Retention of low-fitness genotypes over six decades of admixture between native and introduced tiger salamanders

<p>Abstract</p> <p>Background</p> <p>Introductions of non-native tiger salamanders into the range of California tiger salamanders have provided a rare opportunity to study the early stages of secondary contact and hybridization. We produced first- and second-generation hybrid salamanders in the lab and measured viability among these early-generation hybrid crosses to determine the strength of the initial barrier to gene exchange. We also created contemporary-generation hybrids in the lab and evaluated the extent to which selection has affected fitness over approximately 20 generations of admixture. Additionally, we examined the inheritance of quantitative phenotypic variation to better understand how evolution has progressed since secondary contact.</p> <p>Results</p> <p>We found significant variation in the fitness of hybrids, with non-native backcrosses experiencing the highest survival and F2 hybrids the lowest. Contemporary-generation hybrids had similar survival to that of F2 families, contrary to our expectation that 20 generations of selection in the wild would eliminate unfit genotypes and increase survival. Hybrid survival clearly exhibited effects of epistasis, whereas size and growth showed mostly additive genetic variance, and time to metamorphosis showed substantial dominance.</p> <p>Conclusions</p> <p>Based on first- and second- generation cross types, our results suggest that the initial barrier to gene flow between these two species was relatively weak, and subsequent evolution has been generally slow. The persistence of low-viability recombinant hybrid genotypes in some contemporary populations illustrates that while hybridization can provide a potent source of genetic variation upon which natural selection can act, the sorting of fit from unfit gene combinations might be inefficient in highly admixed populations. Spatio-temporal fluctuation in selection or complex genetics has perhaps stalled adaptive evolution in this system despite selection for admixed genotypes within generations.</p

Optically controlled spin-glasses in multi-qubit cavity systems

Recent advances in nanostructure fabrication and optical control, suggest that it will soon be possible to prepare collections of interacting two-level systems (i.e. qubits) within an optical cavity. Here we show theoretically that such systems could exhibit novel phase transition phenomena involving spin-glass phases. By contrast with traditional realizations using magnetic solids, these phase transition phenomena are associated with both matter and radiation subsystems. Moreover the various phase transitions should be tunable simply by varying the matter-radiation coupling strength.Comment: 4 pages, 3 figure

Non-adaptive phenotypic plasticity: the effects of terrestrial and aquatic herbicides on larval salamander morphology and swim speed

Department of Biology, University of North Carolina, Chapel Hill, NC, USAPhenotypic plasticity, although ubiquitous, may not always be advantageous. Non-adaptive plasticity is likely to occur in response to novel environmental stress. Anthropogenic contaminants, such as herbicides, are novel stressors that are not present in the evolutionary history of most species. We investigated the pattern and consequences of phenotypic plasticity induced by four glyphosate-based herbicides (two terrestrial and two aquatic) in larvae of the spotted salamander, , by determining (1) whether the herbicides induced different morphologies; (2) if different morphologies translated to differences in burst swim performance; and (3) how induced individuals performed relative to non-induced controls. Different herbicide formulations led to the production of significantly different head and tail morphologies, and tail morphology correlated with fastest escape speed. However, escape speed did not vary among treatments. In addition, three out of four herbicide treatments experienced accelerated growth rates, in terms of the lateral size of tails, although the tail shapes were either similar to preliminary controls or intermediate between preliminary and final controls. These observations suggest that herbicide-induced morphology is a case of non-adaptive phenotypic plasticity, and that there is potentially a trade-off between growth and development for larvae exposed to different formulations. Understanding the functional significance of induced phenotypes is important for determining their importance in shaping an organism's ecological interactions and evolutionary trajectories. Furthermore, under different conditions, the morphological changes that we observed in response to exposure to herbicides might affect salamander fitness and influence population dynamics

The First Supernova Explosions: Energetics, Feedback, and Chemical Enrichment

We perform three-dimensional smoothed particle hydrodynamics simulations in a realistic cosmological setting to investigate the expansion, feedback, and chemical enrichment properties of a 200 M_sun pair-instability supernova in the high-redshift universe. We find that the SN remnant propagates for a Hubble time at z = 20 to a final mass-weighted mean shock radius of 2.5 kpc (proper), roughly half the size of the HII region, and in this process sweeps up a total gas mass of 2.5*10^5 M_sun. The morphology of the shock becomes highly anisotropic once it leaves the host halo and encounters filaments and neighboring minihalos, while the bulk of the shock propagates into the voids of the intergalactic medium. The SN entirely disrupts the host halo and terminates further star formation for at least 200 Myr, while in our specific case it exerts positive mechanical feedback on neighboring minihalos by shock-compressing their cores. In contrast, we do not observe secondary star formation in the dense shell via gravitational fragmentation, due to the previous photoheating by the progenitor star. We find that cooling by metal lines is unimportant for the entire evolution of the SN remnant, while the metal-enriched, interior bubble expands adiabatically into the cavities created by the shock, and ultimately into the voids with a maximum extent similar to the final mass-weighted mean shock radius. Finally, we conclude that dark matter halos of at least M_vir > 10^8 M_sun must be assembled to recollect all components of the swept-up gas.Comment: 16 pages, 14 figures, published in Ap

Local radiative feedback in the formation of the first protogalaxies

The formation of the first galaxies is influenced by the radiative feedback from the first generations of stars. This feedback is manisfested by the heating and ionization of the gas which lies within the H II regions surrounding the first stars, as well as by the photodissociation of hydrogen molecules within the larger Lyman-Werner (LW) bubbles that surround these sources. Using a ray-tracing method in three-dimensional cosmological simulations, we self-consistently track the formation of, and radiative feedback from, individual stars in the course of the formation of a protogalaxy. We compute in detail the H II regions of each of these sources, as well as the regions affected by their molecule-dissociating radiation. We follow the thermal, chemical, and dynamical evolution of the primordial gas, as it becomes incorporated into the protogalaxy. While the IGM is, in general, optically thick to LW photons only over physical distances of > 30 kpc at redshifts z < 20, the high molecule fraction that is built up in relic H II regions and their increasing volume-filling fraction renders even the local IGM optically thick to LW photons over physical distances of the order of a few kiloparsecs. We find that efficient accretion onto Population III relic black holes may occur after ~ 60 Myr from the time of their formation, by which time the photo-heated relic H II region gas can cool and re-collapse into the 10^6 M_solar minihalo which hosts the black hole. Also, Pop II.5 stars, postulated to have masses of the order of 10 M_solar, can likely form from this re-collapsing relic H II region gas. Overall, we find that the local radiative feedback from the first generations of stars suppresses the star formation rate by only a factor of, at most, a few.Comment: 29 pages, 7 figures; ApJ in pres

Rapid fixation of non-native alleles revealed by genome-wide SNP analysis of hybrid tiger salamanders

<p>Abstract</p> <p>Background</p> <p>Hybrid zones represent valuable opportunities to observe evolution in systems that are unusually dynamic and where the potential for the origin of novelty and rapid adaptation co-occur with the potential for dysfunction. Recently initiated hybrid zones are particularly exciting evolutionary experiments because ongoing natural selection on novel genetic combinations can be studied in ecological time. Moreover, when hybrid zones involve native and introduced species, complex genetic patterns present important challenges for conservation policy. To assess variation of admixture dynamics, we scored a large panel of markers in five wild hybrid populations formed when Barred Tiger Salamanders were introduced into the range of California Tiger Salamanders.</p> <p>Results</p> <p>At three of 64 markers, introduced alleles have largely displaced native alleles within the hybrid populations. Another marker (<it>GNAT1</it>) showed consistent heterozygote deficits in the wild, and this marker was associated with embryonic mortality in laboratory F2's. Other deviations from equilibrium expectations were idiosyncratic among breeding ponds, consistent with highly stochastic demographic effects.</p> <p>Conclusion</p> <p>While most markers retain native and introduced alleles in expected proportions, strong selection appears to be eliminating native alleles at a smaller set of loci. Such rapid fixation of alleles is detectable only in recently formed hybrid zones, though it might be representative of dynamics that frequently occur in nature. These results underscore the variable and mosaic nature of hybrid genomes and illustrate the potency of recombination and selection in promoting variable, and often unpredictable genetic outcomes. Introgression of a few, strongly selected introduced alleles should not necessarily affect the conservation status of California Tiger Salamanders, but suggests that genetically pure populations of this endangered species will be difficult to maintain.</p

Optical signatures of quantum phase transitions in a light-matter system

Information about quantum phase transitions in conventional condensed matter systems, must be sought by probing the matter system itself. By contrast, we show that mixed matter-light systems offer a distinct advantage in that the photon field carries clear signatures of the associated quantum critical phenomena. Having derived an accurate, size-consistent Hamiltonian for the photonic field in the well-known Dicke model, we predict striking behavior of the optical squeezing and photon statistics near the phase transition. The corresponding dynamics resemble those of a degenerate parametric amplifier. Our findings boost the motivation for exploring exotic quantum phase transition phenomena in atom-cavity, nanostructure-cavity, and nanostructure-photonic-band-gap systems.Comment: 4 pages, 4 figure

On the Anti-Correlation between Duration and Redshift in Gamma-ray Bursts

For gamma-ray bursts (GRBs) with durations greater than two seconds (so-called long GRBs), the intrinsic prompt gamma-ray emission appears, on average, to last longer for bursts at lower redshifts. We explore the nature of this duration-redshift anti-correlation, describing systems and conditions in which this cosmological evolution could arise. In particular, we explore its dependence on metallicity of a massive star progenitor, as we can securely count on the average stellar metallicity to increase with decreasing redshift. Although higher metallicity/lower redshift stars lose mass and angular momentum through line-driven winds, in some cases these stars are able to form more extended accretion disks when they collapse, potentially leading to longer duration GRBs. We also examine how this duration-redshift trend may show up in interacting binary models composed of a massive star and compact object companion, recently suggested to be the progenitors of radio bright GRBs. Under certain conditions, mass loss and equation of state effects from higher metallicity, lower redshift massive stars can decrease the binary separation. This can then lead to spin-up of the massive star and allow for a longer duration GRB upon the massive star's collapse. Finally, the duration-redshift trend may also be supported by a relatively larger population of small-separation binaries born in situ at low redshift.Comment: Accepted to Ap

Proof of concept: Partner-Assisted Interpersonal Psychotherapy for perinatal depression

Although poor partner support is a key risk factor for depression in pregnant and postpartum women, partners are not generally involved in treatment beyond psychoeducation. The aim of this "proof of concept" study was to test safety, acceptability, and feasibility of Partner-Assisted Interpersonal Psychotherapy (PA-IPT), an intervention that includes the partner as an active participant throughout treatment. Women more than 12 weeks estimated gestational age and less than 12 weeks postpartum were invited to participate if they fulfilled DSM-IV criteria for Major Depressive Disorder and reported moderate symptom severity (HAM-D17 ≥16). The open trial included eight acute-phase sessions and a 6-week follow-up assessment. Ten couples completed the acute phase treatment and nine presented for a 6-week follow-up assessment. There were no study-related adverse events, and no women had symptomatic worsening from intake to Session Eight. All partners attended all sessions, no couples dropped out of treatment, and all reported positive treatment satisfaction at the conclusion of the study. Nine of ten women (90 %) met the criteria for clinical response (HAM-D17=9) at the conclusion of acute phase treatment, and eight of the nine (89 %) presenting at a 6-week follow-up assessment met criteria for symptomatic recovery. Incorporating partners in the treatment of major depressive disorders during the perinatal period is safe, acceptable, and feasible, but needs further testing in a larger population to evaluate efficacy