Diversification and convergence following the transition from saltwater to freshwater in stingrays

One of the most fundamental questions in biology is why some groups of organisms are more diverse than others. Classic hypotheses for explaining differences in diversity consider distinctions in time, place, resources, and competitors as the staging grounds for differential diversification. Freshwater and saltwater environments have similar levels of diversity despite significant differences in size, so studying transitions between the two systems can provide insights into evolutionary processes. Despite the challenges associated with this transition, stingrays have invaded freshwater habitats multiple times across different continents, making them useful for better understanding these systems. In this study, we evaluated the frequency of saltwater-freshwater invasions in stingrays, examined three types of diversification among freshwater and saltwater stingrays, and assessed the degree of convergence among freshwater stingrays. We found that, like nearly all other aquatic taxa, stingrays overwhelmingly only transition from saltwater to freshwater. After independent freshwater invasions, river rays did not demonstrate a pattern of increasing morphological or lineage diversification. However, the phenotypic disparity of saltwater stingrays did not follow the Brownian prediction and appeared to spike around two extinction events. Despite not being morphologically distinct from saltwater stingrays, freshwater stingrays do push the boundaries of morphological diversity. Diet guilds did demonstrate morphological differences, with piscivores and molluscivores being distinct from other diet guilds. Freshwater stingrays did not appear to converge morphologically, which may be because there has not been enough time for this to occur among more ancient and more recent freshwater lineages

Diversification and convergence following the transition from saltwater to freshwater in stingrays.

One of the most fundamental questions in biology is why some groups of organisms are more diverse than others. Classic hypotheses for explaining differences in diversity consider distinctions in time, place, resources, and competitors as the staging grounds for differential diversification. Freshwater and saltwater environments have similar levels of diversity despite significant differences in size, so studying transitions between the two systems can provide insights into evolutionary processes. Despite the challenges associated with this transition, stingrays have invaded freshwater habitats multiple times across different continents, making them useful for better understanding these systems. In this study, I evaluated the frequency of saltwater-freshwater invasions in stingrays, examined three types of diversification among freshwater and saltwater stingrays, and assessed the degree of convergence among freshwater stingrays. I found that, like nearly all other aquatic taxa, stingrays overwhelmingly only transition from saltwater to freshwater. After independent freshwater invasions, river rays did not demonstrate a pattern of increasing morphological or lineage diversification. However, the phenotypic disparity of saltwater stingrays did not follow the Brownian prediction and appeared to spike around two extinction events. Despite not being morphologically distinct from saltwater stingrays, freshwater stingrays do push the boundaries of morphological diversity. Diet guilds did demonstrate morphological differences, with piscivores and molluscivores being distinct from other diet guilds. Freshwater stingrays did not appear to converge morphologically, which may be because there has not been enough time for this to occur among more ancient and more recent freshwater lineages

The interaction of oxygen atoms with solid surfaces at eV energies Annual status report, 1 Jun. 1968 - 31 May 1969

Interaction of oxygen atoms with solid surfaces at eV energie

Electronic structure and chemical bonding of nc-TiC/a-C nanocomposites

The electronic structure of nanocrystalline (nc-) TiC/amorphous C nanocomposites has been investigated by soft x-ray absorption and emission spectroscopy. The measured spectra at the Ti 2p and C 1s thresholds of the nanocomposites are compared to those of Ti metal and amorphous C. The corresponding intensities of the electronic states for the valence and conduction bands in the nanocomposites are shown to strongly depend on the TiC carbide grain size. An increased charge-transfer between the Ti 3d-eg states and the C 2p states has been identified as the grain size decreases, causing an increased ionicity of the TiC nanocrystallites. It is suggested that the charge-transfer occurs at the interface between the nanocrystalline TiC and the amorphous C matrix and represents an interface bonding which may be essential for the understanding of the properties of nc-TiC/amorphous C and similar nanocomposites.Comment: 13 pages, 6 figures, 1 table; http://link.aps.org/doi/10.1103/PhysRevB.80.23510

Critical Concentration Of Uranium Solution

The experiments with U(37)O{sub 2}F{sub 2} aqueous solution followed the series of experiments with {sup 233}UO{sub 2}(NO{sub 3}){sub 2} and U(93)O{sub 2}(NO{sub 3}){sub 2} solutions in the 69.2-cm-diam sphere. The critical concentrations of {sup 233}U and {sup 235}U were used to evaluate the ratio of {ovr {eta}{sigma}{sub a}}(233)/{ovr {eta}{sigma}{sub a}}(235) some years ago when the accepted value of {ovr {eta}}(233) was questioned. The purpose of the experiment reported here was to measure the increase in {sup 235}U critical concentration and, hence, the increase in critical mass due to the increase in the {sup 238}U content in the 69.2-cm-diam sphere. The U(37)O{sub 2}F{sub 2} concentration in an aqueous solution was adjusted to that when an aluminum spherical vessel was completely filled and the multiplication factor was greater than unity and the excess reactivity was measured by means of a positive reactor period. The critical conditions are summarized in Table 1. The critical conditions for U(93)O{sub 2}(NO{sub 3}){sub 2} solution in the same sphere are also given for comparison and there is only a small difference in the critical {sup 235}U density or mass. In these well moderated solutions there is only a small amount of neutron absorption in {sup 238}U. A comparison of the calculated multiplication factors using the DSN and ANISN transport codes with different Hansen-Roach 16-group cross-section sets is presented in Table 2. The calculated value of 1.0005 is to be compared to the experimental value of 1.0011

Mahi-mahi (Coryphaena hippurus) life development: morphological, physiological, behavioral and molecular phenotypes.

BackgroundMahi-mahi (Coryphaena hippurus) is a commercially and ecologically important fish species that is widely distributed in tropical and subtropical waters. Biological attributes and reproductive capacities of mahi-mahi make it a tractable model for experimental studies. In this study, life development of cultured mahi-mahi from the zygote stage to adult has been described.ResultsA comprehensive developmental table has been created reporting development as primarily detailed observations of morphology. Additionally, physiological, behavioral, and molecular landmarks have been described to significantly contribute in the understanding of mahi life development.ConclusionRemarkably, despite the vast difference in adult size, many developmental landmarks of mahi map quite closely onto the development and growth of Zebrafish and other warm-water, active Teleost fishes

Large magnetic circular dichroism in resonant inelastic x-ray scattering at the Mn L-edge of Mn-Zn ferrite

We report resonant inelastic x-ray scattering (RIXS) excited by circularly polarized x-rays on Mn-Zn ferrite at the Mn L2,3-resonances. We demonstrate that crystal field excitations, as expected for localized systems, dominate the RIXS spectra and thus their dichroic asymmetry cannot be interpreted in terms of spin-resolved partial density of states, which has been the standard approach for RIXS dichroism. We observe large dichroic RIXS at the L2-resonance which we attribute to the absence of metallic core hole screening in the insulating Mn-ferrite. On the other hand, reduced L3-RIXS dichroism is interpreted as an effect of longer scattering time that enables spin-lattice core hole relaxation via magnons and phonons occurring on a femtosecond time scale.Comment: 7 pages, 2 figures, http://link.aps.org/doi/10.1103/PhysRevB.74.17240

Detecting broad domains and narrow peaks in ChIP-seq data with hiddenDomains

Abstract Background Correctly identifying genomic regions enriched with histone modifications and transcription factors is key to understanding their regulatory and developmental roles. Conceptually, these regions are divided into two categories, narrow peaks and broad domains, and different algorithms are used to identify each one. Datasets that span these two categories are often analyzed with a single program for peak calling combined with an ad hoc method for domains. Results We developed hiddenDomains, which identifies both peaks and domains, and compare it to the leading algorithms using H3K27me3, H3K36me3, GABP, ESR1 and FOXA ChIP-seq datasets. The output from the programs was compared to qPCR-validated enriched and depleted sites, predicted transcription factor binding sites, and highly-transcribed gene bodies. With every method, hiddenDomains, performed as well as, if not better than algorithms dedicated to a specific type of analysis. Conclusions hiddenDomains performs as well as the best domain and peak calling algorithms, making it ideal for analyzing ChIP-seq datasets, especially those that contain a mixture of peaks and domains