771 research outputs found
Eye fluke-induced cataracts in natural fish populations: is there potential for host manipulation?
Manipulation of host phenotype (e.g. behaviour, appearance) is suggested to be a common strategy to enhance transmission in trophically transmitted parasites. However, in many systems, evidence of manipulation comes exclusively from laboratory studies and its occurrence in natural host populations is poorly understood. Here, we examined the potential for host manipulation by Diplostomum eye flukes indirectly by quantifying the physiological effects of parasites on fish. Earlier laboratory studies have shown that Diplostomum infection predisposes fish to predation by birds (definitive hosts of the parasites) by reducing fish vision through cataract formation. However, occurrence of cataracts and the subsequent potential for host manipulation in natural fish populations has remained poorly explored. We studied the occurrence of eye fluke-induced cataracts from 7 common fish species (Gymnocephalus cernuus, Rutilus rutilus, Leuciscus leuciscus, Alburnus alburnus, Osmerus eperlanus, Coregonus lavaretus and Gasterosteus aculeatus) from the Bothnian Bay in the Baltic Sea. We found that the parasite-induced cataracts were common in fish and they also reached high levels which are likely to predispose fish to predation. However, we observed such cataracts only in species with the highest parasite abundances, which suggests that only certain hosts may be strongly affected by the infectio
Acanthocephalan size and sex affect the modification of intermediate host colouration
For trophically transmitted parasites, transitional larval size is often related to fitness. Larger parasites may have higher establishment success and/or adult fecundity, but prolonged growth in the intermediate host increases the risk of failed transmission via natural host mortality. We investigated the relationship between the larval size of an acanthocephalan (Acanthocephalus lucii) and a trait presumably related to transmission, i.e. altered colouration in the isopod intermediate host. In natural collections, big isopods harboured larger worms and had more modified (darker) abdominal colouration than small hosts. Small isopods infected with a male parasite tended to have darker abdominal pigmentation than those infected with a female, but this difference was absent in larger hosts. Female size increases rapidly with host size, so females may have more to gain than males by remaining in and growing mutually with small hosts. In experimental infections, a large total parasite volume was associated with darker host respiratory operculae, especially when it was distributed among fewer worms. Our results suggest that host pigment alteration increases with parasite size, albeit differently for male and female worms. This may be an adaptive strategy if, as parasites grow, the potential for additional growth decreases and the likelihood of host mortality increase
Seasonal changes in host phenotype manipulation by an acanthocephalan: time to be transmitted?
Many complex life cycle parasites exhibit seasonal transmission between hosts. Expression of parasite traits related to transmission, such as the manipulation of host phenotype, may peak in seasons when transmission is optimal. The acanthocephalan Acanthocephalus lucii is primarily transmitted to its fish definitive host in spring. We assessed whether the parasitic alteration of 2 traits (hiding behaviour and coloration) in the isopod intermediate host was more pronounced at this time of year. Refuge use by infected isopods was lower, relative to uninfected isopods, in spring than in summer or fall. Infected isopods had darker abdomens than uninfected isopods, but this difference did not vary between seasons. The level of host alteration was unaffected by exposing isopods to different light and temperature regimes. In a group of infected isopods kept at 4°C, refuge use decreased from November to May, indicating that reduced hiding in spring develops during winter. Keeping isopods at 16°C instead of 4°C resulted in higher mortality but not accelerated changes in host behaviour. Our results suggest that changes in host and/or parasite age, not environmental conditions, underlie the seasonal alteration of host behaviour, but further work is necessary to determine if this is an adaptive parasite strategy to be transmitted in a particular seaso
A Possible Periodicity in the Radio Lightcurves of 3C454.3
During the period 1966.5 - 2006.2 the 15GHz and 8GHz lightcurves of 3C454.3
(z=0.859) show a qsasi-periodicity of ~12.8 yr (~6.9 yr in the rest frame of
the source) with a double-bump structure. This periodic behaviour is
interpreted in terms of a rotating double-jet model in which the two jets are
created from the black holes in a binary system and rotate with the period of
the orbital motion. The periodic variations in the radio fluxes of 3C454.3 are
suggested to be mainly due to the lighthouse effects (or the variation in
Doppler boosting) of the precessing jets which are caused by the orbital
motion. In addition, variations in the mass-flow rates accreting onto the black
holes may be also involved.Comment: 15 pages, 11 figure
Correcting for interplanetary scattering in velocity dispersion analysis of solar energetic particles
To understand the origin of Solar Energetic Particles (SEPs), we must study their injection time relative to other solar eruption manifestations. Traditionally the injection time is determined using the Velocity Dispersion Analysis (VDA) where a linear fit of the observed event onset times at 1 AU to the inverse velocities of SEPs is used to derive the injection time and path length of the first-arriving particles. VDA does not, however, take into account that the particles that produce a statistically observable onset at 1 AU have scattered in the interplanetary space. We use Monte Carlo test particle simulations of energetic protons to study the effect of particle scattering on the observable SEP event onset above pre-event background, and consequently on VDA results. We find that the VDA results are sensitive to the properties of the pre-event and event particle spectra as well as SEP injection and scattering parameters. In particular, a VDA-obtained path length that is close to the nominal Parker spiral length does not imply that the VDA injection time is correct. We study the delay to the observed onset caused by scattering of the particles and derive a simple estimate for the delay time by using the rate of intensity increase at the SEP onset as a parameter. We apply the correction to a magnetically well-connected SEP event of 2000 June 10, and show it to improve both the path length and injection time estimates, while also increasing the error limits to better reflect the inherent uncertainties of VDA.</p
Multidimensionality and intra-individual variation in host manipulation by an acanthocephalan
Approximate action-angle variables for the figure-eight and other periodic three-body orbits
We use the maximally permutation symmetric set of three-body coordinates,
that consist of the "hyper-radius" , the
"rescaled area of the triangle" ) and the (braiding) hyper-angle , to analyze the "figure-eight"
choreographic three-body motion discovered by Moore \cite{Moore1993} in the
Newtonian three-body problem. Here are the two
Jacobi relative coordinate vectors. We show that the periodicity of this motion
is closely related to the braiding hyper-angle . We construct an
approximate integral of motion that together with the hyper-angle
forms the action-angle pair of variables for this problem and show that
it is the underlying cause of figure-eight motion's stability. We construct
figure-eight orbits in two other attractive permutation-symmetric three-body
potentials. We compare the figure-eight orbits in these three potentials and
discuss their generic features, as well as their differences. We apply these
variables to two new periodic, but non-choreographic orbits: One has a
continuously rising in time , just like the figure-eight motion, but
with a different, more complex periodicity, whereas the other one has an
oscillating temporal behavior.Comment: 11 pages, 19 figure
Mass Deficits, Stalling Radii, and the Merger Histories of Elliptical Galaxies
A binary supermassive black hole leaves an imprint on a galactic nucleus in
the form of a "mass deficit," a decrease in the mass of the nucleus due to
ejection of stars by the binary. The magnitude of the mass deficit is in
principle related to the galaxy's merger history, but the relation has never
been quantified. Here, high-accuracy N-body simulations are used to calibrate
this relation. Mass deficits are shown to be approximately 0.5M_{12}, with
M_{12} the total mass of the binary; the coefficient in this relation depends
only weakly on the binary mass ratio or on the galaxy's pre-existing density
profile. Hence, after N mergers, the mass deficit is ~0.5 N M_h with M_h the
final (current) black hole mass. When compared with observed mass deficits,
this result implies between 1 and 3 mergers for most galaxies, in accord with
hierarchical galaxy formation models. Implications for binary stalling radii,
the origin of hyper-velocity stars, and the distribution of dark matter at the
centers of galaxies are discussed.Comment: 11 pages, uses emulateapj.st
Cosmic Black-Hole Hair Growth and Quasar OJ287
An old result ({\tt astro-ph/9905303}) by Jacobson implies that a black hole
with Schwarzschild radius acquires scalar hair, ,
when the (canonically normalized) scalar field in question is slowly
time-dependent far from the black hole, with
time-independent. Such a time dependence could arise in
scalar-tensor theories either from cosmological evolution, or due to the slow
motion of the black hole within an asymptotic spatial gradient in the scalar
field. Most remarkably, the amount of scalar hair so induced is independent of
the strength with which the scalar couples to matter. We argue that Jacobson's
Miracle Hair-Growth Formula implies, in particular, that an
orbiting pair of black holes can radiate {\em dipole} radiation, provided only
that the two black holes have different masses. Quasar OJ 287, situated at
redshift , has been argued to be a double black-hole binary
system of this type, whose orbital decay recently has been indirectly measured
and found to agree with the predictions of General Relativity to within 6%. We
argue that the absence of observable scalar dipole radiation in this system
yields the remarkable bound on the
instantaneous time derivative at this redshift (as opposed to constraining an
average field difference, , over cosmological times), provided
only that the scalar is light enough to be radiated --- i.e. m \lsim 10^{-23}
eV --- independent of how the scalar couples to matter. This can also be
interpreted as constraining (in a more model-dependent way) the binary's motion
relative to any spatial variation of the scalar field within its immediate
vicinity within its host galaxy.Comment: 20 page
- âŠ