Wednesday, February 25, 2015

Incorporating animal mass mortality events in ecology and evolutionary biology

[ This post is by Samuel Fey, Stephanie Carlson, and Adam Siepielski; I am just putting it up.  –B. ]

Many thanks to Andrew for the invitation to write a post on our recent article published in the January 27 issue of PNAS on recent shifts in the occurrence, magnitude, and cause of animal mass mortality events. We thought we would use this opportunity to write about the motivations for this study, our basic findings, and how we hope this study improves our ability to better understand the ecological and evolutionary importance of large animal die-offs.


Fig. 1.  A sunfish and largemouth bass mass mortality event (MME) following a severe winter on Wintergreen Lake, Michigan.  Photo: Gary Mittelbach.

We conceived of this project after reading and listening to a series of media stories on several different animal mass mortality events (MMEs). Such media coverage, whether documenting the death of thousands of birds or a large fish die-off (Fig. 1), understandably attracts attention from readers and listeners. While the circumstances surrounding such events seem largely idiosyncratic, one similarity in how such events were reported is that they are rarely placed into any larger context. As such, we were surprised to learn that no quantitative synthesis of MMEs across animal taxa existed. Thus began the process of combing the scientific literature to generate a database that we hoped could shed light on how the frequency, magnitude, and causes of MMEs have changed through time.

Years later, after reading thousands of morbid accounts of animal morbidity, and with the support of a large research team, we finally analyzed the patterns present in our database (Fig. 2). Briefly, our data suggested that (1) the frequency of large animal die-offs has been increasing through time; (2) that the magnitude of events has been increasing for birds, fishes, and marine invertebrates, invariant for mammals, and has been decreasing in magnitude for amphibians and reptiles; and (3) that events caused by multiple stressors, biotoxicity, and disease have been increasing most rapidly through time.



Fig. 2.  Changes in MME magnitudes through time.  (Click for a larger view.)

Lest we give the impression that this effort represents a perfect approach to understanding the true dynamics of animal die-offs, we try to be as clear as possible in our paper about the limitations surrounding such a synthetic approach. Documenting trends in the frequency of events raises the question of detecting an “epidemic” versus “an epidemic of awareness”. Understanding trends in causes is additionally complicated by methodological improvements allowing greater detection of certain causes. For example, techniques to detect the occurrence of disease as a cause of death have advanced rapidly. Additionally, large animal die-offs reported in the peer-reviewed literature represent only a fraction of the actual events that are reported by state or federal agencies and media organizations, which themselves represent a fraction of events observed by any human anywhere. These factors mean that we do not know the true frequency of MMEs in nature.


Fig. 3.  MMEs most frequently occurred in aquatic ecosystems, where stressors such as dessication contributed to causing MMEs. Photo: Adam Siepielski.

Despite these limitations, we believe that collecting the best available data on such events, and analyzing patterns in these events to the best of our ability, was a worthwhile endeavor. Clearly, there is a need for an improved understanding of mortality events intermediate in scale between background mortality (e.g., a house cat eating a few red-winged blackbirds) and species-level extinctions. This paper represents an early step toward establishing this research program, so many important questions remain unanswered: What does it mean that the magnitudes of large animal die-offs have been increasing for certain taxa but decreasing for others? What is the relationship between large animal die-offs and human-induced changes to the planet at local and global scales? Do the patterns of animal die-offs we found represent an early signal of greater ecological consequences from such human-induced changes?

Although our focus was primarily on the demographic effects of MMEs, the occurrence of these events may also have considerable consequences for microevolutionary processes.  For example, removal of 90% or more of a population may generate extremely strong survival selection and thus the potential for rapid evolution. At the same time, however, such strong selection, combined with the resulting small number of survivors, may place populations at risk of local extinction through demographic stochasticity. Even if an evolutionary-rescue-type scenario occurs, there may be a cost to such adaptation if the MME is a one-time event. As a result, any adaptive evolution could actually be deleterious if the phenotype favored by the MME event is maladaptive once conditions return to “normal”. On the other hand, it may be that such large-scale mortality events do not typically favor any particular phenotype. We simply do not know.

It’s our (possibly naïve) hope that publishing this paper will lead to three outcomes: (1) improved data collection, (2) improved sharing of existing resources on animal MMEs, and (3) generation of interest in the importance of rare events on ecological and evolutionary dynamics. We note that animals are of course not the only organisms subject to MMEs. Whether or not other groups display the kinds of trends we documented is presently unknown.

Given the surprising nature of the shifts in the patterns surrounding MMEs, especially the trends in magnitudes, an adequate research program is needed to better understand and monitor such events. Yet, our database shows that the proportion of an animal population that is affected by such large die-offs – perhaps the single most important metric for contextualizing such events – was reported in only about 10% of all studies. In addition to encouraging better data collection, we also hope to help centralize the collection of data on animal mass mortality events by government agencies, media organizations, and citizen scientists to gain additional insight into the mechanisms underlying these events. Ultimately, we hope that this paper is one of many steps towards better understanding the ecological and evolutionary causes and consequences of rare demographic events.

Tuesday, February 17, 2015

How to fly without wings?



In the continuing spirit of recent “how to” posts on this blog (see previous post), it is timely to answer another pressing question. Today we will discuss “How to fly without wings?”. Humanity has been fascinated by this question for very long indeed – likely even longer than the question of how to get into grad school. Although entering grad school might be a first step towards learning to fly.

Various ways to fly without wings have been proposed. An obvious solution is to make wings. This idea appeared early on; in Greek mythology, for example, we have the story of Icarus, who made wings of wax and feathers. Sadly, when he flew too close to the sun the wax melted, and Icarus fell into the ocean and drowned. Nice try, Icarus – better learn how to swim first.
 
Landscape with the Fall of Icarus, c. 1558, by my favourite painter, Pieter Brueghel de Oude. Icarus is falling into the ocean (bottom right) with wings of feathers secured with wax. The local farmers, shepherds, and fishermen are not impressed by the way Icarus has compromised his evolutionary fitness.
Icarus’ failure reminds us that, gravity being what it is, it is hard to fly without wings without compromising your evolutionary fitness. More generally, it can be tricky to disperse efficiently when you are not very mobile. Studies on natural populations often speculate about the means that dispersal-limited organisms might have used to reach remote places such as inselbergs, islands, or crater lakes, or how such organisms managed to spread across vast geographical ranges. Very often it is argued that transport by birds must have been involved. Alternatively, remote places might have been colonised by good dispersers, and dispersal limitation might only have evolved secondarily. Since good dispersers may carry the genetic material of bad dispersers, it might not even take terribly long for poorly-dispersing ecotypes to evolve. So for Icarus to disperse more effectively, it might have been sufficient to find a partner that did have wings – Nike, the Greek winged goddess of victory, would have been a good choice at the time – and to produce a lot of offspring. Provided that Nike’s functional wing genes were dominant, at least some of their offspring might have been able to fly, thereby spreading Icarus’ genes. But since Icarus never met Mendel nor Nike, and since Greek mythology did not cast any other potential partners with functional wings (the Gorgon sisters being less than desirable mates), things unfortunately did not work out for him.

Still, it does seem a plausible mechanism in nature, as featured in this week’s issue of Molecular Ecology for the salt-marsh beetle Pogonus chalceus, the favourite pet of my colleagues Steven Van Belleghem and Frederik Hendrickx at Ghent University. Steven and Frederik reconstructed the evolutionary history of mtIdh, a gene associated with wing-size polymorphism in P. chalceus. Long-winged individuals (homozygous for the long-winged allele) are able to fly, but short-winged individuals (homozygous for the short-winged allele) are not. Still, the short-winged allele (let’s call it the Icarus allele), which Steven and Frederik found to have evolved only once, has now spread over the whole of Atlantic and Mediterranean Europe, a vast area for such a tiny beetle. This colonisation seemed to have happened relatively rapidly by means of a selective sweep – an evolutionary process that figuratively gives wings to your genes, especially when favoured by selection. Exactly how this evolutionary shift happened is a bit of a mystery, but it is clear that short-winged beetles have not made the same mistake as Icarus. In addition to occasional rides on avian taxis, genetic mechanisms involving long-winged individuals transporting Icarus alleles might have sped up the process.

A) The ancestral long-winged and derived short-winged ecotype of the salt-marsh beetle in their respective non-tidal and tidal habitat. As shown in the picture, these habitat types are sometimes in very close proximity. B) Bayesian mtIdh gene tree covering nearly the entire species range, with lineages associated with the long-winged and short-winged ecotype in red and blue, respectively. C) Distribution of sampled long-winged (in red) and short-winged (in blue) populations in Europe.

Interestingly, these two ecotypes of the salt-marsh beetle are sometimes found in very close proximity (10–20 m) in sympatric mosaics. Short-winged populations live in tidal marshes near the shore, while long-winged individuals tend to avoid that habitat, preferring areas that are more inland. Since the tide comes in twice a day, and because flying is always an option when you have fully developed wings, flying is presumably what long-winged individuals do when their feet get wet. In contrast, there is no escape for the short-winged individuals upon inundation. But since tidal inundations only last six hours, short-wings just trap an air bubble and stay submerged, waiting for better times. This difference in tactics automatically induces partial reproductive isolation between the two types – making wings a magic trait. So, while occasional hybridisation and a selective sweep might be responsible for the rapid spread of the Icarus allele at the regional scale, ecological mechanisms might locally discourage hybridisation, promoting the divergence between short-and long-winged populations.

Steven and Frederik conclude that the adaptive genetic variation underlying the local evolution of short- and long-winged populations has an allopatric origin, confirming that allopatric phases may be important at early stages of speciation with gene flow. But what I believe makes this story even more unique is that the salt marsh beetle system is old enough that we can observe parallel evolution of an adaptive phenotype (the short-winged ecotype), yet young enough that we can trace the evolutionary history back to the original mutation (which seems to have occurred no more than 0.047–0.165 million years ago). Such a comprehensive view on both the origin and the spread of a gene associated with adaptation and ecological speciation is rare indeed. Let’s hope this convinces Icarus to apply for grad school.



The full story:





The news and views:


Tuesday, February 10, 2015

How to Get Into Graduate School


I am often asked by undergraduate students for advice about how to get into graduate school. In the continuing spirit of recent “how to” posts on this blog (listed at the end of this post), it seems timely to collect these thoughts in one place. I will start with the obvious stuff, where I nevertheless hope to provide some novel insights, and I will then move to the less obvious, but perhaps just as important, ideas.

1. Grades

Let’s get this obvious one out of the way first. Good grades will, of course, help in a variety of contexts, most obviously in getting scholarships/fellowships (which, sadly, are largely based on such things) and in getting chosen by admissions committees for internal funding at universities. (Here I am talking about grades in classes, not standardized tests, although the latter can also matter in some cases – this is country/university/department-specific.) For students with exceptionally good grades, getting into graduate school is rather easy and, although the suggestions below will help even such people, this post is mainly intended for the students who have less-than-stellar grades. The reality is that good grades is not a perfect predictor of success in graduate school and, indeed, many outstanding graduate students had mediocre grades as undergraduates. While not suggesting I was “outstanding” in graduate school, I provide my transcripts below as evidence that someone with very poor grades in their early undergraduate career can get into graduate school. (My grades were much better in the last two years of undergrad, which I am sure helped.) In short, strive for good grades but, if you don’t get them it isn’t a death knell for your graduate school aspirations.

My undergrad transcript from a period when I was having way too much fun.
2. Scholarships/fellowships

Monetary constraints mean that professors take fewer students than they would like. As a result, obtaining a scholarship/fellowship that covers your salary/tuition/fees will give you have a huge advantage. In fact, you will pretty much have your pick of the litter when the professor doesn’t have to worry about these issues. Success in getting a scholarship/fellowship depends mostly on grades (but also on the following two points): hence, if you have good grades, you should apply for every decent scholarship/fellowship you can find (often times with the help of your proposed supervisor). (Note that deadlines for applications are often far earlier than you might image, nearly a year in advance of when you would start graduate school – so check the options as early as you can.) In my experience, success mostly comes from programs in your home country. For instance, I have had students with support from SENACYT (Panama), CONACYT (Mexico), CONICYT (Chile), CONCYTEC (Peru), CAPES (Brazil), SENESCYT (Ecuador), NSF (USA), FQRNT (Quebec), and NSERC (Canada). A number of other options exist based on various foundations, companies, or organizations. It is impossible to over-stress how beneficial scholarships/fellowships can be – they evaporate the financial worries, which are often otherwise paramount.

3. Research experience

A much better indicator of success in graduate school is research experience. Thus, make sure you engage in serious research as an undergraduate. Having done so shows you have an interest and ability to do research and it will (hopefully) get you a good letter of recommendation from a professor. Like good grades, this piece of advice might seem obvious: however, I do have something novel to say about it. Too much research experience (working in many labs) is perhaps not optimal unless you have something to show for it. If you bounce around through a bunch of short positions in research labs without publishing anything from the work, it suggests: (1) you can’t stick to any particular thing (you are a research tourist), (2) you can’t see anything through to completion (you are a research tourist), and (3) you don’t know what you want to do (you are a research tourist). Thus, research experience is critical but best when sustained in one or a few labs and – even better – when accompanied by publication success. (Note also that publications in peer-reviewed journals are vastly more important than conference presentations, posters, and pretty much anything else in this context.)

4. Publications

Relatively few students publish as undergraduates – yet some do. If you are one of those few, then you have a huge jump on the competition – even if they have better grades. So how to succeed in doing so? First, seek out a research lab that has a history of undergraduates being authors on papers, ideally as first author. Second, discuss your hope in publishing from the outset of your meetings with the professor (hopefully they bring it up before you have to). Third, carefully follow the suggestions and advice and prescriptions of your research mentor (the prof and the postdoc or grad student with whom you work) as to how to proceed. Note that publishing your work takes vastly longer than you might expect, so you need to get started early, work hard and enthusiastically, and progress efficiently and rapidly. Of course, it is ideal to have a paper accepted before applying for graduate school but having something submitted is the next best thing. (Note that the specific journal doesn’t matter as an undergrad – open access such as PLoS ONE is fine.) Given the time involved, it is important to get involved in research BEFORE your final year – or stay an additional year to focus on research.


5. Contact your hoped-for supervisor

It is absolutely essential to contact your hoped-for graduate supervisor(s) long before the application deadline. Start a conversation with them about research possibilities and administrative hurdles, volunteer in their lab (if local), and stick with them if you don’t get in on your first try. Most supervisors will start to feel a personal responsibility for a student that persists in their interest and will work harder and harder to get that student a position. Indeed, I suspect that personal experience and sustained interaction with a proposed supervisor is the most critical determinant of admission to graduate school apart from having a research publication. Here are some further ideas. When you contact potential supervisors (and you should definitely contact a number of them), DO NOT use a generic email. It is essential that the supervisor think that you are contacting them specifically because you want to work with them – not that you are shot-gunning the faculty lists of universities. Multiple times, I have been discussing students that I hope to accept with another prof, and the prof has said “Oh, that students has also applied to work with me.” Awkward.) Of course, some copy/pasting of text between emails to different supervisors will save time but DO make sure the font is consistent through the email – otherwise it is clear you are copy/pasting, and you are not only shopping, but you are sloppy to boot. DO have some ideas for research but also be flexible. In many cases, professors have funding for particular projects and are much more likely to accept a student who is willing to work in that area (of course, the student should bring novel perspectives to that project).

6. Meet your supervisor in person

Email (keep emailing until they respond) and skype and letters are great starting points but most profs will want to meet prospective students in person. Sometimes universities or departments pay for this (at Ivy League schools, for example) and sometimes the professor will pay. If none of this is suggested, however, and the prospects are looking good (the prof seems genuinely interested), find a way to set up an in person meeting, even if you have to travel there on your own dime. If you get the position, the trip will pay for itself many times over (and the prof will feel guilty if he/she doesn’t accept you) and, if you don’t get the position, at least you will have an interesting trip somewhere new. I won’t provide any advice on how to act on such trips, except to say that you should be enthusiastic but not overbearing.

7. Don’t be picky

If you don’t have stellar grades and lack a publication, you can still be successful if you don’t restrict yourself to a particular location or research topic. Particular places/supervisors/projects are in high demand and, without grades and publications, you are unlikely to be competitive for them. Instead, focus on smaller schools in what might seem like less appealing places (I won’t list any here but I am sure you can think of some – and it is critical to remember that the professor is much more important than the institution in which they work). The competition for positions in such situations will be much lower and profs will be much more willing to look beyond grades and publications, especially if the student is clearly interested and motivated. As for projects, you obviously don’t want to work on something you dislike but, beyond that, the key is to establish your research credentials and get some publications – then you can be more picky in the future. Master’s degrees can be optimal in such cases.

8. Seek out new professors

Here is one trick that, in combination with the previous two points, can tip the balance in your favor. In fact, this strategy has worked for a number of students to whom I have suggested it. New professors generally have big plans and good money (start-up funds) and are anxious to get their research going but, at the same time, are not yet on the radar of most students looking for supervisors. These profs really need to get their lab populated and don’t have the same calibre of applicants as do established researchers (who also often lack flexible funds, such as start-up). Also, by new profs, I mean the newer the better. Indeed, the very best tactic is to contact professors WHO HAVE BEEN HIRED BUT HAVE NOT YET STARTED THEIR POSITION – sometimes they aren’t even listed on the departmental webpages. (Often times you have to find these people by calling the department or by word of mouth when talking to other people at the university.) These profs will likely have few or no applicants, will have most of their funds unspent, and will be at the peak of their motivation to get rolling.

In closing

Those are my suggestions for how to get into graduate school. I hope they help. Yet I need to close with the two most important pieces of advice. The second-most important is Do not give up! Unless you have good grades, getting in graduate school can be a slog. However, if you follow the above advice, you will eventually succeed. I know of many instances where a student did not get a position in one year, but stuck with it and eventually succeeded, through some combination of a new publication, a new scholarship/fellowship, or a growing sense of guilt/responsibility/investment on the part of a professor.

This leaves the most important piece of advice for last – perhaps you actually don’t want to go to graduate school. Graduate school is an immense amount of work – just read PhD comics if you want to get a taste of it – and it can be very stressful. Moreover, continuing in academia or, more generally, getting a job in your chosen field at the level for which you will be qualified will be even more difficult than getting into graduate school. Thus, you should go to graduate school for the right reasons. One of those reasons might (paradoxically) be “I simply want to play around doing research for a while.” In this case, the stress decreases a bit because it doesn’t matter too much how well you do and you don’t care so much if you don’t get a great position in your field. (Of course, this is the worst reason from the perspective of your supervisor – so note that I am not endorsing it.) Another reason is that a career in research is what you really, really want to do with your life. In this case, you will have to work very hard, and success isn’t guaranteed – so proceed with caution and try to have a Plan B. Yet, as far as I am concerned, research – especially in academia – is the best possible job one can have except perhaps for things such as professional fisherman or professional rock climber or successful artist or acclaimed musician. Either way, you had better stop reading blogs and get to work!

See http://rccblog.com/2011/03/04/grad-school/


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Some final small points: The wording of your communications with potential supervisors can be very important. Here are some suggestions for avoiding pitfalls.

Don’t talk about how “world class” the institution or department is – a sort of institution sycophancy. The person you are contacting has their own opinion about the quality of their institution and you can’t win either way. If you say it is world class and the prof thinks it isn’t, then he/she will think you are pandering. If the prof thinks it is world class, then he/she doesn’t need you telling them this. Moreover, the prof wants to think you are interested in working with them rather than you simply want a degree from the institution. (And, of course, the prof is much more important than the institution anyway – at least from the position of a grad student.)

Be careful in talking about how wonderful the professor is – a more traditional sort of sycophancy. This makes most profs uncomfortable. If you are contacting them, then you obviously have a high opinion of their research and so saying this is just redundant. Moreover, most profs want their students to be collaborators rather than minions and so would rather, when possible, not establish a severe hierarchy. Of course, considerable variation exists in how individual profs feel about this.

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Previous posts in this "How to" series

4.     How to choose a journal (+ part 2)

Thursday, February 5, 2015

Just so! How the finch got it's beak.


While some might think the greatest challenge in science is to find an explanation for a particular phenomenon, I would argue that an even greater challenge is to discern from among many reasonable possibilities, which explanation is the correct one. That is, the problem isn’t so much “problems with no solutions” but rather “problems with too many solutions.” A recent trip to Galapagos and a recent paper on zebras have prompted me to ruminate on this topic.

At the most basic level, ADAPTATION is an obvious, and usually safe, one-size-fits-all solution to the problem of understanding variation in organismal traits. Other solutions, such as drift and constraint, are also possible but pale in importance – as I argued in an earlier post. Beyond saying particular differences reflect adaptation, however, we often seek to infer the specific environmental feature driving adaptation. In some cases, this driving feature is obvious: the beaks of Darwin’s finches are the result of adaptation to different food types. In many other cases, the specific force generating natural selection is harder to establish, a point made strongly and cogently by Endler (1986), Wade and Kalisz (1990), and MacColl (2012). Stated another way, a particular trait value in a particular population is almost certainly the result of adaptation – but adaptation to what? Different foods? Different predators? Different parasites? Different abiotic conditions? And which foods, which predators, which parasites, and which abiotic conditions? Thus, the specific selective reason for adaptation of particular organismal traits is often a problem with too many solutions.*

How the zebra got its stripes

Zebras in Krueger National Park, South Africa. Photo A. Hendry.
Classically, zebra stripes were thought to have evolved as an optimal illusion that confuses predators such as lions. This solution is what we all learned as children, and it makes good and obvious sense. No need to look any further. Yet other hypotheses have been suggested. One that has received considerable recent attention is parasite avoidance. Egri et al. (2012) placed similar-shaped but differently-colored models out in nature and found that biting flies were less likely to approach the striped models than the non-striped models. A third hypothesis is that alternating dark and light bands cause differential heating across the skin that generates eddies of air that have a cooling effect. In cases like this, where one problem has multiple solutions, each camp tends to entrench and generate further support for their pet idea rather than stepping back and attempting a test that might formally discriminate among the potential solutions. The paper that partly motivate this post did just that. Larison et al. (2015) examined the relationship among zebra populations between banding patterns and predators (lions), parasites (flies), and temperature. Non-existent correlations for the first two predictors and a strong correlation for the third predictor generates tips the balance in favor of temperature as the driving force behind the evolution of zebra stripes. Of course, I doubt the other hypotheses will die – at least not right away.

From Larison et al.

How the stickleback lost its armor

Marine threespine stickleback colonized freshwater watersheds thousands of times following the retreat of Pleistocene glaciers. Each time they did so, they evolved a dramatic reduction in defensive armor – especially the bony plates on their sides, but also in the size of their pelvis and their dorsal and pelvic spines. Moreover, these evolutionary changes can occur very quickly, such as when humans introduce marine fish into freshwater, eliminate freshwater stickleback thus allowing marine fish to re-invade, or trap marine fish in freshwater. The genetic basis of a number of these changes is well known, but the specific environmental (selective) reason is not. First, the amount of armor in a freshwater population is strongly associated with the resident predators, suggesting that release from the even more intense marine predation is the primary reason for the loss of armor in fresh water. (Even here, uncertainty exists as to which predators – birds, fish, or invertebrates – are the most important.) Second, the amount of armor sometimes correlates strongly with ionic concentrations in fresh water, suggesting that the loss of armor results from limitations in the raw materials needed to build armor. Other ideas abound, including the recent suggestion that armor is too heavy for the low-density medium of fresh water. To date, none of these hypotheses have been strongly excluded from consideration.

Differences in armor plating between marine (top) and freshwater (bottom) stickleback. The image is from Cuvier and modified by D. Kingsley (I found it here)

How the tropics got so speciose

Problems with too many solutions exist not only in evolutionary biology, but also in ecology. For instance, many hypotheses have been suggested for why species richness is higher in the tropics; candidate solutions include increased evolutionary speed (e.g., shorter generation times), fewer disturbances (e.g., a lack of continental glaciers), larger areas provide more opportunities for isolation, and so on. The same explosion of hypotheses attends other ecological phenomena, such as why Atlantic cod populations have not recovered despite 20 years without fishing (e.g., seal predation, Allee effects during breeding, life-history evolution) and why snowshoe hare and lemming populations cycle (e.g., predators, food limitation, stress, life history changes). Interestingly, although these phenomena are “ecological,” many of the proposed solutions are evolutionary.)

One of these hangs on the wall of my office.

How the finch got its beak

This brings me to Galapagos and its finches. More generally, I want to ask how/why beaks evolved. The evolution of this trait was no small thing – bird beaks bear little resemblance to dinosaur teeth. How and why did this change happen? It is surely adaptive, but what was the specific selective force driving the change? Perhaps the most widely accepted solution is that beaks dramatically reduce weight for a flying animal, just as do their hollow bones. (Yet bats have teeth, and some beaks are rather heavy.) Another solution is that beaks were particularly well-suited for eating seeds. (Yet seeds were around for a long, long time before beaks evolved, and many animals that do not have beaks eat seeds.) Yet another is that beaks are so adaptable that a lineage with beaks would be more likely to persist and diversify – the “key innovation” solution. I recently had an epiphany stemming from personal experience that leads me to suggest yet another solution to the evolution of beaks. To illustrate where this epiphany started, I must digress for a moment.

The (really big) beak of the finch - a large-beaked ground finch (Geospiza magnirostris) from Santa Cruz Island. Photo A.Hendry
I take very good care of my teeth. I brush – hard and long – twice a day. I floss religiously once a day – vigorously. And it seemed to work. I don’t think I had a single cavity for the first 20+ years of my life – not one. Yet it has recently all gone to pot. Now I probably have 15 fillings, most of them in the last 5 years. The funny thing is that I tend to notice incipient cavities when I am in the Galapagos, because I get closer to the mirror there than I do at home. At home, I have a counter between me and the mirror and so I never see my teeth closely: not so in Galapagos, where counters aren’t present and sinks are tiny. Last year I noticed some brown smudges on my teeth, which turned out – on my return – to indeed be cavities. This year I noticed some more, and while stewing from the immediate frustration that resulted, I walked out to where Kiyoko, Diana, and Luis were discussing finch beaks. Bang – epiphany.

Tooth decay can’t be stopped, even in modern humans, who are aware of the problem and combat it with the best technologies/tools and the greatest incentives. (How the hell did the dental industry convince employers to offer such good insurance when the same is not true for vision?). Indeed, before these technologies, tools, and incentives, humans suffered horribly from tooth decay. Pretty much any forensic anthropology display at any museum shows numerous instances of horrible abscesses, worn teeth, and missing teeth. Yet even these pre-modern humans knew that tooth decay was a bad thing (some cleaned their teeth) and tried to prevent/fix it. Coincidentally, here at McGill, we have evidence of the earliest dental intervention in history, in an Egyptian mummy housed in our Redpath Museum. We also have display a display of teeth that a street-corner dentist had removed, sort of a “Bad teeth? I can get rid of ‘em” advertisement.

The same problem must attend non-human animals, which do not have the same foresight nor technologies. Such animals should have frequent dental problems that can cause death through systemic infection or starvation. Thus, tooth decay must surely have reduced the fitness of many animals in nature.** Several arguments might be leveled against this hypothesis. First, non-human animals might not live long enough to get tooth decay – but some do live a long time and tooth decay can occur early in life. Second, tooth decay in humans might be somewhat modern problem that evolved after the development of processed sugars – but tooth decay was also prevalent before such sugars. Third, tooth decay might well predate processed sugars but might be due to our high-carbohydrate diet – but other animals also have such diets. Fourth, the ancestor of birds likely replaced its teeth as do most lizards - but this still represents a cost.
A captive lion with so many tooth problems that it "went off its feed" until given false teeth
I suppose you long ago saw where I was going with all this. BIRDS DON’T GET TOOTH DECAY. I propose that bird beaks evolved – at least in part – for this reason. Of course, I am not saying that avoidance of tooth decay was what started beak evolution – but it would certainly be a benefit that could accelerate the process once it started. It is also true that the fitness costs of tooth decay in the ancestor of birds might not have been that dramatic, since dinosaurs seemingly replaced their teeth gradually over their life. Yet this represents a cost of its own; and the signatures of tooth decay have been found in dinosaurs. So, why not?

In closing, I had better make clear that I am just having fun here by posing a “just-so” story for the evolution of bird beaks. This admission would seem to invite the criticism heaped on “the adaptationist programme” ever since Gould and Lewontin’s classic paper The Spandrels of SanMarco and the Panglossian Paradigm. Yet the truth is that just-so stories are always the starting point of any scientific explanation. By this I mean that one can’t possibly test an idea until one first has the idea, and ideas are always just-so stories until they are tested. Now we just need someone to recreate the transition between teeth and beaks so that we can turn our just-so stories into that’s-why stories.


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* Too many solutions to a problem might simply reflect the fact that the solution is multifarious; perhaps adaptation was simultaneously driven by multiple causal factors (predators AND parasites AND temperature) and the fact that different factors might be important in different locations (predators HERE ionic concentrations THERE and buoyancy OVER THERE).


** After writing this post, I looked up “tooth decay in wild animals” on the internet and most places asserted that they don’t get tooth decay – for a variety of reasons. Yet these were just assertions by pundits, not serious analyses by scientists. Then I found “A Literature Review of Dental Pathology and Aging byDental Means in Nondomestic Animals:Part II.” In this paper P.T. Robinson reports that gross examination of herbivores and carnivores from the wild review few cavities but criticizes these counts as biased. (I would add that, if my hypothesis is correct, they might well have died before a hunter could shoot them.) Robinson also reported that more detailed analyses reveal high levels in older individuals of some species, including 25% in old capuchin moneys. Regardless, animals are certainly known to have many dental problems of various sorts that would have the same effect. (Of course, beaks can also break.)

A lion with a broken tooth - from the Mara Predator Project.