Mechanisms Of Speciation Research Articles

Reconstructing the Geography of Speciation from Contemporary Biodiversity Data.

Inferring the geographic mode of speciation could help reveal the evolutionary and ecological mechanisms that underlie the generation of biodiversity. Comparative methods have sought to reconstruct the geographic speciation history of clades, using data on phylogeny and species geographic ranges. However, inference from comparative methods has been limited by uncertainty over whether contemporary biodiversity data retain the historic signal of speciation. We constructed a process-based simulation model to determine the influence of speciation mode and postspeciation range evolution on current biodiversity patterns. The simulations suggest that the signal of speciation history remains detectable in species distributions and phylogeny, even when species ranges have evolved substantially through time. We extracted this signal by using a combination of summary statistics that had good power to distinguish speciation modes and then used these statistics to infer the speciation history of 30 plant and animal clades. The results point to broad taxonomic patterns in the modes of speciation, with strongest support for founder speciation in mammals and birds and strongest support for sympatric speciation in plants. Our model and analyses show that broad-scale comparative methods can be a powerful complementary approach to more focused genomic analyses in the study of the patterns and mechanisms of speciation.

Recent thecideide brachiopods (Thecideida, Thecideoidea) from northern Sulawesi (Indonesia) with discovery of a new Thecidellina species (Thecidellinidae).

The scope of this paper concerns the species diversity of thecideide brachiopods living in the western Pacific equatorial region of Indonesia and the possibilities for circulation and dispersion of thecideide species along the coasts of Sulawesi and the Sea of Bali. The discovery of a new Thecidellina species, Thecidellina mawaliana sp. nov., adds a new genus to the Indonesian fauna. This species has a peculiar biogeography, different from those of Minutella cf. minuta (Cooper, 1981) and Ospreyella mutiara Simon Hoffman, 2013, other thecideides living together with the new species. Unfortunately, attempts to collect molecular sequence information from the specimens failed due to insufficient DNA preservation. Probable speciation mechanisms in this genus are discussed.

Female assortative mate choice functionally validates synthesized male odours of evolving stickleback river-lake ecotypes.

During mate choice decisions, females of many vertebrates use male olfactory cues to achieve immunogenetic optimality of their offspring. Three-spined sticklebacks (Gasterosteus aculeatus) populating habitats that differ in their parasite communities evolve locally adapted combinations of genetic variants encoded at the major histocompatibility complex (MHC). Such adaptation confers optimal resistance to the local parasite fauna. Immunogenetic signatures co-evolved with local parasites favour population-specific assortative mate choice behaviour. Previous studies have shown that female sticklebacks evaluate male MHC-associated olfactory cues during the process of mate choice, but how habitat-specific information is exchanged between males and females has remained elusive. Here, we directly demonstrate the molecular nature of the olfactory cue providing habitat-specific information. Under controlled laboratory conditions, females that are ready to mate prefer mixtures of synthetic MHC peptide ligands mimicking the optimal allele number of their original population. These results imply that female sticklebacks can determine the number of MHC alleles of their prospective mates, compare it to their own immunogenetic status, and, if optimal with respect to the immunogenetic complementarity, accept the male as mate. Our results suggest a potentially common mechanism of ecological speciation in vertebrates that is based on the olfactory assessment of habitat-specific immunogenetic diversity.

Plant adaptation and speciation studied by population genomic approaches.

Ever since Darwin, one of the major challenges in evolutionary biology is to unravel the process and mechanisms of adaptation and speciation. Population genomics-the analysis of whole-genome polymorphism data from large population samples-is a critical approach to study adaptation and speciation, as population genomics datasets enable us to: (1) perform genome-wide association studies (GWAS) to find genes underlying adaptive phenotypic variations; (2) scan the footprints of selection across the genome to pinpoint loci under selection; and (3) infer the structure and demographic history of populations. Here, we review recent studies of plants using population genomics, covering those focusing on interactions with other organisms, adaptations to local climatic conditions, and the genomic causes and consequences of reproductive isolation. Integrative studies involving GWAS, selection scans, functional studies, and fitness measurements in the field have successfully identified loci for adaptation, revealed the molecular basis of genetic trade-offs, and shown that fitness can be predicted by polygenic effects of a number of loci associated with local climate. We highlight the importance of the measurement of fitness and phenotypes in the field, which can be powerful tools when combined with population genomic analyses.

Phylogenetic Relationships and Evolutionary Trends in the Cactus Family.

Members of the cactus family are keystone species of arid and semiarid biomes in the Americas, as they provide shelter and resources to support other members of ecosystems. Extraordinary examples are the several species of flies of the genus Drosophila that lay eggs and feed in their rotting stems, which provide a model system for studying evolutionary processes. Although there is significant progress in understanding the evolution of Drosophila species, there are gaps in our knowledge about the cactus lineages hosting them. Here, we review the current knowledge about the evolution of Cactaceae, focusing on phylogenetic relationships and trends revealed by the study of DNA sequence data. During the last several decades, the availability of molecular phylogenies has considerably increased our understanding of the relationships, biogeography, and evolution of traits in the family. Remarkably, although succulent cacti have very low growth rates and long generation times, they underwent some of the fastest diversifications observed in the plant kingdom, possibly fostered by strong ecological interactions. We have a better understanding of the reproductive biology, population structure and speciation mechanisms in different clades. The recent publication of complete genomes for some species has revealed the importance of phenomena such as incomplete lineage sorting. Hybridization and polyploidization are common in the family, and have been studied using a variety of phylogenetic methods. We discuss potential future avenues for research in Cactaceae, emphasizing the need of a concerted effort among scientists in the Americas, together with the analyses of data from novel sequencing techniques.

Hybrid Sterility with Meiotic Metaphase Arrest in Intersubspecific Mouse Crosses.

Although organisms belonging to different species and subspecies sometimes produce fertile offspring, a hallmark of the speciation process is reproductive isolation, characterized by hybrid sterility (HS) due to failure in gametogenesis. In mammals, HS is usually exhibited by males, the heterogametic sex. The phenotypic manifestations of HS are complex. The most frequently observed are abnormalities in both autosomal and sex chromosome interactions that are linked to meiotic prophase arrest or postmeiotic spermiogenesis aberrations and lead to defective or absent gametes. The aim of this study was to determine the HS phenotypes in intersubspecific F1 mice produced by matings between Mus musculus molossinus-derived strains and diverse Mus musculus domesticus-inbred laboratory mouse strains. Most of these crosses produced fertile F1 offspring. However, when female BALB/cJ (domesticus) mice were mated to male JF1/MsJ (molossinus) mice, the (BALBdomxJF1mol)F1 males were sterile, whereas the (JF1molxBALBdom)F1 males produced by the reciprocal crossings were fertile; thus the sterility phenotype was asymmetric. The sterile (BALBdomxJF1mol) F1 males exhibited a high rate of meiotic metaphase arrest with misaligned chromosomes, probably related to a high frequency of XY dissociation. Intriguingly, in the sterile (BALBdomxJF1mol)F1 males we observed aberrant allele-specific expression of several meiotic genes, that play critical roles in important meiotic events including chromosome pairing. Together, these observations of an asymmetrical HS phenotype in intersubspecific F1 males, probably owing to meiotic defects in the meiotic behavior of the XY chromosomes pair and possibly also transcriptional misregulation of meiotic genes, provide new models and directions for understanding speciation mechanisms in mammals.

Transcriptomes Divergence of Ricotia lunaria Between the Two Micro-Climatic Divergent Slopes at "Evolution Canyon" I, Israel.

As one of the hotspot regions for sympatric speciation studies, Evolution Canyon (EC) became an ideal place for its high level of microclimatic divergence interslopes. In this study, to highlight the genetic mechanisms of sympatric speciation, phenotypic variation on flowering time and transcriptomic divergence were investigated between two ecotypes of Ricotia lunaria, which inhabit the opposite temperate and tropical slopes of EC I (Lower Nahal Oren, Mount Carmel, Israel) separated by 100 m at the bottom of the slopes. Growth chamber results showed that flowering time of the ecotype from south-facing slope population # 3 (SFS 3) was significantly 3 months ahead of the north-facing slope population # 5 (NFS 5). At the same floral development stage, transcriptome analysis showed that 1,064 unigenes were differentially expressed between the two ecotypes, which enriched in the four main pathways involved in abiotic and/or biotic stresses responses, including flavonoid biosynthesis, α-linolenic acid metabolism, plant–pathogen interaction and linoleic acid metabolism. Furthermore, based on Ka/Ks analysis, nine genes were suggested to be involved in the ecological divergence between the two ecotypes, whose homologs functioned in RNA editing, ABA signaling, photoprotective response, chloroplasts protein-conducting channel, and carbohydrate metabolism in Arabidopsis thaliana. Among them, four genes, namely, SPDS1, FCLY, Tic21 and BGLU25, also showed adaptive divergence between R. lunaria and A. thaliana, suggesting that these genes could play an important role in plant speciation, at least in Brassicaceae. Based on results of both the phenotype of flowering time and comparative transcriptome, we hypothesize that, after long-time local adaptations to their interslope microclimatic environments, the molecular functions of these nine genes could have been diverged between the two ecotypes. They might differentially regulate the expression of the downstream genes and pathways that are involved in the interslope abiotic stresses, which could further diverge the flowering time between the two ecotypes, and finally induce the reproductive isolation establishment by natural selection overruling interslope gene flow, promoting sympatric speciation.

Fine-scale population differences in Atlantic cod reproductive success: A potential mechanism for ecological speciation in a marine fish.

Successful resource‐management and conservation outcomes ideally depend on matching the spatial scales of population demography, local adaptation, and threat mitigation. For marine fish with high dispersal capabilities, this remains a fundamental challenge. Based on daily parentage assignments of more than 4,000 offspring, we document fine‐scaled temporal differences in individual reproductive success for two spatially adjacent (<10 km) populations of a broadcast‐spawning marine fish. Distinguished by differences in genetics and life history, Atlantic cod (Gadus morhua) from inner‐ and outer‐fjord populations were allowed to compete for mating and reproductive opportunities. After accounting for phenotypic variability in several traits, reproductive success of outer‐fjord cod was significantly lower than that of inner‐fjord cod. This finding, given that genomically different cod ecotypes inhabit inner‐ and outer‐fjord waters, raises the intriguing hypothesis that the populations might be diverging because of ecological speciation. Individual reproductive success, skewed within both sexes (more so among males), was positively affected by body size, which also influenced the timing of reproduction, larger individuals spawning later among females but earlier among males. Our work suggests that spatial mismatches between management and biological units exist in marine fishes and that studies of reproductive interactions between putative populations or ecotypes can provide an informative basis on which determination of the scale of local adaptation can be ascertained.

Immigrant and extrinsic hybrid inviability contribute to reproductive isolation between lake and river cichlid ecotypes.

Understanding how reproductive barriers evolve and which barriers contribute to speciation requires the examination of organismal lineages that are still in the process of diversification and the study of the full range of reproductive barriers acting at different life stages. Lake and river ecotypes of the East African cichlid fish Astatotilapia burtoni show habitat-specific adaptations, despite different levels of genetic differentiation, and thus represent an ideal model to study the evolution of reproductive barriers. To evaluate the degree of reproductive isolation between genetically divergent lake and river populations, we performed a mesocosm mating experiment in a semi-natural setting at Lake Tanganyika. We assessed reproductive isolation in the presence of male-male competition by analyzing survival and growth rates of introduced adults and their reproductive success from genetic parentage of surviving offspring. The genetically divergent river population showed reduced fitness in terms of survival, growth rate, and mating success in a lake-like environment. Hybrid offspring between different populations showed intermediate survival consistent with extrinsic postzygotic reproductive barriers. Our results suggest that both prezygotic (immigrant inviability) and postzygotic reproductive barriers contribute to divergence, and highlight the value of assessing multiple reproductive barriers acting at different stages and in natural contexts to understand speciation mechanisms.

Floral uniformity through evolutionary time in a species-rich tree lineage.

Changes in floral morphology are expected across evolutionary time and are often promoted as important drivers in angiosperm diversification. Such a statement, however, is in contrast to empirical observations of species-rich lineages that show apparent conservative floral morphologies even under strong selective pressure to change from their environments. Here, we provide quantitative evidence for prolific speciation despite uniform floral morphology in a tropical species-rich tree lineage. We analyse floral disparity in the environmental and phylogenetic context of Myrcia (Myrtaceae), one of the most diverse and abundant tree genera in Neotropical biomes. Variation in floral morphology among Myrcia clades is exceptionally low, even among distantly related species. Discrete floral specialisations do occur, but these are few, present low phylogenetic signal, have no strong correlation with abiotic factors, and do not affect overall macroevolutionary dynamics in the lineage. Results show that floral form and function may be conserved over large evolutionary time scales even in environments full of opportunities for ecological interactions and niche specialisation. Species accumulation in diverse lineages with uniform flowers apparently does not result from shifts in pollination strategies, but from speciation mechanisms that involve other, nonfloral plant traits.

The contribution of sexual selection to ecological and mutation-order speciation.

Abundant evidence supports a role for sexual selection in the evolution of reproductive isolation, and it is thus unsurprising that much attention has been given, both conceptually and empirically, to understanding its role in speciation. In doing so, debate has arisen on how sexual selection fits within the much used ecological versus mutation-order classification of speciation mechanisms, with sexual selection often presented as a distinct third alternative. We argue that models of speciation by sexual selection include a fundamental role of divergent selection between environments or mutation order in initiating the process. Rather than representing a unique mechanism, sexual selection layers a coevolutionary process between males and females on top of the classic mechanisms such that the evolution of each sex can now be driven by divergent selection, mutation order, and selection arising from interactions with the other sex. In addition to blurring the distinction between ecological and mutation-order speciation, this coevolutionary process is likely to speed divergence. Sexual selection is not unique in this way; coevolutionary processes can similarly arise from ecological interactions between populations or species, with similar results. Ultimately, understanding the contribution of sexual selection to speciation will require identifying the processes that drive the divergence of mating biases.

High Zn Concentration Pyrrolidinium-Dicyanamide-Based Ionic Liquid Electrolytes for Zn2+/Zn0 Electrochemistry in a Flow Environment

The cycling performance of N-butyl-N-methylpyrrolidinium dicyanamide [C4mpyr][dca] ionic liquid (IL) with H2O additive for application in a Zn2+/Zn0 redox couple is reported for the first time under realistic flow conditions using a 3D printed flow half-cell prototype. This IL electrolyte displayed a superior performance at high current densities (3 mA cm–2) under the flow condition, in terms of cycling efficiency (60 ± 2% vs 45 ± 3%) and long-term cycling stability (>200 cycles) in contrast to similar experiments performed under a static or “no flow” condition. This is possibly due to different Zn2+ speciation mechanisms and/or different structuring of the IL cation and anion at the electrode/electrolyte interface under static and dynamic conditions. Significantly, [C4mpyr][dca] IL allowed a high solubility of the Zn(dca)2 salt, up to a ∼1:1 molar ratio, which is desirable for achieving a high energy density. This high concentration IL electrolyte composition, which has been studied here for the first ti...

Genetic divergence and the number of hybridizing species affect the path to homoploid hybrid speciation

Hybridization is often maladaptive and in some instances has led to the loss of biodiversity. However, hybridization can also promote speciation, such as during homoploid hybrid speciation, thereby generating biodiversity. Despite examples of homoploid hybrid species, the importance of hybridization as a speciation mechanism is still widely debated, and we lack a general understanding of the conditions most likely to generate homoploid hybrid species. Here we show that the level of genetic divergence between hybridizing species has a large effect on the probability that their hybrids evolve reproductive isolation. We find that populations of hybrids formed by parental species with intermediate levels of divergence were more likely to mate assortatively, and discriminate against their parental species, than those generated from weakly or strongly diverged parental species. Reproductive isolation was also found between hybrid populations, suggesting differential sorting of parental traits across populations. Finally, hybrid populations derived from three species were more likely to evolve reproductive isolation than those derived from two species, supporting arguments that hybridization-supplied genetic diversity can lead to the evolution of novel "adaptive systems" and promote speciation. Our results illustrate when we expect hybridization and admixture to promote hybrid speciation. Whether homoploid hybrid speciation is a common speciation mechanism in general remains an outstanding empirical question.

In search of the Goldilocks zone for hybrid speciation.

Hybridization has recently gained considerable interest both as a unique opportunity for observing speciation mechanisms and as a potential engine for speciation. The latter remains a controversial topic. It was recently hypothesized that the reciprocal sorting of genetic incompatibilities from parental species could result in hybrid speciation, when the hybrid population maintains a mixed combination of the parental incompatibilities that prevents further gene exchange with both parental populations. However, the specifics of the purging/sorting process of multiple incompatibilities have not been examined theoretically. We here investigate the allele-frequency dynamics of an isolated hybrid population that results from a single hybridization event. Using models of two or four loci, we investigate the fate of one or two genetic incompatibilities of the Dobzhansky-Muller type (DMIs). We study how various parameters affect both the sorting/purging of the DMIs and the probability of observing hybrid speciation by reciprocal sorting. We find that the probability of hybrid speciation is strongly dependent on the linkage architecture (i.e. the order and recombination rate between loci along chromosomes), the population size of the hybrid population, and the initial relative contributions of the parental populations to the hybrid population. We identify a Goldilocks zone for specific linkage architectures and intermediate recombination rates, in which hybrid speciation becomes highly probable. Whereas an equal contribution of parental populations to the hybrid population maximizes the hybrid speciation probability in the Goldilocks zone, other linkage architectures yield unintuitive asymmetric maxima. We provide an explanation for this pattern, and discuss our results both with respect to the best conditions for observing hybrid speciation in nature and their implications regarding patterns of introgression in hybrid zones.

RNA-seq coupled to proteomic analysis reveals high sperm proteome variation between two closely related marine mussel species

Speciation mechanisms in marine organisms have attracted great interest because of the apparent lack of substantial barriers to genetic exchange in marine ecosystems. Marine mussels of the Mytilus edulis species complex provide a good model to study mechanisms underlying species formation. They hybridise extensively at many localities and both pre- and postzygotic isolating mechanisms may be operating. Mussels have external fertilisation and sperm cells should show specific adaptations for survival and successful fertilisation. Sperm thus represent key targets in investigations of the molecular mechanisms underlying reproductive isolation. We undertook a deep transcriptome sequencing (RNA-seq) of mature male gonads and a 2DE/MS-based proteome analysis of sperm from Mytilus edulis and M. galloprovincialis raised in a common environment. We provide evidence of extensive expression differences between the two mussel species, and general agreement between the transcriptomic and proteomic results in the direction of expression differences between species. Differential expression is marked for mitochondrial genes and for those involved in spermatogenesis, sperm motility, sperm-egg interactions, the acrosome reaction, sperm capacitation, ATP reserves and ROS production. Proteins and their corresponding genes might thus be good targets in further genomic analysis of reproductive barriers between these closely related species. SignificanceModel systems for the study of fertilization include marine invertebrates with external fertilisation, such as abalones, sea urchins and mussels, because of the ease with which large quantities of gametes released into seawater can be collected after induced spawning. Unlike abalones and sea urchins, hybridisation has been reported between mussels of different Mytilus spp., which thus makes them very appealing for the study of reproductive isolation at both pre- and postzygotic levels. There is a lack of empirical proteomic studies on sperm samples comparing different Mytilus species, which could help to advance this study. A comparative analysis of sperm proteomes across different taxa may provide important insights into the fundamental molecular processes and mechanisms involved in reproductive isolation. It might also contribute to a better understanding of sperm function and of the adaptive evolution of sperm proteins in different taxa. There is now growing evidence from genomics studies that multiple protein complexes and many individual proteins might have important functions in sperm biology and the fertilisation process. From an applied perspective, the identification of sperm-specific proteins could also contribute to the improved understanding of fertility problems and as targets for fertility control.

Hybridization and polyploidization within the Chenopodium album aggregate analysed by means of cytological and molecular markers

Hybridization and polyploidization represent an important speciation mechanism in the diploid-polyploid complex of the Chenopodium album aggregate. In the present study we successfully reconstructed the evolutionary histories of the majority of Eurasian representatives of the C. album aggregate, resulting in the most comprehensive phylogenetic analysis of this taxonomically intricate group of species to date. We applied a combination of classical karyology for precise chromosome number determination, genomic in-situ hybridization for the determination of genomic composition, flow cytometry for the estimation of genome size and sequencing of plastid (cpDNA) and nuclear (ribosomal internal transcribed spacer – ITS and the introns of the FLOWERING LOCUS T LIKE genes – FTL) markers for a phylogenetic reconstruction and the identification of parental genomes in polyploid taxa. The FTL markers identified eight well supported evolutionary lineages. Five of them include at least one diploid species, and the remaining three comprise solely the subgenomes of polyploids that probably represent extinct or unknown diploid taxa. The existence of eight basic diploid lineages explains the origin of seven Eurasian polyploid groups and brings evidence of a nearly unlimited number of subgenomic combinations. The supposed promiscuity generated new species wherever different diploid lineages met each other and gave rise to tetraploid species or whenever they met other tetraploid species to produce hexaploid species throughout their evolutionary history. Finally, we unravelled a surprisingly simple scheme of polyploid species formation within the C. album aggregate. We determined seven groups of polyploid species differing in their origin in either Eurasia or Africa and convincingly demonstrated that (1) all Chenopodium polyploid species under study are of allopolyploid origin, (2) there are eight major monophyletic evolutionary lineages represented by extant or extinct/unknown diploid taxa, (3) those monophyletic lineages represent individual subgenomes, (4) hybridization among the lineages created seven subgenomic combinations of polyploid taxa, (5) taxa represented by particular subgenome combinations were further subjected to diversification, and (6) the majority of species are relatively young, not exceeding the age of the Quaternary period.

Sequestration of a Transposon-Derived siRNA by a Target Mimic Imprinted Gene Induces Postzygotic Reproductive Isolation in Arabidopsis

Genomic imprinting is an epigenetic phenomenon occurring in mammals and flowering plants, causing genes to be expressed depending on their parent oforigin. In plants, genomic imprinting is mainly confined to the endosperm, a nutritive tissue supporting embryo growth, similar to the placenta in mammals. Here, we show that the paternally expressed imprinted gene PEG2 transcript sequesters the transposable element (TE)-derived small interfering RNA (siRNA) siRNA854 in the endosperm. siRNA854 is present in the vegetative cell of pollen and transferred to the central cell of the female gametophyte after fertilization, where it is captured by PEG2. Depletion of siRNA854 as a consequence of increased PEG2 transcript levels establishes a reproductive barrier and prevents successful hybridizations between plants differing in chromosome number (ploidy). Thus, the balance of a male gamete accumulating TE-derived siRNA and a paternally expressed imprinted gene regulate triploid seed viability, revealing a transgenerational speciation mechanism.

Multilocus molecular systematics of the circumtropical reef-fish genus Abudefduf (Pomacentridae): history, geography and ecology of speciation.

We investigated a pantropical sub-family and genus of damselfishes, the sergeant-majors (Pomacentridae: Abudefdufinae: Abudefduf), to identify the tempo and mechanisms of speciation in the lineage. We examined sequence capture data from 500 loci and 20 species, with multiple individuals sampled from across the geographic ranges of widespread species. Utilizing a maximum likelihood framework, as well as a time-calibrated Bayesian phylogeny, the following key questions are addressed: What is the historical tempo of speciation? What are the relative contributions of vicariant, peripatric and parapatric speciation to sergeant-major diversity? How is speciation related to major variation in trophic ecology? The approximately 20 species of sergeant-majors fall into three main lineages. The ancestral condition appears to be benthivory, which is predominant in two lineages comprising six species. The remaining species of sergeant-majors, of which there are at least 15, fall within a clade composed entirely of planktivores. This clade is sister to a benthivore clade that included one species, Abudefduf notatus, in transition to planktivory. Most speciation of sergeant-majors, which appeared ∼24 million years ago, occurred in the last 10 million years. Present distributional patterns indicate vicariant speciation precipitated by the closure of land barriers between both sides of the Atlantic and the Pacific, and the emergence of land between the Indian and Pacific Oceans. Within this backdrop, frequent oscillations in sea level over the last 10 million years also appear to have generated conditions suitable for both peripatric and vicariant speciation, and most speciation within the genus appears linked to these changes in sea level. Diversification within the genus has been concentrated in planktivorous seargeant-majors rather than benthivores. The root cause is unclear, but does not appear to be related to differences in dispersal potential, which is greater in the planktivorous species, due to the ability of their post-larval juveniles to raft with floating debris. This elevated speciation rate in planktivores and their propensity to form local endemics may reflect relaxation of selective pressures (e.g., on crypticity) that limit speciation in benthivorous sergeant-majors. Finally, our data allow us to clarify relationships of geminate sergeant-major species, indicating that there are subdivisions within the Atlantic for both benthivore and planktivore geminate pairs that may have misled previous studies.

Modification of silica nanosheets by gemini surfactants with different spacers and its superb adsorption for rhodamine B

To systematically investigate the effect of the non-polar spacer length of gemini surfactants on the adsorption characteristic of organo silica nanosheets (organo-SiNSs), a series of gemini surfactants with different non-polar spacer chain lengths (G16-2-16, G16-3-16, G16-4-16 and G16-6-16) were designed and introduced into silica nanosheets (SiNSs) for the removal of rhodamine B (RhB). Differences in the structure and surface properties of organo-SiNSs were characterized by FT-IR, XRD, TG, BET and zeta potential. Effects of concentration of modifiers and RhB, contact time, pH and temperature have been studied. The adsorption mechanism of different molecular speciation of RhB has been investigated in detail. Gemini surfactants with shorter spacer chain promote the modification process and easily intercalate into interlayer space. Suitable packing density of surfactants on the surface of organo-SiNSs is beneficial to RhB adsorption, and the adsorption capacities of organo-SiNSs decrease in the order G16-3-16-SiNSs (223.36 mg g−1) > G16-4-16-SiNSs (216.18 mg g−1) > G16-6-16-SiNSs (204.88 mg g−1) > G16-2-16-SiNSs (198.09 mg g−1). Hydrophobic interaction between surfactants and RhB plays a dominated role in RhB adsorption; molecular speciation of RhB, electrostatic interaction and competitive adsorption also affect the adsorption. Organo-SiNSs exhibited high adsorption capacity and rapid adsorption equilibrium toward RhB at a low modifier dosage (0.42 mmol for 1 g raw SiNSs). It has been demonstrated that organo-SiNSs can be regenerated at least for 5 cycles. Moreover, the adsorption isotherm data was proved in good agreement with the Redlich Peterson model and the kinetics data was fitted well with pseudo-second-order kinetic model.

Comparative genomics and the nature of placozoan species.

Placozoans are a phylum of nonbilaterian marine animals currently represented by a single described species, Trichoplax adhaerens, Schulze 1883. Placozoans arguably show the simplest animal morphology, which is identical among isolates collected worldwide, despite an apparently sizeable genetic diversity within the phylum. Here, we use a comparative genomics approach for a deeper appreciation of the structure and causes of the deeply diverging lineages in the Placozoa. We generated a high-quality draft genome of the genetic lineage H13 isolated from Hong Kong and compared it to the distantly related T. adhaerens. We uncovered substantial structural differences between the two genomes that point to a deep genomic separation and provide support that adaptation by gene duplication is likely a crucial mechanism in placozoan speciation. We further provide genetic evidence for reproductively isolated species and suggest a genus-level difference of H13 to T. adhaerens, justifying the designation of H13 as a new species, Hoilungia hongkongensis nov. gen., nov. spec., now the second described placozoan species and the first in a new genus. Our multilevel comparative genomics approach is, therefore, likely to prove valuable for species distinctions in other cryptic microscopic animal groups that lack diagnostic morphological characters, such as some nematodes, copepods, rotifers, or mites.