need their services.

Gall fly larvae represent a high-protein meal when most other insects are underground.  A number of predators and parasitoids take advantage of the bounty.  Woodpeckers, chickadees, beetles, and wasps all partake in the fly larva feast.  In our most recent foray into the world of gall fly biology, we observed that already by January, 70% of the galls no longer housed gall fly larvae.

The entire sample of galls serves as a 'before predation' example; the subset that still contains viable fly larvae represents the 'after predation' survivors.  The data set is perfectly amenable to graphing using histograms and statistical analysis.

As predicted in the published literature, my students found that 2 bird species accounted for most of the larger galls, and many of the smaller galls hosted wasp rather than fly larvae.  The student data set shows strong evidence of stabilizing selection.  It seems that it is in this case better to be average than to be exceptionally large or small. 

By coincidence, my daughter's first-grade class used galls as a study system for life cycles and food webs during the same time period.  The first graders did not want to kill the larvae and so I was assigned to release them to 'the wild'.  The larvae sat in my car in a paper cup during a day when the temperature dipped to several degrees below freezing.  The larvae were as soft and squishy as when they were removed from the galls, despite the fact that my water bottle in the same car was frozen solid.  It was a nice illustration of the antifreeze properties of the larval tissue.

We will revisit the gall fly population on campus late in the semester to see if additional months of exposure to bird predation has further reduced the proportion of surviving flies. Dr Abrahanson's generosity in sharing what he has learned serves as an example to all of us academics studying our sometimes obscure topics.  We have each in our own way figured out how to wring data from all sorts of bizarre systems.  There are tricks that we have learned from colleagues or gleaned from conferences.  We should share these tips! 

The images used on this page are from Wikimedia Commons:
http://commons.wikimedia.org/wiki/File:SolidagoGall-AcheneSK.jpg 
http://commons.wikimedia.org/wiki/File:GoldenrodGallFlyLarva.jpg