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13 Dec 2016
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Repeated replacements of an intrabacterial symbiont in the tripartite nested mealybug symbiosisHusnik F, McCutcheon JP https://doi.org/10.1073/pnas.1603910113Obligate dependence does not preclude changing partners in a Russian dolls symbiotic systemRecommended by Emmanuelle Jousselin and Fabrice VavreSymbiotic associations with bacterial partners have facilitated important evolutionary transitions in the life histories of eukaryotes. For instance, many insects have established long-term interactions with intracellular bacteria that provide them with essential nutrients lacking in their diet. However, despite the high level of interdependency among organisms involved in endosymbiotic systems, examples of symbiont replacements along the evolutionary history of insect hosts are numerous.
In their paper, Husnik and McCutcheon [1] test the stability of symbiotic systems in a particularly imbricated Russian-doll type interaction, where one bacterium lives insides another bacterium, which itself lives inside insect cells. For their study, they chose representative species of mealybugs (Pseudococcidae), a species rich group of sap-feeding insects that hosts diverse and complex symbiotic systems. In species of the subfamily Pseudococcinae, data published so far suggest that the primary symbiont, a ß-proteobacterium named Tremblaya princeps, is supplemented by a second bacterial symbiont (a ϒ-proteobaterium) that lives within its cytoplasm; both participate to the metabolic pathways that provide essential amino acids and vitamins to their hosts. Here, Husnik and McCutcheon generate host and endosymbiont genome data for five phylogenetically divergent species of Pseudococcinae in order to better understand: 1) the evolutionary history of the symbiotic associations; 2) the metabolic roles of each partner, 3) the timing and origin of Horizontal Gene Transfers (HGT) between the hosts and their symbionts. Reference [1] Husnik F., McCutcheon JP. 2016. Repeated replacements of an intrabacterial symbiont in the tripartite nested mealybug symbiosis. PNAS 113: E5416-E5424. doi: 10.1073/pnas.1603910113 | Repeated replacements of an intrabacterial symbiont in the tripartite nested mealybug symbiosis | Husnik F, McCutcheon JP | <p>Stable endosymbiosis of a bacterium into a host cell promotes cellular and genomic complexity. The mealybug *Planococcus citri* has two bacterial endosymbionts with an unusual nested arrangement: the γ-proteobacterium *Moranella endobia* lives ... | Phylogenetics / Phylogenomics, Species interactions | Emmanuelle Jousselin | 2016-12-13 14:27:09 | View | ||
13 Dec 2016
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A supergene determines highly divergent male reproductive morphs in the ruffKüpper C, Stocks M, Risse JE, dos Remedios N, Farrell LL, McRae SB, Morgan TC, Karlionova N, Pinchuk P, Verkuil YI, et al. https://doi.org/10.1038/ng.3443Supergene Control of a Reproductive PolymorphismRecommended by Thomas Flatt and Laurent KellerTwo back-to-back papers published earlier this year in Nature Genetics provide compelling evidence for the control of a male reproductive polymorphism in a wading bird by a "supergene", a cluster of tightly linked genes [1-2]. The bird in question, the ruff (Philomachus pugnax), has a rather unusual reproductive system that consists of three distinct types of males ("reproductive morphs"): aggressive "independents" who represent the majority of males; a smaller fraction of non-territorial "satellites" who are submissive towards "independents"; and "faeders" who mimic females and are rare. Previous work has shown that the male morphs differ in major aspects of mating and aggression behavior, plumage coloration and body size, and that – intriguingly – this complex multi-trait polymorphism is apparently controlled by a single autosomal Mendelian locus with three alleles [3]. To uncover the genetic control of this polymorphism two independent teams, led by Terry Burke [1] and Leif Andersson [2], have set out to analyze the genomes of male ruffs. Using a combination of genomics and genetics, both groups managed to pin down the supergene locus and map it to a non-recombining, 4.5 Mb large inversion which arose 3.8 million years ago. While "independents" are homozygous for the ancestral uninverted sequence, "satellites" and "faeders" carry evolutionarily divergent, dominant alternative haplotypes of the inversion. Thus, as in several other notable cases, for example the supergene control of disassortative mating, aggressiveness and plumage color in white-throated sparrows [4], of mimicry in Heliconius and Papilio butterflies [5-6], or of social structure in ants [7], an inversion – behaving as a single "locus" – underpins the mechanistic basis of the supergene. More generally, and beyond inversions, a growing number of studies now shows that selection can favor the evolution of suppressed recombination, thereby leading to the emergence of clusters of tightly linked loci which can then control – presumably due to polygenic gene action – a suite of complex phenotypes [8-10]. A largely unresolved question in this field concerns the identity of the causative alleles and loci within a given supergene. Recent progress on this question has been made for example in Papilio polytes butterflies where a mimicry supergene has been found to involve – surprisingly – only a single but large gene: multiple mimicry alleles in the doublesex gene are maintained in strong linkage disequilibrium via an inversion. It will clearly be of great interest to see future examples of such a fine-scale genetic dissection of supergenes. In conclusion, we were impressed by the data and analyses of Küpper et al. [1] and Lamichhaney et al. [2]: both papers beautifully illustrate how genomics and evolutionary ecology can be combined to make new, exciting discoveries. Both papers will appeal to readers with an interest in supergenes, inversions, the interplay of selection and recombination, or the genetic control of complex phenotypes. References [1] Küpper C, Stocks M, Risse JE, dos Remedios N, Farrell LL, McRae SB, Morgan TC, Karlionova N, Pinchuk P, Verkuil YI, et al. 2016. A supergene determines highly divergent male reproductive morphs in the ruff. Nature Genetics 48:79-83. doi: 10.1038/ng.3443 [2] Lamichhaney S, Fan G, Widemo F, Gunnarsson U, Thalmann DS, Hoeppner MP, Kerje S, Gustafson U, Shi C, Zhang H, et al. 2016. Structural genomic changes underlie alternative reproductive strategies in the ruff (Philomachus pugnax). Nature Genetics 48:84-88. doi: 10.1038/ng.3430 [3] Lank DB, Smith CM, Hanotte O, Burke T, Cooke F. 1995. Genetic polymorphism for alternative mating behaviour in lekking male ruff Philomachus pugnax. Nature 378:59-62. doi: 10.1038/378059a0 [4] Tuttle Elaina M, Bergland Alan O, Korody Marisa L, Brewer Michael S, Newhouse Daniel J, Minx P, Stager M, Betuel A, Cheviron Zachary A, Warren Wesley C, et al. 2016. Divergence and Functional Degradation of a Sex Chromosome-like Supergene. Current Biology 26:344-350. doi: 10.1016/j.cub.2015.11.069 [5] Joron M, Frezal L, Jones RT, Chamberlain NL, Lee SF, Haag CR, Whibley A, Becuwe M, Baxter SW, Ferguson L, et al. 2011. Chromosomal rearrangements maintain a polymorphic supergene controlling butterfly mimicry. Nature 477:203-206. doi: 10.1038/nature10341 [6] Kunte K, Zhang W, Tenger-Trolander A, Palmer DH, Martin A, Reed RD, Mullen SP, Kronforst MR. 2014. doublesex is a mimicry supergene. Nature 507:229-232. doi: 10.1038/nature13112 [7] Wang J, Wurm Y, Nipitwattanaphon M, Riba-Grognuz O, Huang Y-C, Shoemaker D, Keller L. 2013. A Y-like social chromosome causes alternative colony organization in fire ants. Nature 493:664-668. doi: 10.1038/nature11832 [8] Thompson MJ, Jiggins CD. 2014. Supergenes and their role in evolution. Heredity 113:1-8. doi: 10.1038/hdy.2014.20 [9] Schwander T, Libbrecht R, Keller L. 2014. Supergenes and Complex Phenotypes. Current Biology 24:R288-R294. doi: 10.1016/j.cub.2014.01.056 [10] Charlesworth D. 2015. The status of supergenes in the 21st century: recombination suppression in Batesian mimicry and sex chromosomes and other complex adaptations. Evolutionary Applications 9:74-90. doi: 10.1111/eva.12291 | A supergene determines highly divergent male reproductive morphs in the ruff | Küpper C, Stocks M, Risse JE, dos Remedios N, Farrell LL, McRae SB, Morgan TC, Karlionova N, Pinchuk P, Verkuil YI, et al. | <p>Three strikingly different alternative male mating morphs (aggressive 'independents', semicooperative 'satellites' and female-mimic 'faeders') coexist as a balanced polymorphism in the ruff, *Philomachus pugnax*, a lek-breeding wading bird1, 2,... | Adaptation, Genotype-Phenotype, Life History, Population Genetics / Genomics, Reproduction and Sex | Thomas Flatt | 2016-12-13 17:28:13 | View | ||
13 Dec 2016
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Structural genomic changes underlie alternative reproductive strategies in the ruff (Philomachus pugnax)Lamichhaney S, Fan G, Widemo F, Gunnarsson U, Thalmann DS, Hoeppner MP, Kerje S, Gustafson U, Shi C, Zhang H, et al. https://doi.org/10.1038/ng.3430Supergene Control of a Reproductive PolymorphismRecommended by Thomas Flatt and Laurent KellerTwo back-to-back papers published earlier this year in Nature Genetics provide compelling evidence for the control of a male reproductive polymorphism in a wading bird by a "supergene", a cluster of tightly linked genes [1-2]. The bird in question, the ruff (Philomachus pugnax), has a rather unusual reproductive system that consists of three distinct types of males ("reproductive morphs"): aggressive "independents" who represent the majority of males; a smaller fraction of non-territorial "satellites" who are submissive towards "independents"; and "faeders" who mimic females and are rare. Previous work has shown that the male morphs differ in major aspects of mating and aggression behavior, plumage coloration and body size, and that – intriguingly – this complex multi-trait polymorphism is apparently controlled by a single autosomal Mendelian locus with three alleles [3]. To uncover the genetic control of this polymorphism two independent teams, led by Terry Burke [1] and Leif Andersson [2], have set out to analyze the genomes of male ruffs. Using a combination of genomics and genetics, both groups managed to pin down the supergene locus and map it to a non-recombining, 4.5 Mb large inversion which arose 3.8 million years ago. While "independents" are homozygous for the ancestral uninverted sequence, "satellites" and "faeders" carry evolutionarily divergent, dominant alternative haplotypes of the inversion. Thus, as in several other notable cases, for example the supergene control of disassortative mating, aggressiveness and plumage color in white-throated sparrows [4], of mimicry in Heliconius and Papilio butterflies [5-6], or of social structure in ants [7], an inversion – behaving as a single "locus" – underpins the mechanistic basis of the supergene. More generally, and beyond inversions, a growing number of studies now shows that selection can favor the evolution of suppressed recombination, thereby leading to the emergence of clusters of tightly linked loci which can then control – presumably due to polygenic gene action – a suite of complex phenotypes [8-10]. A largely unresolved question in this field concerns the identity of the causative alleles and loci within a given supergene. Recent progress on this question has been made for example in Papilio polytes butterflies where a mimicry supergene has been found to involve – surprisingly – only a single but large gene: multiple mimicry alleles in the doublesex gene are maintained in strong linkage disequilibrium via an inversion. It will clearly be of great interest to see future examples of such a fine-scale genetic dissection of supergenes. In conclusion, we were impressed by the data and analyses of Küpper et al. [1] and Lamichhaney et al. [2]: both papers beautifully illustrate how genomics and evolutionary ecology can be combined to make new, exciting discoveries. Both papers will appeal to readers with an interest in supergenes, inversions, the interplay of selection and recombination, or the genetic control of complex phenotypes. References [1] Küpper C, Stocks M, Risse JE, dos Remedios N, Farrell LL, McRae SB, Morgan TC, Karlionova N, Pinchuk P, Verkuil YI, et al. 2016. A supergene determines highly divergent male reproductive morphs in the ruff. Nature Genetics 48:79-83. doi: 10.1038/ng.3443 [2] Lamichhaney S, Fan G, Widemo F, Gunnarsson U, Thalmann DS, Hoeppner MP, Kerje S, Gustafson U, Shi C, Zhang H, et al. 2016. Structural genomic changes underlie alternative reproductive strategies in the ruff (Philomachus pugnax). Nature Genetics 48:84-88. doi: 10.1038/ng.3430 [3] Lank DB, Smith CM, Hanotte O, Burke T, Cooke F. 1995. Genetic polymorphism for alternative mating behaviour in lekking male ruff Philomachus pugnax. Nature 378:59-62. doi: 10.1038/378059a0 [4] Tuttle Elaina M, Bergland Alan O, Korody Marisa L, Brewer Michael S, Newhouse Daniel J, Minx P, Stager M, Betuel A, Cheviron Zachary A, Warren Wesley C, et al. 2016. Divergence and Functional Degradation of a Sex Chromosome-like Supergene. Current Biology 26:344-350. doi: 10.1016/j.cub.2015.11.069 [5] Joron M, Frezal L, Jones RT, Chamberlain NL, Lee SF, Haag CR, Whibley A, Becuwe M, Baxter SW, Ferguson L, et al. 2011. Chromosomal rearrangements maintain a polymorphic supergene controlling butterfly mimicry. Nature 477:203-206. doi: 10.1038/nature10341 [6] Kunte K, Zhang W, Tenger-Trolander A, Palmer DH, Martin A, Reed RD, Mullen SP, Kronforst MR. 2014. doublesex is a mimicry supergene. Nature 507:229-232. doi: 10.1038/nature13112 [7] Wang J, Wurm Y, Nipitwattanaphon M, Riba-Grognuz O, Huang Y-C, Shoemaker D, Keller L. 2013. A Y-like social chromosome causes alternative colony organization in fire ants. Nature 493:664-668. doi: 10.1038/nature11832 [8] Thompson MJ, Jiggins CD. 2014. Supergenes and their role in evolution. Heredity 113:1-8. doi: 10.1038/hdy.2014.20 [9] Schwander T, Libbrecht R, Keller L. 2014. Supergenes and Complex Phenotypes. Current Biology 24:R288-R294. doi: 10.1016/j.cub.2014.01.056 [10] Charlesworth D. 2015. The status of supergenes in the 21st century: recombination suppression in Batesian mimicry and sex chromosomes and other complex adaptations. Evolutionary Applications 9:74-90. doi: 10.1111/eva.12291 | Structural genomic changes underlie alternative reproductive strategies in the ruff (Philomachus pugnax) | Lamichhaney S, Fan G, Widemo F, Gunnarsson U, Thalmann DS, Hoeppner MP, Kerje S, Gustafson U, Shi C, Zhang H, et al. | <p>The ruff is a Palearctic wader with a spectacular lekking behavior where highly ornamented males compete for females1, 2, 3, 4. This bird has one of the most remarkable mating systems in the animal kingdom, comprising three different male morph... | Adaptation, Behavior & Social Evolution, Genotype-Phenotype, Life History, Population Genetics / Genomics, Quantitative Genetics, Reproduction and Sex | Thomas Flatt | 2016-12-13 17:46:54 | View | ||
13 Dec 2016
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Addicted? Reduced host resistance in populations with defensive symbiontsMartinez J, Cogni R, Cao C, Smith S, Illingworth CJR & Jiggins FM https://doi.org/10.1098/rspb.2016.0778Hooked on WolbachiaRecommended by Ana Rivero and Natacha KremerThis very nice paper by Martinez et al. [1] provides further evidence, if further evidence was needed, of the extent to which heritable microorganisms run the evolutionary show. Reference [1] Martinez J, Cogni R, Cao C, Smith S, Illingworth CJR & Jiggins FM. 2016. Addicted? Reduced host resistance in populations with defensive symbionts. Proceedings of the Royal Society of London B 283:20160778. doi: 10.1098/rspb.2016.0778 | Addicted? Reduced host resistance in populations with defensive symbionts | Martinez J, Cogni R, Cao C, Smith S, Illingworth CJR & Jiggins FM | <p>Heritable symbionts that protect their hosts from pathogens have been described in a wide range of insect species. By reducing the incidence or severity of infection, these symbionts have the potential to reduce the strength of selection on gen... | Adaptation, Evolutionary Applications, Evolutionary Ecology, Experimental Evolution, Life History | Ana Rivero | 2016-12-13 20:08:37 | View | ||
13 Dec 2016
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Prezygotic isolation, mating preferences, and the evolution of chromosomal inversionsDagilis AJ, Kirkpatrick M https://doi.org/10.1111/evo.12954The spread of chromosomal inversions as a mechanism for reinforcementRecommended by Denis Roze and Thomas BroquetSeveral examples of chromosomal inversions carrying genes affecting mate choice have been reported from various organisms. Furthermore, inversions are also frequently involved in genetic isolation between populations or species. Past work has shown that inversions can spread when they capture not only some loci involved in mate choice but also loci involved in incompatibilities between hybridizing populations [1]. In this new paper [2], the authors derive analytical approximations for the selection coefficient associated with an inversion suppressing recombination between a locus involved in mate choice and one (or several) locus involved in Dobzhansky-Muller incompatibilities. Two mechanisms for mate choice are considered: assortative mating based on the allele present at a single locus, or a trait-preference model where one locus codes for the trait and another for the preference. The results show that such an inversion is generally favoured, the selective advantage associated with the inversion being strongest when hybridization is sufficiently frequent. Assuming pairwise epistatic interactions between loci involved in incompatibilities, selection for the inversion increases approximately linearly with the number of such loci captured by the inversion. This paper is a good read for several reasons. First, it presents the problem clearly (e.g. the introduction provides a clear and concise presentation of the issue and past work) and its crystal-clear writing facilitates the reader's understanding of theoretical approaches and results. Second, the analysis is competently done and adds to previous work by showing that very general conditions are expected to be favourable to the spread of the type of inversion considered here. And third, it provides food for thought about the role of inversions in the origin or the reinforcement of divergence between nascent species. One result of this work is that an inversion linked to pre-zygotic isolation "is favoured so long as there is viability selection against recombinant genotypes", suggesting that genetic incompatibilities must have evolved first and that inversions capturing mating preference loci may then enhance pre-existing reproductive isolation. However, the results also show that inversions are more likely to be favoured in hybridizing populations among which gene flow is still high, rather than in more strongly isolated populations. This matches the observation that inversions are more frequently observed between sympatric species than between allopatric ones. References [1] Trickett AJ, Butlin RK. 1994. Recombination Suppressors and the Evolution of New Species. Heredity 73:339-345. doi: 10.1038/hdy.1994.180 [2] Dagilis AJ, Kirkpatrick M. 2016. Prezygotic isolation, mating preferences, and the evolution of chromosomal inversions. Evolution 70: 1465–1472. doi: 10.1111/evo.12954 | Prezygotic isolation, mating preferences, and the evolution of chromosomal inversions | Dagilis AJ, Kirkpatrick M | <p>Chromosomal inversions are frequently implicated in isolating species. Models have shown how inversions can evolve in the context of postmating isolation. Inversions are also frequently associated with mating preferences, a topic that has not b... | Adaptation, Evolutionary Theory, Genome Evolution, Hybridization / Introgression, Population Genetics / Genomics, Speciation | Denis Roze | 2016-12-13 22:11:54 | View | ||
14 Dec 2016
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The Red Queen lives: epistasis between linked resistance lociMetzger CMJA, Luijckx P, Bento G, Mariadassou M, Ebert D. https://doi.org/10.1111/evo.12854Evidence of epistasis provides further support to the Red Queen theory of host-parasite coevolutionRecommended by Adele Mennerat and Thierry LefèvreAccording to the Red Queen theory of antagonistic host-parasite coevolution, adaptation of parasites to the most common host genotype results in negative frequency-dependent selection whereby rare host genotypes are favoured. Assuming that host resistance relies on a genetic host-parasite (mis)match involving several linked loci, then recombination appears as much more efficient than parthenogenesis in generating new resistant host genotypes. This has long been proposed to explain one of the biggest so-called paradoxes in evolutionary biology, i.e. the maintenance of recombination despite its twofold cost. Evidence from various study systems indicates that successful infection (and hence host resistance) depends on a genetic match between the parasite’s and the host’s genotype via molecular interactions involving elicitor/receptor mechanisms. However the key assumption of epistasis, i.e. that this genetic host-parasite match involves several linked resistance loci, remained unsupported so far. Metzger and coauthors [1] now provide empirical support for it. Daphnia magna can reproduce both sexually and clonally and their well-studied interaction with Pasteuria ramosa makes them an excellent model system to investigate the genetics of host resistance. D. magna hosts were found to be either resistant (complete lack of attachment of parasite spores to the host’s foregut) or susceptible (full attachment). In this study the authors carried out an elegant Mendelian genetic investigation by performing multiple crosses between four host genotypes differing in their resistance to two different parasite isolates [1]. Their results show that resistance of D. magna to each of the two P. ramosa isolates relies on Mendelian inheritance at two loci that are linked (A and B), each of them having two alleles with dominant resistance; furthermore resistance to one parasite isolate confers susceptibility to the other. They also show that a third locus appears to confer double resistance (C), but that even double resistant hosts remain susceptible to other parasite isolates, and hence that universal host resistance is lacking – all of this supporting the Red Queen theory. This paper demonstrates with a high level of clarity that host resistance is governed by multiple linked loci. The assumption of epistasis between resistance loci is supported, which makes it possible for sexual recombination to be maintained by antagonistic host-parasite coevolution. Reference [1] Metzger CMJA, Luijckx P, Bento G, Mariadassou M, Ebert D. 2016. The Red Queen lives: epistasis between linked resistance loci. Evolution 70:480-487. doi: 10.1111/evo.12854 | The Red Queen lives: epistasis between linked resistance loci | Metzger CMJA, Luijckx P, Bento G, Mariadassou M, Ebert D. | <p>A popular theory explaining the maintenance of genetic recombination (sex) is the Red Queen Theory. This theory revolves around the idea that time-lagged negative frequency-dependent selection by parasites favors rare host genotypes generated t... | Evolutionary Dynamics, Evolutionary Theory, Reproduction and Sex, Species interactions | Adele Mennerat | 2016-12-14 13:58:53 | View | ||
16 Dec 2016
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Spatiotemporal microbial evolution on antibiotic landscapesBaym M, Lieberman TD, Kelsic ED, Chait R, Gross R, Yelin I, Kishony R https://doi.org/10.1126/science.aag0822A poster child for experimental evolutionRecommended by Daniel Rozen and Arjan de VisserEvolution is usually studied via two distinct approaches: by inferring evolutionary processes from relatedness patterns among living species or by observing evolution in action in the laboratory or field. A recent study by Baym and colleagues in Science [1] has now combined these approaches by taking advantage of the pattern left behind by spatially evolving bacterial populations. Evolution is often considered too slow to see, and can only be inferred by studying patterns of relatedness using phylogenetic trees. Increasingly, however, researchers are moving nature into the lab and watching as evolution unfolds under their noses. The field of experimental evolution follows evolutionary change in the laboratory over 10s to 1000s of generations, yielding insights into bacterial, viral, plant, or fly evolution (among many other species) that are simply not possible in the field. Yet, as powerful as experimental evolution is, it lacks a posterchild. There is no Galapagos finch radiation, nor a stunning series of cichlids to showcase to our students to pique their interests. Let’s face it, E. coli is no stickleback! And while practitioners of experimental evolution can explain the virtues of examining 60,000 generations of bacterial evolution in action, appreciating this nevertheless requires a level of insight and imagination that often eludes students, who need to see “it” to get it. Enter MEGA, an idea and a film that could become the new face of experimental evolution. It replaces big numbers of generations or images of scientists, with an actual picture of the scientific result. MEGA, or Microbial Evolution and Growth Arena, is essentially an enormous petri dish and is the brainchild of Michael Baym, Tami Leiberman and their colleagues in Roy Kishony’s lab at Technion Israel Institute of Technology and Harvard Medical School. The idea of MEGA is to allow bacteria to swim over a spatially defined landscape while adapting to the local conditions, in this case antibiotics. When bacteria are inoculated onto one end of the plate they consume resources while swarming forward from the plate edge. In a few days, the bacteria grow into an area with antibiotics to which they are susceptible. This stops growth until a mutation arises that permits the bacteria to jump this hurdle, after which growth proceeds until the next hurdle of a 10-fold higher antibiotic concentration, and so on. By this simple approach, Baym et al. [1] evolved E. coli that were nearly 105-fold more resistant to two different antibiotics in just over 10 days. In addition, they identified the mutations that were required for these changes, showed that mutations conferring smaller benefits were required before bacteria could evolve maximal resistance, observed changes to the mutation rate, and demonstrated the importance of spatial structure in constraining adaptation. For one thing, the rate of resistance evolution is impressive, and also quite scary given the mounting threat of antibiotic-resistant pathogens. However, MEGA also offers a uniquely visual insight into evolutionary change. By taking successive images of the MEGA plate, the group was able to watch the bacteria move, get trapped because of their susceptibility to the antibiotic, and then get past these traps as new mutations emerged that increased resistance. Each transition showcases evolution in real time. In addition, by leaving a spatial pattern of evolutionary steps behind, the MEGA plate offers unique opportunities to thoroughly investigate these steps when the experiment is finished. For instance, subsequent steps in mutational pathways can be characterized, but also their effects on fitness can be quantified in situ by measuring changes in survival and reproduction. This new method is undoubtedly a boon to the field of experimental evolution and offers endless opportunities for experimental elaboration. Perhaps of equal importance, MEGA is a tool that is portable to the classroom and to the public at large. Don’t believe in evolution? Watch this. You only have time for a short internship or lab practical? No problem. Don’t worry much about antibiotic resistance? Check this out. Like the best experimental tools, MEGA is simple but allows for complicated insights. And even if it is less charismatic than a finch, it still allows for the kinds of “gee-whiz” insights that will get students hooked on evolutionary biology. Reference [1] Baym M, Lieberman TD, Kelsic ED, Chait R, Gross R, Yelin I, Kishony R. 2016. Spatiotemporal microbial evolution on antibiotic landscapes. Science 353:1147-1151. doi: 10.1126/science.aag0822 | Spatiotemporal microbial evolution on antibiotic landscapes | Baym M, Lieberman TD, Kelsic ED, Chait R, Gross R, Yelin I, Kishony R | <p>A key aspect of bacterial survival is the ability to evolve while migrating across spatially varying environmental challenges. Laboratory experiments, however, often study evolution in well-mixed systems. Here, we introduce an experimental devi... | Adaptation, Evolutionary Applications, Experimental Evolution | Daniel Rozen | 2016-12-14 14:26:06 | View | ||
14 Dec 2016
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Evolution of resistance to single and combined floral phytochemicals by a bumble bee parasitePalmer-Young EC, Sadd BM, Adler LS https://doi.org/10.1111/jeb.13002The medicinal value of phytochemicals is hindered by pathogen evolution of resistanceRecommended by Alison Duncan and Sara MagalhaesAs plants cannot run from their enemies, natural selection has favoured the evolution of diverse chemical compounds (phytochemicals) to protect them against herbivores and pathogens. This provides an opportunity for plant feeders to exploit these compounds to combat their own enemies. Indeed, it is widely known that herbivores use such compounds as protection against predators [1]. Recently, this reasoning has been extended to pathogens, and elegant studies have shown that some herbivores feed on phytochemical-containing plants reducing both parasite abundance within hosts [2] and their virulence [3]. References [1] Duffey SS. 1980. Sequestration of plant natural products by insects. Annual Review of Entomology 25: 447-477. doi: 10.1146/annurev.en.25.010180.002311 [2] Richardson LL et al. 2015. Secondary metabolites in floral nectar reduce parasite infections in bumblebees. Proceedings of the Royal Society of London B 282: 20142471. doi: 10.1098/rspb.2014.2471 [3] Lefèvre T et al. 2010. Evidence for trans-generational medication in nature. Ecology Letters 13: 1485-93. doi: 10.1111/j.1461-0248.2010.01537.x [4] Palmer-Young EC, Sadd BM, Adler LS. 2017. Evolution of resistance to single and combined floral phytochemicals by a bumble bee parasite. Journal of Evolutionary Biology 30: 300-312. doi: 10.1111/jeb.13002 [5] Müller CB, Schmid-Hempel P. 1993. Exploitation of cold temperature as defence against parasitoids in bumblebees. Nature 363: 65-67. doi: 10.1038/363065a0 [6] Potts SG et al. 2010. Global pollinator declines: trends, impacts and drivers. Trends in Ecology and Evolution 25: 345-353. doi: 10.1016/j.tree.2010.01.007 | Evolution of resistance to single and combined floral phytochemicals by a bumble bee parasite | Palmer-Young EC, Sadd BM, Adler LS | <p>Repeated exposure to inhibitory compounds can drive the evolution of resistance, which weakens chemical defence against antagonists. Floral phytochemicals in nectar and pollen have antimicrobial properties that can ameliorate infection in polli... | Evolutionary Ecology | Alison Duncan | 2016-12-14 16:47:14 | View | ||
14 Dec 2016
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High Rates of Species Accumulation in Animals with Bioluminescent Courtship DisplaysEllis EA, Oakley TH https://doi.org/10.1016/j.cub.2016.05.043Bioluminescent sexually selected traits as an engine for biodiversity across animal speciesRecommended by Astrid Groot and Carole SmadjaIn evolutionary biology, sexual selection is hypothesized to increase speciation rates in animals, as theory predicts that sexual selection will contribute to phenotypic diversification and affect rates of species accumulation at macro-evolutionary time scales. However, testing this hypothesis and gathering convincing evidence have proven difficult. Although some studies have shown a strong correlation between proxies of sexual selection and species diversity (mostly in birds), this relationship relies on some assumptions on the link between these proxies and the strength of sexual selection and is not detected in some other taxa, making taxonomically widespread conclusions impossible. In a recent study published in Current Biology [1], Ellis and Oakley provide strong evidence that bioluminescent sexual displays have driven high species richness in taxonomically diverse animal lineages, providing a crucial link between sexual selection and speciation. Ellis and Oakley [1] explored the scientific literature for well-resolved evolutionary trees with branches containing bioluminescent lineages and identified lineages that use light for courtship or camouflage in a wide range of marine and terrestrial taxa including insects, crustaceans, cephalopods, segmented worms, and fishes. The researchers counted the number of species in each bioluminescent clade and found that all groups with light-courtship displays had more species and faster rates of species accumulation than their non-luminous most closely related sister lineages or ancestors. In contrast, those groups that used bioluminescence for predator avoidance had a lower than expected rate of species richness on average. Nicely encompassing a diversity of taxa and neatly controlling for the rate of species accumulation of the encompassing clade, the results of Ellis and Oakley are clear-cut and provide the most comprehensive evidence to date for the hypothesis that sexual displays can act as drivers of speciation. One question this study incites is what is happening in terms of sexual selection in species displaying defensive bioluminescence or no bioluminescence at all: do those lineages use no mating signals at all or other mating signals that are less apparent, and will those experience lower levels of sexual selection than bioluminescent mating signals, i.e. consistent with Ellis and Oakley results? It would also be interesting to investigate the diversification rates in animal species using other modalities, such as chemical, acoustic or any other type of signals used by males, females or both sexes, to determine what types of sexual signals may be more generally drivers of speciation. References [1] Ellis EA, Oakley TH. 2016. High Rates of Species Accumulation in Animals with Bioluminescent Courtship Displays. Current Biology 26:1916–1921. doi: 10.1016/j.cub.2016.05.043 [2] Davis MP, Holcroft NI, Wiley EO, Sparks JS, Smith WL. 2014. Species-specific bioluminescence facilitates speciation in the deep sea. Marine Biology 161:11391148. doi: 10.1007/s00227-014-2406-x [3] Davis MP, Sparks JS, Smith WL. 2016. Repeated and Widespread Evolution of Bioluminescence in Marine Fishes. PLoS One 11:e0155154. doi: 10.1371/journal.pone.0155154 [4] Claes JM, Nilsson D-E, Mallefet J, Straube N. 2015. The presence of lateral photophores correlates with increased speciation in deep-sea bioluminescent sharks. Royal Society Open Science 2:150219. doi: 10.1098/rsos.150219 | High Rates of Species Accumulation in Animals with Bioluminescent Courtship Displays | Ellis EA, Oakley TH | <p>One of the great mysteries of evolutionary biology is why closely related lineages accumulate species at different rates. Theory predicts that populations undergoing strong sexual selection will more quickly differentiate because of increased p... | Adaptation, Evolutionary Ecology, Sexual Selection, Speciation | Astrid Groot | 2016-12-14 19:01:59 | View | ||
15 Dec 2016
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Basidiomycete yeasts in the cortex of ascomycete macrolichensSpribille T, Tuovinen V, Resl P, et al. https://doi.org/10.1126/science.aaf8287New partner at the core of macrolichen diversityRecommended by Enric Frago and Benoit FaconIt has long been known that most multicellular eukaryotes rely on microbial partners for a variety of functions including nutrition, immune reactions and defence against enemies. Lichens are probably the most popular example of a symbiosis involving a photosynthetic microorganism (an algae, a cyanobacteria or both) living embedded within the filaments of a fungus (usually an ascomycete). The latter is the backbone structure of the lichen, whereas the former provides photosynthetic products. Lichens are unique among symbioses because the structures the fungus and the photosynthetic microorganism form together do not resemble any of the two species living in isolation. Classic textbook examples like lichens are not often challenged and this is what Toby Spribille and his co-authors did with their paper published in July 2016 in Science [1]. This story started with the study of two species of macrolichens from the class of Lecanoromycetes that are commonly found in the mountains of Montana (US): Bryoria fremontii and B. tortuosa. For more than 90 years, these species have been known to differ in their chemical composition and colour, but studies performed so far failed in finding differences at the molecular level in both the mycobiont and the photobiont. These two species were therefore considered as nomenclatural synonyms, and the origin of their differences remained elusive. To solve this mystery, the authors of this work performed a transcriptome-wide analysis that, relative to previous studies, expanded the taxonomic range to all Fungi. This analysis revealed higher abundances of a previously unknown basidiomycete yeast from the genus Cyphobasidium in one of the lichen species, a pattern that was further confirmed by combining microscopy imaging and the fluorescent in situ hybridisation technique (FISH). Finding out that a previously unknown micro-organism changes the colour and the chemical composition of an organism is surprising but not new. For instance, bacterial symbionts are able to trigger colour changes in some insect species [2], and endophyte fungi are responsible for the production of defensive compounds in the leaves of several grasses [3]. The study by Spribille and his co-authors is fascinating because it demonstrates that Cyphobasidium yeasts have played a key role in the evolution and diversification of Lecanoromycetes, one of the most diverse classes of macrolichens. Indeed these basidiomycete yeasts were not only found in Bryoria but in 52 other lichen genera from all six continents, and these included 42 out of 56 genera in the family Parmeliaceae. Most of these sequences formed a highly supported monophyletic group, and a molecular clock revealed that the origin of many macrolichen groups occurred around the same time Cyphobasidium yeasts split from Cystobasidium, their nearest relatives. This newly discovered passenger is therefore an ancient inhabitant of lichens and has driven the evolution of this emblematic group of organisms. This study raises an important question on the stability of complex symbiotic partnerships. In intimate obligatory symbioses the evolutionary interests of both partners are often identical and what is good for one is also good for the other. This is the case of several insects that feed on poor diets like phloem and xylem sap, and which carry vertically-transmitted symbionts that provide essential nutrients. Molecular phylogenetic studies have repeatedly shown that in several insect groups transition to phloem or xylem feeding occurred at the same time these nutritional symbionts were acquired [4]. In lichens, an outstanding question is to know what was the key feature Cyphobasidium yeasts brought to the symbiosis. As suggested by the authors, these yeasts are likely to be involved in the production of secondary defensive metabolites and architectural structures, but, are these services enough to explain the diversity found in macrolichens? This paper is an appealing example of a multipartite symbiosis where the different partners share an ancient evolutionary history. References [1] Spribille T, Tuovinen V, Resl P, et al. 2016. Basidiomycete yeasts in the cortex of ascomycete macrolichens. Science 353:488–92. doi: 10.1126/science.aaf8287 [2] Tsuchida T, Koga R, Horikawa M, et al. 2010. Symbiotic Bacterium Modifies Aphid Body Color. Science 330:1102–1104. doi: 10.1126/science.1195463 [3] Clay K. 1988. Fungal Endophytes of Grasses: A Defensive Mutualism between Plants and Fungi. Ecology 69:10–16. doi: 10.2307/1943155 [4] Moran NA. 2007. Symbiosis as an adaptive process and source of phenotypic complexity. Proceeding of the National Academy of Science USA 104:8627–8633. doi: 10.1073/pnas.0611659104 | Basidiomycete yeasts in the cortex of ascomycete macrolichens | Spribille T, Tuovinen V, Resl P, et al. | <p>For over 140 years, lichens have been regarded as a symbiosis between a single fungus, usually an ascomycete, and a photosynthesizing partner. Other fungi have long been known to occur as occasional parasites or endophytes, but the one lichen–o... | Adaptation, Evolutionary Ecology, Genome Evolution, Genotype-Phenotype, Life History, Macroevolution, Molecular Evolution, Phylogenetics / Phylogenomics, Speciation, Species interactions | Enric Frago | 2016-12-15 05:46:14 | View |
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