Papers

2014
Rosser N, Dasmahapatra KK, Mallet J. Stable Heliconius butterfly hybrid zones are correlated with a local rainfall peak at the edge of the Amazon basin. Evolution. 2014;68 :3470-3484.Abstract

Multilocus clines between Mullerian mimetic races of Heliconius butterflies provide a classic example of the maintenance of hybrid zones and their importance in speciation. Concordant hybrid zones in the mimics Heliconius erato and H. melpomene in northern Peru were carefully documented in the 1980s, and this prior work now permits a historical analysis of the movement or stasis of the zones. Previous work predicted that these zones might be moving toward the Andes due to selective asymmetry. Extensive deforestation and climate change might also be expected to affect the positions and widths of the hybrid zones. We show that the positions and shapes of these hybrid zones have instead remained remarkably stable between 1985 and 2012. The stability of this interaction strongly implicates continued selection, rather than neutral mixing following secondary contact. The stability of cline widths and strong linkage disequilibria (gametic correlation coefficients Rmax = 0.35-0.56 among unlinked loci) over 25 years suggest that mimetic selection pressures on each color pattern locus have remained approximately constant (s approximately 0.13-0.40 per locus in both species). Exceptionally high levels of precipitation at the edge of the easternmost Andes may act as a population density trough for butterflies, trapping the hybrid zones at the foot of the mountains, and preventing movement. As such, our results falsify one prediction of the Pleistocene Refugium theory: That the ranges of divergent species or subspecies should be centered on regions characterized by maxima of rainfall, with hybrid zones falling in more arid regions between them.

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doi:10.1111/evo.12539

2013
Mérot C, Mavárez J, Evin A, Dasmahapatra KK, Mallet J, Lamas G, Joron M. Genetic differentiation without mimicry shift in a pair of hybridizing Heliconius species (Lepidoptera: Nymphalidae). Biological Journal of the Linnean Society. 2013;109 :830-847.Abstract

Butterflies in the genus Heliconius have undergone rapid adaptive radiation for warning patterns and mimicry, andare excellent models to study the mechanisms underlying diversification. In Heliconius, mimicry rings typicallyinvolve distantly related species, whereas closely related species often join different mimicry rings. Genetic andbehavioural studies have shown how reproductive isolation in many pairs of Heliconius taxa is largely mediatedby natural and sexual selection on wing colour patterns. However, recent studies have uncovered new cases inwhich pairs of closely related species are near-perfect mimics of each other. Here, we provide morphometric andgenetic evidence for the coexistence of two closely related, hybridizing co-mimetic species on the eastern slopes ofthe Andes, H. melpomene amaryllis and H. timareta ssp. nov., which is described here as H. timareta thelxinoe.A joint analysis of multilocus genotyping and geometric morphometrics of wing shape shows a high level ofdifferentiation between the two species, with only limited gene flow and mixing. Some degree of genetic mixing canbe detected, but putative hybrids were rare, only one of 175 specimens being a clear hybrid. In contrast, we foundphenotypic differentiation between populations of H. timareta thelxinoe, possibly indicative of strong selection forlocal mimicry in different communities. In this pair of species, the absence of breakdown of genetic isolation despitenear-identical wing patterns implies that factors other than wing patterns keep the two taxa apart, such aschemical or behavioural signals, or ecological adaptation along a strong altitudinal gradient. © 2013 The LinneanSociety of London, Biological Journal of the Linnean Society, 2013

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doi:10.1111/bij.12091

Mallet J. Introgression: Brower's criticisms. Part I. New evidence for hybridization and introgression is unsettling. eratosignis [Internet]. 2013. BLOG
Mallet J. Introgression: Brower's criticisms. Part II. Itemized critiques by Brower (2012), and comments thereon. eratosignis [Internet]. 2013. BLOG
Merrill RM, Naisbit RE, Mallet J, Jiggins CD. Ecological and genetic factors influencing the transition between host-use strategies in sympatric Heliconius butterflies. Journal of Evolutionary Biology. 2013;26 :1959-67.Abstract

Shifts in host-plant use by phytophagous insects have played a central role in their diversification. Evolving host-use strategies will reflect a trade-off between selection pressures. The ecological niche of herbivorous insects is partitioned along several dimensions, and if populations remain in contact, recombination will break down associations between relevant loci. As such, genetic architecture can profoundly affect the coordinated divergence of traits and subsequently the ability to exploit novel habitats. The closely related species Heliconius cydno and H. melpomene differ in mimetic colour pattern, habitat and host-plant use. We investigate the selection pressures and genetic basis underlying host-use differences in these two species. Host-plant surveys reveal that H. melpomene specializes on a single species of Passiflora. This is also true for the majority of other Heliconius species in secondary growth forest at our study site, as expected under a model of interspecific competition. In contrast, H. cydno, which uses closed-forest habitats where both Heliconius and Passiflora are less common, appears not to be restricted by competition and uses a broad selection of the available Passiflora. However, other selection pressures are likely involved, and field experiments reveal that early larval survival of both butterfly species is highest on Passiflora menispermifolia, but most markedly so for H. melpomene, the specialist on that host. Finally, we demonstrate an association between host-plant acceptance and colour pattern amongst interspecific hybrids, suggesting that major loci underlying these important ecological traits are physically linked in the genome. Together, our results reveal ecological and genetic associations between shifts in habitat, host use and mimetic colour pattern that have likely facilitated both speciation and coexistence.

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doi: 10.1111/jeb.12194

Briscoe AD, Macias-Munoz A, Kozak KM, Walters JR, Yuan F, Jamie GA, Martin SH, Dasmahapatra KK, Ferguson LC, Mallet J, et al. Female behaviour drives expression and evolution of gustatory receptors in butterflies. PLoS Genetics. 2013;9 :e1003620.Abstract

Secondary plant compounds are strong deterrents of insect oviposition and feeding, but may also be attractants for specialist herbivores. These insect-plant interactions are mediated by insect gustatory receptors (Grs) and olfactory receptors (Ors). An analysis of the reference genome of the butterfly Heliconius melpomene, which feeds on passion-flower vines (Passiflora spp.), together with whole-genome sequencing within the species and across the Heliconius phylogeny has permitted an unprecedented opportunity to study the patterns of gene duplication and copy-number variation (CNV) among these key sensory genes. We report in silico gene predictions of 73 Gr genes in the H. melpomene reference genome, including putative CO2, sugar, sugar alcohol, fructose, and bitter receptors. The majority of these Grs are the result of gene duplications since Heliconius shared a common ancestor with the monarch butterfly or the silkmoth. Among Grs but not Ors, CNVs are more common within species in those gene lineages that have also duplicated over this evolutionary time-scale, suggesting ongoing rapid gene family evolution. Deep sequencing ( approximately 1 billion reads) of transcriptomes from proboscis and labial palps, antennae, and legs of adult H. melpomene males and females indicates that 67 of the predicted 73 Gr genes and 67 of the 70 predicted Or genes are expressed in these three tissues. Intriguingly, we find that one-third of all Grs show female-biased gene expression (n = 26) and nearly all of these (n = 21) are Heliconius-specific Grs. In fact, a significant excess of Grs that are expressed in female legs but not male legs are the result of recent gene duplication. This difference in Gr gene expression diversity between the sexes is accompanied by a striking sexual dimorphism in the abundance of gustatory sensilla on the forelegs of H. melpomene, suggesting that female oviposition behaviour drives the evolution of new gustatory receptors in butterfly genomes.

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(Open Access) doi:10.1371/journal.pgen.1003620

Martin SH, Dasmahapatra KK, Nadeau NJ, Salazar C, Walters JR, Simpson F, Blaxter M, Manica A, Mallet J, Jiggins CD. Genome-wide evidence for speciation with gene flow in Heliconius butterflies. Genome Research. 2013;23 :1817-1828.Abstract

Most speciation events probably occur gradually, without complete and immediate reproductive isolation, but the full extent of gene flow between diverging species has rarely been characterized on a genome-wide scale. Documenting the extent and timing of admixture between diverging species can clarify the role of geographic isolation in speciation. Here we use new methodology to quantify admixture at different stages of divergence in Heliconius butterflies, based on whole-genome sequences of 31 individuals. Comparisons between sympatric and allopatric populations of H. melpomene, H. cydno, and H. timareta revealed a genome-wide trend of increased shared variation in sympatry, indicative of pervasive interspecific gene flow. Up to 40% of 100-kb genomic windows clustered by geography rather than by species, demonstrating that a very substantial fraction of the genome has been shared between sympatric species. Analyses of genetic variation shared over different time intervals suggested that admixture between these species has continued since early in speciation. Alleles shared between species during recent time intervals displayed higher levels of linkage disequilibrium than those shared over longer time intervals, suggesting that this admixture took place at multiple points during divergence and is probably ongoing. The signal of admixture was significantly reduced around loci controlling divergent wing patterns, as well as throughout the Z chromosome, consistent with strong selection for Mullerian mimicry and with known Z-linked hybrid incompatibility. Overall these results show that species divergence can occur in the face of persistent and genome-wide admixture over long periods of time.

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(Open Access) doi:10.1101/gr.159426.113

Nadeau NJ, Martin SH, Kozak KM, Salazar C, Dasmahapatra KK, Davey JW, Baxter SW, Blaxter ML, Mallet J, Jiggins CD. Genome-wide patterns of divergence and gene flow across a butterfly radiation. Molecular Ecology. 2013;22 :814-826.Abstract

The Heliconius butterflies are a diverse recent radiation comprising multiple levels of divergence with ongoing gene flow between species. The recently sequenced genome of Heliconius melpomene allowed us to investigate the genomic evolution of this group using dense RAD marker sequencing. Phylogenetic analysis of 54 individuals robustly supported reciprocal monophyly of H. melpomene and Heliconius cydno and refuted previous phylogenetic hypotheses that H. melpomene may be paraphylectic with respect to H. cydno. Heliconius timareta also formed a monophyletic clade closely related but distinct from H. cydno with Heliconius heurippa falling within this clade. We find evidence for genetic admixture between sympatric populations of the sister clades H. melpomene and H. cydno/timareta, particularly between H. cydno and H. melpomene from Central America and between H. timareta and H. melpomene from the eastern slopes of the Andes. Between races, divergence is primarily explained by isolation by distance and there is no detectable genetic population structure between parapatric races, suggesting that hybrid zones between races are not zones of secondary contact. Our results also support previous findings that colour pattern loci are shared between populations and species with similar colour pattern elements. Furthermore, this pattern is almost unique to these genomic regions, with only a very small number of other loci showing significant similarity between populations and species with similar colour patterns.

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doi: 10.1111/j.1365-294X.2012.05730.x

Abbott R, Albach D, Ansell S, Arntzen JW, Baird SJ, Bierne N, Boughman J, Brelsford A, Buerkle CA, Buggs R, et al. Hybridization and speciation. Journal of Evolutionary Biology. 2013;26 :229-246.Abstract

Hybridization has many and varied impacts on the process of speciation. Hybridization may slow or reverse differentiation by allowing gene flow and recombination. It may accelerate speciation via adaptive introgression or cause near-instantaneous speciation by allopolyploidization. It may have multiple effects at different stages and in different spatial contexts within a single speciation event. We offer a perspective on the context and evolutionary significance of hybridization during speciation, highlighting issues of current interest and debate. In secondary contact zones, it is uncertain if barriers to gene flow will be strengthened or broken down due to recombination and gene flow. Theory and empirical evidence suggest the latter is more likely, except within and around strongly selected genomic regions. Hybridization may contribute to speciation through the formation of new hybrid taxa, whereas introgression of a few loci may promote adaptive divergence and so facilitate speciation. Gene regulatory networks, epigenetic effects and the evolution of selfish genetic material in the genome suggest that the Dobzhansky-Muller model of hybrid incompatibilities requires a broader interpretation. Finally, although the incidence of reinforcement remains uncertain, this and other interactions in areas of sympatry may have knock-on effects on speciation both within and outside regions of hybridization.

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doi:10.1111/j.1420-9101.2012.02599.x

2012
Hill RI, Elias M, Dasmahapatra KK, Jiggins CD, Koong V, Willmott KR, Mallet J. Ecologically relevant cryptic species in the highly polymorphic Amazonian butterfly Mechanitis mazaeus sensu lato (Lepidoptera: Nymphalidae; Ithomiini). Biological Journal of the Linnean Society. 2012;106 :540-560.Abstract

The understanding of mimicry has relied on a strong biosystematic framework ever since early naturalists firstrecognized this textbook example of natural selection. We follow in this tradition, applying new biosystematicsinformation to resolve problems in an especially difficult genus of tropical butterflies. Mechanitis species areimportant components of Neotropical mimetic communities. However, their colour pattern variability has presentedchallenges for systematists, and has made it difficult to study the very mimicry they so nicely illustrate. The SouthAmerican Mechanitis mazaeus and relatives have remained particularly intractable. Recent systematists haverecognized one highly polytypic species, whereas earlier work recognized the melanic Andean foothill races as adistinct species: Mechanitis messenoides. Recent molecular evidence suggests M. mazaeus and M. messenoides aregenetically well differentiated, but evidence of morphological and ecological differences indicative of separatespecies was still lacking. Thus, it remains to be conclusively demonstrated whether this is an extreme case of apolymorphic mimetic species, or whether distinct co-mimetic lineages are involved. Here we provide evidence thatM. mazaeus and M. messenoides are ecologically distinct and identify consistent morphological differences in bothadult and immature stages. These ecological and morphological differences are correlated with mitochondrialsequence data. In spite of some overlap in almost all traits, wing shape, adult colour pattern, and larval colourpattern differ between the two species, in addition to clutch size and larval host use in local sympatry. Althoughthree well-differentiated mitochondrial DNA (mtDNA) haplogroups were identified within these two species, one forM. mazaeus and two within M. messenoides, no morphological or ecological differences were found between twomtDNA haplogroups, both of which appear to belong to M. messenoides. We conclude that M. mazaeus andM. messenoides are distinct although highly polymorphic species, each with multiple sympatric co-mimetic forms,and suggest that further work is needed to clarify the identity of other phenotypes and subspecies of Mechanitis.© 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106, 540–560.

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doi:10.1111/j.1095-8312.2012.01874.x

Mallet J, Dasmahapatra KK. Hybrid zones and the speciation continuum in Heliconius butterflies. Molecular Ecology. 2012;21 :5643-5645.Abstract

Tropical butterflies in the genus Heliconius have long 25 been models in26 the study of the stages of speciation. Heliconius are unpalatable to27 predators, and many species are notable for multiple geographic28 populations with striking warning colour pattern differences associated29 with Müllerian mimicry. There is a speciation continuum evident in30 Heliconius hybrid zones, across which mimicry patterns are often31 different, but where hybrids are common and little else differs, through32 to 'bimodal' hybrid zones with strongly marked molecular differences33 with few hybrids, through to 'good' sympatric species. Now Arias et al.34 (2012) have found an intermediate case in Colombian Heliconius cydno35 showing evidence for assortative mating and molecular differences, but36 where hybrids are abundant.

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doi:10.1111/mec.12058

Mallet J. The struggle for existence. How the notion of carrying capacity, K, obscures the links between demography, Darwinian evolution and speciation. Evolutionary Ecology Research. 2012;14 :627–665.Abstract

Question: Population ecology and population genetics are treated separately in mosttextbooks. However, Darwin’s term the ‘struggle for existence’ included both naturalselection and ecological competition. Using the simplest possible mathematical models, thispaper searches for historical reasons for the lack of unity in ecological and evolutionarythought.Assumptions and methods: Logistic density-dependent population growth and Lotka-Volterracompetition models are used throughout. Derivations of the logistic from first principles ofresource use, competition for space, and births and deaths of individuals are documented.A full range of possible kinds of natural selection, including constant selection, density- andfrequency-dependent selection, as well as hard and soft selection, can emerge cleanly asnatural outcomes from the simplest-imaginable haploid models derived from Lotka-Volterracompetition. Extensions to incorporate more realism, including non-linear per capita densitydependence, Allee effects, complex life histories, discrete generations, diploid Mendeliangenetics, sexual populations, and speciation are briefly discussed.Conclusions: Widespread use of r-K (‘carrying capacity’) models of population growthappears to have catalysed fundamental discords in ecology, and between ecology and evolution.Verhulst’s original polynomial form of the logistic, here termed the r-α model, is both morenatural in theory, and accords better with empirical data. The r-α formulation explainsapparent paradoxes involving the r-K logistic, including controversial aspects of r- andK-selection. Adoption of first-principles birth–death or r-α modelling clarifies natural selectionin density-regulated populations, and leads to an improved understanding of Darwinianevolution and speciation.

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Rosser N, Phillimore AB, Huertas B, Willmott KR, Mallet J. Testing historical explanations for gradients in species richness in heliconiine butterflies of tropical America. Biological Journal of the Linnean Society. 2012;105 :479-497.Abstract

We compiled a large database of 58 059 point locality records for 70 species and 434 subspecies of heliconiinebutterflies and used these data to test evolutionary hypotheses for their diversification. To study geographicalpatterns of diversity and contact zones, we mapped: (1) species richness; (2) mean molecular phylogenetic terminalbranch length; (3) subspecies richness and the proportion of specimens that were subspecific hybrids, and (4)museum sampling effort. Heliconiine species richness is high throughout the Amazon region and peaks near theequator in the foothills and middle elevations of the eastern Andes. Mean phylogenetic terminal branch length islowest in the eastern Andes and tends to be low in species-rich areas. By contrast, areas of high subspeciesrichness, where subspecies overlap in range and/or hybridize, are concentrated along the course of the AmazonRiver, with the eastern Andes slopes and foothills relatively depauperate in terms of local intraspecific phenotypicdiversity. Spatial gradients in heliconiine species richness in the Neotropics are consistent with the hypothesis thatspecies richness gradients are driven at least in part by variation in speciation and/or extinction rates, resultingin observed gradients in mean phylogenetic branch length, rather than via evolutionary age or niche conservatismalone. The data obtained in the present study, coupled with individual case studies of recently evolved Heliconiusspecies, suggest that the radiation of heliconiine butterflies occurred predominantly on the eastern slopes of theAndes in Colombia, Ecuador, and Peru, as well as in the upper/middle Amazon basin. © 2012 The Linnean Societyof London, Biological Journal of the Linnean Society, 2012, 105, 479–497.

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doi:10.1111/j.1095-8312.2011.01814.x

Heliconius_Genome_Consortium. Butterfly genome reveals promiscuous exchange of mimicry adaptations among species. Nature. 2012;487 :94-98.Abstract

The evolutionary importance of hybridization and introgression has long been debated. Hybrids are usually rare and unfit, but even infrequent hybridization can aid adaptation by transferring beneficial traits between species. Here we use genomic tools to investigate introgression in Heliconius, a rapidly radiating genus of neotropical butterflies widely used in studies of ecology, behaviour, mimicry and speciation. We sequenced the genome of Heliconius melpomene and compared it with other taxa to investigate chromosomal evolution in Lepidoptera and gene flow among multiple Heliconius species and races. Among 12,669 predicted genes, biologically important expansions of families of chemosensory and Hox genes are particularly noteworthy. Chromosomal organization has remained broadly conserved since the Cretaceous period, when butterflies split from the Bombyx (silkmoth) lineage. Using genomic resequencing, we show hybrid exchange of genes between three co-mimics, Heliconius melpomene, Heliconius timareta and Heliconius elevatus, especially at two genomic regions that control mimicry pattern. We infer that closely related Heliconius species exchange protective colour-pattern genes promiscuously, implying that hybridization has an important role in adaptive radiation.

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doi: 10.1038/nature11041

Boenigk J, Ereshefsky M, Hoef-Emden K, Mallet J, Bass D. Concepts in protistology: species definitions and boundaries. European Journal of Protistology. 2012;48 :96-102.Abstract

This paper summarises the Symposium 'Concepts in Protistology', during the VI European Congress of Protistology, Berlin, 25-29 July 2011. There is an increasing focus on cataloguing the number of species on earth, species barcoding initiatives, and the increasing need to reconcile molecular with morphological data in protists within a taxonomic framework. We identify several obstructions to defining species in protists, including the high incidence of asexuality, high levels of both morphological conservation and evolutionary convergence, high levels of genetic diversity that cannot so far be correlated with phenotypic characters, conflicting signals between both genetic and phenotypic taxonomic markers, and different requirements and challenges of species definition in different protist groups. We assert that there is no species 'category' for protists, and recommend that a working definition of species is clarified on a case-by-case basis. Thus, a consensus approach may emerge within protist groups, but any one approach is unlikely to encompass a wide phylogenetic range. However, as long as clarity of intent and method is maintained, the utility of the term 'species' in protists will also be maintained as a reproducible and convenient (if artificial) way of referring to particular lineages within a tightly defined context.

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doi: 10.1016/j.ejop.2011.11.004

Merrill RM, Wallbank RW, Bull V, Salazar PC, Mallet J, Stevens M, Jiggins CD. Disruptive ecological selection on a mating cue. Proceedings of the Royal Society B: Biological Sciences. 2012;279 :4907-4913.Abstract

Adaptation to divergent ecological niches can result in speciation. Traits subject to disruptive selection that also contribute to non-random mating will facilitate speciation with gene flow. Such 'magic' or 'multiple-effect' traits may be widespread and important for generating biodiversity, but strong empirical evidence is still lacking. Although there is evidence that putative ecological traits are indeed involved in assortative mating, evidence that these same traits are under divergent selection is considerably weaker. Heliconius butterfly wing patterns are subject to positive frequency-dependent selection by predators, owing to aposematism and Mullerian mimicry, and divergent colour patterns are used by closely related species to recognize potential mates. The amenability of colour patterns to experimental manipulation, independent of other traits, presents an excellent opportunity to test their role during speciation. We conducted field experiments with artificial butterflies, designed to match natural butterflies with respect to avian vision. These were complemented with enclosure trials with live birds and real butterflies. Our experiments showed that hybrid colour-pattern phenotypes are attacked more frequently than parental forms. For the first time, we demonstrate disruptive ecological selection on a trait that also acts as a mating cue.

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doi: 10.1098/rspb.2012.1968

Nadeau NJ, Whibley A, Jones RT, Davey JW, Dasmahapatra KK, Baxter SW, Quail MA, Joron M, ffrench-Constant RH, Blaxter ML, et al. Genomic islands of divergence in hybridizing Heliconius butterflies identified by large-scale targeted sequencing. Philosophical Transactions of the Royal Society B. 2012;367 :343-53.Abstract

Heliconius butterflies represent a recent radiation of species, in which wing pattern divergence has been implicated in speciation. Several loci that control wing pattern phenotypes have been mapped and two were identified through sequencing. These same gene regions play a role in adaptation across the whole Heliconius radiation. Previous studies of population genetic patterns at these regions have sequenced small amplicons. Here, we use targeted next-generation sequence capture to survey patterns of divergence across these entire regions in divergent geographical races and species of Heliconius. This technique was successful both within and between species for obtaining high coverage of almost all coding regions and sufficient coverage of non-coding regions to perform population genetic analyses. We find major peaks of elevated population differentiation between races across hybrid zones, which indicate regions under strong divergent selection. These 'islands' of divergence appear to be more extensive between closely related species, but there is less clear evidence for such islands between more distantly related species at two further points along the 'speciation continuum'. We also sequence fosmid clones across these regions in different Heliconius melpomene races. We find no major structural rearrangements but many relatively large (greater than 1 kb) insertion/deletion events (including gain/loss of transposable elements) that are variable between races.

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doi: 10.1098/rstb.2011.0198

Cook LM, Grant BS, Saccheri IJ, Mallet J. Selective bird predation on the peppered moth: the last experiment of Michael Majerus. Biology Letters. 2012;8 :609-612.Abstract

Colour variation in the peppered moth Biston betularia was long accepted to be under strong natural selection. Melanics were believed to be fitter than pale morphs because of lower predation at daytime resting sites on dark, sooty bark. Melanics became common during the industrial revolution, but since 1970 there has been a rapid reversal, assumed to have been caused by predators selecting against melanics resting on today's less sooty bark. Recently, these classical explanations of melanism were attacked, and there has been general scepticism about birds as selective agents. Experiments and observations were accordingly carried out by Michael Majerus to address perceived weaknesses of earlier work. Unfortunately, he did not live to publish the results, which are analysed and presented here by the authors. Majerus released 4864 moths in his six-year experiment, the largest ever attempted for any similar study. There was strong differential bird predation against melanic peppered moths. Daily selection against melanics (s approximately 0.1) was sufficient in magnitude and direction to explain the recent rapid decline of melanism in post-industrial Britain. These data provide the most direct evidence yet to implicate camouflage and bird predation as the overriding explanation for the rise and fall of melanism in moths.

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(Open Access) doi: 10.1098/rsbl.2011.1136

Kronforst MR, Barsh GS, Kopp A, Mallet J, Monteiro A, Mullen SP, Protas M, Rosenblum EB, Schneider CJ, Hoekstra HE. Unraveling the thread of nature's tapestry: the genetics of diversity and convergence in animal pigmentation. Pigment Cell and Melanoma Research . 2012;25 :411-433.Abstract

Animals display incredibly diverse color patterns yet little is known about the underlying genetic basis of these phenotypes. However, emerging results are reshaping our view of how the process of phenotypic evolution occurs. Here, we outline recent research from three particularly active areas of investigation: melanin pigmentation in Drosophila, wing patterning in butterflies, and pigment variation in lizards. For each system, we highlight (i) the function and evolution of color variation, (ii) various approaches that have been used to explore the genetic basis of pigment variation, and (iii) conclusions regarding the genetic basis of convergent evolution which have emerged from comparative analyses. Results from these studies indicate that natural variation in pigmentation is a particularly powerful tool to examine the molecular basis of evolution, especially with regard to convergent or parallel evolution. Comparison of these systems also reveals that the molecular basis of convergent evolution is heterogeneous, sometimes involving conserved mechanisms and sometimes not. In the near future, additional work in other emerging systems will substantially expand the scope of available comparisons.

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(Open Access) doi: 10.1111/j.1755-148X.2012.01014.x

2011
Mallet, J. & Dasmahapatra K. Catfish mimics (News and Views on Alexandrou et al. article in same issue). Nature. 2011;469 :41-42.Abstract

Mutualism can be a double-edged sword if the animals concerned also competefor food. This may explain the discovery that mimic catfish in the Amazon rarelyengage in mimicry with related species.

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