2,250 research outputs found
Reproduction, early development, and larval rearing strategies for two sponge-dwelling neon gobies, Elacatinus lori and E.colini
A major goal of the aquaculture industry is to reduce collection pressure on wild populations by developing captive breeding techniques for marine ornamental species, particularly coral reef fishes. The objective of this study was to develop a rearing protocol for two recently described species of neon gobies that are endemic to the Mesoamerican Barrier Reef: 1) Elacatinus lori; and 2) Elacatinus colini. First, the current study describes the reproductive behavior and larval development of both species. Second, it evaluates the effects of different rotifer and Artemia densities on the survival and growth of E. lori and E. colini larvae. Third, it compares the survival and growth of E. colini larvae fed wild plankton to those fed a combination of rotifers and Artemia. Once acclimated, pairs of E. lori began spawning in 53.2 ± 12.4 d (mean ± sd), while pairs of E. colini took only 12.2 ± 10.3 d. E. lori produced more embryos per clutch (1009 ± 477) than E. colini (168 ± 83). E. lori larvae hatched 8.18 ± 0.4 days after initial observation with a notochord length of 3.67 ± 0.2 mm. In comparison, E. colini larvae hatched 6.8 ± 0.4 days after initial observation with a notochord length of 3.51 ± 2.3 mm. Both species settled as early as 28 days post hatch at 9–9.5 mm standard length, following the fusion of the pelvic fins to form a pelvic disc. During rotifer density trials, from 0 to 6 days post hatch, there was no significant difference in survival or standard length between treatments fed 10, 15 or 20 rotifers ml^− 1 for either species. During Artemia density trials, from 6 to 14 days post hatch, control treatments fed solely on 15 rotifers ml^− 1 had significantly higher survival than treatments that were fed rotifers in combination with 3, 6 or 9 Artemia ml^− 1. Finally, E. colini larvae that were fed wild plankton had significantly higher survival and growth than those fed with a combination of 15 rotifers ml^− 1 and 3 Artemia ml^− 1. The results of this study suggest that Artemia nauplii are not a suitable prey for E. lori or E. colini larvae. Our results demonstrate the feasibility of rearing E. lori and E. colini to settlement, and suggest that 10–20 rotifers ml^− 1 and wild plankton provide a viable starting point for optimizing the survival and growth of Elacatinus spp. larvae.We would like to thank the Belizean government and Fisheries Department for permission to conduct this research. Thank you to the staff at the International Zoological Expeditions for their support in the field. Special thanks to Katrina Catalano, Kevin David, Robin Francis, Jeremiah Seymour, James Ferrito, Derek Scolaro and Alex Ascher for their assistance in the lab and rearing larvae. Dr. John Crawford, Dr. Karen Warkentin and Dr. Jacqueline Webb provided helpful comments on this manuscript. This research comprises a portion of JEM's doctoral thesis requirements (Boston University). Funding was provided by a start-up award to PMB from the Trustees of Boston University, the IDC account of JA and a Warren McLeod Summer Research Scholarship awarded by the Boston University Marine Department to JEM. Additional funding was provided by two NSF grants (OCE-1260424 and OCE-1459546), and an NSF Doctoral Dissertation Improvement Grant (IOS-1501651). The authors would also like to thank the Marine Aquarium Societies of North America's Dr. Junda Lin Memorial Fund for Publishing Open Access Marine Aquarium Research for offsetting the open access publishing costs of this article. More info at tiny.cc/MASNAPubFund. All work was approved by the Belize Fisheries Department and the Boston University IACUC (protocol # 10-036). (Trustees of Boston University; Warren McLeod Summer Research Scholarship - Boston University Marine Department; OCE-1260424 - NSF; OCE-1459546 - NSF; IOS-1501651 - NSF Doctoral Dissertation Improvement Grant; IDC account; Marine Aquarium Societies of North America's Dr. Junda Lin Memorial Fund for Publishing Open Access Marine Aquarium Research)Published versio
The Netherlands on European political axes: Coalition building, diplomatic relations and new alliances in a Brexit era
The purpose of this study was to determine if and to which extent there has been a shift in the position of the Netherlands in European Union coalition-building, focusing on the pre-Brexit phase that began with the Brexit referendum in the United Kingdom (23 June 2016) and finished with the UK’s formal withdrawal (31 January 2020). The UK’s departure from the EU has ensued an economic and demographic shift towards the EU’s south and east. This raises questions about the position of the Netherlands in a post-Brexit EU. Using the lenses of Liberal Intergovernmentalism and Constructivism, we found a more assertive attitude of the Netherlands towards the EU as a direct result of the loss of an important liberal and heavyweight partner. We have witnessed an increase in networking events during the pre-Brexit phase, aimed at enhancing diplomatic relations with other Member States, as well as in political discourse and events in which visions for (the future of) the EU were explicitly addressed. It was shown that the Netherlands has come to the fore by undertaking an active leadership role in forging new coalitions to secure its interest in a post-Brexit EU. A prime outcome of this is the New Hanseatic League, comprised of small and medium-sized northern EU Member States. A second result is the apparent Dutch leading role within the so-called Frugal Four. These findings corroborate the assumptions that the Netherlands primarily partakes in ad-hoc, theme-specific coalitions.O objetivo deste estudo consistiu em determinar se, e em que medida, houve uma mudança na posição dos PaÃses Baixos no processo de formação de coligações da União Europeia, centrando-se na fase pré-Brexit, com inÃcio no referendo Brexit no Reino Unido (23 de Junho de 2016) e desfecho na retirada formal do Reino Unido (31 de Janeiro de 2020). A saÃda do Reino Unido da UE resultou numa reorientação económica e demográfica para o sul e leste da UE. Isso suscita algumas questões sobre a posição dos PaÃses Baixos numa UE pós-Brexit. Sob as lentes do intergovernamentalismo liberal e construtivismo, verificámos uma atitude mais assertiva dos PaÃses Baixos em relação à UE como resultado direto da perda de um importante parceiro liberal e um peso-pesado. Assistimos a um aumento de eventos de networking durante a fase pré-Brexit, que visavam reforçar as relações diplomáticas com outros Estados-Membros, e o mesmo se verificou no discurso polÃtico e nos eventos em que as visões para a UE (e o seu futuro) foram explicitamente abordadas. Constatou-se que os PaÃses Baixos têm vindo a assumir um papel de liderança ativa na formação de novas coligações para assegurar os seus interesses numa UE pós-Brexit. Um importante resultado deste processo é a Nova Liga Hanseática, composta por pequenos e médios Estados-Membros do Norte da UE. Um segundo resultado é o aparente papel de liderança dos neerlandeses no seio dos chamados Frugal Four. Estas conclusões corroboram os pressupostos de que os PaÃses Baixos participam sobretudo em coligações ad-hoc e orientadas para temas especÃficos
Unveiling the environment surrounding LMXB SAX J1808.4-3658
Low-mass X-ray binaries (LMXBs) are a natural workbench to study accretion
disk phenomena and optimal background sources to measure elemental abundances
in the Interstellar medium (ISM). In high-resolution XMM-Newton spectra, the
LMXB SAX J1808.4-3658 showed in the past a neon column density significantly
higher than expected given its small distance, presumably due to additional
absorption from a neon-rich circumstellar medium (CSM). It is possible to
detect intrinsic absorption from the CSM by evidence of Keplerian motions or
outflows. For this purpose, we use a recent, deep (100 ks long),
high-resolution Chandra/LETGS spectrum of SAX J1808.4-3658 in combination with
archival data. We estimated the column densities of the different absorbers
through the study of their absorption lines. We used both empirical and
physical models involving photo- and collisional-ionization in order to
determine the nature of the absorbers. The abundances of the cold interstellar
gas match the solar values as expected given the proximity of the X-ray source.
For the first time in this source, we detected neon and oxygen blueshifted
absorption lines that can be well modeled with outflowing photoionized gas. The
wind is neon rich (Ne/O>3) and may originate from processed, ionized gas near
the accretion disk or its corona. The kinematics (v=500-1000 km/s) are indeed
similar to those seen in other accretion disks. We also discovered a system of
emission lines with very high Doppler velocities (v~24000 km/s) originating
presumably closer to the compact object. Additional observations and UV
coverage are needed to accurately determine the wind abundances and its
ionization structure.Comment: 12 pages, 10 figures, accepted for publication on A&
Efficient construction of free energy profiles of breathing metal–organic frameworks using advanced molecular dynamics simulations
In order to reliably predict and understand the breathing behavior of highly flexible metal–organic frameworks from thermodynamic considerations, an accurate estimation of the free energy difference between their different metastable states is a prerequisite. Herein, a variety of free energy estimation methods are thoroughly tested for their ability to construct the free energy profile as a function of the unit cell volume of MIL-53(Al). The methods comprise free energy perturbation, thermodynamic integration, umbrella sampling, metadynamics, and variationally enhanced sampling. A series of molecular dynamics simulations have been performed in the frame of each of the five methods to describe structural transformations in flexible materials with the volume as the collective variable, which offers a unique opportunity to assess their computational efficiency. Subsequently, the most efficient method, umbrella sampling, is used to construct an accurate free energy profile at different temperatures for MIL-53(Al) from first principles at the PBE+D3(BJ) level of theory. This study yields insight into the importance of the different aspects such as entropy contributions and anharmonic contributions on the resulting free energy profile. As such, this thorough study provides unparalleled insight in the thermodynamics of the large structural deformations of flexible materials
On the Putative Detection of z>0 X-ray Absorption Features in the Spectrum of Markarian 421
In a series of papers, Nicastro et al. have reported the detection of z>0
OVII absorption features in the spectrum of Mrk421 obtained with the Chandra
Low Energy Transmission Grating Spectrometer (LETGS). We evaluate this result
in the context of a high quality spectrum of the same source obtained with the
Reflection Grating Spectrometer (RGS) on XMM-Newton. The data comprise over
955ks of usable exposure time and more than 26000 counts per 50 milliAngstrom
at 21.6 Angstroms. We concentrate on the spectrally clean region (21.3 < lambda
< 22.5 Angstroms) where sharp features due to the astrophysically abundant OVII
may reveal an intervening, warm--hot intergalactic medium (WHIM). We do not
confirm detection of any of the intervening systems claimed to date. Rather, we
detect only three unsurprising, astrophysically expected features down to the
Log(N_i)~14.6 (3 sigma) sensitivity level. Each of the two purported WHIM
features is rejected with a statistical confidence that exceeds that reported
for its initial detection. While we can not rule out the existence of fainter,
WHIM related features in these spectra, we suggest that previous discovery
claims were premature. A more recent paper by Williams et al. claims to have
demonstrated that the RGS data we analyze here do not have the resolution or
statistical quality required to confirm or deny the LETGS detections. We show
that our careful analysis resolves the issues encountered by Williams et al.
and recovers the full resolution and statistical quality of the RGS data. We
highlight the differences between our analysis and those published by Williams
et al. as this may explain our disparate conclusions.Comment: 19 pages/7 figures/4 tables. 060424 submitted to ApJ 060522
re-submitted following ApJ reques
Insight into deep-sea life – Cibicidoides pachyderma substrate and pHdependent behaviour following disturbance
Most palaeo-deep-water reconstructions are based on geochemical information stored in the calcareous shells of
Cibicidoides species but hardly anything is known about their life cycle, population dynamics or ecology. The
number of specimens of a single Cibicidoides species can locally be very limited and species may be lacking
completely during certain intervals in the geological past. As a consequence, geochemical analyses are often
carried out on lumped Cibicidoides spp. assuming that they share the same epizoic to epifaunal habitat and
precipitated their shell in comparable offsets to surrounding bottom water mass properties. However, there is a
growing body of evidence that particularly Cibicidoides pachyderma and its morphotypes C. mundulus and C.
kullenbergi, may not be reliable bottom water recorders.
We have recently developed aquaria that allowed, for the first time, observations of Cibicidoides pachyderma
var. C. mundulus under in situ pressure and temperature. Experiments were carried out with and without artificial
sediments to simulate soft sediments and rocks, respectively. Seawater was set to pH 8 and pH 7.4 to simulate
more or less particulate carbon export or more or less ventilation of bottom water. Our experiments demonstrate
that C. mundulus may opt for an epifaunal or an infaunal habitat depending on elapsed time following physical
disturbance, pH, current activity, the availability of sediments and growth. The specimen's initial response
following transfer from atmospheric pressure into the high-pressure aquaria was to immerse into the sediment or
to cover more or less parts of the test with aggregated sediments or algae. However, within 24 h a strong
rheotaxis became apparent and most specimens moved to sites of increased current activity under normal pH
conditions (pH 8). Only few specimens remained in algae cysts or in the sediment in the pH-8 experiment. On the
contrary, all specimens under pH 7.4 agglutinated a firm sediment cyst around their test and remained infaunal
throughout the experimental period of three months.
Independent of pH, growth was only observed in specimens that lived within an agglutinated cyst or infaunal.
A solid thick cyst covered the specimens of the pH 7.4 experiment throughout the experiment and possibly
restricted water exchange between the in-cyst water and the surrounding artificial bottom water mass. We
suggest that a more fragile and possibly more porous sedimentary envelope may, at least temporally, have
covered the infaunal specimens under pH 8 but no evidence for this was found upon termination of the experiment
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