Sunday, June 23, 2013

The Living Dead: Darwin's finches and museums.

“Darwin’s finches are dull to look at, not only in their orderly ranks in museum trays, but also when they hop about the ground or perch in the trees of the Galapagos, making dull unmusical noises.”
(David Lack 1947)

I have seen thousands of Darwin’s finches hopping about in the wild and handled many hundreds of them from capture in mist nets to release back into nature – surely something that only a few hundred human beings have every done. So why should I feel awe when faced by 168 of them arrayed before me in their orderly ranks in museum trays? Surely I shouldn’t – and yet that is precisely the feeling I had when handling collections in the Harvard University Museum of Comparative Zoology during the filming of a documentary about selection imposed by humans.

The Living Dead

Perhaps my awe stemmed from the fact that the museum where I work, the Redpath Museum at McGill University, does not have any Darwin’s finches – despite the fact that McGill was where Peter and Rosemary Grant started their celebrated studies and where I have worked on Darwin’s finches for more than a decade*.  Amazing but true – and the main reason is that the Galapagos National Park Service does not allow export of finches (or anything else for that matter). I can see why, of course – because otherwise every one of the tourists would want their own preserved finch to take home as a souvenir. Hell, I would want one too. But surely this shouldn’t apply – within reason – to scientists. In fact, old museum collections from before these draconian rules were put into place have yielded outstanding insights into what has happened to finches from an evolutionary and conservation perspective – as evidenced in this cool paper by Ken Petren. It seems to me that the value of museum collections, including new ones, is very high and the potential impact on finch populations in Galapagos is vanishingly small. In fact, I would bet that the number of Darwin’s finches killed by taxis driving on roads in Galapagos every year exceeds the number of Darwin’s finches in all of the world’s museum collections to date.

Or perhaps it was because the collection had some amazing specimens, including a lot of finches collected in 1929, some collected in 1891, and one that might have been collected before Darwin. As hard as that may be to believe, curator Jeremiah Trimble told me the one specimen came from the private collection of an individual who died around that time – and people certainly did visit the Galapagos for centuries before Darwin. Or maybe this finch saw Darwin back in 1835 and maybe just narrowly avoided a blast from his shotgun. Sadly, however, sufficient information to resolve its collection date and location does not exist for this specimen. It was also fascinating to see the early days of confusion regarding species identification (before David Lack finally convinced everyone in 1947) play themselves out in additions and crossings-out on yellowing bits of paper tied to the feet of finches who were born and died before World War II. Ah the good old days of Geospiza strenuaGeospiza nebulosa, and up to 67 others? In fact, a number of the specimens did not yet have the new (already more than a half-century old) established scientific names on them. And how cool was it to see those old English island names, some of which are so much cooler than the modern Spanish ones? Wouldn’t it be great to say I work on Indefatigable Island rather than the mundane Santa Cruz Island?

Beak diversity in the seed eating ground finches

Or perhaps it was just because museums – particularly old ones – have the aura of mystery about them that, while not replacing the excitement of seeing wild animals doing their thing in nature, augments and expands our sense of wonder and discovery. Perhaps I might – simply in the course of rummaging through these simultaneously sad and yet somehow hopeful rows of feathers and beaks with their vacantly staring cotton eyes – find some new species or have some new realization. As you might imagine, this didn’t happen while looking at these well studied birds. Personal discoveries did, however, happen several times while browsing the public displays. Check out this sampling, starting with my own initially exciting thoughts and then any cold hard reality that came later courtesy of that killjoy Google.

1. The spookfish “has two corneal openings in each eye and uses tiny mirrors to see what is above and below at the same time.” What the f***? I had no idea. How did that evolve? And this was just one fish among a number of others that I did know about but hadn’t seen in the flesh, even in jars: the gulper eel with a mouth many times larger than its body, the tripod fish that stands high above the sediment on absurdly long and stiff fins, and many more. (Google later informed me that the brownsnout spookfish is indeed the only fish with mirrors in its eyes. In addition, the spookfish group as a whole is the same as the amazing barreleye fishes, which I already knew about but still haven’t seen in the flesh. Barreleyes are absolutely amazing  – check out this NGS video. And you can see a tripod fish in action here.).

Gulper eel

2. How about the Cotton Pygmy Goose? We normally think of geese as big, certainly bigger than ducks. So I was rather shocked to be browsing at random along those old-school museum style rows and rows of bird specimens mounted in glass cases and labeled with nothing more than a name and a location. Heightening the effect, this goose was, probably coincidentally, mounted alongside an Oriole that was almost as big. No kidding, I even have the picture to prove it. I had no idea such a thing existed. Why should one goose evolve to be so tiny when all other geese are so much bigger? (Google notes that the Cotton Pygmy Goose is actually a duck – however, it is still the smallest waterfowl in the world, so it remains pretty cool.). 

Death match or epic rap battle? Maroon Oriole v. Cotton Pygmy Goose

3. And then I saw the incredibly colorful and beautiful Tangara tanagers – another amazing example of sexual selection driving extravagant colors – or is it? I read in the text beside the display that the sexes in this group are identical, whereas most other traits that evolved through sexual selection are more exaggerated in one sex (usually males) than the other. So either sexual selection is driving male color and females are simply being dragged along genetically (they do share many of the same genes after all) or they are used for species recognition (but are these birds really so clueless as to need this much color divergence) or maybe it is somehow naturally selected (but why would it be so different – seemingly at random – among species)? I suspect that this topic has been well studied but, at that the moment standing in front of that display, it was fun to make the “discovery” myself. (Limited success on Google suggests that the topic actually hasn’t studied in much detail.)

Tangara Tanagers - a mystery to me.

And on and on and on – one amazing critter after another, a reasonable number of which were totally new to me. Although none of these things were my discoveries in the real sense, they still felt like it in the moment. (Of course, none of these things were discovered by their European “discoverers” either – having been seen by indigenous people long before.) When I get home I can’t wait to kick my kids’ butts in our dinner game “what did I learn today that was new”, I can’t wait. Until then, I just have to say:

"Darwin’s finches are exciting to look at, not only when they hop about the ground or perch in the trees of the Galapagos, but also in their orderly ranks in museum trays, making no noises whatsoever.” (Andrew Hendry 2013)


For some of our work on Darwin's finches, look here.


Lest it seem I am disparaging the Redpath Museum and aggrandizing the MCZ, I would note the latter’s great pride in their Laborador Duck, one of about 40 in the world and “one of the museum’s great treasures.” The truth is that the Redpath Museum also has a Labrador Duck, albeit not a male. Our duck even graced the cover of a book about the quest to see all 40+ specimens - probably because, while not beautiful, it has a certain je ne sais quoi.

The Labrador Duck outside my office in the Redpath Museum, McGill University.

Friday, June 7, 2013

Academic dispersal

My name is Ben Haller.  I was a graduate student once, but I have reached my next life stage.  It is time to disperse.  During my juvenile stage, I worked on my PhD with Andrew at McGill; protected from predators, and optimally oxygenated as he fanned his nest, I flourished and grew.  But now I have hatched; I passed my defense on June 3rd, moved from Montreal to New York on June 4th, and submitted my final thesis on June 6th.  Now it’s time for me to start foraging for myself.

My thesis, "The role of heterogeneity in adaptation and speciation", is still grinding its way through McGill’s bureaucracy, but I’ve posted it online at the link given.  At 309 pages, it’s a bit of a long read, so I’ll give a quick summary here!

Chapter 1 is a broad introduction to foundational concepts, ranging from adaptation and fitness landscapes to gene flow, reproductive isolation, and magic traits.  One of the key ideas presented is the idea of “squashed stabilizing selection”, a combination of stabilizing selection and negative frequency-dependent selection (Fig. 1).

Figure 1. Types of selection: (a) directional, (b) stabilizing, (c) stabilizing and directional, (d) disruptive, and (e) “squashed stabilizing selection”. Top panels show the fitness function: fitness as a function of phenotype. Bottom panels show the effect on a population’s phenotypic distribution, before (solid line) and after (dotted line) selection.  See thesis for details.

Chapter 2, “Solving the paradox of stasis: Squashed stabilizing selection and the limits of detection”, is currently in revision at Evolution.  In it, I use an individual-based model to show various reasons why stabilizing selection might be difficult to detect even when it’s present, perhaps explaining the low rate of detection of stabilizing selection in Kingsolver et al. (2001).  This might help to resolve the long-standing “paradox of stasis”, since it suggests that stabilizing selection might be common in nature despite its infrequent detection.  Furthermore, my results suggest that squashed stabilizing selection might be quite common in nature, which might be quite important in explaining patterns of standing genetic variation and speciation (Fig. 2).

Figure 2. Absolute frequency histograms of linear selection gradients, β, and quadratic selection gradients, γ, observed for the modeled population.  White bar areas represent non-significant selection, black bar areas represent significant selection.  The left column summarizes model realizations without competition, showing that stabilizing selection is detected much more frequently than disruptive selection in that scenario.  The right column summarizes model realizations with negative frequency-dependent intraspecific competition, showing that disruptive selection is more commonly detected in that scenario. Overall, significant selection is rarely detected, as in studies in natural populations.

Chapter 3, “Evolutionary branching in complex landscapes”, is in press now at the American Naturalist.  It uses an individual-based model to examine the effects of complex spatial environmental heterogeneity on evolutionary branching in asexual populations.  Among other results, we find a novel “refugium effect” that promotes branching in complex landscapes that combine steep gradients and patchy heterogeneity (Fig. 3).
Figure 3. A complexly heterogeneous landscape. In the steep gradient on the right side of the landscape (blue), refugia are generated by the spatially continuous patchiness (green).  These refugia can provide evolutionary stepping-stones that promote adaptation to the harsh conditions of the gradient, which might otherwise be too extreme to allow evolutionary branching to occur.  This “refugium effect” appears to promote branching in complexly heterogeneous landscapes.

Chapter 4, “A tale of two morphs: Modeling plant-pollinator interactions, reproductive isolation, and local adaptation in parapatry”, is currently in review at Evolution.  It examines the idea that heterostyly, floral syndrome that involves two different floral morphs with different, and reciprocal, reproductive organ positions, might allow reproductive isolation to develop between parapatric populations, promoting adaptive divergence and speciation (Fig. 4).  We show that this outcome does appear plausible, but that other interesting outcomes can also occur, including strongly asymmetric gene flow that might promote the development of dioecy from heterostyly.

Figure 4. An illustration of the hypothesized mechanism of reproductive isolation between populations of heterostylous plants, as a result of the combination of precise pollen transfer and reciprocal herkogamy.  Differential organ positioning between the populations is the result of adaptation to different local pollinators, and results in decreased pollen flow between the differently adapted flowers.

Chapter 5 presents some concluding remarks and a discussion of future research directions.  I use a flowchart to show how the preceding chapters fit together into an overall conceptual framework (Fig. 5).

Figure 5. A flowchart depicting the chain of causation that propagates heterogeneity upward from its initial ecological causes (squashed stabilizing selection and environmental heterogeneity) into heterogeneity among individuals, populations, and species.

My defense went pretty smoothly, all things considered.  I was quite nervous when I started talking – so nervous that people in the audience could tell I was nervous, which I can usually conceal!  But I settled in, and except for some difficult questions from one member of the committee, I felt fairly confident through most of it.  As Andrew told me repeatedly in the days before my defense, there really isn’t anything to worry about; if you’re not ready to defend, your advisor or your committee or your thesis examiners will tell you so.  By the time you get the green light to defend, you’re ready.  So don’t sweat it.  I’ve heard some people say that they actually enjoyed their defense, and were sad when it was over; I can’t say that I shared that feeling, though!

So what’s next?  I’ll be starting a postdoc in Montpellier this fall, working with Luis-Miguel Chevin at CEFE/CNRS, assuming I can convince the French government to issue me a visa.  We’re interested in looking at questions having to do with G matrices, multidimensional niche spaces, phenotypic plasticity, and lots of other cool stuff.  Stay tuned for details!  Will I fall prey to selection against migrants, providing a cautionary tale to those contemplating their own dispersals?  Or will I survive, and reproduce my ideas, showing that gene flow can have positive effects on adaptive divergence in changing environments?  Will I reach reproductive maturity, and start spawning new graduate students of my own?  Or will senescence take its toll, as my papers collect dust but not citations, and potential mate-collaborators leave me for more dominant scientists?  Only time will tell!

Until the fall, I’m more or less homeless; my wife and I plan to road-trip around the U.S., visiting friends and going to the Evolution 2013 conference in Snowbird, Utah.  Maybe I’ll see you there!

Canyonlands National Park in Utah, not so very far from Snowbird.  If you attend Evolution 2013, take some extra days (or weeks!), rent a car, and see the Southwest!
(Photo credit: Ben Haller)

Thursday, June 6, 2013

Carnival of Evolution #60

Carnival of Evolution #60 is now up!  Our contribution this month is from Hendry Lab member Kiyoko Gotanda, making us all envious with her adventures in the Galápagos.  As usual, there’s a wide variety of other nifty entries about evolution, so check it out!

The theme this month was 60th anniversaries, since it’s Carnival #60.  2013 is also the 60th anniversary of the discovery of the structure of DNA by Watson, Crick, and Franklin, so...