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How adaptive plasticity evolves when selected against

Posted by on Mar 12, 2019 in Posts | 0 comments


Yes, that is the surprise title of Alfredo’s new paper in PLoS Computation Biology! When we discover examples of adaptive plasticity we usually think that it evolved because selection favoured it. But can adaptive plasticity evolve when selection favours non-plastic individuals?

Think of a population of insects that hatches, reproduces and dies twice every year: once in spring and once in autumn. Spring and autumn conditions may be very different, but plasticity could allow the insects to cope with both seasons. Yet, insects born in spring never experience autumn, and vice versa, so natural selection cannot directly favour plasticity. In fact, plastic individuals may do worse than individuals that are not plastic, which means plasticity could consistently be selected against.

This problem is similar to tuning the learning rate in Machine Learning. To teach a machine how to solve a problem, we give it a set of example questions we already know the answer to. Each time the machine gives us the wrong answer, we change its parameters to produce a new answer that is closer to the right one. If the examples share a consistent logic, the machine will eventually find this logic. But if we change the model’s parameters too much with every example shown, the machine will just repeat the solution for the last example, which prevents it from finding the underlying logic that connects the examples.

Just like in machine learning, organisms receive a set of questions in the form of environmental cues and need to provide the right answer in terms of a fit phenotype. Adaptive plasticity is the solution that produces the right phenotype for every environment. Organisms that see only one environment per lifetime could easily “forget” that plasticity is adaptive and instead only produce the right phenotype for their last environment. The offspring of insects that live in spring would be better matched to spring, even though they will have to deal with autumn conditions.

So when does learning theory predict that a machine will learn the logic of plasticity rather than the last solution? And do those predictions hold for a simple representation of evolution by natural selection? To find out, have a look at the paper!

Solved: the genetics of colour polymorphism in wall lizards

Posted by on Mar 1, 2019 in Posts | 0 comments

A new paper in PNAS reveals that the orange and yellow ventral colour morphs in wall lizards is caused by regulatory changes in pterin and carotenoid genes. Interestingly, it seems like the alleles are old and occasionally shared between species. Miguel Carneiro and his team at CIBIO and Leif Andersson at Uppsala led the work, and we helped with the genome, samples, and other bits and pieces. The chromosome-scale genome assembly is of high quality and should become a useful resource – so just get in touch if you want to know if the wallies are right for you too!

A new take on the epigenetic signatures of prenatal stress

Posted by on Dec 5, 2018 in Posts | 0 comments

The conditions encountered in the womb can have life-long impact on health. It is usually assumed that this is because embryos respond to adverse conditions by programming their gene expression. In collaboration with Bas Heijmans and others, we propose that these effects also can be caused by selection on stochastic epigenetic variation. The paper is published in Cell Reports and there is also a press release.

The concept of fetal programming is based on the idea that embryos modify their physiology in response to the uterine environment. This may be good if conditions stay as predicted. But it may have negative health effects later in life if the conditions change. The concept of programming has been backed up by associations between adverse prenatal conditions and patterns of DNA methylation – an epigenetic mark that regulates gene expression.

Our simple insight is that the uterine environment does not need to induce changes in DNA methylation for this association between adverse prenatal conditions and DNA methylation to arise. In the early embryo, stochastic differences in gene expression can become stabilized by DNA methylation, resulting in embryos with different epigenomic profiles. Not programmed by the environment, these random differences in gene expression (and hence DNA methylation) may nevertheless provide some embryos with a survival advantage when conditions are harsh. In other words, adverse maternal conditions may impose selection on random variation in DNA methylation.

Human embryo at 8-cell stage. (C) Yorgos Nikas/Science Photo Library

We used a mechanistic simulation model to illustrate how selection reduce DNA methylation variance at loci that influence implantation success. The prediction fits very well with empirical data from offspring conceived during the Dutch Hunger Winter, a famine at the end of World War II. This makes selection on stochastic epigenetic variation a reasonable explanation for the epigenetic signatures of prenatal exposure to adverse conditions.

This new hypothesis is not only of academic interest. Fetal programming implies that the behaviour or physiology of the mother causes the offspring phenotype to change. In contrast, a selective process does not bring new phenotypes into being, it changes the distribution of already existing variants. This difference may influence which preventive strategies and treatments that are most likely to be effective. That different mechanisms can be responsible for the same pattern is also relevant to society. As Sarah Richardson has pointed out, careless discussion of epigenetic research on how early life affects health across generations could be harmful.



Developmental Bias and Evolution at Santa Fe

Posted by on Nov 20, 2018 in Posts | 0 comments

The third and final workshop funded by our EES grant took on the role of developmental bias in evolution. Like the meeting in February, Santa Fe greeted us with snow, jetlag, and huevos rancheros for breakfast.

The workshop showcased the extraordinary breadth of approaches used to understand if, and how, developmental processes direct evolution. Ecologists, developmental biologists, and palaeontologists explained what data are out there and what they mean. Theoretical biologists and computer scientists convincingly showed that the role of development not only can be formulated in precise terms, but that there are predictions ready to be tested. Judging from the work presented, we can look forward to some very interesting studies doing just that in the near future.

As there should be, there was both unity and spirited disagreement – with views ranging from development as constraint to development as the main driver of evolution. History and philosophy of biology again proved useful to understand this diversity. While debate over the role of development in evolution is as old as evolutionary science, contemporary research really does seem to bring new insights – conceptually, theoretically and empirically.

One way to think of developmental bias is through the use of morphospaces. The morphospace of several groups of reptiles (including dinosaurs) that lived around 230-200 million year ago, using two (undefined) shape characters. Reproduced from the Palaeobiology Research Group of the University of Bristol, UK

Origin-Of-Life researcher Wim Hordijk kindly summarized his views of the meeting on this blog. The Lund crew – Tobias, Alfredo, Nathalie, Reinder, and Illiam – are very grateful to the SFI for hosting, and the organisers for giving us a lot of things to think of. Next up – the Evolution Evolving meeting at Cambridge. See you there!

 

Another bad day for anticipatory maternal effects

Posted by on Nov 20, 2018 in Posts | 0 comments

A new study on water fleas, headed by Reinder and Alex, suggests that a classic example of adaptive maternal effects is not as adaptive as we might have thought.

Some years ago, Tobias, Sinead and Shinichi did a meta-analysis that seemed to undermine the idea that maternal effects are designed to transfer information about the local environment. Reviewers and editors did not really want to hear that, and the paper proved somewhat difficult to publish (but has been well received and cited). But one ‘anticipatory maternal effects’ appeared well supported: water fleas exposed to toxic cyanobacteria produced offspring that were more tolerant to the toxin.

So, to understand how this maternal effect evolves, Reinder and Alex challenged water flea mothers and offspring with cyanobacteria that produce the toxin microcystin. But rather than just expose the animals throughout their lives, they also exposed mothers at different times during her life. The rationale is that maternal effects that have been selected to transmit information are expected to behave like signals – triggered and delivered by a system well designed to pass on information with limited cost to the receiver.

It turned out that offspring indeed were somewhat better able to handle the toxin when their mothers had been exposed late in their lives. In other words, tolerance or resistance can be transmitted to the next generation through non-genetic means. But there was not much to suggest that the mechanism has been selected to transmit information about the presence of cyanobacteria. Instead, our experimental evidence – along with a meta-analysis of Daphnia research – fits better with a model of passive transfer of tolerance rather than an anticipatory maternal effect. Again, reviewers and editors were not very happy to hear this, and this paper also proved somewhat difficult to publish.

We should not be too surprised of these results, however. Not all plastic responses that allow organisms to cope with stress are properly seen as adaptations to cope with the stressor.

Genetically identical sisters, raised in two different environments. Daphnia raised in the microcystin treatment (on the right) displays smaller body size and carries less eggs than her sister from the control treatment

We can think of these maternal effects as – in Mary-Jane West-Eberhard terms – examples of phenotypic accommodation that have not yet been followed by genetic accommodation.

But while our results question if there really has been selection for maternal transfer of information about microcystin exposure, the study is still not quite conclusive. Two kinds of follow-up studies would be particularly informative.

Endless replications

The first is to contrast responses of populations of water fleas with different evolutionary histories of exposure. This kind of comparison can effectively reveal if plastic responses in naïve animals become fine-tuned over evolutionary time (see a nice example from house finches here).

The second is to reveal the mechanism of the maternal effect. This would not only tell us ‘how it works’, but – keeping the comparison with signals in mind – whether or not the mechanism has properties that we expect of systems designed to transmit information.

We have our ideas about what is going on, and Alex has just completed a set of experiments that can tell us more. In the meantime, we hope that this paper will inspire more studies to look at maternal effects as a window into the evolutionary transition from stress-induced responses to local adaptation. To get started, please see here and here.

 

Lund workshop on the evolutionary origins of individuality

Posted by on Sep 8, 2018 in Posts | 0 comments

The evolutionary process is itself evolving. Perhaps the best example is the origin of new reproductive organizations that are capable of evolving by natural selection. Single celled organisms evolved into multicellular organisms, some of which – leaf cutter ants, for example – appear to have evolved into collectives that deserve the label superorganism.

Last week our group hosted a small workshop to bring together researchers that use different approaches to tackle how and why such transitions in individuality happens. The aim was to share insights from projects within our Templeton-funded grant, and to spread ideas to local Lund researchers.

The presentations generated a lot of great discussions, which continued over dinner and at the pub. Richard Watson showed how learning theory bring clarity to the conditions that are necessary for transitions in individuality to happen. Andy Gardner explained how focusing on lower-level evolutionary individuals – genes – can help to understand how conflicts between cells within bodies arise, evolve and become resolved. Charlie Cornwallis and Maria Coelho-Svensson discussed how one can put theory to the test using green algae that come together in groups. Social insects provide another interesting example, and Heikki Helanterä showed how they can shed light on the transition from solitary to collective life cycles.

Evolutionary transitions in individuality is fundamentally about explaining how a developmental organization evolves from social or ecological interactions between the lower-level individuals. This is difficult to address without paying attention to mechanism. Miguel Brun-Usan showed how mechanistic models of cell behaviour provide a window into the conditions that promote transitions in individuality. Some of the order comes from self-organization, a topic theoretically explored by Edith Invernizzi in the context of nest building in social insects.  Finally, Jonathan Birch discussed another evolving relationship between the organism and its surroundings – the evolutionary route towards organisms that are capable of conscious thought.

Thanks to all the speakers and the many Lund researchers and students that attended the workshop. It was great fun and we cannot wait to see more from all of these projects.

Developmental Bias and Evolution

Posted by on Jul 30, 2018 in Posts | 0 comments


A recurrent theme in evolutionary biology is to contrast natural selection and developmental constraint – two forces pitted against each other as competing explanations for organismal form. A recent Perspective in the journal Genetics explains why this juxtaposition is deeply misleading. There is also a blog about the paper here.

Our starting point is that characters often evolve through changes in how genes, cells, and tissues regulate each other. Once we study the evolution of such regulatory interactions, it turns out that they do not only limit evolution, but also may facilitate the capacity to adapt and diversify. The paper gives an introduction to recent theoretical and empirical research, and explains how this work is now beginning to reveal how evolution of the evolutionary process itself contributes to diversification and adaptation.

 

Three new papers on thermal biology of reptile embryos

Posted by on May 28, 2018 in Posts | 0 comments

Most reptiles lay eggs in sand or soil, under logs or in rock crevices. These are places where the temperature often fluctuates, sometimes becoming dangerously high or low. The pervasive effects of temperature on biological systems begs the question how embryos respond in the short term, and how populations adapt in the long term. This question is now thoroughly explored in a theme issue of the Journal of Experimental Zoology, with contributions from our group.

In a study on wall lizards led by Nathalie Feiner, we reveal a pervasive effect of temperature on gene expression in early embryos. The strongest responses were found for genes involved in transcriptional and translational regulation and chromatin remodelling, suggesting possible epigenetic mechanisms underlying thermal acclimation. In another paper, ploughing through 50 years of experimental studies, Dan Noble, Geoff While, and colleagues summarize research on thermal plasticity in reptile embryos, and demonstrate how future progress can be made through meta-analytic and comparative work. The data are accessible to everyone through a paper in the journal Scientific Data, and can be downloaded through this online data base. More papers in this special issue are available through the Journal of Experimental Zoology online early.

 

Anolis symposium in Miami

Posted by on Apr 4, 2018 in Posts | 0 comments

The organizers had chosen an appropriate setting for the 2018 Anolis symposium – sunny Miami, Florida, at the Fairchild Botanical Garden that ‘hosts’ six Anolis species. Since Nathalie was working at the museum collection of the University of Florida, she took the opportunity to join for two days of Anolis fun.

The meeting was the fifth of its kind, with the first taking place already in 1972. That is an average of one meeting every 9th year! Not very frequent, but it means the symposium already is a classic event. The program was full, but the organizers had scheduled long coffee and lunch breaks to make sure there was enough time to explore the Botanical Garden, in particular to meet our scaly friends, of course.

There were 31 talks. These covered pretty much every question that can be asked about Anolis lizards: behaviour, ecology, population biology, developmental biology, genome biology and evolution. Several talks were on urban ecology since many Anolis species have developed a taste for busy metropolitan environments, something that is easily observed in Miami. Most speakers presented ongoing work which generated a lot of fruitful discussions. Nathalie presented her work on the relationship between transposable elements (TE) and diversification rates in Anolis, and how transposable elements may be responsible for some pretty cool changes in Hox gene expression. TEs were new to many in the audience, but Nathalie managed to get the ecologists excited about genome biology.

The talks were great. But the best thing about the symposium was to meet other Anolis enthusiasts and to talk (and see!) ‘Anolis’ for a whole weekend! For Nathalie – the only representative of the old world, as pointed out by Jonathan Losos – it was a fantastic opportunity to exchange ideas with those who shared an interest in evo-devo. There was a lot of successful exchange of ideas – from practical matters like the best way to image embryos, to the conceptual issues surrounding the role of development in evolution.

And look who turned up! Sozos Michaelides – who finished his PhD in our group three years ago – has abandoned the wall lizards and is now disentangling the introduction histories of Anolis lizards with Jason Kolbe at Rhode Island.

Thanks to James Stroud, Anthony Geneva and Jonathan Losos for a fantastic job with the organization. James, the local amongst the organizers, made sure that everyone got a taste of the Caribbean – serving Cuban delights during coffee and lunch breaks, and homebrewed beer (‘Lizard lager’ and ‘Anole ale’) in the evening. The next meeting is scheduled for the year 2025 – we look forward to it!

 

 

Evolving Evolutionary Biology at the Santa Fe Institute

Posted by on Feb 23, 2018 in Posts | 0 comments

Researchers from around the world gathered at a snow-covered Santa Fe Institute to discuss the evolutionary implications of extra-genetic inheritance. The workshop – Integrating Development and Inheritance – was organized by Tobias and colleagues as part of the EES research program. For two and a half days the participants – biologists, mathematicians, computer scientists, anthropologists, historians and philosophers of science – presented their work and took part in lively and constructive discussions about the nature of inheritance and why it matters to evolution.

The workshop kicked off with some historical background to the separation of inheritance and development, and how this shaped the development of research programs within evolutionary biology. The biology talks covered many different mechanisms by which parents influence the development of their offspring – from epigenetic inheritance in plants to whale culture. Attendees further discussed how empirical work and mathematical modelling best can proceed with constructive views of development and inheritance. For the full program, please see here.

We are very grateful to all the participants for their outstanding presentations and engaging and constructive contribution to the discussions. Nothing beats learning about one’s own field through talking to people with different backgrounds and expertise. Judging from the talks, we have a lot of exciting empirical and theoretical research and philosophy and history of science to look forward to. An extra thanks to Michael Lachmann and the Santa Fe Institute for hosting us. We will be back in November!

Two PhD positions available to study the evolutionary origin of family living

Posted by on Feb 9, 2018 in Posts | 0 comments

We are looking for two students interested in doing their PhD on the evolutionary origin and diversification of social complexity in lizards. The positions are part of a research project funded by the Australian Research Council and the successful candidates will be based either at the University of Tasmania (primary supervisor Geoff While) or at Macquarie University (primary supervisor Martin Whiting). The Lund collaborators are Tobias and Charlie Cornwallis. For more information on the position, please read here, or contact any one of us directly.

 

Winter is coming!

Posted by on Feb 9, 2018 in Posts | 0 comments

Winter is not really the best time of year in Skåne, unless you really enjoy all those different shades of grey. To get a feeling of a proper Swedish winter, the group packed their warmest clothes (and triple pairs of socks) and headed up to Sunne, where Tobias was born and raised. Winter in Värmland is the real thing – snow-covered forests, ice-covered lakes and the hope of a rare wolf spotting.

Tobias’ parents opened up their whole house for us, and his brother served as the cross-country skiing coach and ‘vallachef’. People from eight nationalities put on their skis – some for the very first time – and headed out to the tracks. Everybody had healthy rosy cheeks and slightly frozen toes by the end, and incredibly nobody was injured! In fact, Yang and Mara both proved to be natural talents at skiing, despite the limited snow cover in Chengdu and Murcia. This was extra impressive considering that Yang broke his ‘low Celsius record’ two days in a row and had only once seen this much snow before – an occasion he described as “catastrophic”!

Ice-fishing released a lot of creative forces in the group. Pumping up a groovy atmosphere in the glorious sunshine, Illiam and Alfredo managed to pull up several perch while the others skied across the lake. Back at the house, an old snow racer could of course not be resisted. The greatest daredevil and air-time record-setter was Reinder, perhaps due to limited childhood experience of what happens when you go down hills really fast…

After these lovely but chilly outdoor activities we enjoyed cosy evenings around the fireplace with games and wine. Alex turned out to have the best strategic skills whereas Illiam proved to have the gift of storytelling (a.k.a. lying). Nathalie turned out to be an amazing air pilot, Hanna a master of skull-drumming and Tobias – well, he was still the real Harry even when everyone else had lost track.

Many thanks to the Uller family for an amazing weekend. We’ll see you again next time… ;-)!

 

 

 

 

 

 

 

Live bearing promotes the evolution of sociality

Posted by on Dec 12, 2017 in Posts | 0 comments

Some lizards and snakes tend to hang out in family groups, not unlike the more familiar social groups of birds and mammals. Our recent study, headed by Ben Halliwell and Geoff While and published in Nature Communications, show that the evolution of social grouping is much more likely to have happened in lizards and snakes that give birth to live young. There could be a number of reasons that transitions to sociality are more common for live bearing species.

The most obvious one – and the theoretical rationale behind this study – is that giving birth to live young makes interactions between parents and offspring more likely than in species that lay eggs. And interaction among kin, in turn, is what causes natural selection for group living.

(C) Dale Burzacott

Some lizards – in particular the Egernia – in fact have quite complex kin-based social structures. As expected, such groups have almost exclusively evolved in live-bearing lineages. Interestingly, egg guarding does not seem to have the same positive effect on the evolution of sociality. Maybe this is because the ecology needs to be right as well to select for delayed dispersal and parental tolerance of offspring. For the full story, please download the paper here.

 

Evolutionary adaptation to climate: same same, but different

Posted by on Nov 22, 2017 in Posts | 0 comments

A new study published in Evolution – headed by Nathalie – reveals how embryonic gene expression patterns change as non-native lizards adapt to cool climate.

Populations adapting independently to the same environment provide important insights into the repeatability of evolution. In the 20th century, common wall lizards (Podarcis muralis) from southern and western Europe were introduced to England, north of their native range. We have previously shown that non-native populations of both lineages have adapted to the shorter season and lower egg incubation temperature by increasing the absolute rate of embryonic development.

In this new study, we show that embryos from non-native populations exhibit gene expression profiles consistent with directional selection following introduction. However, different genes are affected in lizards from France and Italy. The biological function of these genes are quite similar, though, and consistent with mechanisms that should speed up development. These results indicate that small populations are able to adapt to new climatic regimes, but the means by which they do so may largely be determined by founder effects and other sources of genetic drift.

 

Heredity in Evolutionary Theory

Posted by on Sep 26, 2017 in Posts | 0 comments

It may not have escaped your attention that biologists are taking a more inclusive view on heredity these days, regularly referring to epigenetic or behavioural inheritance, for instance. It is often difficult to understand what this means, however, or why it matters. Tobias and Heikki Helanterä take a closer look at heredity in evolutionary theory in a new book from Oxford University Press – Challenging the Modern Synthesis: Adaptation, Development & Inheritance, edited by philosophers of biology Philippe Huneman and Denis Walsh. A pre-print version of the chapter can be found here.

In evolutionary biology, there are arguably four main ways to think of heredity:  as transmission of genes and other ‘particles’, as a phenotypic covariance, as transmission of information, and as the outcome of developmental processes. These are not mutually exclusive, and which one that is adopted or emphasized is partly a pragmatic decision based on the research question at hand (e.g., Tobias regularly makes use of all four), and partly a reflection of one’s conceptual framework (e.g., in some people’s minds heredity can only be genetic and strictly separated from development, and if you think otherwise you are either an idiot or, worse, a Lysenkoist in disguise).

 

When empirical research reveals new mechanisms by which parents influence their offspring – like the persistence of DNA methylation from mother to offspring or offspring learning how to forage from their father – researchers naturally accommodate these findings according to how they think of heredity. But it also leads the odd biologist (and non-biologists) to question the coherence of her current conceptual framework, which is why ‘extra-genetic inheritance’ can be perceived as a challenge to the traditional view of evolution (i.e., the ‘modern synthesis’ – if you do not like this term, just think of a colleague who thinks that all fundamental problems in phenotypic evolution can/should be answered without referring to development). And, as we know, conceptual change can make some new research questions appear more interesting or relevant than they did before, whereas others may fade into oblivion.

Illiam Jackson joins the group

Posted by on Sep 7, 2017 in Posts | 0 comments

Target of illiams PhD work – Agnostus pisiformis fossil. Scalebar is 2 mm.

It is often pointed out that there is a strange gap between evolutionary biology and palaeontology. Particularly considering that it is hard to find something so obviously relevant to evolution as the fossil record… Anyway, we now hope to reduce this gap thanks to Illiam Jackson. Illiam did his PhD in palaeobiology in Uppsala under the supervision of Graham Budd (although he likes to point out that his first degree was in Biology). He joins us with a passion for morphometrics, and for making development relevant also to the study of fossils. Illiam will continue his work on plasticity and evolution of trilobite-ish arthropods here at Lund, but he will also – together with Nathalie Feiner – explore if developmental plasticity shapes adaptive radiation of lizards. Welcome Illiam!

Highlights from ESEB 2017

Posted by on Aug 29, 2017 in Posts | 0 comments

This year’s European Society for Evolutionary Biology meeting was held in Groningen. ESEB is always a great opportunity to see old friends, learn new things, and – somewhat jealously! – see the progress on the most famous study systems in evolutionary biology, such as cichlids, Heliconius butterflies, and bird beaks. And progress there was. Among the most memorable were further evidence from the Seehausen group – presented by Joana Meier and others – that hybridization has played a creative role in fish evolution in both African and European lakes, and a tour-de force of Heliconius evolutionary genomics in a plenary by Chris Jiggins (there is a book, not only for butterfly lovers!). Hybridization was hot at the meeting so it was a shame that Yang was unable to join this year. Wallies were represented, however, by a nice talk on the ventral colour polymorphism by Pedro Andrade. Chances are they will make a big splash next year in Montpellier!

To be fair, ESEB has never been a hotspot for development and this year was no different. Manhattan plots abound, but there was generally little process-oriented research to allow us to connect genotype and phenotype. Exceptions included an excellent plenary by Renee Duckworth, where she demonstrated how to integrate proximate and ultimate causation to understand why organisms change over time or, in this case, why they may not do so. Another exceptional talk was delivered by Alex Badyaev, expanding on his recent papers on the evolution of carotenoid colouration in birds. Describing evolution as transitions between external and internal control in regulatory networks, this work demonstrated the potential for taking a comparative network approach to study innovation and diversification from a developmental perspective.

Other welcome islands in the sea of genomics of adaptation include Andreas Wagner’s plenary on innovation and modularity, or a talk by Christoph Thies from Richard Watson’s group who presented some refreshing ideas on evolutionary transitions in individuality and demonstrated how to capture this process formally. Plasticity and evolution was represented here and there, including an update on the spadefoot toad story by Ivan Gomez-Mestre.

Judging from the ESEB talks, evolutionary biologists are very interested in extra-genetic inheritance. Most talks – including a pretty well-attended symposium keynote by Tobias – revealed this interest to largely be about adaptive function, but with some nice links to life history and ageing (many thanks to Foteini Spagopolou and the other organisers). With a better integration between development and evolution we may look forward to more work on how inheritance systems actually originate and evolve. Chances are Daphnia will deliver some of the pieces of the puzzle and Reinder’s poster – showing preliminary data that quantify the extent of extra-genetic inheritance – was indeed well attended.

The poster sessions were actually one of the meeting’s highlight. Taking place in what resembled an aircraft hangar, it was cool and spacious. And there was wine. Nathalie – presenting her work on the evolution of embryonic gene expression in wall lizards adapting to cool climate – was super busy explaining her findings to other attendees. The whole meeting was full on – I did not even manage to talk to many of the people I know well!

It is always nice to visit Groningen, a place where many of the most creative researchers in evolutionary biology took their first steps as MSc students. With 1600 attendees, these meetings are really too big to take on, but the organising committee – headed by Leo Beukeboom and Simon Verhulst – did a great job pulling it all together. We are already looking forward to see what Turku and Prague can come up with in the years to come!

 

Friends shape the distribution of genetic variation

Posted by on Aug 18, 2017 in Posts | 0 comments

Small encounters can have large impacts. This counts for animals as well. Particular for social animals – such as great tits – encounters with others affect how they move around and where they eventually settle. And this influences with whom they mate and how successful they are in life. In a new paper published in Molecular Ecology, Reinder Radersma and colleagues from Oxford and Sheffield show that the social environment has a large impact on the movement of great tits – a bird species roaming around Wytham Woods and many other Eurasian forests. These movements affect the distribution of genotypes, which is crucial for how the population can evolve. After all, the distribution of genotypes across an area shapes the genetic combinations that arise and thus, the opportunity for local adaptation.

A particular difficulty when investigating how movements are affected by social interactions is that it is very hard to separate social effects from other factors which vary in space. For instance, when food is not equally distributed – as is often the case – animals might aggregate in food-rich areas. It may look like individuals choose to interact, because many individuals are at the same location. However, it is simply the food, not the company, that is the attraction.

 

Reinder and his colleagues used techniques recently developed for spatial statistics and extended its use to analyze social networks to separate the effects of spatial variables and social interactions on tit movement.

They show that the movement of individuals and therefore the distribution of genotypes is strongly affected by the preference to move around with the same individuals, in other words, hanging out with “friends”. In addition, the birds do not befriend simply individuals that live in close proximity, because neighbors have similar genotypes. Instead, they pick friends that are genetically different from themselves. As a result, the genetic structure of the population is affected by both social and spatial effects.

 

Why do lizards smell?

Posted by on Aug 2, 2017 in Posts | 0 comments

Many male lizards produce secretions that they rub on the ground of their territories. The function of these secretions remains contentious, in particular whether or not they serve as indicators of male fighting ability or suitability as a mate. A new paper, published in Evolution, suggests that sexual selection on chemical composition is, in fact, quite weak.

Headed by recent PhD graduate Hannah MacGregor, and in collaboration with Geoff While and Patrizia d’Ettorre, we analysed the chemical composition of secretions from male lizards from France and Italy. The results confirmed previous work showing that chemical profiles can correlate with male secondary sexual characters. However, the correlations were generally weak and inconsistent across the season and between populations. More importantly, there was little evidence that a male’s chemicals make him have more offspring.

That sexual selection on the femoral secretions is weak was further supported by the overall neutral pattern of introgression of chemical profiles in the hybrid zone between the highly sexually selected form (the ‘Tuscan’ lizards) and the ancestral phenotype (details on this hybrid zone can be found here). Nevertheless, three candidate compounds were candidates for asymmetric introgression via direct selection or genetic linkage with visual or behavioural characters.

On the whole, these results are bad news for the hypothesis that chemical communication is sexually selected in wall lizards. Instead, femoral secretions probably function as signature mixtures; that is, they help lizards to keep track of who’s who and to resolve territorial disputes. Yet, every now and then, a particular compound may become consistently selected – perhaps due to genetic linkage – and evolve a more signal-like function. May we speculate that this process can be facilitated by introgressive hybridization?

New philosophy of biology paper

Posted by on May 26, 2017 in Posts | 0 comments

Ever wondered why there is such intense disagreement over the evolutionary significance of development, non-genetic forms of inheritance, and niche construction? If so, you may be helped by a recent analysis by Tobias and Heikki Helanterä. The paper, accepted in the premier philosophy of science journal British Journal for the Philosophy of Science, uses niche construction as a case study to demonstrate how the way we think of causality in biological systems shape the structure of evolutionary explanations.

Richard Lewontin famously described evolution by natural selection in terms of three principles: variation, differential fitness and inheritance. Organisms fulfil these principles and so they evolve, diversify and adapt. But this does not tell us how the principles are causally related, nor how they should best be construed.

The classic instantiation of Lewontin’s principle describes evolution in genetic terms. This version is what we are taught at school. What we are not often taught, however, is that the genetic instantiation imposes a large degree of autonomy on the biological processes that produce variation, differential fitness, and heredity. Variable rates of survival determine what features will occur in the next generation. But selection does not affect the process of inheritance; inheritance is merely the passing on of whatever genes were selected. The variation that fuels evolution is similarly autonomous. Mutations occur randomly with respect to their consequences for development and fitness, and the acquisition of new variants does not change how variation is transmitted down generations. The result is an ordered set of causally autonomous processes; each step determines (partly) the inputs for the next step, but not how those inputs will be processed.

nicheconstruction

 

The autonomy of variation, differential fitness and inheritance is deeply entrenched in contemporary evolutionary biology. But it is a convenient heuristic and not a logical necessity, and it may or may not accurately capture biological reality. Many biologists suspect that it does not and that, in the real world, causes of variation, fitness, and heredity are intertwined. Tobias and Heikki show that such alternative instantiations of the principles of evolution by natural selection can affect the structure of evolutionary theory. And this, in turn, can make it perfectly valid to consider both natural selection and niche construction part of an evolutionary explanation for why organisms are well suited to their environments.

Failing to appreciate how different instantiations of Lewontin’s principles affect causal explanation in evolution is a major source of communication failure surrounding not only niche construction, but also developmental plasticity, extra-genetic inheritance and other phenomena.

Tobias and Heikki also suggests another reason people do not seem to understand each other: the views held by scientists on how science works. Many scientists expect their deep-held views, such as the core of the genetic instantiation of evolution by natural selection, to be falsified by data before they consider alternatives. Other scientists put less emphasis on anomalies and evaluate conceptual frameworks primarily on their ability to stimulate useful research. These different perspectives on scientific progress cut across disciplines but are rarely made explicit in scientific debates.

Nevertheless, philosophy of science is important to understand what the contention actually is about. If one considers niche construction theory an attempt to formulate an alternative research programme, it should be evaluated on the basis of its ability to stimulate new questions and predict patterns and phenomena that would otherwise appear surprising; not on the basis of whether or not it falsifies the genetic perspective. On the other hand, those arguing for more substantial conceptual change must strive towards showing that their framework leads to a different, theoretically and empirically progressive, research programme. Maybe the need for scientific pluralism is a good topic to bring up at your next coffee break?