Over-reviewed?

EP: Please submit original research articles for your presentations, not review papers.

Student X: What is a review paper?

EP: It is a summary of prior studies.

Student X: Why should we not pick them?

EP: Because they are summaries. The data are in the original studies – that is what I want you to focus on.

Student X: Submits review paper.

I have now had this conversation, and this result, more than once. So, why are my students picking reviews? And what does this have to do with eco-evolutionary dynamics when my class is on marine global change?

When considering these questions, I had a thought – maybe my students are picking reviews because there are so many out there. Perhaps a student choosing a paper at random has a relatively high likelihood of picking a review.

This reminded me of a question posed at the recent QCBS working group – is eco-evolutionary dynamics “over-reviewed?” This question stemmed from a recent flurry of reviews on the topic and the brief proposal that our working group supply yet another (we opted against). So I thought… if selecting at random, is an undergraduate student taking a course on eco-evolutionary dynamics more or less likely to select a review paper compared to a student taking a course on marine global change?

I did a bit of searching on Web of Science, and it turns out that reviews make up a larger proportion of papers on the topic of eco-evolutionary dynamics than on the topic of marine global change. For example, searches on “eco-evolutionary dynamics,” “niche construction,” “community genetics,” and “contemporary evolution” all independently yielded about 25% review papers (if papers categorized as “editorial material” are combined with papers categorized as “reviews”). Searches for common topics in marine global change, such as “coral bleaching,” “ocean acidification,” and “arctic warming” all independently yielded around 10% reviews.

So, it is unlikely my students are selecting at random. They are actively picking reviews – perhaps because reviews often present a more straightforward message than original research articles. And if the topic of my class was eco-evolutionary dynamics, they might be picking even more reviews. Of course, my quick-and-dirty analysis is admittedly imperfect. Many early research papers we would now consider to be eco-evolutionary dynamics, do not use one of the key words I searched. Nonetheless, 25% is a surprisingly high proportion.

So, is eco-evolutionary dynamics over-reviewed? Perhaps I will delve more deeply into that question next time. I have to get cracking on a paper on “the eco-evolutionary dynamics of marine global change.” It promises to be one heck of a review!

Eco-evolutionary dynamics in salmon

Empirical support for eco-evolutionary dynamics has emerged from several fish systems and a recent paper published in Heredity presents the case for diverse and strong effects in Pacific salmon (Carlson et al. 2011, Heredity 106(3): xxx-xxx). Several aspects of salmon biology make them amenable to the study of eco-evolutionary dynamics: they are philopatric (return to their natal sites to breed), anadromous (migrate between freshwater breeding and marine feeding grounds), and semelparous (die at the end of their first breeding season). Consequently, discrete populations can be subject to local selection pressures during their breeding season, presumably driving divergence in traits that can influence ecological processes. And such effects seem likely given their large adult body size and dense breeding populations that can change many features of the stream environment.

Building on earlier research that revealed the importance of water level and bears as sources of natural selection acting on breeding salmon, Carlson and colleagues (2011) explored the consequences of phenotypic change due to selection within a generation on salmon population dynamics, community interactions, and ecosystem processes. Despite a rash of recent studies documenting eco-evolutionary dynamics, little attention has been paid to the importance of this aspect of selection on ecological dynamics. Carlson and colleagues (2011) show how selection on body size simplifies age structure and strengthens cohort effects, which then alters population dynamics. They suggest two possibilities for how selection on salmon body size might then influence community interactions, namely through possible effects on bear energy stores (smaller salmon are less energetically rewarding, which might require increased foraging effort by bears) and aquatic insect community dynamics (smaller salmon dig shallower nests, which might differentially influence benthic invertebrates). Finally, the authors calculate the relative importance of selection (phenotypic shifts due size-dependent mortality) versus ecology (size-independent mortality) in determining the flux of salmon biomass across habitats. They report that selection can alter fluxes between habitats by up to 11% due to interannual variation in water level and up to 9% due to interannual variation in selection due to bears. The resulting combined effects of selection within a generation may have large cumulative effects on ecosystem processes. The authors speculate on such effects by comparing body size among nearby populations of salmon.

The authors thus conclude that phenotypic change within a generation due to selection influences ecological dynamics, and so should be considered within a complete eco-evolutionary framework. They also show that salmon are likely to be a good place to study eco-evolutionary dynamics.

Stephanie Carlson (Assistant Professor in the Department of Environmental Science, Policy, and Management, University of California, Berkeley)

Carlson, SM, Quinn, TP, and Hendry, AP. (2011). Eco-evolutionary dynamics in Pacific salmon. Heredity 106(3): xxx-xxx.

(http://www.nature.com/hdy/journal/vaop/ncurrent/pdf/hdy2010163a.pdf)

What did I learn today? Lessons from Leuven.

Andrew Hendry aghast at the apparent co-evolution of Belgian beers and glasses.

Every night at dinner, my family plays a game of “what did you learn that was new today.” Each of us has to come up with some new bit of knowledge, usually science-related, that emerged during the day. Often Aspen (7 years old) tells us about some new animal from a BBC video that we watched the night before. Usually Cedar (4 years old) tells us about how chameleons turn red when they are mad. She tells us this nearly every night and so it isn’t exactly new, but it is cool enough that we don’t mind. And then it comes to Heather or I. Sometimes we struggle to remember something new that we learned, which either means we knew a lot already or we didn’t pay much attention that day. This struggle has made me increasingly take mental notes of things that I learned on any given day to then relate to the family that night.

These past few days the task would have been easy. I have been attending a symposium on Eco-evolutionary dynamics, held at K.U. Leuven, Belgium. A host of talks from Belgians plus some visitors, as well as discussions in various restaurants and bars, has yielded a variety of cool new findings – new to me at least. For instance, I learned that only a few months of evolution in warm temperatures by previously cold-adapted Daphnia can make them perform as well – or better – in warm temperatures than Daphnia that had evolved in warm temperatures for centuries. I learned that the population size of southern elephant seals was probably upwards of one million individuals only a century ago. I learned that unrelated armoured catfish species, which have poison glands that deter consumption by predators, converge on similar color patterns in the same locations, presumably because this provides a more effective warning to predators (Mullerian mimicry). I learned that cuckoos, which lay their eggs in the nests of other birds, showed increasing convergence of egg shell color toward that of their host species (because the host would be less likely to reject the eggs) over the 20 years that a monk sampled nests in the early 20^th century. I learned that wolf spiders in Galapagos have independently evolved similar species in similar habitats on different islands. And so on and so on. Too bad I can’t spread these observations out and use them over a few weeks of family dinners.

But it wasn’t only science. I also learned that Belgian bars keep a specific glass for each of the dozens of Belgian beers they serve. It seems that each brewery has promoted – and provided – a signature glass that (presumably) best suits that beer. I am sceptical. Are they really trying to convince us that the co-evolution of beer and glass is so perfect that every brewery has discovered the best glass shape for their specific beer – and that this shape is different for each beer? Or would Westmalle Dubbel taste just as good – or better – in a Rochefort glass as in a Westmalle Dubbel glass? I doubt that the matching of beer to glass is really that critical. Maybe it is instead like sexual selection: the match tastes no better than a non-match but the chooser (us) thinks a match is somehow sexier than a non-match. So, with that in mind, my goal tonight is to buy four different beers, pour each into the four glasses corresponding to those beers, and then subject myself, Joost Raeymaekers, and Katja Rasanen to a blind 16-glass taste test. Here’s hoping we make it through the night.

Whisky Rescue

A wintery Mont St Hilaire is the location for the second Quebec Centre for Biodiversity Science (QCBS) workshop, this one on eco-evolutionary dynamics. A diverse group of ecologists and evolutionary biologists from south and north of the border met to argue and debate the new synthesis; when is it important, why is it important, how often? they cried. The ideas flowed almost as freely as the whisky, but by day 2 a new framework was emerging. Experiments for new data, analysis for new insights, and a synthesis to end all syntheses. One synthesis to rule them all!!!

An iconic example of eco-evolutionary dynamics is evolutionary rescue, the poorly understood means by which evolution can propel a population away from extinction. Few have considered the ecological consequences of evolutionary rescue, and fewer still, the community context in which these dynamics play out. The group will explore beyond genetic variation to also consider plasticity, niche construction, and evolutionary history. A new experimental model (marmite to the rescue) will be brought to bare (!) on the problem, and new theory to pierce the confusion.

By now the whisky fumes have penetrated the deeper parts of our muddled brains and we are staggering to the early hours of the late evening...Vellend aghast at East coast arrogance, Beisner aghast at the size of her glass, Yale obsessed with Bieber, Perry and Alewives...and a brand new H-index (how many degrees of separatation from Hutchinson)

Got to go, my whisky is getting lonely and my snowballs are getting cold. Andy Gonzalez signing off

More adventures in Speciation

As Andrew’s last post demonstrates, uncovering the primary mechanisms of speciation - barriers to gene exchange between populations - remains a topic of active debate, even among the most eminent researchers in the field. Part of this debate potentially, and perhaps paradoxically, is a result of the fact that the field was dominated by conceptual and theoretical contributions until the last decade which has seen an explosion of empirical research. The main conceptual mechanisms of speciation, measured as the accumulation of reproductive isolation, are rooted in sexual selection, ecological differences (i.e. natural selection) and physical isolation. Data from different systems often fit nicely into one of these three umbrellas, lending support to the original theories, but leave us scratching our heads to understand which mechanism(s) are THE main drivers of the process. Our latest paper,recently published in PLoS ONE (http://dx.plos.org/10.1371/journal.pone.0015659) suggests that rather than looking for a single winner, the answer may become clearer by closer integration. In collaboration with researchers from the University of Maine and Dalhousie University, we examined patterns of female mate choice and male mating success in Trinidadian guppies from nine populations in 4 different rivers.

Avid readers of this blog or anyone who has picked up a biology textbook, will be familiar with the guppies, as they are one of the few model organisms for studying adaptation in the wild. The guppy’s small size, agility, and freakishly high fecundity allowed it to colonize upstream sections of rivers above large waterfalls, unlike its larger, predatory neighbours. This sets the stage for a natural laboratory for observation and experimentation as upstream guppies have escaped to guppy heaven, banishing their cousins to the hell of a life of high mortality risks. But of course, what doesn’t kill you makes you stronger, and high-predation guppies have indeed adapted to their lives in hell allowing them to escape quickly, mature early, hide well, and limit their sexual colouration to remain as inconspicuous as possible. Their cousins above are not so careful or visually discreet. Males in particular are generally more colourful, possibly because females generally prefer to mate with colourful males. When these guys move or get flushed downstream, we know they suffer the consequences with reduced survival.

Since ecological and physical isolation has led to adaptive differences in multiple traits, one of which is a target of both mate choice and survival, the stage is set for speciation as far as has been documented in similar systems. Yet, evidence for reproductive isolation between guppy populations has so far been sparse and inconsistent. What we found is that while low-predation females consistently discriminate against high-predation males (regardless of their river of origin), high-predation females only discriminate against low-predation males from upstream in their own rivers. This pattern is not only consistent in lab tests from paired populations in three different rivers, but also evident in the field experiments. Here, we set up enclosures in a high-predation stream and allowed resident males and two populations of low-predation males (one neighbour population and another further away) to compete for fertilizations with resident virgin females. Paternity analyses revealed that high-predation males only substantially outcompete the neighbouring low-predation males. Together, this study shows evidence for mating isolation in guppies but this isolation is likely driven by more than one mechanism: for females in high-predation environments, it’s selection against maladapted low-predation migrant males (reinforcement), whereas for low-predation females it’s selection against particular traits related to survival in high-predation. What these traits are specifically, how they influence mating success, and how preferences are evolving and respond to selection remain open questions and important areas for future research.

So although the latest chapter in the guppy story doesn’t necessarily fall into textbook expectations, it nonetheless shows the strength in not only looking for evidence of speciation where it’s most likely to be found, but by focusing on situations where it isn’t apparent we may be able to start to untangle the ecological limits to evolutionary differentiation and the evolutionary limits to ecological differentiation.

Magic and muggle in Austria speciation meeting

Set against a backdrop of vineyards and castles, and held in the summer palace of the Hapsburgs in Laxenburg, was the First European Conference on Speciation Research, organized by Ulf Dieckmann and Ake Brannstrom. Thirty or so talks and many posters fomented a great environment for argument and debate – with or without liquid encouragement.

A principle item of argument was the role of “magic traits” in speciation. The term was originally coined by Sergey Gavrilets in a derisive way to suggest the implausibility of natural populations having traits (or genes) that were under divergent natural selection and also influenced mate choice. Traits/genes like this make speciation, particularly sympatric speciation, much easier and frequently appear in theoretical models demonstrating that sympatric speciation is “plausible.” The funny thing was that empiricists quickly pointed to a large number of traits that seemingly do have these joint effects, including body size in stickleback, beak size in finches, color in butterflies and hamlet fishes, and habitat choice in herbivorous insects. And so magic traits quickly became a rallying point for people studying speciation in sympatry or parapatry: i.e., speciation with gene flow. Now many empirical studies invoke the existence of apparent magic traits in their study system as a way of suggesting an easy, perhaps even inevitable route to speciation. And new theoretical models are now invoking magic traits in a proactive way, rather than cloaking them in alternative genetic structures and explained them away in an apologetic fashion.

So what’s to debate? The first point was that some people felt the term shouldn’t be invoked because it implied that such traits are not believable – when they may actually be common. Others at the meeting disliked the term because it wasn’t defined precisely – although several people are working on doing precisely this. My own point of concern was partly related to this ambiguity. In particular, just how much of the reproductive isolation evolving between two species must such a dual-effect trait explain to warrant the term “magic.” To me, magic implied something important - perhaps speciation wouldn’t have occurred without the magic trait. But it was pointed out by Maria Servedio that the original definition doesn’t imply any effect size. I resisted this for some time, but then realized that not all magic has to be important. Hermione might use “trivial magic” to make a feather float, whereas she might use “important magic” to save Harry’s life. Both actions are magic but only the latter matters. So maybe we need to distinguish “trivial magic traits” from “important magic traits.” Best of all, however, Eva Kisdi noted that the appropriate antonym for a non-magic trait is clearly a “muggle trait,” and so I realized I loved the term.

And so I stayed out until 2 am drinking and arguing with Maria Servedio, Dan Bolnick, Louis Bernatchez, and Isabelle Olivieri. Then I caught a cab for the airport at 4:30 am, and watched the magic of lightly falling snow illuminated by the light from ancient buildings against the inky backdrop of the pre-dawn sky. Trivial perhaps – but no less magic to a muggle.

Other blog posts about the conference:

http://benaustria.blogspot.com/2010/12/speciation-2010.html

http://svenssonresearchlaboratory.blogspot.com/2010/12/greetings-from-speciation-meeting-in.html

Anthropogenic disturbance and evolutionary parameters from a natural population of lemon sharks

Little is known about the potential for adaptive evolution to save natural populations faced with environmental change, despite an increasingly present human hand in modifying their environment. These modifications likely reduce the degree to which populations are adapted to their local conditions, thereby decreasing mean fitness and possibly leading to local extinction. Such adaptive processes depend on several factors such as population connectivity, initial population size, mortality rates, adaptive plasticity (or maternal effects), genetic variation, and the strength and form of selection. And yet few studies to date assess if and how each of these factors has changed in the face of anthropogenic forces.

A recent paper from the Hendry lab attempted to fill this gap by combining long-term monitoring (13 years) of marked lemon sharks (Negaprion brevirostris) at an isolated nursery lagoon (Bimini, Bahamas) with genetic pedigree reconstruction (DiBattista et al. 2011, Evolutionary Applications 4[1]: 1-17). DiBattista et al. (2011) assessed whether habitat loss influenced population size, juvenile mortality, maternal effects, genetic variation, and selection in this lemon shark population. This analysis was only possible because recent human activities (i.e., mangrove removal) associated with a large-scale development project at Bimini conveniently bisected their dataset. Contrary to expectation, they found that samples after the disturbance (relative to before the disturbance) showed an increase in 1) the number of sharks breeding at this site, 2) neutral genetic variation, and 3) additive genetic variation for several key juvenile life-history traits (i.e., body size and growth). They also found a dramatic change in selection acting on those same life-history traits; habitat loss here appears to have changed which phenotypes are now favored by natural selection.

The authors therefore conclude that some species may be tolerant to some habitat loss, although this likely depends on the length and duration of the disturbance. Similarly, high levels of gene flow among population may act to buffer losses in neutral and additive genetic variation, and in some cases increase it. Based on the observed changes in the strength and sometimes direction of natural selection acting on life-history traits in this population, it would seem that habitat loss may impede adaptive processes by altering the fitness landscape.

Joseph DiBattista (NSERC postdoctoral fellow at the Hawaii Institute of Marine Biology, University of Hawaii)

Photo Credit

DiBattista JD, Feldheim KA, Garant D, Gruber SH, and Hendry AP (2011). Anthropogenic disturbance and evolutionary parameters: A lemon shark population experiencing habitat loss. Evolutionary Applications 4(1): 1-17.

(http://onlinelibrary.wiley.com/doi/10.1111/eva.2010.4.issue-1/issuetoc)

Photo Credit: Matthew Potenski (http://www.matthewpotenskiphoto.com/)

*Save one, none of the other authors were bitten, maimed, or otherwise harmed during the tagging of said lemon sharks.