1,561 research outputs found
Environmental constraints influencing survival of an African parasite in a north temperate habitat: effects of temperature on development within the host
The monogenean Protopolystoma xenopodis has been established in Wales for >40 years following introduction with Xenopus laevis from South Africa. This provides an experimental system for determining constraints affecting introduced species in novel environments. Parasite development post-infection was followed at 15, 20 and 25 °C for 15 weeks and at 10 °C for51 year and correlated with temperatures recorded inWales. Development was slowed/arrested at410 °C which reflects habitat conditions for >6 months/year. There was wide variation in growth at constant temperature (body size differing by >10 times) potentially attributable in part to genotype-specific host-parasite interactions. Parasite density had no effect on size but host sex did: worms in males were 1·8 times larger than in females. Minimum time to patency was 51 days at 25 °C and 73 days at 20 °C although some infections were still not patent at both temperatures by 105 days p.i. In Wales, fastest developing infections may mature within one summer (about 12 weeks), possibly accelerated by movements of hosts into warmer surface waters. Otherwise, development slows/stops in OctoberâApril, delaying patency to about 1 year p.i., while wide variation in developmental rates may impose delays of 2 years in some primary infections and even longer in secondary infections
Environmental constraints influencing survival of an African parasite in a north temperate habitat: effects of temperature on egg development
SUMMARYFactors affecting survival of parasites introduced to new geographical regions include changes in environmental temperature. Protopolystoma xenopodis is a monogenean introduced with the amphibian Xenopus laevis from South Africa to Wales (probably in the 1960s) where low water temperatures impose major constraints on life-cycle processes. Effects were quantified by maintenance of eggs from infections in Wales under controlled conditions at 10, 12, 15, 18, 20 and 25°C. The threshold for egg viability/ development was 15°C. Mean times to hatching were 22 days at 25°C, 32 days at 20°C, extending to 66 days at 15°C. Field temperature records provided calibration of transmission schedules. Although egg production continues year-round, all eggs produced during >8 months/ year die without hatching. Output contributing significantly to transmission is restricted to 10 weeks (May-mid-July). Host infection, beginning after a time lag of 8 weeks for egg development, is also restricted to 10 weeks (July-September). Habitat temperatures (mean 15·5°C in summer 2008) allow only a narrow margin for life-cycle progress: even small temperature increases, predicted with 'global warming', enhance infection. This system provides empirical data on the metrics of transmission permitting long-term persistence of isolated parasite populations in limiting environments
Gendered Dietary Supplements: Does the Marketing Reflect Different Formulations?
Many dietary supplements are marketed with gendered terms, such as âfor herâ and âfor him.â However, whether these statements reflect different nutrient contents of products and a biological basis has not been systematically examined. PURPOSE: The purpose of this analysis was to compare the micronutrient content of dietary supplements that are sold in separate forms based on gendered marketing. METHODS: The National Institutes of Health Dietary Supplements Label Database (DSLD) was searched using gendered terms, such as âhers,â âher,â âwomen,â âhis,â âhim,â and âmen.â Eighty-nine pairs of micronutrient-containing products that were commercially available as a womenâs version and a menâs version were identified. Nutrients included in the analysis included common vitamins (biotin, choline, folate/folic acid, niacin, pantothenic acid, riboflavin, thiamine, and vitamins A, B12, B6, C, D, E, and K) and minerals (calcium, chloride, chromium, copper, iodine, iron, magnesium, manganese, molybdenum, phosphorus, potassium, selenium, and zinc). Nutrient quantities in units of % Daily Value (%DV) were compared between gendered marketing categories using independent-samples t-tests and calculation of effect sizes using Cohenâs d. Data were analyzed using R (v. 4.2.1) and the rstatix package. RESULTS: Statistically significant differences were observed between gendered marketing categories for iron (n=40 pairs; womenâs: 85±42%; menâs: 6±14%; p\u3c0.001; effect size: 2.56 [large]) and calcium (n=62 pairs; womenâs: 26±19%; menâs: 16±13%; p=0.03; effect size: 0.57 [moderate]), but no other nutrients. CONCLUSION: Micronutrient-containing supplements marketed specifically to women and men primarily had similar micronutrient content, except for higher iron and calcium in womenâs products. For iron, this difference is reflective of anticipated biological need, as acknowledged by a higher Recommended Dietary Allowance (RDA) for adolescent and adult females up to age 50 (8 to 27 mg/d) as compared to males (8 mg/d). For calcium, the RDA is equivalent for males and females at all ages, except for ages 51-70 years (females: 1,200 mg/d; males: 1,000 mg/d). Therefore, the observed differences in iron and calcium appear to have a legitimate biological basis, although for specific age ranges. In conclusion, few differences in micronutrient content were seen between products marketed specifically as womenâs or menâs products. However, the observed differences in iron and calcium may be reflective of biological need in select age groups
Halos of Spiral Galaxies. III. Metallicity Distributions
(Abriged) We report results of a campaign to image the stellar populations in
the halos of highly inclined spiral galaxies, with the fields roughly 10 kpc
(projected) from the nuclei. We use the F814W (I) and F606W (V) filters in the
Wide Field Planetary Camera 2, on board the Hubble Space telescope. Extended
halo populations are detected in all galaxies. The color-magnitude diagrams
appear to be completely dominated by giant-branch stars, with no evidence for
the presence of young stellar populations in any of the fields. We find that
the metallicity distribution functions are dominated by metal-rich populations,
with a tail extending toward the metal poor end. To first order, the overall
shapes of the metallicity distribution functions are similar to what is
predicted by simple, single-component model of chemical evolution with the
effective yields increasing with galaxy luminosity. However, metallicity
distributions significantly narrower than the simple model are observed for a
few of the most luminous galaxies in the sample. It appears clear that more
luminous spiral galaxies also have more metal-rich stellar halos. The
increasingly significant departures from the closed-box model for the more
luminous galaxies indicate that a parameter in addition to a single yield is
required to describe chemical evolution. This parameter, which could be related
to gas infall or outflow either in situ or in progenitor dwarf galaxies that
later merge to form the stellar halo, tends to act to make the metallicity
distributions narrower at high metallicity.Comment: 20 pages, 8 figures (ApJ, in press
The compositional and metabolic responses of gilthead seabream (Sparus aurata) to a gradient of dietary fish oil and associated n-3 long-chain PUFA content
The authors express their gratitude to the technical team at the BioMar Feed Trial Unit, Hirtshals, in particular, Svend JĂžrgen Steenfeldt for expert care of the experimental subjects, for training and supervision provided by laboratory staff at Nutrition Analytical Services and Molecular Biology at the Institute of Aquaculture, University of Stirling, UK. S. J. S. Hâs. PhD was co-funded by BioMar and the Marine Alliance for Science and Technology Scotland. BioMar provided the experimental feeds, trial facilities and fish, and covered travel expenses. V. K. and J. T. designed and executed the nutritional trial and all authors contributed to planning the analyses. V. K., J. T. and S. J. S. H. carried out the sampling. O. M., D. R. T and S. A. M. M. supervised the lead author. M. B. B. provided training in molecular biology to S. J. S. H. who carried out all analytical procedures. S. J. S. H. analysed all of the data and prepared the manuscript. Subsequently the manuscript was shared between all authors who made amendments, contributions and recommendations. The authors declare that there are no conflicts of interestPeer reviewedPublisher PD
Does the Number Density of Elliptical Galaxies Change at z<1?
We have performed a detailed V/Vmax test for a sample of the Canada-France
Redshift Survey (CFRS) for the purpose of examining whether the comoving number
density of field galaxies changes significantly at redshifts of z<1. Taking
into account the luminosity evolution of galaxies which depends on their
morphological type through different history of star formation, we obtain
\sim 0.5 in the range of 0.3<z<0.8, where reliable redshifts were
secured by spectroscopy of either absorption or emission lines for the CFRS
sample. This indicates that a picture of mild evolution of field galaxies
without significant mergers is consistent with the CFRS data. Early-type
galaxies, selected by their (V-I)_{AB} color, become unnaturally deficient in
number at z>0.8 due to the selection bias, thereby causing a fictitious
decrease of . We therefore conclude that a reasonable choice of upper
bound of redshift z \sim 0.8 in the V/Vmax test saves the picture of passive
evolution for field ellipticals in the CFRS sample, which was rejected by
Kauffman, Charlot, & White (1996) without confining the redshift range.
However, about 10% of the CFRS sample consists of galaxies having colors much
bluer than predicted for irregular galaxies, and their \avmax is significantly
larger than 0.5. We discuss this population of extremely blue galaxies in terms
of starburst that has just turned on at their observed redshifts.Comment: 11 pages including 3 figures, to appear in ApJ Letter
Metallicities of 0.3<z<1.0 Galaxies in the GOODS-North Field
We measure nebular oxygen abundances for 204 emission-line galaxies with
redshifts 0.3<z<1.0 in the Great Observatories Origins Deep Survey North
(GOODS-N) field using spectra from the Team Keck Redshift Survey (TKRS). We
also provide an updated analytic prescription for estimating oxygen abundances
using the traditional strong emission line ratio, R_{23}, based on the
photoionization models of Kewley & Dopita (2003). We include an analytic
formula for very crude metallicity estimates using the [NII]6584/Halpha ratio.
Oxygen abundances for GOODS-N galaxies range from 8.2< 12+log(O/H)< 9.1
corresponding to metallicities between 0.3 and 2.5 times the solar value. This
sample of galaxies exhibits a correlation between rest-frame blue luminosity
and gas-phase metallicity (i.e., an L-Z relation), consistent with L-Z
correlations of previously-studied intermediate-redshift samples. The zero
point of the L-Z relation evolves with redshift in the sense that galaxies of a
given luminosity become more metal poor at higher redshift. Galaxies in
luminosity bins -18.5<M_B<-21.5 exhibit a decrease in average oxygen abundance
by 0.14\pm0.05 dex from z=0 to z=1. This rate of metal enrichment means that
28\pm0.07% of metals in local galaxies have been synthesized since z=1, in
reasonable agreement with the predictions based on published star formation
rate densities which show that ~38% of stars in the universe have formed during
the same interval. (Abridged)Comment: AASTeX, 49 pages, 16 figures, accepted for publication in The
Astrophysical Journa
A backwards approach to the formation of disk galaxies I. Stellar and gas content
A simple chemical enrichment code is described where the two basic mechanisms
driving the evolution of the ages and metallicities of the stellar populations
are the star formation efficiency and the fraction of gas ejected from the
galaxy. Using the observed Tully-Fisher relation in different passbands as a
constraint, it is found that a steep correlation between the maximum disk
rotational velocity and star formation efficiency must exist either for a
linear or a quadratic Schmidt law. Outflows do not play a major role. The
redshift evolution of disk galaxies is explored, showing that a significant
change in the slope of the Tully-Fisher relation is expected because of the
different age distributions of the stellar components in high and low-mass disk
galaxies. The slope measured in the rest frame B,K bands is found to change
from 3(B); 4(K) at z=0 up to 4.5(B); 5(K) at z~1, with a slight dependence on
formation redshift.Comment: Accepted for publication in ApJ. Uses emulateapj.sty. 12 pages with
10 embedded EPS figure
Old and young bulges in late-type disk galaxies
ABRIDGED: We use HSTACS and NICMOS imaging to study the structure and colors
of a sample of nine late-type spirals. We find: (1) A correlation between bulge
and disks scale-lengths, and a correlation between the colors of the bulges and
those of the inner disks. Our data show a trend for bulges to be more
metal-enriched than their surrounding disks, but otherwise no simple
age-metallicity connection between these systems; (2) A large range in bulge
stellar population properties, and, in particular, in stellar ages.
Specifically, in about a half of the late-type bulges in our sample the bulk of
the stellar mass was produced recently. Thus, in a substantial fraction of the
z=0 disk-dominated bulged galaxies, bulge formation occurs after the
formation/accretion of the disk; (3) In about a half of the late-type bulges in
our sample, however, the bulk of the stellar mass was produced at early epochs;
(4) Even these "old" late-type bulges host a significant fraction of stellar
mass in a young(er) c component; (5) A correlation for bulges between stellar
age and stellar mass, in the sense that more massive late-type bulges are older
than less massive late-type bulges. Since the overall galaxy luminosity (mass)
also correlates with the bulge luminosity (mass), it appears that the galaxy
mass regulates not only what fraction of itself ends up in the bulge component,
but also "when" bulge formation takes place. We show that dynamical friction of
massive clumps in gas-rich disks is a plausible disk-driven mode for the
formation of "old" late-type bulges. If disk evolutionary processes are
responsible for the formation of the entire family of late-type bulges, CDM
simulations need to produce a similar number of initially bulgeless disks in
addition to the disk galaxies that are observed to be bulgeless at z=0.Comment: ApJ in press; paper with high resolution figures available at
http://www.exp-astro.phys.ethz.ch/carollo/carollo1_2006.pdf; B, I, and H
surface brightness profiles published in electronic tabular for
Testing the Relation Between the Local and Cosmic Star Formation Histories
Recently, there has been great progress toward observationally determining
the mean star formation history of the universe. When accurately known, the
cosmic star formation rate could provide much information about Galactic
evolution, if the Milky Way's star formation rate is representative of the
average cosmic star formation history. A simple hypothesis is that our local
star formation rate is proportional to the cosmic mean. In addition, to specify
a star formation history, one must also adopt an initial mass function (IMF);
typically it is assumed that the IMF is a smooth function which is constant in
time. We show how to test directly the compatibility of all these assumptions,
by making use of the local (solar neighborhood) star formation record encoded
in the present-day stellar mass function. Present data suggests that at least
one of the following is false: (1) the local IMF is constant in time; (2) the
local IMF is a smooth (unimodal) function; and/or (3) star formation in the
Galactic disk was representative of the cosmic mean. We briefly discuss how to
determine which of these assumptions fail, and improvements in observations
which will sharpen this test.Comment: 14 pages in LaTeX (uses aaspp4.sty). 5 postscript figures. To appear
in the Astrophysical Journa
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