Physical constraints on thermoregulation and flight drive morphological evolution in bats.

Body size and shape fundamentally determine organismal energy requirements by modulating heat and mass exchange with the environment and the costs of locomotion, thermoregulation, and maintenance. Ecologists have long used the physical linkage between morphology and energy balance to explain why the body size and shape of many organisms vary across climatic gradients, e.g., why larger endotherms are more common in colder regions. However, few modeling exercises have aimed at investigating this link from first principles. Body size evolution in bats contrasts with the patterns observed in other endotherms, probably because physical constraints on flight limit morphological adaptations. Here, we develop a biophysical model based on heat transfer and aerodynamic principles to investigate energy constraints on morphological evolution in bats. Our biophysical model predicts that the energy costs of thermoregulation and flight, respectively, impose upper and lower limits on the relationship of wing surface area to body mass (S-MR), giving rise to an optimal S-MR at which both energy costs are minimized. A comparative analysis of 278 species of bats supports the model's prediction that S-MR evolves toward an optimal shape and that the strength of selection is higher among species experiencing greater energy demands for thermoregulation in cold climates. Our study suggests that energy costs modulate the mode of morphological evolution in bats­hence shedding light on a long-standing debate over bats' conformity to ecogeographical patterns observed in other mammals­and offers a procedure for investigating complex macroecological patterns from first principles.

Baseline and stress-induced steroid plasma levels and immune function vary annually and are associated with vocal activity in male toads (Rhinella icterica).

Theoretical models predict that elevated androgen and glucocorticoid levels in males during the reproductive season promote immunosuppression. However, some studies report decreased stress response during this season. This study investigated annual variation in plasma corticosterone and testosterone levels, plasma bacterial killing ability (BKA), and neutrophil to lymphocyte ratio (NLR) in free-living male toads (Rhinella icterica). Toads were sampled in the field (baseline) and 1 h-post restraint over five months, and we considered the occurrence of vocal activity. Baseline corticosterone, testosterone, and BKA showed higher values during the reproductive period, specifically in calling male toads. The NLR was similar throughout the year, but higher values were observed in calling toads. Moreover, baseline NLR and BKA were positively correlated with both testosterone and corticosterone, suggesting higher steroid levels during reproduction are associated with enhanced cellular and humoral immunity. Despite fluctuation of baseline values, post-restraint corticosterone levels remained uniform over the year, indicating that toads reached similar maximum values throughout the year. Testosterone levels decreased following restraint before one specific reproductive period but increased in response to restraint during and after this period. Meanwhile, BKA decreased due to restraint only after the reproductive period, indicating immune protection and resilience to immunosuppression by stressors associated with steroid hormones during reproduction. Our results show that baseline and stress-induced hormonal and immune regulation varies throughout the year and are associated with vocal activity in R. icterica males, indicating a possible compromise between steroids and immune function in anuran males.

Frequency of NMOSD misdiagnosis in a cohort from Latin America: Impact and evaluation of different contributors.

BACKGROUND: Neuromyelitis optica spectrum disorder (NMOSD) misdiagnosis (i.e. the incorrect diagnosis of patients who truly have NMOSD) remains an issue in clinical practice. We determined the frequency and factors associated with NMOSD misdiagnosis in patients evaluated in a cohort from Latin America. METHODS: We retrospectively reviewed the medical records of patients with NMOSD, according to the 2015 diagnostic criteria, from referral clinics in six Latin American countries (Argentina, Chile, Paraguay, Colombia, Ecuador, and Venezuela). Diagnoses prior to NMOSD and ultimate diagnoses, demographic, clinical and paraclinical data, and treatment schemes were evaluated. RESULTS: A total of 469 patients presented with an established diagnosis of NMOSD (73.2% seropositive) and after evaluation, we determined that 56 (12%) patients had been initially misdiagnosed with a disease other than NMOSD. The most frequent alternative diagnoses were multiple sclerosis (MS; 66.1%), clinically isolated syndrome (17.9%), and cerebrovascular disease (3.6%). NMOSD misdiagnosis was determined by MS/NMOSD specialists in 33.9% of cases. An atypical MS syndrome was found in 86% of misdiagnosed patients, 50% had NMOSD red flags in brain and/or spinal magnetic resonance imaging (MRI), and 71.5% were prescribed disease-modifying drugs. CONCLUSIONS: NMOSD misdiagnosis is relatively frequent in Latin America (12%). Misapplication and misinterpretation of clinical and neuroradiological findings are relevant factors associated with misdiagnosis.

Effects of food intake and hydration state on behavioral thermoregulation and locomotor activity in the tropidurid lizard Tropidurus catalanensis.

Theoretical models predict that lizards adjust their body temperature through behavioral thermoregulation as a function of food availability. However, behavioral thermoregulation is also governed by interactions among physiological and ecological factors other than food availability, such as hydration state, and sometimes it can even conflict with the locomotor activity of animals. Here, we aimed to investigate the role of food intake and hydration state on behavioral thermoregulation and voluntary locomotor activity in the lizard Tropidurus catalanensis We hypothesized that food intake can influence behavioral thermoregulation via an interaction with hydration state. We also hypothesized that lizards should endeavor to spend as little time as possible to reach their preferred body temperature to defend other physiological and/or ecological functions. We collected lizards in the field and brought them to the laboratory to measure the preferred temperature selected in a thermal gradient and the total distance traveled by them in fed and unfed conditions and with variable hydration state. Our results showed that food consumption was the most important predictor of preferred temperature. In contrast, either the hydration state alone or its interaction with food consumption did not have important effects on the lizards' thermal preference. Also, we found that the total distance traveled by lizards was not affected by food intake and was barely affected by the hydration state. We provide an experimental approach and a robust analysis of the factors that influence behavioral thermoregulation and locomotor activity in a tropical lizard.

Ecological constraints to match field and preferred temperatures in lizards Tropidurus catalanensis (Squamata; Tropiduridae).

We compared microhabitat and body temperatures in the field with thermal preferences of Tropidurus catalanensis to investigate if they match or diverge as demonstration respectively of suitability or poor-quality of the thermal environment. As T. catalanensis is subjected to variable thermal conditions along its distribution and may be jeopardized by the climate change, we measured its thermal preferences after exposure to milder (17 °C-27 °C) and warmer (22 °C-32 °C) thermal conditions to evaluate acclimatory responses and tolerances and vulnerabilities to warming. Field body temperatures tended to be similar to minimum preferred body temperatures, and microhabitat and body temperatures in the field were cooler in the remaining comparisons with thermal preferences [preferred (Tpref), set-point range (Tset), minimum preferred (Tpref_min) and maximum preferred (Tpref_max) body temperatures], suggesting there was a constraint to warming up in nature. The minimum preferred body temperatures may be a threshold separating proper functioning from markedly noxious impacts due to progressive impairment by the cooling. Difficulties to warm and keep suitable body temperatures may jeopardize overall ecophysiological and behavioral processes with implications for maintenance, fitness, and survival. The constraints to warm may impact T. catalanensis differently depending on its body size and its properties of heat conservation (thermal inertia). Smaller and larger T. catalanensis may respectively cool down easier and have difficulties to warm up, being jeopardized by the constraints due to the cold. The warmer preferred body temperatures coupled with the cooler microhabitats and bodies in nature complicate to anticipate how individuals will respond to climate change, but the acclimation to the warmer temperatures led six of them to death, suggesting they had limited tolerance to heat and would be vulnerable to global warming.

Hormonal correlates of the annual cycle of activity and body temperature in the South-American tegu lizard (Salvator merianae).

Life history transitions and hormones are known to interact and influence many aspects of animal physiology and behavior. The South-American tegu lizard (Salvator merianae) exhibits a profound seasonal shift in metabolism and body temperature, characterized by high daily activity during warmer months, including reproductive endothermy in spring, and metabolic suppression during hibernation in winter. This makes S. merianae an interesting subject for studies of interrelationships between endocrinology and seasonal changes in physiology/behavior. We investigated how plasma concentrations of hormones involved in regulation of energy metabolism (thyroid hormones T4 and T3; corticosterone) and reproduction (testosterone in males and estrogen/progesterone in females) correlate with activity and body temperature (Tb) across the annual cycle of captive held S. merianae in semi-natural conditions. In our initial model, thyroid hormones and corticosterone showed a positive relationship with activity and Tb with independent of sex: T3 positively correlated with activity and Tb, while T4 and corticosterone correlated positively with changes in Tb only. This suggests that thyroid hormones and glucocorticoids may be involved in metabolic transitions of annual cycle events. When accounting for sex-steroid hormones, our sex separated models showed a positive relationship between testosterone and Tb in males and progesterone and activity in females. Coupling seasonal endocrine measures with activity and Tb may expand our understanding of the relationship between animal's physiology and its environment. Manipulative experiments are required in order to unveil the directionality of influences existing among abiotic factors and the hormonal signaling of annual cyclicity in physiology/behavior.

Assessment of Predictors of Sun Sensitivity as Defined by Fitzpatrick Skin Phototype in an Ecuadorian Population and Its Correlation with Skin Damage.

BACKGROUND: The Fitzpatrick skin phototype scale (FSPTS) is a widely used instrument to assess skin type. METHODS: A cross-sectional survey collected responses from 254 subjects from Quito regarding self-reported FSPTS, gender, age, education, and tobacco and alcohol consumption. Univariate and multivariate logistic regression analyses were performed to determine if ethnicity, hair color, and eye color significantly predict FSPTS. In addition, we studied the correlation between FSPTS and the SCINEXA scale with Pearson's correlation coefficient. RESULTS: Ethnicity, eye color, and hair color are significant independent predictors of FSPTS (p < 0.0001). CONCLUSIONS: Patient self-reported race and pigmentary phenotypes are inaccurate predictors of sun sensitivity as defined by Fitzpatrick skin phototype. Our study does not fully represent the population of the country. There are limitations to using patient-reported race and appearance in predicting individual sunburn risk.

Seasonal changes in plasma concentrations of the thyroid, glucocorticoid and reproductive hormones in the tegu lizard Salvator merianae.

The tegu lizard Salvator merianae is a large, widely distributed teiid lizard endemic to South America that exhibits annual cycles of high activity during the spring and summer, and hibernation during winter. This pattern of activity and hibernation is accompanied by profound seasonal changes in physiology and behavior, including endothermy during the austral spring. The unusual combination of seasonal endothermy, hibernation and oviparity, in a non-avian, non-mammalian species, makes S. merianae an interesting subject for study of comparative aspects of endocrine regulation of seasonal changes in physiology. In the present study, we first validated commercially available immunoassay kits for quantification of hormone concentrations of the reproductive (testosterone, estradiol and progesterone), adrenal (corticosterone), and thyroid [thyroxine (T4) and triiodothyronine (T3)] axes in plasma of an outdoor, captive adult male and female S. merianae in southeastern Brazil. All assays exhibited parallelism and accuracy with S. merianae plasma. We next assessed patterns of concentration of these hormones across the annual cycle of S. merianae. Testosterone in males and estradiol in females peaked in spring coincident with the peak in reproductive behavior. Progesterone in females was significantly elevated in October coincident with putative ovulation when gravid females build nests. Thyroid hormones, known for regulating energy metabolism, varied seasonally with some sex-dependent differences. T4 gradually increased from an annual nadir during pre-hibernation and hibernation to high concentrations during spring in both sexes. In contrast, T3 did not vary seasonally in males, but females showed a two-fold increase in T3 during the spring reproductive season. T3 may be involved in energy investment during the seasonal production of large clutches of eggs. Corticosterone was significantly elevated during the active season in both sexes, suggesting its involvement in mobilization of energy stores and modulation of behavior (territoriality) and physiology. Ours is the first investigation of concurrent changes in reproductive, thyroid and adrenal hormone concentrations in this endemic and physiologically unique South American lizard. Our findings set the stage for future investigations to determine the extent to which these hormones influence activity and thermoregulation in S. merianae.

Interactive effects of experimental heating rates, ontogeny and body mass on the upper thermal limits of anuran larvae.

Biological and methodological factors influence the upper thermal limits (UTL) of ectothermic animals, but most factors have been studied independently. Few studies have integrated variables, so our understanding about sources of UTL variation remains fragmentary. Thereby, we investigated synergic effects of experimental protocols (heating rates, ΔTs) and biological factors (ontogeny and body mass) on the UTL on the larvae of two anuran species (Physalaemus nattereri and Boana pardalis), specifically their Critical Thermal Maximum (CTmax). The species displayed slightly different responses to ΔTs: In B. pardalis tadpoles both average and variance of CTmax increased at a fastest ΔT, the same response happened in P. nattereri tadpoles at slow and moderate ΔTs. Also, the CTmax of P. nattereri declined at the end of metamorphosis independently of ΔT, but tadpoles at all developmental stages still displayed higher heat tolerance at the slow ΔT. Finally, we detected small, synergic effects of body mass and ΔTs on the CTmax of both species. In small B. pardalis tadpoles and premetamorphic P. nattereri tadpoles, body mass had a positive effect on CTmax, but only at slow and moderate ΔTs, probably indicating physiological responses. A similar trend was observed in large B. pardalis tadpoles at the fast ΔT, but this result is likely to be influenced by thermal inertia. Our findings contribute to integrate the understanding of factors influencing UTL in small ectothermic animals. This understanding is critical to discuss the physiological component of vulnerability to climate change that is related to acute temperatures.

Discovery of tumor-specific irreversible inhibitors of stearoyl CoA desaturase.

A hallmark of targeted cancer therapies is selective toxicity among cancer cell lines. We evaluated results from a viability screen of over 200,000 small molecules to identify two chemical series, oxalamides and benzothiazoles, that were selectively toxic at low nanomolar concentrations to the same 4 of 12 human lung cancer cell lines. Sensitive cell lines expressed cytochrome P450 (CYP) 4F11, which metabolized the compounds into irreversible inhibitors of stearoyl CoA desaturase (SCD). SCD is recognized as a promising biological target in cancer and metabolic disease. However, SCD is essential to sebocytes, and accordingly SCD inhibitors cause skin toxicity. Mouse sebocytes did not activate the benzothiazoles or oxalamides into SCD inhibitors, providing a therapeutic window for inhibiting SCD in vivo. We thus offer a strategy to target SCD in cancer by taking advantage of high CYP expression in a subset of tumors.

The Role of Feeding Specialization on Post-Prandial Metabolic Rate in Snakes of the Genus Bothrops.

Feeding specialization is a recurrent issue in the evolution of snakes and is sometimes associated to morphological and/or behavioral adaptations that improve snake performance to exploit a particular food type. Despite its importance for animal fitness, the role of physiological traits has been much less studied than morphological and behavioral traits in the evolution of feeding specialization in snakes. In this context, the energetic cost of post-prandial period is an important physiological factor due to the remarkable effect on the snake energy budget. We collected data on post-prandial metabolic rate (SDA) in five species of pit vipers from the genus Bothrops with different degrees of mammal feeding specialization to test the hypothesis that feeding specialist species have lower energy costs during the digestion of their regular food item when compared to species with a more generalist diet. Our results support this hypothesis and suggest that ontogenetic changes in diet can be accompanied by changes in energy cost of the digestion process.

Exploratory study of the reproducibility of the SCore for INtrinsic and EXtrinsic skin aging (SCINEXA) scale in "Ruta Escondida de la Mitad del Mundo", Ecuador, 2017.

BACKGROUND: Few studies have been published related to the analysis of different skin aging parameters for whole-body skin using the SCINEXA scale for skin damage. The aim of this study was to evaluate the reproducibility of the SCINEXA scale (SCore for INtrinsic and EXtrinsic skin Aging) in South-Americans non-Caucasian population of a region of Ecuador. METHODS: Exploratory observational study. Thirty subjects of both genders, over 40 years old and living in a rural area with particular characteristics regarding sun exposure were included. The SCINEXA scale was applied at three different time points to assess its reproducibility. Repeated measures analysis of variance was used for comparison of mean SCINEXA scores. Intraclass correlation coefficient, 95% CI and "Cronbach's alpha" coefficient were performed to measure reproducibility. RESULTS: Among participants, 86.7% were female; mean age was over 67 years old, with mainly low educational level, and almost half had more than six hours of sun exposure per day. Test-retest reproducibility of this scale demonstrated almost perfect agreement. The SCINEXA score was greater than 2 points in half of the subjects, reflecting aging due to sun exposure. LIMITATIONS: Most participants were women from one town in a particular geographical area, and the sample size was small. Genetic determinants of skin phenotypes were not assessed. CONCLUSIONS: The SCINEXA score is reproducible in South American non-Caucasian subjects of a particular region of the country. Damage from sun exposure was evident in participants.

Assessing Antibacterial Potential of Components of Phyllomedusa distincta Skin and its Associated Dermal Microbiota.

The granular glands of anuran skin secrete an array of bioactive molecules that protect a frog against pathogens and predators. The skin also harbors a microbial community. Although there is evidence to suggest that the microbiota complement the innate immune defense systems against pathogen infection, the effect of the frog bioactive molecules on its resident microbiota has not yet been fully investigated. In the present study, the skin microbiota of Phyllomedusa distincta obtained from two different geographical areas was evaluated with molecular and culture-based approaches. The antagonistic effects exhibited by the host's microbiota and by a novel dermaseptin peptide isolated from P. distincta skin were investigated. Four isolated bacterial colonies displayed antimicrobial activity against known frog pathogens. Our results were consistent with the hypothesis that microbiota from P. distincta may interact with pathogenic microorganisms to protect a frog's health. On the other hand, the novel dermaseptin peptide exhibited an antimicrobial effect on pathogens as well as on some of the bacteria obtained from the skin microbiota. The richness of bacteria on P. distincta skin was further investigated by 16S rRNA gene clone libraries, which revealed that the family Enterobacteriaceae was prevalent, but a high variability at the species level was observed among individual frogs. Differences observed on the microbiota of frogs from contrasting habitats indicated an influence of the environment on the structure of the skin microbiota of P. distincta.

Thermal ecology of montane Atelopus (Anura: Bufonidae): A study of intrageneric diversity.

Harlequin frogs (Bufonidae: Atelopus) are among the most threatened frog genus in the world and reach very high elevations in the tropical Andes and the Sierra Nevada de Santa Marta (SNSM). Learning about their thermal ecology is essential to infer sensitivity to environmental changes, particularly climate warming. We report on the activity temperature and thermoregulatory behavior of three high-elevation species of harlequin frogs, Atelopus nahumae, Atelopus laetissimus and Atelopus carrikeri. The first two mentioned live in streams in Andean rain forests, whereas A. carrikeri inhabits paramo streams in the SNSM. We studied the thermal ecology of these species in tree localities differing in altitude, and focused on activity body, operative, substrate and air temperature. A main trend was lower body temperature as elevation increased, so that differences among species were largely explained by differences in substrate temperature. However, this temperature variation was much lower in forest species than paramo species. The Atelopus species included in this work proved to be thermoconformers, a trend that not extended to all congenerics at high elevation. This diversity in thermal ecology poses important questions when discussing the impact of climate warming for high-elevation harlequin frogs. For example, forest species show narrow thermal ranges and, if highly specialized, may be more susceptible to temperature change. Paramo species such as A. carrikeri, in contrast, may be more resilient to temperature change.

Upper thermal tolerance plasticity in tropical amphibian species from contrasting habitats: implications for warming impact prediction.

Tropical ectothermic species are currently depicted as more vulnerable to increasing temperatures because of the proximity between their upper thermal limits and environmental temperatures. Yet, the acclimatory capacity of thermal limits has rarely been measured in tropical species, even though they are generally predicted to be smaller than in temperate species. We compared critical thermal maximum (CTmax) and warming tolerance (WT: the difference between CTmax and maximum temperature, Tmax), as well as CTmax acclimatory capacity of toad species from the Atlantic forest (AF) and the Brazilian Caatinga (CAA), a semi-arid habitat with high temperatures. Acclimation temperatures represented the mean temperatures of AF and CAA habitats, making estimates of CTmax and WT more ecologically realistic. CAA species mean CTmax was higher compared to AF species in both acclimation treatments. Clutches within species, as well as between AF and CAA species, differed in CTmax plasticity and we discuss the potential biological meaning of these findings. We did not find a trade-off between absolute CTmax and CTmax plasticity, indicating that species can have both high CTmax and high CTmax plasticity. Although CTmax was highly correlated to Tmax, CTmax plasticity was not related to Tmax or Tmax coefficients of variation. CAA species mean WT was lower than for AF species, but still very high for all species, diverging from other studies with tropical species. This might be partially related to over-estimation of vulnerability due to under-appreciation of realistic acclimation treatments in CTmax estimation. Thus, some tropical species might not be as vulnerable to warming as previously predicted if CTmax is considered as a shifting population parameter.

Extreme operative temperatures are better descriptors of the thermal environment than mean temperatures.

In ecological studies of thermal biology the thermal environment is most frequently described using the mean or other measures of central tendency in environmental temperatures. However, this procedure may hide biologically relevant thermal variation for ectotherms, potentially misleading interpretations. Extremes of operative temperatures (EOT) can help with this problem by bracketing the thermal environment of focal animals. Within this paper, we quantify how mean operative temperatures relate to the range of simultaneously available operative temperatures (a measure of error). We also show how EOT: 1) detect more thermal differences among microsites than measures of central tendency, like the mean OT, 2) allow inferring on microsite use by ectothermic animals, and 3) clarify the relationships between field operative temperatures and temperatures measured at weather stations (WS). To do that, we explored operative temperatures measured at four sites of the Brazilian Caatingas and their correspondent nearest weather stations. We found that the daily mean OT can hide temperature ranges of 41 °C simultaneously available at our study sites. In addition, EOT detected more thermal differences among microsites than central quantiles. We also show how EOT allow inferring about microsite use of ectothermic animals in a given site. Finally, the daily maximum temperature and the daily temperature range measured at WSs predicted well the minimum available field OT at localities many kilometers away. Based on our results, we recommend the use of EOT, instead of mean OT, in thermal ecology studies.

Impacts of a Simulated Infection on the Locomotor Behavior of Invasive and Noninvasive Species of Congeneric Anurans.

AbstractLocomotion is essential for survival, but it requires resources such as energy and metabolites and therefore may conflict with other physiological processes that also demand resources, particularly expensive processes such as immunological responses. This possible trade-off may impose limits on either the magnitude of immune responses or the patterns of activity and performance. Previous studies have shown that invasive species may have a depressed immune response, allowing them to maintain locomotor function and reproduction even when sick. This may contribute to the ecological success of invasive species in colonization and dispersal. In contrast, noninvasive species tend to reduce activity as a response to infection. Here, we studied the impact of a simulated infection on locomotor performance and voluntary movement in the anurans Xenopus laevis (a globally invasive species) and Xenopus allofraseri (a noninvasive congeneric). We found that a simulated infection reduces locomotor performance in both species, with an accentuated effect on X. allofraseri. Voluntary movement was marginally different between species. Our data suggest that a simulated infection leads to behavioral depression and reduced locomotor performance in anurans and show that this effect is limited in the invasive X. laevis. Contrasting responses to an immune challenge have been reported in the few amphibian taxa analyzed to date and suggest relationships between ecology and immunology that deserve further investigation. Specifically, a depressed immune response may underlie a propension to invasion in some species. Whether this is a general trend for invasive species remains to be tested, but our data add to the growing body of work documenting depressed immune systems in invasive species.

Imaging brain glucose metabolism in vivo reveals propionate as a major anaplerotic substrate in pyruvate dehydrogenase deficiency.

A vexing problem in mitochondrial medicine is our limited capacity to evaluate the extent of brain disease in vivo. This limitation has hindered our understanding of the mechanisms that underlie the imaging phenotype in the brain of patients with mitochondrial diseases and our capacity to identify new biomarkers and therapeutic targets. Using comprehensive imaging, we analyzed the metabolic network that drives the brain structural and metabolic features of a mouse model of pyruvate dehydrogenase deficiency (PDHD). As the disease progressed in this animal, in vivo brain glucose uptake and glycolysis increased. Propionate served as a major anaplerotic substrate, predominantly metabolized by glial cells. A combination of propionate and a ketogenic diet extended lifespan, improved neuropathology, and ameliorated motor deficits in these animals. Together, intermediary metabolism is quite distinct in the PDHD brain-it plays a key role in the imaging phenotype, and it may uncover new treatments for this condition.

Implementation and optimisation of a high-temperature loading strategy of liquid standards in the quantification of volatile organic compounds using solid sorbents.

High-temperature liquid standard loading strategy onto solid sorbent traps for calibration of thermal desorption-GC-MS techniques for the analysis of volatile organic compounds is evaluated and optimised. With this proposed set-up, volatilised liquid-loaded standards interact in gas phase with solid sorbent particles. Response factor for 15 volatile compounds with different vapour pressures have been evaluated and compared with common strategies based on liquid matrix interactions. Using gas matrix strategy improves signal output in the range 10-700%. Average increase for benzene, toluene, ethylbenzene and xylenes is 480%. Reported systematic bias between liquid standards and gas samples are reduced, enhancing thermal desorption methodologies on one of its more important issues. In addition, the proposed system improves the average repeatability to a 3.2%, over 13 times some reported data. The use of an ultra-thin GC capillary column of 150 µm id performs better peak resolution in about 60% the time with usual 250 µm id capillary columns. The usefulness of this proposed optimised procedure has been proved in real air matrix samples, through a large study with the reliable characterisation of 93 different volatile compounds in the ambient air of a municipal solid waste treatment area.