The parallel evolution in amniotes seen through the eye of functional nodal mutations

Introduction In this article the authors describe an evolutionary convergence in mammals, birds, and reptiles, based on genomic data from NCBI. The evolution of different species and lineages is due to mutations that can appear and accumulate in organisms over time. Those mutations need a high functional potential and have to be conserved in time in order to form new species. The conservation of mutations can occur via selection pressure, mutational compensation, and/or by the separation of members from the same species by geological and environmental events. In this comprehensive study, the authors describe, a genomic landscape of the parallel evolution by analysing functional nodal mutations (fNMs) by using different types of DNA (mitochondrial and nucleic), the thermostability of mtDNA encoding RNA genes, and the structural proximity of proteins, using the available 3D structures from PDB database. Functional nodal mutations (fNMs) can be separated in single nodal (fSNMs), recurrent nodal mutations (fRNMs), occured independently in unrelated lineages and recurrent combinations of nodal mutations (fRCNMs) recurred independently along with other nodal mutations in combinations in more than a single lineage. The recurrent ones can be taken in consideration the most when we are talking about the convergent adaptive responses, that means …

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Evolution of Darwin’s finches and their beaks revealed by genome sequencing

Introduction Darwin’s finches from Galapagos and Cocos Island are classic example of young adaptive radiation, entirely intact because none of the species having become extinct as a result of human activity. They have diversified in beak sizes and shapes, feeding habits and diets in adapting to different food resources. Although traditional taxonomy of Darwin’s is based on morphology and has been largely supported by observations of breeding birds finches, in this paper, authors showed the results of whole-genome re-sequencing of 120 individuals representing all of the Darwin’s finch species inhabiting Galapagos archipelago (Fig. 1a) and two close relatives, trying to analyse patterns of intra-and interspecific genome diversity and phylogenetic relationships among the species. Figure 1a. Sample location of Darwin’s finches Summary and comments of the paper The authors analyzed location and phylogeny of Darwin’s finches and found widespread evidence of interspecific gene flow that may have enhanced evolutionary diversification throughout phylogeny. They also reported discovery of a locus with the major effect on beak shape. They generated 10x sequence coverage per individual bird and using 2×100 base-pair (bp) paired-end reads and found evidence of introgression from three sources: ABBA-BABA tests, discrepancies between phylogenetic trees based on autosomal and sex linked …

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The genomic substrate for adaptive radiation in African cichlid fish

In African lakes, cichlid fishes are famous for large, diverse and replicated adaptive radiations. Nearly 1,500 new species of cichlid fish evolved in a few million years when environmentally determined opportunity for sexual selection and ecological niche expansion was met by an evolutionary lineage with unusual potential to adapt, speciate and diversify. The phenotypic diversity encompasses variation in behaviour, body shape, coloration and ecological specialization. The frequent occurrence of convergent evolution of similar ecotypes suggests a primary role of natural selection in shaping cichlid phenotypic diversity. To identify the ecological and molecular basis of divergent evolution in the cichlid system, David et al. [1] sequenced the genomes and transcriptomes of five lineages of African cichlids, Pundamilia nyererei (endemic of Lake Victoria); Neolamprologus brichardi (endemic of Lake Tanganyika); Metriaclima zebra (endemic of Lake Malawi); Oreochromis niloticus (from rivers across northern Africa); Astatotilapia burtoni (from rivers connected to Lake Tanganyika). These five lineages diverged primarily through geographical isolation, and three of them subsequently underwent adaptive radiations in the three largest lakes of Africa. Authors comprehensively investigate the features from these massive genomic data. Here is some interesting finding: Accelerated gene evolution was assessed by non-synonymous/synonymous ratio. Compare with stickleback fish, O. niloticus has significant …

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Evolution at two levels of gene expression in yeast

Protein abundances mainly determined by the balance of transcriptional and translational regulation. Because of the limited technology for the translational research, however, gene expression evolution was based almost entirely on studies of transcriptional regulation. With the quickly development of ribosome profiling–isolating and sequencing short fragments of mRNA bound by actively translating ribosomes–now we can study translational regulation conveniently and efficiently. Simultaneous detection of regulatory divergence at two levels In this paper, firstly, in order to assess the relative contributions of regulatory elements evolution to the changes in mRNA abundance and translation rate, the authors applied ribosome profiling and RNAseq to two species of Saccharomyces yeast (S. cerevisiae and  S. paradoxus )and their interspecific hybrid (figure 1). Within hybrids, both alleles share the same trans-acting cellular environment. Therefore, different mRNA abundance or translation efficiency is caused by cis-regulatory divergence. By applied these methods, the authors showed cis-regulatory divergence in both transcription and translation are abundant, almost 35% orthologs have significant divergence in translational efficiency, as compared with 61% with significant divergence in mRNA abundance. Because they identified cis-regulatory elements change at two regulatory levels simultaneously, an interesting question will be asked is whether changes at the two levels could be reinforcing (acting at the same direction) or opposing (acting in opposite directions). Compared …

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The African Genome Variation Project shapes medical genetics in Africa.

  Despite being the world’s most genetically diverse continent, only a handful of studies attempted to understand the genetic risks for diseases of the African populations. This study shines light not only on the genetic diversity to help learn more about the variants that are associated with malaria and hypertension, but also on the population history across sub-Saharan African populations. Beside the comprehensive map of the African variants obtained from genotypes of 1,481 individuals and whole-genome sequences of 320 individuals, authors offered a design of the array suitable to capturing variants of African populations. Summary and comments of the paper Population structure in SSA. Comparing ~2.2 million variants of 18 ethno-linguistic groups from sub-Saharan Africa (SSA), authors found modest differentiation among SSA populations (mean pairwise Fst = 0.019) and among Niger-Congo language groups (mean pairwise Fst = 0.009). In the article, authors suggested that the modest differentiation among Niger-Congo language group showed evidence for ‘Bantu expansion’. However, the Fig1.a shows sample distribution mostly next to the Western, East and South African coasts, rather then inside of continent where the Bantu expansion occurred, therefore indicating the sampling bias. Furthermore, the authors found a high proportion of unshared and novel variants in …

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Stick Insect Genomes Reveal Natural Selection’s Role in Parallel Speciation

Parallel evolution provides evidence for evolution by natural selection and can cause repeated divergence at specific genes. The parallel evolution of phenotypic traits under similar environmental pressures was estimated to cover almost half of same genomic regions. However, the genomic footprints of parallel evolution on parallel speciation is not clearly known yet. In a recent study, Víctor Soria-Carrasco et al. investigated the natural selection’s role in parallel speciation with stick insect populations. Herbivorous stick insect (Timema cristinae) is an endemic species to California and adapted to different host plants, Adenostoma fasciculatum and Ceanothus spinosus. Researchers investigated the whole genome divergence by parallel speciation in a nice experimental set up with this species. T.cristinae individuals were sampled from four replicate population pairs where 3 of them were adjacent and one was 6.4 km far away. They annotated the reference genome for the species and resequenced 160 individuals sampled from field transplant experiment. In the first part of the study, the data obtained was used to analyse the effects of adaptation on genomic divergence in different scales and aspects. The results showed that the divergence between ecotype pairs varied geographically. Principal components analysis and phylogenomic trees clustered the individuals by geography, not …

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Electrogenic fish – what’s in charge of the charge?

Electric organs – organs that are capable of creating and discharging electricity – have evolved independently in at least six different lineages of fish (Torpediniformes, Rajiformes, Mormyroidea, Euteleostei, Siluriformes, Gymnotiformes) and play an important role in communication, navigation, defense and predation. To investigate whether the convergent evolution of these organs has a common genetic basis, Jason Gallant and his coworkers studied the transcriptome of five species of electrogenic fish in three different lineages: Electrophorus electricus, Sternopygus macrurus, Eigenmannia virescens (Gymnotiforme), Malapterurus electricus (Siluriforme) and Brienomyrus brachyistius (Mormyroidea). Electric organs are comprised of arrays of electrocytes – asymmetric cells that are enriched in cation-specific ion channels on one and sodium pumps on the opposing side. The resulting ion flux slowly charges the electrocyte membrane and upon activation by a neuronal stimulus, the voltage is discharged, generating an electrical pulse from the fish. Although the morphology of electric organs and electrocytes varies substantially amongst these species, they are all muscle-derived tissue and originate developmentally from muscle progenitor cells. Since this evolution of muscular to electrogenic tissue has occurred several times independently, the authors investigated, whether the underlying genetic mechanisms are shared. To address this question, Gallant et al. first sequenced and assembled …

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Population Genomics Reveal Recent Speciation and Rapid Evolutionary Adaptation in Polar Bears

The polar bear (Ursus maritimus) is a carnivorous species which is closely related to the brown bear (Ursus arctos) and is adapted to the severe living conditions of the High Arctic due to the great physiological changes happened during evolutionary speciation. Despite numerous researches it is still unclear when exactly this two species diverged. That’s why, Liu with colleagues in their work tried to determine a reliable divergence time of polar bear and brown bear populations and investigated demographic history as well as selection and adaptation of polar bears. Summary By applying a population genomic framework the authors analyzed 89 complete nuclear genomes of polar bears and brown bears. They showed that two species diverged 479-343 thousand years ago (kya) and found 16 genes under strong positive selection on the polar bear in comparison with the brown bear. They analyzed more precisely nine of these genes that are known to be associated with high risk of cardiomyopathy and vascular diseases in humans. However, in polar bears these genes are responsible for an important reorganization of the cardiovascular system which allowed them to survive in extreme life’s conditions within Arctic Circle (e.g. very low temperatures, high physical activity in cold water, high …

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Single and independent mutations lead to an adaptive and complex color phenotype in deer mice living on the light-colored soils of the Nebraska Sand Hills

Pleiotropy of genes is often the main solution to explain genetic basis of complex phenotypes (i.e., those composed of multiple traits). But dissection of those genes or loci are rarely studied, and it remains unclear which of single pleiotropic mutations or multiple mutations with independent effects are responsible to elaborate complex phenotypes. Linnen et al. are interested in coloration of the deer mice (Peromyscus maniculatus) present on the light-colored soils of the Nebraska Sand Hills. Adaptation for crypsis is the strongest hypothesis to explain prevalence of the light morph compared to the black morph,  and they wanted to dissect the genetic basis of this adaptation. This study is composed of two main parts : first to understand and to evaluate the complexity of coloration phenotype and then to find the mutations responsible of those variation in traits and on which morph selection is acting on. First of all, they implemented an experimentation with plasticine models to count the number of attacks on each coloration morph. As they expected, statistical test reveals that the dark models are significantly more attacked than light models. Closer inspection reveals multiple pigmentation traits and pattern that differ between the light and the dark morph to compose complex coloration …

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Genome-wide signatures of convergent evolution in echolocating mammals (Parker et al., 2013)

Phenotype convergence is a fascinating topic in evolution. Usually species evolve by divergence, starting from a common ancestor and then developing different genomic changes that lead to different phenotypes. which are then selected by the environment. Nevertheless, it has been observed in several examples that two or more different species, even very far-related in the phylogenetic tree, appear to have developed, after their divergence, similar phenotypic traits in order to adapt to the environment, therefore leading to an apparent convergence of their branches. The aim of this work is to investigate the hypothesis according to which convergent phenotypes are not just a lucky coincidence produced by different point-mutations occurred in different species, but rather that a convergent phenotype is associated with the same mutation in all the species involved, and that these mutations are not happen by chance but are pushed by adaptation to the environment. In order to do it, this group analysed sequence identities in the genomes of species that developed independently echolocation, certainly a very complex feature that it’s hard to believe it has developed in different species just by chance. The first step was building the gene set to work on. Therefore, they sequenced the genome …

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