The evolutionary genetics of highly divergent alleles of the mimicry locus in Papilio dardanus

Background: The phylogenetic history of genes underlying phenotypic diversity can offer insight into the evolutionary origin of adaptive traits. This is especially true where single genes have large phenotypic effects, for example in determining polymorphic mimicry in butterflies. Here, we characterise the evolutionary history of two candidate genes for the mimicry switch in the polymorphic Batesian mimic Papilio dardanus coding for the transcription factors engrailed and invected. Results: We show that phased haplotypes associated with the dominant morphs f. poultoni and f. planemoides are phylogenetically highly divergent, in particular at non-synonymous sites. Some non-synonymous changes are shared between the divergent alleles suggesting either convergence or a shared ancestry. Gene trees for invected do not show this pattern. Despite their great divergence, all engrailed alleles of P. dardanus were monophyletic with respect to alleles of closely related species. Phylogenetic analyses therefore reveal no evidence for introgression from other species. A McDonald-Kreitman test conducted on a population sample from South Africa confirms a significant excess of intraspecific non-synonymous diversity in P. dardanus engrailed, suggesting long-term balanced polymorphism at this locus. Conclusions: The divergence between engrailed haplotypes suggests an evolutionary history distorted by selection with multiple changes reflecting recurrent selective sweeps. The high level of intraspecific polymorphism observed is characteristic of balancing selection on this locus, as expected if the gene engrailed is under phenotypic selection for the maintenance of multiple mimetic morphs. Non-synonymous changes in key functional portions of a major transcription factor are likely to be deleterious but if maintained in a dominant allele at low frequency, heterozygosity would reduce the associated genetic load

Signatures of selection in loci governing major colour patterns in Heliconius butterflies and related species.

BACKGROUND: Protein-coding change is one possible genetic mechanism underlying the evolution of adaptive wing colour pattern variation in Heliconius butterflies. Here we determine whether 38 putative genes within two major Heliconius patterning loci, HmYb and HmB, show evidence of positive selection. Ratios of nonsynonymous to synonymous nucleotide changes (ω) were used to test for selection, as a means of identifying candidate genes within each locus that control wing pattern. RESULTS: Preliminary analyses using 454 transcriptome and Bacterial Artificial Chromosome (BAC) sequences from three Heliconius species highlighted a cluster of genes within each region showing relatively higher rates of sequence evolution. Other genes within the region appear to be highly constrained, and no ω estimates exceeded one. Three genes from each locus with the highest average pairwise ω values were amplified from additional Heliconius species and races. Two selected genes, fizzy-like (HmYb) and DALR (HmB), were too divergent for amplification across species and were excluded from further analysis. Amongst the remaining genes, HM00021 and Kinesin possessed the highest background ω values within the HmYb and HmB loci, respectively. After accounting for recombination, these two genes both showed evidence of having codons with a signature of selection, although statistical support for this signal was not strong in any case. CONCLUSIONS: Tests of selection reveal a cluster of candidate genes in each locus, suggesting that weak directional selection may be occurring within a small region of each locus, but coding changes alone are unlikely to explain the full range of wing pattern diversity. These analyses pinpoint many of the same genes believed to be involved in the control of colour patterning in Heliconius that have been identified through other studies implementing different research methods.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are

Vector competence of Aedes aegypti mosquitoes for filarial nematodes is affected by age and nutrient limitation

Mosquitoes are one of the most important vectors of human disease. The ability of mosquitoes to transmit disease is dependent on the age structure of the population, as mosquitoes must survive long enough for the parasites to complete their development and infect another human. Age could have additional effects due to mortality rates and vector competence changing as mosquitoes senesce, but these are comparatively poorly understood. We have investigated these factors using the mosquito Aedes aegypti and the filarial nematode Brugia malayi. Rather than observing any effects of immune senescence, we found that older mosquitoes were more resistant, but this only occurred if they had previously been maintained on a nutrient-poor diet of fructose. Constant blood feeding reversed this decline in vector competence, meaning that the number of parasites remained relatively unchanged as mosquitoes aged. Old females that had been maintained on fructose also experienced a sharp spike in mortality after an infected blood meal ("refeeding syndrome") and few survived long enough for the parasite to develop. Again, this effect was prevented by frequent blood meals. Our results indicate that old mosquitoes may be inefficient vectors due to low vector competence and high mortality, but that frequent blood meals can prevent these effects of age

Breeding for specific bioregions: a genotype by environment study of horticultural and nutritional traits integrating breeder and farmer priorities for organic broccoli cultivar improvement

The genotype by environment interaction study of broccoli, amongst others demonstrates that traits of a cultivar are sometimes ranked differently when grown in an organic production system compared to a conventional system. This has strong implications for breeding strategies. The breeders interviewed acknowledged that more attention on abiotic and biotic stress resistance in a broccoli breeding programme is needed which is in accordance with the farmers' varietal requirements. The first findings of the field trials show that cultivar performance is influenced by season and region, and differences in treatment (organic versus conventional management). The field trials showed that there are cultivars with broad adaptation such as "Green Goliath". These cultivars performed across locations, seasons and treatments within the sub-top group, however, organic farmers would benefit more from cultivars specifically adapted to their region and season. The trial results showed a wide range of glucosinolate levels. Glucoraphanin was very genotype dependent, while glucobrassicin and neoglucobrassicin were more influenced by abiotic and biotic environmental factors. Therefore, there are opportunities for nutritional performance enhancement under organic conditions which would provide an added value to the product quality with respect to human and plant health. Further elaboration of the dataset will contribute to the design of regional breeding strategies for improved broccoli cultivars for the organic market

Deep Convergence, Shared Ancestry, and Evolutionary Novelty in the Genetic Architecture of Heliconius Mimicry

Convergent evolution can occur through different genetic mechanisms in different species. It is now clear that convergence at the genetic level is also widespread, and can be caused by either (i) parallel genetic evolution, where independently evolved convergent mutations arise in different populations or species, or (ii) collateral evolution in which shared ancestry results from either ancestral polymorphism or introgression among taxa. The adaptive radiation of Heliconius butterflies shows color pattern variation within species, as well as mimetic convergence between species. Using comparisons from across multiple hybrid zones, we use signals of shared ancestry to identify and refine multiple putative regulatory elements in Heliconius melpomene and its comimics, Heliconius elevatus and Heliconius besckei, around three known major color patterning genes: optix, WntA, and cortex. While we find that convergence between H. melpomene and H. elevatus is caused by a complex history of collateral evolution via introgression in the Amazon, convergence between these species in the Guianas appears to have evolved independently. Thus, we find adaptive convergent genetic evolution to be a key driver of regulatory changes that lead to rapid phenotypic changes. Furthermore, we uncover evidence of parallel genetic evolution at some loci around optix and WntA in H. melpomene and its distant comimic Heliconius erato. Ultimately, we show that all three of convergence, conservation, and novelty underlie the modular architecture of Heliconius color pattern mimicry

The evolution of TEP1, an exceptionally polymorphic immunity gene in Anopheles gambiae

<p>Abstract</p> <p>Background</p> <p>Host-parasite coevolution can result in balancing selection, which maintains genetic variation in the susceptibility of hosts to parasites. It has been suggested that variation in a thioester-containing protein called <it>TEP1 </it>(AGAP010815) may alter the ability of <it>Anopheles </it>mosquitoes to transmit <it>Plasmodium </it>parasites, and high divergence between alleles of this gene suggests the possible action of long-term balancing selection. We studied whether <it>TEP1 </it>is a case of an ancient balanced polymorphism in an animal immune system.</p> <p>Results</p> <p>We found evidence that the high divergence between <it>TEP1 </it>alleles is the product of genetic exchange between <it>TEP1 </it>and other TEP loci, i.e. gene conversion. Additionally, some <it>TEP1 </it>alleles showed unexpectedly low variability.</p> <p>Conclusion</p> <p>The <it>TEP1 </it>gene appears to be a chimera produced from at least two other <it>TEP </it>loci, and the divergence between <it>TEP1 </it>alleles is probably not caused by long-term balancing selection, but is instead due to two independent gene conversion events from one of these other genes. Nevertheless, <it>TEP1 </it>still shows evidence of natural selection, in particular there appears to have been recent changes in the frequency of alleles that has diminished polymorphism within each allelic class. Although the selective force driving this dynamic was not identified, given that susceptibility to <it>Plasmodium </it>parasites is known to be associated with allelic variation in <it>TEP1</it>, these changes in allele frequencies could alter the vectoring capacity of populations.</p

Natural selection and genetic diversity in the butterfly Heliconius melpomene

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What shapes the continuum of reproductive isolation? Lessons from Heliconius butterflies

The process by which species evolve can be illuminated by investigating barriers that limit gene flow between taxa. Recent radiations, such as Heliconius butterflies, offer the opportunity to compare isolation between pairs of taxa at different stages of ecological, geographical, and phylogenetic divergence. Here, we report a comparative analysis of existing and novel data in order to quantify the strength and direction of isolating barriers within a well-studied clade of Heliconius Our results highlight that increased divergence is associated with the accumulation of stronger and more numerous barriers to gene flow. Wing pattern is both under natural selection for Müllerian mimicry and involved in mate choice, and therefore underlies several isolating barriers. However, pairs which share a similar wing pattern also display strong reproductive isolation mediated by traits other than wing pattern. This suggests that, while wing pattern is a key factor for early stages of divergence, it may become facultative at later stages of divergence. Additional factors including habitat partitioning, hybrid sterility, and chemically mediated mate choice are associated with complete speciation. Therefore, although most previous work has emphasized the role of wing pattern, our comparative results highlight that speciation is a multi-dimensional process, whose completion is stabilized by many factors.This work was supported by ERC Starting Grant Stg-243179 (MimEvol) and French Research Agency grant ANR-12-JSV7-0005 (HybEvol) to M.J. C.S. was funded by the Universidad del Rosario FIUR grant QDN-DG001 and COLCIENCIAS (Grant FP44842-5-2017). R.M.M. was funded by a Research Fellowship at King's College, Cambridge, UK. R.M.M. and C.D.J. were funded by an ERC grant (Speciation Genetics 339873)

Comparative genomics of the mimicry switch in Papilio dardanus

The African Mocker Swallowtail, Papilio dardanus, is a textbook example in evolutionary genetics. Classical breeding experiments have shown that wing pattern variation in this polymorphic Batesian mimic is determined by the polyallelic H locus that controls a set of distinct mimetic phenotypes. Using bacterial artificial chromosome (BAC) sequencing, recombination analyses and comparative genomics, we show that H co-segregates with an interval of less than 500 kb that is collinear with two other Lepidoptera genomes and contains 24 genes, including the transcription factor genes engrailed (en) and invected (inv). H is located in a region of conserved gene order, which argues against any role for genomic translocations in the evolution of a hypothesized multi-gene mimicry locus. Natural populations of P. dardanus show significant associations of specific morphs with single nucleotide polymorphisms (SNPs), centred on en. In addition, SNP variation in the H region reveals evidence of non-neutral molecular evolution in the en gene alone. We find evidence for a duplication potentially driving physical constraints on recombination in the lamborni morph. Absence of perfect linkage disequilibrium between different genes in the other morphs suggests that H is limited to nucleotide positions in the regulatory and coding regions of en. Our results therefore support the hypothesis that a single gene underlies wing pattern variation in P. dardanus

Women’s empowerment through seed improvement and seed governance: Evidence from participatory barley breeding in pre-war Syria

Approaches to food security primarily focus on technological solutions, seeking to produce more food, preferably with fewer resources. It has been argued that access to food involves issues of resource distribution and social marginalization. Governance is seen as one of the keys to redressing the institutional inequity that affects resource distribution. Rural women’s empowerment is seen as a means to reduce social marginalization and to hasten progress towards hunger eradication and gender equitable institutions. Building on the empirical findings of a six-year study (2006–2011) undertaken in the context of a participatory barley breeding (PBB) programme in pre-war Syria, this paper establishes the links between women’s empowerment, seed improvement through PPB and seed governance vis-à-vis household food security. The study shows how the programme enhanced the empowerment of the respondent women and how gender-blind seed governance regimes at national and international levels restricted the empowerment of these women ultimately affecting the pillars of food security. We discuss some of the challenges encountered by the study in conceptualizing and operationalizing gender analysis to enhance women’s empowerment. The article further discusses the interplay of processes to both discipline gender norms and provides transformational opportunities towards gender equity created by public spaces such as the PBB programme. The article contributes to current discussions on the effective pathways to develop smallholder agriculture, enhance gender equity and enhance food security and rural livelihoods in the dry areas of the temperate world