Lower TBS Research Articles

Simulated increased soft tissue thickness artefactually decreases trabecular bone score: a phantom study.

BackgroundTrabecular bone score (TBS), which has been proposed to be used in complementary with bone mineral density (BMD) to improve the assessment of fracture risk, is negatively associated with body mass index (BMI). The effect of soft tissue, which is expected to be thicker in subjects with high BMI, on TBS was studied using three scan types: Hologic with fast array mode (Hfa), Hologic with high definition mode (Hhd), and GE-Lunar iDXA.MethodsA spine phantom provided by Hologic for routine quality control procedure was scanned using three scan types: Hfa, Hhd, and iDXA. The phantom was scanned with an overlying soft tissue equivalent material (bolus used in radiotherapy) of 0 (without), 1, 2.5, 3.5, 5 and 7.5 cm thick. For each setting, 30 acquisitions were performed in the same way as for the quality control procedure. TBS was calculated using TBS iNsight® software version 2.1 on the same regions of interest as those used for lumbar spine BMD.ResultsMean ± SD TBS of the phantom (without overlying soft tissue) were 1.379 ± 0.018, 1.430 ± 0.009, and 1.423 ± 0.005 using Hfa, Hhd, and iDXA, respectively. A one-way repeated measures ANOVA showed that there were statistically differences in TBS due to different thicknesses of soft tissue equivalent materials for all three scan types (p < 0.001). A Tukey post-hoc test revealed that the decrease in TBS was statistically significant (p < 0.001) when the soft tissue thickness was 1 cm (−0.0246 ± 0.0044, −0.0319 ± 0.0036, and −0.0552 ± 0.0015 for Hfa, Hhd, and iDXA, respectively). Although to a lesser degree, the effects were also statistically significant for BMD (p < 0.05): an increase for Hfa and Hhd but a decrease for iDXA. However, these changes did not exceed the least significant change (LSC) derived from patients.ConclusionsIncreased soft tissue thickness results in lower TBS value. Although BMD is also affected, it is unlikely to pose a clinical problem because the change is unlikely to exceed the patient-derived LSC.

Spine bone texture assessed by trabecular bone score (TBS) predicts osteoporotic fractures in men: The Manitoba Bone Density Program

IntroductionOne quarter of osteoporotic fractures occur in men. TBS, a gray-level measurement derived from lumbar spine DXA image texture, is related to microarchitecture and fracture risk independently of BMD. Previous studies reported the ability of spine TBS to predict osteoporotic fractures in women. Our aim was to evaluate the ability of TBS to predict clinical osteoporotic fractures in men. Methods3620 men aged ≥50 (mean 67.6years) at the time of baseline DXA (femoral neck, spine) were identified from a database (Province of Manitoba, Canada). Health service records were assessed for the presence of non-traumatic osteoporotic fracture after BMD testing. Lumbar spine TBS was derived from spine DXA blinded to clinical parameters and outcomes. We used Cox proportional hazard regression to analyze time to first fracture adjusted for clinical risk factors (FRAX without BMD), osteoporosis treatment and BMD (hip or spine). ResultsMean followup was 4.5years. 183 (5.1%) men sustain major osteoporotic fractures (MOF), 91 (2.5%) clinical vertebral fractures (CVF), and 46 (1.3%) hip fractures (HF). Correlation between spine BMD and spine TBS was modest (r=0.31), less than correlation between spine and hip BMD (r=0.63). Significantly lower spine TBS were found in fracture versus non-fracture men for MOF (p<0.001), HF (p<0.001) and CVF (p=0.003). Area under the receiver operating characteristic curve (AUC) for incident fracture discrimination with TBS was significantly better than chance (MOF AUC=0.59, p<0.001; HF AUC=0.67, p<0.001; CVF AUC=0.57, p=0.032). TBS predicted MOF and HF (but not CVF) in models adjusted for FRAX without BMD and osteoporosis treatment. TBS remained a predictor of HF (but not MOF) after further adjustment for hip BMD or spine BMD. ConclusionWe observed that spine TBS predicted MOF and HF independently of the clinical FRAX score, HF independently of FRAX and BMD in men. Studies with more incident fractures are needed to confirm these findings.

Trabecular Bone Score and Hip Geometry in Relation to Body Composition and Biochemical Markers in Women With Severe Anorexia Nervosa

(p50.36).TBS was associated with the presence of OPF (OR51.63[1.222.17]). TBS was significantly lower in all subjects with p_GC use than in subjects on GCs only presently (p50.025), whereas BMD was not significantly different (p50.19). Finally, in only those subjects without fracture, p_GC users had a lower TBS compared with current GC users (p!0.03) while no difference was observed for subjects with fracture (p50.76). Conclusion: GCs induced a microarchitectural texture impairment whereas no change was observed with BMD measurement. These results are consistent with previous TBS studies on GCs. We have also observed that past use of GCs has a negative effect on microarchitectural texture which is similar to the presence of an OPF. TBS is a reliable tool for management of patients with present or past GC treatment, and outperforms BMD measurement in its ability to identify a population on glucocorticoids at greater risk for fracture. Disclosure of Interest: E. Leib: None Declared, R. Winzenrieth Salary from: Med-Imaps, D. Hans Stock owner of: Med-Imaps

Ways to measure body temperature in the field

Body temperature (Tb) represents one of the key parameters in ecophysiological studies with focus on energy saving strategies. In this study we therefore comparatively evaluated the usefulness of two types of temperature-sensitive passive transponders (LifeChips and IPTT-300) and one data logger (iButton, DS1922L) mounted onto a collar to measure Tb in the field. First we tested the accuracy of all three devices in a water bath with water temperature ranging from 0 to 40°C. Second, we evaluated the usefulness of the LifeChips and the modified iButtons for measuring Tb of small heterothermic mammals under field conditions. For this work we subcutaneously implanted 14 male edible dormice (Glis glis) with transponders, and equipped another 14 males with data loggers to simultaneously record Tb and oxygen consumption with a portable oxygen analyzer (Oxbox). In one individual we recorded Tb with both devices and analyzed recorded Tb patterns.LifeChips are able to measure temperature within the smallest range from 25 to 40°C with an accuracy of 0.07±0.12°C. IPTT-300 transponders measured temperature between 10 and 40°C, but accuracy decreased considerably at values below 30°C, with maximal deviations of nearly 7°C. An individual calibration of each transponder is therefore needed, before using it at low Tbs. The accuracy of the data logger was comparatively good (0.12±0.25°C) and stable over the whole temperature range tested (0–40°C). In all three devices, the repeatability of measurements was high.LifeChip transponders as well as modified iButtons measured Tb reliably under field conditions. Simultaneous Tb-recordings in one edible dormouse with an implanted LifeChip and a collar-mounted iButton revealed that values of both measurements were closely correlated. Taken together, we conclude that implanted temperature-sensitive transponders represent an appropriate and largely non-invasive method to measure Tb also under field conditions.

Vertebral microarchitecture and fragility fracture in men: A TBS study

IntroductionAlthough osteoporosis is considered a disease of women, 25% of the individuals with osteoporosis are men. BMD measurement by DXA is the gold standard used to diagnose osteoporosis and assess fracture risk. Nevertheless, BMD does not take into account alterations of microarchitecture. TBS is an index of bone microarchitecture extracted from the spine DXA. Previous studies have reported the ability of the spine TBS to predict osteoporotic fractures in women. This is the first case-controlled study in men to evaluate the potential diagnostic value of TBS as a complement to bone mineral density (BMD), by comparing men with and without fractures. MethodsTo be eligible for this study, subjects had to be non-Hispanic US white men aged 40 and older. Furthermore, subjects were excluded if they have or have had previously any treatment or illness that may influence bone metabolism. Fractured subjects were included if the presence of at least one fracture was confirmed. Cases were matched for age (±3years) and BMD (±0.04g/cm2) with three controls. BMD and TBS were first retrospectively evaluated at AP spine (L1–L4) with a Prodigy densitometer (GE-Lunar, Madison, USA) and TBS iNsight® (Med-Imaps, France) in Lausanne University Hospital blinded from clinical outcome. Inter-group comparisons were undertaken using Student's t-tests or Wilcoxon signed rank tests. Odds ratios were calculated per one standard deviation decrease as well as areas under the receiver operating curve (AUC). ResultsAfter applying inclusion/exclusion criteria, a group of 180 male subjects was obtained. This group consists of 45 fractured subjects (age=63.3±12.6years, BMI=27.1±4.2kg/m2) and 135 control subjects (age=62.9±11.9years, BMI=26.7±3.9kg/m2) matched for age (p=0.86) and BMD (p=0.20). A weak correlation was obtained between TBS and BMD and between TBS and BMI (r=0.27 and r=−0.28, respectively, p<0.01). Subjects with fracture have a significant lower TBS compared to control subjects (p=0.013), whereas no differences were obtained for BMI, height and weight (p>0.10). TBS OR per standard deviation is 1.55 [1.09–2.20] for all fracture type. When considering vertebral fracture only TBS OR reached 2.07 [1.14–3.74]. ConclusionThis study showed the potential use of TBS in men. TBS revealed a significant difference between fractured and age- and spine BMD-matched nonfractured subjects. These results are consistent with those previously reported on for men of other nationalities.

Evaluating spine micro-architectural texture (via TBS) discriminates major osteoporotic fractures from controls both as well as and independent of site matched BMD: the Eastern European TBS study

The aim of the study was to assess the clinical performance of the model combining areal bone mineral density (aBMD) at spine and microarchitecural texture (TBS) for the detection of the osteoporotic fracture. The Eastern European Study is a multicenter study (Serbia, Bulgaria, Romania and Ukraine) evaluating the role of TBS in routine clinical practice as a complement to aBMD. All scans were acquired on Hologic Discovery and GE Prodigy densitometers in a routine clinical manner. The additional clinical values of aBMD and TBS were analyzed using a two steps classification tree approach (aBMD followed by TBS tertiles) for all type of osteoporotic fracture (All-OP Fx). Sensitivity, specificity and accuracy of fracture detection as well as the Net Reclassification Index (NRI) were calculated. This study involves 1031 women subjects aged 45 and older recruited in east European countries. Clinical centers were cross-calibrated in terms of BMD and TBS. As expected, areal BMD (aBMD) at spine and TBS were only moderately correlated (r (2) = 0.19). Prevalence rate for All-OP Fx was 26 %. Subjects with fracture have significant lower TBS and aBMD than subjects without fracture (p < 0.01). TBS remains associated with the fracture even after adjustment for age and aBMD with an OR of 1.27 [1.07-1.51]. When using aBMD T-score of -2.5 and the lowest TBS tertile thresholds, both BMD and TBS were similar in terms of sensitivity (35 vs. 39 %), specificity (78 vs. 80 %) and accuracy (64 vs. 66 %). aBMD and TBS combination, induced a significant improvement in sensitivity (+28 %) and accuracy (+17 %) compared to aBMD alone whereas a moderate improvement was observed in terms of specificity (+9 %). The overall combination gain was 36 % as expressed using the NRI. aBMD and TBS combination decrease significantly the number of subjects needed to diagnose from 7 for aBMD alone to 2. In a multi-centre Eastern European cohort, we have shown that the use of TBS in addition to the aBMD permit to reclassified correctly more than one-third of the overall subjects. Furthermore, the number of subjects needed to diagnose fell to 2 subjects. Economical studies have to be performed to evaluate the gain induced by the use of TBS for the healthcare system.

Thermoregulation in leopard tortoises in the Nama-Karoo: The importance of behaviour and core body temperatures

Despite being ectotherms, reptiles have an ability to thermoregulate which is enhanced by adopting a variety of behavioural mechanisms. Different behavioural postures, the use of retreat sites and selection of microhabitats enable reptiles to maintain their core body temperatures (Tb) above that of ambient temperatures (Ta) in winter or below Ta maximum in summer. This study describes the daily activity patterns of leopard tortoises (Stigmochelys pardalis) in relation to Tb and Ta, and the extent to which leopard tortoises can manipulate their Tb in response to seasonal changes in Ta. Ten and nine leopard tortoises were radio-tracked in 2002 and 2003, respectively and cloacal Tb and behaviours observed. Core Tbs were measured using Thermocron iButtons™ surgically implanted into the body cavities of 4 and 5 adult telemetered tortoises for summer and winter 2003, respectively. There were seasonal differences in the extent to which certain behaviours were practiced and the time of day that these occurred. Leopard tortoises generally had unimodal activity patterns in winter and bimodal ones in summer. In winter tortoises were active at lower Tbs, and at lower Ta, than in summer. Tortoises maintained their core Tb well below Ta minimum profiles in summer and well above these in winter. Core Tb closely followed the increase in Ta minimum profiles in the mornings, however tortoises exhibited an extended thermal lag when Ta minimum profiles cooled overnight. By using different behavioural mechanisms in summer and winter, leopard tortoises maintained their core Tb at different levels compared with Ta minimum and maximum profiles. Consequently although they are ectotherms, they maintained their core Tb independent of Ta.

Thermal preferences of hatchling saltwater crocodiles (Crocodylus porosus) in response to time of day, social aggregation and feeding

Three month old hatchling Crocodylus porosus with data loggers in their stomachs were placed in thermal gradients, in isolation (N=16) and in groups of 4 (N=8 groups; 32 individuals). Mean Tb and variation in Tb (SD) was not different whether individual crocodiles in isolation were fasted or fed, or if individuals were housed in isolation (I) or in groups (G). However, individuals in isolation (N=16) maintained slightly lower Tbs than those in groups (N=32) during the early morning (06:00–11:00h). The overall mean Tb recorded for fasted individuals in the isolated and group treatments (N=48) was 30.9±2.3°C SD, with 50% of Tbs (Tset) between 29.4°C and 32.6°C, and a voluntary maximum and minimum of 37.6°C and 23.2°C respectively. During the day (11:00–17:00h), individuals in isolation and in groups selected the warmer parts of the gradient on land, where they moved little. Outside of this quiescent period (QP), activity levels were much higher and they used the water more. There was a strong diurnal cycle for fasted individuals in isolation and in groups, with Tb during the QP (31.9±2.09°C; N=48) significantly higher than during the non-quiescent period (NQP: 30.6±2.31°C). Thermal variation (SD) in Tb was relatively stable throughout the day, with the highest variation at around dusk and early evening (18:00–20:00h), which coincided with a period of highest activity. The diurnal activity cycle appears innate, and may reflect the need to engage in feeding activity at the water's edge in the early evening, despite ambient temperatures being cooler, with reduced activity and basking during the day. If so, preferred Tb may be more accurately defined as the mean Tb during the QP rather than the NQP. Implications for the thermal environment best suited for captive C. porosus hatchlings are discussed.

Assimilation efficiency and gut passage time in an African elapid snake, Hemachatus haemachatus

We measured apparent assimilation efficiency (AAE) and gut passage time in the African elapid snake Hemachatus haemachatus under laboratory conditions. AAE was dependent on food type, being 89.8% when snakes were fed frogs and 82.8% when fed mice. Differences in AAE for different meal types could be ascribed to the indigestible hair in mouse meals because differences were lost once this component of the mouse meals was removed from the calculation. AAE did not depend on snake body mass and there was no significant difference between AAE measures made at 20°C and 27°C for mouse meals. Gut passage time was 25% faster at 27°C than at 20°C, but was not affected by food type or snake body mass. Larger meals took longer to digest. Thus, H. haemachatus appears to offset reduced digestive performance at lower temperatures by retaining food in the gut for longer when at lower body temperatures (Tbs). These results fit an emerging pattern in snakes whereby digestive efficiency is generally high and insensitive to Tb over the selected thermal range, but may become dependent at lower Tbs when digestion is eventually arrested. The rate of digestion is highly temperature-sensitive and is fastest in the selected Tb range. Diet appears to affect digestive efficiency owing, mainly, to the presence of indigestible components such as hair. Using a comparative framework, venom does not appear to improve digestion for this species, at least over the temperature range tested, relative to other snake species in the literature.

Trabecular bone score (TBS) the new parameter of 2D texture analysis for the evaluation of 3D bone micro architecture status

X-ray is a technology that is used for numerous applications in the medical field. The process of X-ray projection gives a 2-dimension (2D) grey-level texture from a 3- dimension (3D) object. Until now no clear demonstration or correlation has positioned the 2D texture analysis as a valid indirect evaluation of the 3D microarchitecture. TBS is a new texture parameter based on the measure of the experimental variogram. TBS evaluates the variation between 2D image grey-levels. The aim of this study was to evaluate existing correlations between 3D bone microarchitecture parameters - evaluated from μCT reconstructions - and the TBS value, calculated on 2D projected images. 30 dried human cadaveric vertebrae were acquired on a micro-scanner (eXplorer Locus, GE) at isotropic resolution of 93 μm. 3D vertebral body models were used. The following 3D microarchitecture parameters were used: Bone volume fraction (BV/TV), Trabecular thickness (TbTh), trabecular space (TbSp), trabecular number (TbN) and connectivity density (ConnD). 3D/2D projections has been done by taking into account the Beer-Lambert Law at X-ray energy of 50, 100, 150 KeV. TBS was assessed on 2D projected images. Correlations between TBS and the 3D microarchitecture parameters were evaluated using a linear regression analysis. Paired T-test is used to assess the X-ray energy effects on TBS. Multiple linear regressions (backward) were used to evaluate relationships between TBS and 3D microarchitecture parameters using a bootstrap process. BV/TV of the sample ranged from 18.5 to 37.6% with an average value at 28.8%. Correlations' analysis showedthat TBSwere strongly correlatedwith ConnD(0.856≤r≤0.862; p<0.001),with TbN (0.805≤r≤0.810; p<0.001) and negatively with TbSp (−0.714≤r≤−0.726; p<0.001), regardless X-ray energy. Results show that lower TBS values are related to degraded microarchitecture, with low ConnD, low TbN and a high TbSp. The opposite is also true. X-ray energy has no effect onTBS neither on the correlations betweenTBS and the 3Dmicroarchitecture parameters. In this study, we demonstrated that TBS was significantly correlated with 3D microarchitecture parameters ConnD and TbN, and negatively with TbSp, no matter what X-ray energy has been used. This article is part of a Special Issue entitled ECTS 2011. Disclosure of interest: None declared.

Uncertainties in Microwave Properties of Frozen Precipitation: Implications for Remote Sensing and Data Assimilation

Abstract A combined active/passive modeling system that converts CloudSat observations to simulated microwave brightness temperatures (TB) is used to assess different ice particle models under precipitating conditions. Simulation results indicate that certain ice models (e.g., low-density spheres) produce excessive scattering and implausibly low simulated TBs for stratiform precipitation events owing to excessive derived ice water paths (IWPs), while other ice models produce unphysical TB depressions due to the combined effects of elevated derived IWP and excessive particle size distribution–averaged extinction. An ensemble of nonspherical ice particle models, however, consistently produces realistic results under most circumstances and adequately captures the radiative properties of frozen hydrometeors associated with precipitation—with the possible exception of very high IWP events. Large derived IWP uncertainties exceeding 60% are also noted and may indicate IWP retrieval accuracy deficiencies using high-frequency passive microwave observations. Simulated TB uncertainties due to the ice particle model ensemble members approach 9 (5) K at 89 (157) GHz for high ice water path conditions associated with snowfall and ∼2–3 (∼1–2) K under typical stratiform rain conditions. These uncertainties, however, display considerable variability owing to ice water path, precipitation type, satellite zenith angle, and frequency. Comparisons between 157-GHz simulations and observations under precipitating conditions produce low biases (&amp;lt;1.5 K) and high correlations, but lower-frequency channels display consistent negative biases of 3–4 K in precipitating regions. Sample error correlations and covariance matrices for select microwave frequencies also show strong functional relationships with ice water path and variability depending on precipitation type.

Advantage to lower body temperatures for a small mammal (Rattus fuscipes) experiencing chronic cold

Cold environments are challenging for small endotherms because they must increase heat production to compensate for increased heat loss to the environment. Mammals that endure cold without entering torpor may have thicker fur and a lower body temperature (Tb) than those in warm environments to save energy. Activity levels also may be reduced in the cold. We aimed to determine whether activity level, exposure to chronic cold, or an interaction between the 2 could reduce the Tb of an endotherm. Wild bush rats (Rattus fuscipes) were brought into captivity and acclimated to cold (12uC) or warm (22uC) ambient temperatures and were either sedentary or exercised. Daily exercise increased maximum Tb in cold-acclimated bush rats but also decreased minimum Tb. Mean (6SE) daily Tb was significantly lower in cold-acclimated bush rats (sedentary: 36.5uC 6 0.1uC; exercised: 36.4uC 6 0.2uC) compared to warm-acclimated bush rats (sedentary: 37.3uC 6 0.2uC; exercised: 37.0uC 6 0.1uC). Body temperature decreased significantly over the time of cold acclimation. Thicker fur and lower Tbs in cold-acclimated bush rats conferred an energy saving equivalent to 11% of daily food intake in exercised rats and 22% of daily food intake in sedentary rats. The lower Tbs recorded in some small mammals in winter are not necessarily due to lower levels of activity but can result from a regulated reduction in Tb in response to cooler ambient temperatures. DOI: 10.1644/10-MAMM-A-003.1.

Ecology of Sceloporus undulatus speari (Sauria: Phrynosomatidae) from North-Central Chihuahua, México

Abstract We studied the ecology of a population of Sceloporus undulatus speari from the Transmontane Sand Dune region of northern Chihuahua, Mexico. Most of the individuals in our population used fence posts or yucca plants as perches and were only rarely seen on the ground. The majority of individuals in our population were seen in full sun, although a substantial number were in shade. Mean body temperature in our population was 35.2°C. Individuals first seen in full sun had lower Tbs than individuals first seen in shade. Lizards using different microhabitats (e.g., yucca vs. fence post) had different body temperatures. Clutch size in our population was 5.23 eggs per clutch. Clutch size in our population was not statistically significantly related to female body size; however, the trend was for an increase in clutch size with SVL, with the smallest females having the smallest clutches. We found no evidence for sexual dimorphism in body size (SVL) in our population of S. undulatus, but males had larger he...

Periodic arousal from hibernation is necessary for initiation of immune responses in ground squirrels.

Golden-mantled ground squirrels (Spermophilus lateralis) undergo seasonal hibernation during which core body temperature (T(b)) values are maintained 1-2 degrees C above ambient temperature. Hibernation is not continuous. Squirrels arouse at approximately 7-day intervals, during which T(b) increases to 37 degrees C for approximately 16 h; thereafter, they return to hibernation and sustain low T(b)s until the next arousal. Over the course of the hibernation season, arousals consume 60-80% of a squirrel's winter energy budget, but their functional significance is unknown and disputed. Host-defense mechanisms appear to be downregulated during the hibernation season and preclude normal immune responses. These experiments assessed immune function during hibernation and subsequent periodic arousals. The acute-phase response to bacterial lipopolysaccharide (LPS) was arrested during hibernation and fully restored on arousal to normothermia. LPS injection (ip) resulted in a 1-1.5 degrees C fever in normothermic animals that was sustained for > 8 h. LPS was without effect in hibernating squirrels, neither inducing fever nor provoking arousal, but a fever did develop several days later, when squirrels next aroused from hibernation; the duration of this arousal was increased sixfold above baseline values. Intracerebroventricular infusions of prostaglandin E(2) provoked arousal from hibernation and induced fever, suggesting that neural signaling pathways that mediate febrile responses are functional during hibernation. Periodic arousals may activate a dormant immune system, which can then combat pathogens that may have been introduced immediately before or during hibernation.

Constraints on Temperature Regulation in Two SympatricPodarcisLizards during Autumn

We studied the impact of restrictions by the thermal environments on body temperatures (Tbs) and microhabitat use of the lacertid lizards Podarcis melisellensis and Podarcis muralis in a Mediterranean area (Croatia) during autumn. The thermal conditions at available microhabitats were assessed with copper models that measured the operative temperatures (Te) at different sites. We estimated the thermal suitability of microhabitats by quantifying the extent of similarity between the Tes and the range of selected temperatures (i.e., the Tbs that lizards maintain in zero-cost conditions in a laboratory thermogradient; Tsel). Both species maintained, throughout most of day, Tbs that were on average 2–4 C below both Tsel and the Tbs recorded in the field during summer. Nevertheless, the Tbs measured during autumn were in the upper range of available Tes and were much closer to the Tsel than were the Tes. In addition, lizards were most often observed in the warmest microhabitats and were often seen basking. These results indicate that lizards were actively thermoregulating. The Te measurements show that lizards encounter suitable thermal conditions (i.e., where Tes is within Tsel) in only a restricted subset of the available microhabitats and during only a relatively short period of the day. Thus, lizards are constrained to maintain relatively low Tbs during autumn by the generally low available Tes. Although lizards were clearly thermoregulating, they appeared to accept lower Tbs during activity in autumn than in summer. A possible reason for this seasonal shift in activity Tbs is that achievement of higher Tbs during autumn is only feasible by confining activities to some specific microhabitats, which may severely constrain other behaviors, such as foraging.

Body Temperatures of Female Sceloporus grammicus: Thermal Stress or Impaired Mobility?

Females of some lizard species exhibit lower body temperatures (Tbs) when reproductive (gravid or pregnant) than when not reproductive. Two hypotheses have been invoked to explain this phenomenon. One, the thermal stress hypothesis, is that the thermal optimum for embryos is lower than that of the female, and females thus actively select relatively low Tbs. The other, the encumbrance hypothesis, is that females are encumbered by their clutch/litter and thus passively accept relatively low Tbs. We collected field data on the thermal biology of Sceloporus grammicus at a high elevation site in Mexico during two seasons. In March, when thermoregulation was facilitated by high ambient temperature, lizards had high Tbs overall, and reproductive females had significantly lower Tbs than males; these observations were in accord with the thermal stress hypothesis. In June/July, when thermoregulation was difficult as a result of low ambient temperatures, lizards had low Tbs overall, and reproductive females had considerably lower Tbs than nonreproductive females. Thus, when thermal opportunities were limited, reproductive females had more difficulty thermoregulating than did nonreproductive females. These observations were in accord with the encumbrance hypothesis. The encumbrance hypothesis was also supported by the observation that females grew more slowly when reproductive than when nonreproductive. Thus, we suggest that the thermal stress and the encumbrance hypotheses are not alternatives but are complementary explanations for the thermal behavior of female Sceloporus.

Temperature Relationships in the High-Altitude Viviparous Lizard, Sceloporus jarrovi

-The thermal ecology of Sceloporus jarrovi was studied in the Chiricahua Mountains of southeastern Arizona at different elevations and times of year. Mean body temperature (Tb) was 31.8 C (range 6.6-38.8 C). Mean air temperature (Ta) was 20.6 C (range 5.0-36.2 C). The slope of the regression of Tb on Ta was 0.37. Winter Tbs were lower than summer Tbs. Low elevation lizards had higher Tbs than high elevation lizards. Males and females had similar Tbs. Pregnant females had lower Tbs than nonpregnant females. Pregnant females also had a lower slope for the Tb on Ta regression than nonpregnant females. Body temperatures of pregnant females at early stages of pregnancy (November) were not significantly different from pregnant females at late stages of pregnancy (May). Sceloporus jarrovi maintained lower Tbs than the sympatric lizard Sceloporus scalaris. These two species have different Tb on Ta regressions.

Detection of the Depth-Hoar Layer in the Snow-Pack of the Arctic Coastal Plain of Alaska, U.S.A., Using Satellite Data

AbstractThe snow-pack on the Arctic Coastal Plain of Alaska has a well-developed depth-hoar layer which forms each year at the base of the snow-pack due to upward vapor transfer resulting from a temperature gradient in the snow-pack. The thickness of the depth-hoar layer tends to increase inland where greater temperature extremes (in particular, lower minimum temperatures) permit larger temperature gradients to develop within the snow-pack. Brightness temperature (TB) data were analyzed from October through May for four winters using the 37 GHz horizontally polarized Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR). By mid-winter each year, a decrease in TB of approximately 20K was found between coastal and inland sites on the Arctic Coastal Plain of Alaska. Modeling has indicated that a thicker depth-hoar layer in the inland sites could be responsible for the lower TBs. The large grain-sizes of the depth-hoar crystals scatter the upwelling radiation moreso than do smaller crystals, and greater scattering lowers the microwave TB. Using a two-layered radiative transfer model, the crystal diameter in the top layer was assumed to be 0.50 mm. The crystals in the depth-hoar layer may be 5–10 mm in diameter but the effective crystal diameter used in the radiative-transfer model is 1.40 mm. The crystal size used in the model had to be adjusted downward, relative to the actual crystal size, because the hollow, cup-shaped depth-hoar crystals are not as effective at scattering the microwave radiation as are spherical crystals that are assumed in the model. In the model, when the thickness of the depth-hoar layer was increased from 5 cm to 10 cm, a 21K decrease in TB resulted. This is comparable to the decrease in TB observed from coastal to inland sites in the study area.

Measurement and Modeling of Microwave Emission from Forested Snowfields in Michigan

Forest cover was found to confuse the normally inverse relationship between microwave brightness temperature (TB) and snow depth in dry snowpacks in the lower peninsula of Michigan during February of 1979 and 1980. However, even in the presence of forest cover, consisting of a mixture of hardwoods and softwoods, the average Nimbus-7 SMMR 37 GHz vertically and horizontally polarized TBs were 11° and 19° K lower during the study period in February of 1979 versus February of 1980. This is attributed to deeper average snowcover for the study period in 1979 (43.8 cm) as compared to 1980 (9.9 cm) since lower TBs accompany deeper snow under dry snowpack conditions. 37 GHz brightness temperature was correlated with snow depth for the study periods in 1979 and 1980, resulting in positive relationships instead of the expected inverse relationships. Because the snow depth increased with increasing forest cover in the lower peninsula of Michigan, it was assumed that the emissivity of the forest cover overwhelmed that of the snow - both in 1979 and 1980 causing higher TBs in more heavily forested areas. Using a simple model, we removed the effects of the trees from the TB/snow depth relationship. A new value, TBR, residual brightness temperature, derived from the 37 GHz data, was correlated with snow depth for selected time periods in February 1979 and 1980 resulting in inverse relationships of R ≡ .82 and .77 respectively. In addition, SMMR data of August 1979 were correlated with percent forest cover to determine the TB of the study area in the absence of snow. The lower SMMR frequencies (10.69 and 6.6 GHz) showed statistically significant inverse relationships with forest cover during the August study period. These inverse relationships were probably due to increased soil moisture in the more heavily forested areas in the northern half of lower peninsula of Michigan thus causing lower TBs.