Evolutionary Stasis Research Articles

Evolutionary stasis in pollen morphogenesis due to natural selection.

The contribution of developmental constraints and selective forces to the determination of evolutionary patterns is an important and unsolved question. We test whether the long-term evolutionary stasis observed for pollen morphogenesis (microsporogenesis) in eudicots is due to developmental constraints or to selection on a morphological trait shaped by microsporogenesis: the equatorial aperture pattern. Most eudicots have three equatorial apertures but several taxa have independently lost the equatorial pattern and have microsporogenesis decoupled from aperture pattern determination. If selection on the equatorial pattern limits variation, we expect to see increased variation in microsporogenesis in the nonequatorial clades. Variation of microsporogenesis was studied using phylogenetic comparative analyses in 83 species dispersed throughout eudicots including species with and without equatorial apertures. The species that have lost the equatorial pattern have highly variable microsporogenesis at the intra-individual and inter-specific levels regardless of their pollen morphology, whereas microsporogenesis remains stable in species with the equatorial pattern. The observed burst of variation upon loss of equatorial apertures shows that there are no strong developmental constraints precluding variation in microsporogenesis, and that the stasis is likely to be due principally to selective pressure acting on pollen morphogenesis because of its implication in the determination of the equatorial aperture pattern.

Abstract 2884: Tumor-driven eutrophication of the tumor ecosystem selects for cancer cell clones that overcome evolutionary inertia leading to increased metastatic capacity

Abstract Cancer biology has striking parallels to the ecological frameworks of conservation biologists: multiple ecosystems (tumor sites) within a larger biosphere (body), interacting species (cell types), resource cycling (cell signaling and metabolism), and ultimate ecosystem collapse. While tumor heterogeneity is typically attributed to intrinsic genetic instability, we propose that it is due to the evolution of cancer cells under the selection of ecological pressures in the tumor ecosystem. Like any ecosystem, a healthy organ requires balanced feedback mechanisms to respond dynamically to small perturbations. Small disturbances result in a robust ecosystem, such as immunity following viral infection. In contrast, the native ecosystem is unable to recover from catastrophic perturbation such as an invasive species: cancer. Invasive species are inherent ecosystem engineers that alter their habitat and modify resource availability. As a tumor grows, it consumes high levels of nutrients and oxygen and increases the local concentration of cellular waste, analogous to the ecological process of eutrophication associated with polluted swamps. The “cancer swamp” is a hypoxic, acidic, and nutrient-poor habitat. This ecosystem engineering alters the selective pressure and subsequent adaptation of the cancer cells. According to evolutionary inertia, while all cancer cells have the capacity to attain metastatic traits, an unchanged trait will remain unchanged (stasis) and a trait undergoing a change will maintain that change (thrust) unless an external force acts upon it. We hypothesize that the cancer swamp provides the external force to instigate evolutionary thrust by exerting selective pressure to promote the generation of clones with high metastatic capacity. To test this, mice will be inoculated with epithelial prostate cancer cells (PC3-Epi) or prostate cancer cells that have undergone EMT and display increased metastatic capacity (PC3-EMT). At time points prior to, during the establishment of, and after formation of the cancer swamp, tumors will be excised and cells exiting the primary tumor into the circulation will be assessed. We expect that PC3-Epi cells will have a greater than 1:1 ratio of migrating cells : primary tumor burden and that the migrating cells will become more EMT-like as the cancer swamp evolves and the tumor cells overcome evolutionary stasis. Because the PC3-EMT cells have already attained evolutionary thrust towards a metastatic phenotype, we expect migrating tumor cells to be unaffected by the pressures of the growing cancer swamp. Using ecological models to understand cancer biology introduces new avenues for therapy and metastatic prediction. Conservation biology provides several promising strategies that can be adapted to treat cancer including ecological traps, invasive species management, and land use restoration of the cancer swamp. Citation Format: Sarah R. Amend, Kenneth Pienta. Tumor-driven eutrophication of the tumor ecosystem selects for cancer cell clones that overcome evolutionary inertia leading to increased metastatic capacity. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2884. doi:10.1158/1538-7445.AM2015-2884

Evolutionary Stasis in Cycad Plastomes and the First Case of Plastome GC-Biased Gene Conversion.

In angiosperms, gene conversion has been known to reduce the mutational load of plastid genomes (the plastomes). Particularly, more frequent gene conversions in inverted repeat (IR) than in single copy (SC) regions result in contrasting substitution rates between these two regions. However, little has been known about the effect of gene conversion in the evolution of gymnosperm plastomes. Cycads (Cycadophyta) are the second largest gymnosperm group. Evolutionary study of their plastomes is limited to the basal cycad genus, Cycas. In this study, we addressed three questions. 1) Do the plastomes of other cycad genera evolve slowly as previously observed in the plastome of Cycas taitungensis? 2) Do substitution rates differ between their SC and IR regions? And 3) Does gene conversion occur in the cycad plastomes? If yes, is it AT-biased or GC-biased? Plastomes of eight species from other eight genera of cycads were sequenced. These plastomes are highly conserved in genome organization. Excluding ginkgo, cycad plastomes have significantly lower synonymous and nonsynonymous substitution rates than other gymnosperms, reflecting their evolutionary stasis in nucleotide mutations. In the IRs of cycad plastomes, the reduced substitution rates and GC-biased mutations are associated with a GC-biased gene conversion (gBGC) mechanism. Further investigations suggest that in cycads, gBGC is able to rectify plastome-wide mutations. Therefore, this study is the first to uncover the plastomic gBGC in seed plants. We also propose a gBGC model to interpret the dissimilar evolutionary patterns as well as the compositionally biased mutations in the SC and IR regions of cycad plastomes.

A global transition to ferruginous conditions in the early Neoproterozoic oceans

Eukaryotic life expanded during the Proterozoic eon1, 2.5 to 0.542 billion years ago, against a background of fluctuating ocean chemistry2, 3, 4. After about 1.8 billion years ago, the global ocean is thought to have been characterized by oxygenated surface waters, with anoxic and sulphidic waters in middle depths along productive continental margins and anoxic and iron-containing (ferruginous) deeper waters5, 6, 7. The spatial extent of sulphidic waters probably varied through time5, 6, but this surface-to-deep redox structure is suggested to have persisted until the first Neoproterozoic glaciation about 717 million years ago8, 9, 10, 11. Here we report an analysis of ocean redox conditions throughout the Proterozoic using new and existing iron speciation and sulphur isotope data from multiple cores and outcrops. We find a global transition from sulphidic to ferruginous mid-depth waters in the earliest Neoproterozoic, coincident with the amalgamation of the supercontinent Rodinia at low latitudes. We suggest that ferruginous conditions were initiated by an increase in the oceanic influx of highly reactive iron relative to sulphate, driven by a change in weathering regime and the uptake of sulphate by extensive continental evaporites on Rodinia. We propose that this transition essentially detoxified ocean margin settings, allowing for expanded opportunities for eukaryote diversification following a prolonged evolutionary stasis before one billion years ago.

Deep-Mud Microbes Proffer Evidence of Evolutionary Stasis

Comparisons of microbial communities yield evidence for evolutionary stasis—that is, the organisms not changing for billions of years while the niche they occupy remains unchanged, according to J. William Schopf at the University of California, Los Angeles, and his collaborators there and at several other institutions in the United States, Australia, and Chile. More specifically, recently recognized sulfur-cycling microbial communities recovered from off the coast of South America are strikingly similar to their counterparts from fossil microbial communities in Northern and Western Australia, the researchers say. Details appeared 17 February 2015 in the Proceedings of the National Academy of Sciences (www.pnas.org/cgi/doi/10.1073/pnas.1419241112).

Fish Out of Water: Evolutionary and Ecological Issues in the Conservation of Fishes in Water-Altered Environments: Introduction to the Symposium: Eco-Evolutionary Change and the Conundrum of Darwinian Debt

Human impacts on aquatic systems are pervasive and often extreme worldwide, resulting in numerous fish species, as well as other aquatic organisms, being at risk of extinction. Until recently, however, species targeted in conservation efforts have been treated as static units, rather than as locally evolving populations. The intent of the ASIH 2013 symposium, Fish Out of Water: Evolutionary and Ecological Issues in the Conservation of Fishes in Water-Altered Environments, was to examine fish assemblage responses to anthropogenic impacts and the potential for altered evolutionary trajectories. The recent realization that feedback between ecology and evolution can occur on ecological time scales emphasizes that ecological studies cannot assume evolutionary stasis. The cyclical interaction of ecology and evolution, termed eco-evolution, suggests that both directions of effect, ecology to evolution and evolution to ecology, are substantial. Such interactions seem to be particularly likely in many impoundments. For instance, various species of fishes show shifts in morphology in reservoir compared to stream environments, although the changes are generally species-specific or system-specific. In general, conservation efforts to recover populations that have changed in response to human-altered habitats could be compromised if systems are returned to quasi-normal states because of Darwinian debt, the situation where evolutionary recovery from genetic changes caused by anthropogenic impacts can take longer than the time required to induce the changes, resulting in evolutionary costs for future generations.

Molecular cytogenetics ofAndroctonusscorpions: an oasis of calm in the turbulent karyotype evolution of the diverse family Buthidae

Recent cytogenetic and genomic studies suggest that morphological and molecular evolution is decoupled in the basal arachnid order Scorpiones. Extraordinary karyotype variation has been observed particularly in the family Buthidae, which is unique among scorpions for its holokinetic chromosomes. We analyzed the karyotypes of four geographically distant species of the genus Androctonus Ehrenberg, 1828 (Androctonus australis, Androctonus bourdoni, Androctonus crassicauda, Androctonus maelfaiti) (Scorpiones: Buthidae) using both classic and molecular cytogenetic methods. The mitotic complement of all species consisted of 2n = 24 elements. Fluorescence in situ hybridization with a fragment of the 18S ribosomal RNA gene, a cytogenetic marker well known for its mobility, identified a single interstitial rDNA locus on the largest chromosome pair in all species examined. Our findings thus support the evolutionary stasis of the Androctonus karyotype, which is discussed with respect to current hypotheses on chromosome evolution both within and beyond the family Buthidae. Differences in karyotype dynamics between Androctonus spp. and the other buthids can help us better understand the driving forces behind their chromosome evolution and speciation. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115, 69–76.

Sulfur-cycling fossil bacteria from the 1.8-Ga Duck Creek Formation provide promising evidence of evolution's null hypothesis

The recent discovery of a deep-water sulfur-cycling microbial biota in the ∼ 2.3-Ga Western Australian Turee Creek Group opened a new window to life's early history. We now report a second such subseafloor-inhabiting community from the Western Australian ∼ 1.8-Ga Duck Creek Formation. Permineralized in cherts formed during and soon after the 2.4- to 2.2-Ga "Great Oxidation Event," these two biotas may evidence an opportunistic response to the mid-Precambrian increase of environmental oxygen that resulted in increased production of metabolically useable sulfate and nitrate. The marked similarity of microbial morphology, habitat, and organization of these fossil communities to their modern counterparts documents exceptionally slow (hypobradytelic) change that, if paralleled by their molecular biology, would evidence extreme evolutionary stasis.

Comparative genomics reveals insights into avian genome evolution and adaptation.

Birds are the most species-rich class of tetrapod vertebrates and have wide relevance across many research fields. We explored bird macroevolution using full genomes from 48 avian species representing all major extant clades. The avian genome is principally characterized by its constrained size, which predominantly arose because of lineage-specific erosion of repetitive elements, large segmental deletions, and gene loss. Avian genomes furthermore show a remarkably high degree of evolutionary stasis at the levels of nucleotide sequence, gene synteny, and chromosomal structure. Despite this pattern of conservation, we detected many non-neutral evolutionary changes in protein-coding genes and noncoding regions. These analyses reveal that pan-avian genomic diversity covaries with adaptations to different lifestyles and convergent evolution of traits.

Cool sperm: why some placental mammals have a scrotum.

Throughout the Cenozoic, the fitness benefits of the scrotum in placental mammals presumably outweighed the fitness costs through damage, yet a definitive hypothesis for its evolution remains elusive. Here, I present an hypothesis (Endothermic Pulses Hypothesis) which argues that the evolution of the scrotum was driven by Cenozoic pulses in endothermy, that is, increases in normothermic body temperature, which occurred in Boreotheria (rodents, primates, lagomorphs, carnivores, bats, lipotyphylans and ungulates) in response to factors such as cursoriality and climate adaptation. The model argues that stabilizing selection maintained an optimum temperature for spermatogenesis and sperm storage throughout the Cenozoic at the lower plesiomorphic levels of body temperature that prevailed in ancestral mammals for at least 163million years. Evolutionary stasis may have been driven by reduced rates of germ-cell mutations at lower body temperatures. Following the extinction of the dinosaurs at the Cretaceous-Palaeogene boundary 65.5mya, immediate pulses in endothermy occurred associated with the dramatic radiation of the modern placental mammal orders. The fitness advantages of an optimum temperature of spermatogenesis outweighed the potential costs of testes externalization and paved the way for the evolution of the scrotum. The scrotum evolved within several hundred thousand years of the K-Pg extinction, probably associated initially with the evolution of cursoriality, and arguably facilitated mid- and late Cenozoic metabolic adaptations to factors such as climate, flight in bats and sociality in primates.

Evolutionary stasis and lability in thermal physiology in a group of tropical lizards

Understanding how quickly physiological traits evolve is a topic of great interest, particularly in the context of how organisms can adapt in response to climate warming. Adjustment to novel thermal habitats may occur either through behavioural adjustments, physiological adaptation or both. Here, we test whether rates of evolution differ among physiological traits in the cybotoids, a clade of tropical Anolis lizards distributed in markedly different thermal environments on the Caribbean island of Hispaniola. We find that cold tolerance evolves considerably faster than heat tolerance, a difference that results because behavioural thermoregulation more effectively shields these organisms from selection on upper than lower temperature tolerances. Specifically, because lizards in very different environments behaviourally thermoregulate during the day to similar body temperatures, divergent selection on body temperature and heat tolerance is precluded, whereas night-time temperatures can only be partially buffered by behaviour, thereby exposing organisms to selection on cold tolerance. We discuss how exposure to selection on physiology influences divergence among tropical organisms and its implications for adaptive evolutionary response to climate warming.

BOOM AND BUST: ANCIENT AND RECENT DIVERSIFICATION IN BICHIRS (POLYPTERIDAE: ACTINOPTERYGII), A RELICTUAL LINEAGE OF RAY-FINNED FISHES

Understanding the history that underlies patterns of species richness across the Tree of Life requires an investigation of the mechanisms that not only generate young species-rich clades, but also those that maintain species-poor lineages over long stretches of evolutionary time. However, diversification dynamics that underlie ancient species-poor lineages are often hidden due to a lack of fossil evidence. Using information from the fossil record and time calibrated molecular phylogenies, we investigate the history of lineage diversification in Polypteridae, which is the sister lineage of all other ray-finned fishes (Actinopterygii). Despite originating at least 390 million years (Myr) ago, molecular timetrees support a Neogene origin for the living polypterid species. Our analyses demonstrate polypterids are exceptionally species depauperate with a stem lineage duration that exceeds 380 million years (Ma) and is significantly longer than the stem lineage durations observed in other ray-finned fish lineages. Analyses of the fossil record show an early Late Cretaceous (100.5-83.6 Ma) peak in polypterid genus richness, followed by 60 Ma of low richness. The Neogene species radiation and evidence for high-diversity intervals in the geological past suggest a "boom and bust" pattern of diversification that contrasts with common perceptions of relative evolutionary stasis in so-called "living fossils."

Djebelemur, a tiny pre-tooth-combed primate from the Eocene of Tunisia: a glimpse into the origin of crown strepsirhines.

BackgroundMolecular clock estimates of crown strepsirhine origins generally advocate an ancient antiquity for Malagasy lemuriforms and Afro-Asian lorisiforms, near the onset of the Tertiary but most often extending back to the Late Cretaceous. Despite their inferred early origin, the subsequent evolutionary histories of both groups (except for the Malagasy aye-aye lineage) exhibit a vacuum of lineage diversification during most part of the Eocene, followed by a relative acceleration in diversification from the late Middle Eocene. This early evolutionary stasis was tentatively explained by the possibility of unrecorded lineage extinctions during the early Tertiary. However, this prevailing molecular view regarding the ancient origin and early diversification of crown strepsirhines must be viewed with skepticism due to the new but still scarce paleontological evidence gathered in recent years.Methodological/Principal FindingsHere, we describe new fossils attributable to Djebelemur martinezi, a≈50 Ma primate from Tunisia (Djebel Chambi). This taxon was originally interpreted as a cercamoniine adapiform based on limited information from its lower dentition. The new fossils provide anatomical evidence demonstrating that Djebelemur was not an adapiform but clearly a distant relative of lemurs, lorises and galagos. Cranial, dental and postcranial remains indicate that this diminutive primate was likely nocturnal, predatory (primarily insectivorous), and engaged in a form of generalized arboreal quadrupedalism with frequent horizontal leaping. Djebelemur did not have an anterior lower dentition as specialized as that characterizing most crown strepsirhines (i.e., tooth-comb), but it clearly exhibited a transformed antemolar pattern representing an early stage of a crown strepsirhine-like adaptation (“pre-tooth-comb”).Conclusions/SignificanceThese new fossil data suggest that the differentiation of the tooth-comb must postdate the djebelemurid divergence, a view which hence constrains the timing of crown strepsirhine origins to the Middle Eocene, and then precludes the existence of unrecorded lineage extinctions of tooth-combed primates during the earliest Tertiary.

Stasis and convergence characterize morphological evolution in eupolypod II ferns.

Patterns of morphological evolution at levels above family rank remain underexplored in the ferns. The present study seeks to address this gap through analysis of 79 morphological characters for 81 taxa, including representatives of all ten families of eupolypod II ferns. Recent molecular phylogenetic studies demonstrate that the evolution of the large eupolypod II clade (which includes nearly one-third of extant fern species) features unexpected patterns. The traditional 'athyrioid' ferns are scattered across the phylogeny despite their apparent morphological cohesiveness, and mixed among these seemingly conservative taxa are morphologically dissimilar groups that lack any obvious features uniting them with their relatives. Maximum-likelihood and maximum-parsimony character optimizations are used to determine characters that unite the seemingly disparate groups, and to test whether the polyphyly of the traditional athyrioid ferns is due to evolutionary stasis (symplesiomorphy) or convergent evolution. The major events in eupolypod II character evolution are reviewed, and character and character state concepts are reappraised, as a basis for further inquiries into fern morphology. Characters were scored from the literature, live plants and herbarium specimens, and optimized using maximum-parsimony and maximum-likelihood, onto a highly supported topology derived from maximum-likelihood and Bayesian analysis of molecular data. Phylogenetic signal of characters were tested for using randomization methods and fitdiscrete. The majority of character state changes within the eupolypod II phylogeny occur at the family level or above. Relative branch lengths for the morphological data resemble those from molecular data and fit an ancient rapid radiation model (long branches subtended by very short backbone internodes), with few characters uniting the morphologically disparate clades. The traditional athyrioid ferns were circumscribed based upon a combination of symplesiomorphic and homoplastic characters. Petiole vasculature consisting of two bundles is ancestral for eupolypods II and a synapomorphy for eupolypods II under deltran optimization. Sori restricted to one side of the vein defines the recently recognized clade comprising Rhachidosoraceae through Aspleniaceae, and sori present on both sides of the vein is a synapomorphy for the Athyriaceae sensu stricto. The results indicate that a chromosome base number of x =41 is synapomorphic for all eupolypods, a clade that includes over two-thirds of extant fern species. The integrated approach synthesizes morphological studies with current phylogenetic hypotheses and provides explicit statements of character evolution in the eupolypod II fern families. Strong character support is found for previously recognized clades, whereas few characters support previously unrecognized clades. Sorus position appears to be less complicated than previously hypothesized, and linear sori restricted to one side of the vein support the clade comprising Aspleniaceae, Diplaziopsidaceae, Hemidictyaceae and Rachidosoraceae - a lineage only recently identified. Despite x =41 being a frequent number among extant species, to our knowledge it has not previously been demonstrated as the ancestral state. This is the first synapomorphy proposed for the eupolypod clade, a lineage comprising 67 % of extant fern species. This study provides some of the first hypotheses of character evolution at the family level and above in light of recent phylogenetic results, and promotes further study in an area that remains open for original observation.

Phenetic diversity and spatial structure of chars (Salvelinus) of the Kronotskaya riverine-lacustrine system (Eastern Kamchatka)

Chars of the genus Salvelinus inhabiting the Kronotskaya riverine-lacustrine system (Eastern Kamchatka) were studied. It was found that the morphological and genetic polymorphism in chars of Lake Kronotskoe is higher than was believed earlier: to date, five forms of chars have been identified in the Lake Kronotskoe basin. The description, external morphology and biological attributes of chars inhabiting the basin of the lake and the anadromous malma (S. malma) from the Kronotskaya River below the rapids are given. The differences between the forms of chars are continual, and the outermost forms are often connected by a continuous series of transitional forms. According to the morphological and genetic characteristics, the anadromous malma from the lower reaches of the Kronotskaya River is not isolated from the lake chars: by the whole set of characters its position is intermediate between all lacustrine forms. Chars from the Kronotskaya riverine-lacustrine system are represented by the anadromous malma from the lower reaches of the Kronotskaya River and by a metapopulation of lacustrinechars whose forms are not completely isolated genetically. Currently, the chars of the Kronotskaya system are in a quasi-stationary state, when an evolutionary stasis of the lacustrine forms is ensured.

Phylogenetic analyses of Gammaridae crustacean reveal different diversification patterns among sister lineages in the Tethyan region.

The Gammaridae shows the greatest disparity in species diversity and distribution pattern in the Amphipoda, with some genera ranging from the Palearctic to Nearctic, while others are limited to the Mediterranean region or ancient Tethyan margins. Here we present the first molecular phylogenetic analysis of the Gammaridae to investigate its evolutionary history using four genetic markers and a comprehensive set of taxa representing 198 species. The phylogenetic results revealed that the Gammaridae originated from the Tethyan region in the Cretaceous, and split into three morphologically and geographically distinct lineages by the end of the Paleocene. Diversification analysis combined with paleogeological evidence suggested that the Tethyan changes induced by sea-level fluctuation and tectonic uplift triggered different diversification modes and range expansions for the three lineages. The Gammarus lineage underwent an early rapid radiation across Eurasia and North America, then declined towards modern species. Pontogammarids maintained stable diversification with restricted distributions around the Tethyan basin, whereas sarothrogammarids experienced evolutionary stasis by stranding on the ancient Tethyan margins. Our findings suggest that environmental changes have played an important role in the diversification of Gammaridae lineages, which could be an opportunity to promote adaptive radiations in new habitats, or constraints resulting in evolutionary relicts.

Phylogenetic Patterns of Human Coxsackievirus B5 Arise from Population Dynamics between Two Genogroups and Reveal Evolutionary Factors of Molecular Adaptation and Transmission

The aim of this study was to gain insights into the tempo and mode of the evolutionary processes that sustain genetic diversity in coxsackievirus B5 (CVB5) and into the interplay with virus transmission. We estimated phylodynamic patterns with a large sample of virus strains collected in Europe by Bayesian statistical methods, reconstructed the ancestral states of genealogical nodes, and tested for selection. The genealogies estimated with the structural one-dimensional gene encoding the VP1 protein and nonstructural 3CD locus allowed the precise description of lineages over time and cocirculating virus populations within the two CVB5 clades, genogroups A and B. Strong negative selection shaped the evolution of both loci, but compelling phylogenetic data suggested that immune selection pressure resulted in the emergence of the two genogroups with opposed evolutionary pathways. The genogroups also differed in the temporal occurrence of the amino acid changes. The virus strains of genogroup A were characterized by sequential acquisition of nonsynonymous changes in residues exposed at the virus 5-fold axis. The genogroup B viruses were marked by selection of three changes in a different domain (VP1 C terminus) during its early emergence. These external changes resulted in a selective sweep, which was followed by an evolutionary stasis that is still ongoing after 50 years. The inferred population history of CVB5 showed an alternation of the prevailing genogroup during meningitis epidemics across Europe and is interpreted to be a consequence of partial cross-immunity.

Molecular characterization of human parainfluenza virus type 1 in infants attending Mbagathi District Hospital, Nairobi, Kenya: a retrospective study

Human parainfluenza virus type 1 (HPIV-1), a paramyxovirus, is a leading cause of pediatric respiratory hospitalizations globally. Currently, there is no clinically successful vaccine against HPIV-1. Hence, there is a need to characterize circulating strains of this virus to establish the feasibility of developing a vaccine against the virus. The variable HPIV-1 hemagglutin-neuraminidase (HN) protein is found in the envelope of HPIV-1, where it initiates the infection process by binding to cellular receptors. HN is also the major antigen against which the human immune response is directed against. The present study focused on identifying mutations in the HN gene that would be useful in understanding the evolution of HPIV-1. 21 HPIV-1 isolates were obtained after screening nasopharyngeal samples from patients with influenza-like illness. The samples were collected from Mbagathi District Hospital Nairobi from the period July 2007 to December 2010. RT-PCR was carried out on the isolates using HN-specific primers to amplify a 360 nt in the most polymorphic region and the amplicons sequenced. Genomic data were analysed using a suite of bioinformatic software. Forty eight polymorphic sites with a total of 55 mutations were identified at the nucleotide level and 47 mutations at 23 positions at the amino acid level. There was more radical nonsynonymous amino acid changes (seven positions) observed than conservative nonsynonymous changes (one position) on the HN gene fragment. No positively selected sites were found in the HN protein. The result from the analysis of 21 HPIV-1 Mbagathi isolates demonstrated that the HN gene which is the major antigenic target was under purifying (negative) selection displaying evolutionary stasis.

The great opportunity to view stasis with an ecological lens

AbstractA major challenge facing conservation biology today is predicting how often species will be able to adapt to environmental change. We need to know which, and under what environmental conditions, ecologically important traits are likely to evolve and keep species in the evolutionary game. Conservation biologists currently lack enough data across a broad range of traits and taxa to address this problem, which impedes the development of scenarios of possible adaptive management responses. Here I outline how trait‐based data and methods that palaeobiologists use to address the long‐term dynamics of evolving lineages can be applied to address this challenge. We need an impassioned community‐wide effort to view evolutionary stasis with an ecological lens.

Evolutionary rewiring: a modified prokaryotic gene-regulatory pathway in chloroplasts

Photosynthetic electron transport regulates chloroplast gene transcription through the action of a bacterial-type sensor kinase known as chloroplast sensor kinase (CSK). CSK represses photosystem I (PS I) gene transcription in PS I light and thus initiates photosystem stoichiometry adjustment. In cyanobacteria and in non-green algae, CSK homologues co-exist with their response regulator partners in canonical bacterial two-component systems. In green algae and plants, however, no response regulator partner of CSK is found. Yeast two-hybrid analysis has revealed interaction of CSK with sigma factor 1 (SIG1) of chloroplast RNA polymerase. Here we present further evidence for the interaction between CSK and SIG1. We also show that CSK interacts with quinone. Arabidopsis SIG1 becomes phosphorylated in PS I light, which then specifically represses transcription of PS I genes. In view of the identical signalling properties of CSK and SIG1 and of their interactions, we suggest that CSK is a SIG1 kinase. We propose that the selective repression of PS I genes arises from the operation of a gene-regulatory phosphoswitch in SIG1. The CSK-SIG1 system represents a novel, rewired chloroplast-signalling pathway created by evolutionary tinkering. This regulatory system supports a proposal for the selection pressure behind the evolutionary stasis of chloroplast genes.