151 research outputs found
Sensible heat loss from Muskoxen (Ovibos moschatus) feeding in winter: small calves are not at a thermal disadvantage compared with adult cows
Muskoxen (Ovibos moschatus) are large (\u3e200 kg adult body mass) mammalian herbivores that overwinter in the polar regions. Calves are around one-third the body mass of mature females and may be expected to suffer greater thermal stresses in winter compared with adults because the ratio of surface area to volume (SA : vol) is much greater for calves than for adults. We found that during feeding bouts, when animals are fully exposed to environmental conditions, calves did lose sensible (dry) heat more readily than adults (W m(-2)) in still air conditions. However, calves and cows lost less than 2%-6% of their estimated daily digestible energy intake as conductive, convective, and radiant heat losses accumulated during feeding bouts. More important, calves did not lose relatively more heat than larger adults in terms of sensible losses as part of their daily energy intake. Coat surface temperatures were only 2 degrees-5 degrees C above ambient even when air temperature fell to -40 degrees C. Body temperatures recorded deep within the ear canal near the tympanum fluctuated in both cows and calves. Muskoxen combine peripheral heterothermy and an exceptional winter coat to minimize sensible heat loss in winter. These mechanisms appear to have circumvented some of the thermal problems normally associated with a high SA : vol ratio in calves, which reflects the strong selection to conserve energy in winter
Digestive plasticity of the small intestine and the fermentative hindgut in a marsupial herbivore, the tammar wallaby (Macropus eugenii)
We investigated the effects of a ground, pelleted diet versus natural forage on the gross morphology of the gastrointestinal tract of a medium- sized (5 - 7 kg body mass) macropodid marsupial, the tammar wallaby ( Macropus eugenii). The empty wet mass ( g) of the small intestine of tammar wallabies maintained on a pelleted diet for 6 weeks was 22% greater than that of animals maintained on natural forage, once body mass was taken into account by ANCOVA. Similarly, the body-mass-adjusted length of the tammar wallaby caecum and proximal colon combined was 25% longer in animals maintained on the pelleted diet compared with those maintained on forage. Our data suggest that food particle size may be directly involved in controlling the size of the post-gastric alimentary tract in tammar wallabies, and thus in their diet choice and nutritional ecology. Notably, this is the first study that links phenotypic plasticity of the gut directly to diet in a marsupial and we conclude that the tammar wallaby is an excellent model for exploring the causes and consequences of digestive plasticity in macropodid marsupials
Parallax and Luminosity Measurements of an L Subdwarf
We present the first parallax and luminosity measurements for an L subdwarf,
the sdL7 2MASS J05325346+8246465. Observations conducted over three years by
the USNO infrared astrometry program yield an astrometric distance of
26.7+/-1.2 pc and a proper motion of 2.6241+/-0.0018"/yr. Combined with
broadband spectral and photometric measurements, we determine a luminosity of
log(Lbol/Lsun) = -4.24+/-0.06 and Teff = 1730+/-90 K (the latter assuming an
age of 5-10 Gyr), comparable to mid-type L field dwarfs. Comparison of the
luminosity of 2MASS J05325346+8246465 to theoretical evolutionary models
indicates that its mass is just below the sustained hydrogen burning limit, and
is therefore a brown dwarf. Its kinematics indicate a ~110 Myr, retrograde
Galactic orbit which is both eccentric (3 <~ R <~ 8.5 kpc) and extends well
away from the plane (Delta_Z = +/-2 kpc), consistent with membership in the
inner halo population. The relatively bright J-band magnitude of 2MASS
J05325346+8246465 implies significantly reduced opacity in the 1.2 micron
region, consistent with inhibited condensate formation as previously proposed.
Its as yet unknown subsolar metallicity remains the primary limitation in
constraining its mass; determination of both parameters would provide a
powerful test of interior and evolutionary models for low-mass stars and brown
dwarfs.Comment: Accepted to ApJ 10 September 2007; 13 pages, 5 figures, 3 tables,
formatted in emulateapj styl
Scaling at different ontogenetic stages : gastrointestinal tract contents of a marsupial foregut fermenter, the western grey kangaroo Macropus fuliginosus melanops
Prominent ontogenetic changes of the gastrointestinal tract (GIT) should occur in mammals whose neonatal diet of milk differs from that of adults, and especially in herbivores (as vegetation is particularly distinct from milk), and even more so in foregut fermenters, whose forestomach only becomes functionally relevant with vegetation intake. Due to the protracted lactation in marsupials, ontogenetic differences can be particularly well investigated in this group. Here, we report body mass (BM) scaling relationships of wet GIT content mass in 28 in-pouch young (50 g to 3 kg) and 15 adult (16–70 kg) western grey kangaroos Macropus fuliginosus melanops. Apart from the small intestinal contents, in-pouch young and adults did not differ in the scaling exponents (‘slope’ in log-log plots) but did differ in the scaling factor (‘intercept’), with an implied substantial increase in wet GIT content mass during the out-of-pouch juvenile period. In contrast to forestomach contents, caecum contents were elevated in juveniles still in the pouch, suggestive of fermentative digestion of milk and intestinal secretion residues, particularly in the caecum. The substantial increase in GIT contents (from less than 1 to 10–20% of BM) was associated mainly with the increase in forestomach contents (from 25 to 80% of total GIT contents) and a concomitant decrease in small intestine contents (from 50 to 8%), emphasizing the shifting relevance of auto-enzymatic and allo-enzymatic (microbial) digestion. There was a concomitant increase in the contents-to-tissue ratio of the fermentation chambers (forestomach and caecum), but this ratio generally did not change for the small intestine. Our study not only documents significant ontogenetic changes in digestive morpho-physiology, but also exemplifies the usefulness of intraspecific allometric analyses for quantifying these changes.The Australian Research Councilhttp://www.elsevier.com/locate/cbpahj2021Anatomy and PhysiologyCentre for Veterinary Wildlife Studie
Astrometry and Photometry for 1000 L, T, and Y Dwarfs from the UKIRT Hemisphere Survey
We present positions, proper motions, and near-infrared photometry for 966
known objects with spectral types later than M observed as part of the the
UKIRT Hemisphere Survey (UHS). We augment the photometry and astrometry from
UHS with information from Gaia DR3, Pan-STARRS DR2, and CatWISE 2020 to produce
a database of homogeneous photometry and astrometry for this sample. The
multi-epoch survey strategy of UHS allows us to determine proper motions for
most sources, with a median proper motion uncertainty of 3.6 mas
yr. Our UHS proper motion measurements are generally in good agreement
with those from Gaia DR3, Pan-STARRS, and CatWISE 2020, with UHS proper motions
typically more precise than those from CatWISE 2020 and Pan-STARRS but not Gaia
DR3. We critically analyze publicly available spectra for 406 members of this
sample and provide updated near-infrared spectral types for 100 objects.
We determine typical colors as a function of spectral type and provide absolute
magnitude vs. spectral type relations for UHS - and -band photometry.
Using newly determined proper motions, we highlight several objects of
interest, such as objects with large tangential velocities, widely separated
co-moving companions, and potential members of young nearby associations.Comment: Accepted to A
Digestive plasticity of the small intestine and the fermentative hindgut in a marsupial herbivore, the tammar wallaby (Macropus eugenii)
The Milky Way Tomography with SDSS: III. Stellar Kinematics
We study Milky Way kinematics using a sample of 18.8 million main-sequence
stars with r<20 and proper-motion measurements derived from SDSS and POSS
astrometry, including ~170,000 stars with radial-velocity measurements from the
SDSS spectroscopic survey. Distances to stars are determined using a
photometric parallax relation, covering a distance range from ~100 pc to 10 kpc
over a quarter of the sky at high Galactic latitudes (|b|>20 degrees). We find
that in the region defined by 1 kpc <Z< 5 kpc and 3 kpc <R< 13 kpc, the
rotational velocity for disk stars smoothly decreases, and all three components
of the velocity dispersion increase, with distance from the Galactic plane. In
contrast, the velocity ellipsoid for halo stars is aligned with a spherical
coordinate system and appears to be spatially invariant within the probed
volume. The velocity distribution of nearby ( kpc) K/M stars is complex,
and cannot be described by a standard Schwarzschild ellipsoid. For stars in a
distance-limited subsample of stars (<100 pc), we detect a multimodal velocity
distribution consistent with that seen by HIPPARCOS. This strong
non-Gaussianity significantly affects the measurements of the velocity
ellipsoid tilt and vertex deviation when using the Schwarzschild approximation.
We develop and test a simple descriptive model for the overall kinematic
behavior that captures these features over most of the probed volume, and can
be used to search for substructure in kinematic and metallicity space. We use
this model to predict further improvements in kinematic mapping of the Galaxy
expected from Gaia and LSST.Comment: 90 pages, 26 figures, submitted to Ap
Preliminary Trigonometric Parallaxes of 184 Late-T and Y Dwarfs and an Analysis of the Field Substellar Mass Function into the "Planetary" Mass Regime
We present preliminary trigonometric parallaxes of 184 late-T and Y dwarfs
using observations from Spitzer (143), USNO (18), NTT (14), and UKIRT (9). To
complete the 20-pc census of T6 dwarfs, we combine these measurements with
previously published trigonometric parallaxes for an additional 44 objects and
spectrophotometric distance estimates for another 7. For these 235 objects, we
estimate temperatures, sift into five 150K-wide bins covering the
range 300-1050K, determine the completeness limit for each, and compute space
densities. To anchor the high-mass end of the brown dwarf mass spectrum, we
compile a list of early- to mid-L dwarfs within 20 pc. We run simulations using
various functional forms of the mass function passed through two different sets
of evolutionary code to compute predicted distributions in . The
best fit of these predictions to our L, T, and Y observations is a simple
power-law model with (where ),
meaning that the slope of the field substellar mass function is in rough
agreement with that found for brown dwarfs in nearby star forming regions and
young clusters. Furthermore, we find that published versions of the log-normal
form do not predict the steady rise seen in the space densities from 1050K to
350K. We also find that the low-mass cutoff to formation, if one exists, is
lower than 5 , which corroborates findings in young, nearby
moving groups and implies that extremely low-mass objects have been forming
over the lifetime of the Milky Way.Comment: 86 pages with 19 figures. Accepted for publication in The
Astrophysical Journal Supplement Series on 2018 Dec 0
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