Acclimation Process Research Articles

Optimizing Acclimatization for Channa punctatus in Different Laboratory Environments

The present study was conducted to investigate the optimized acclimatization process of Channa punctatus, a freshwater air breathing fish in varying laboratory conditions, using four different tanks setups – glass bottom, sand bottom, sand-soil mix and mud bottom. The study aimed to identify the optimal condition for survival and adaptability. Observation also included mortality rates, changes in pigmentation and behavioral anomalies. Results indicated that tank with mud bottom provided the best environment for acclimatization, highest survival rates and least stress indicators. These findings offered a valuable insight for laboratory studies and conservation efforts involving Channa punctatus under controlled conditions.

Acclimatation of Microbial Biomass to Effluents From a Swine Slaughterhouse in Batch Reactors

Objective: To evaluate the acclimatization of microbial biomass in sequential reactors to optimize the treatment of wastewater from pig slaughterhouses. Theoretical framework: The meat industry generates highly contaminated wastewater. Biological treatments, such as aerobic and anaerobic systems, are more efficient and sustainable than physicochemical ones. Materials and methods: Industrial effluents were collected in a pig slaughterhouse and then characterized. The microbial biomass was collected from the same slaughterhouse and was subjected to an acclimatization process in a sequential batch reactor. Results and discussion: The results showed that the wastewater from the pig slaughterhouse had high levels of BOD, COD and suspended solids, exceeding the limits established by local regulations. During the acclimatization process, the microbial biomass demonstrated a gradual improvement in its COD removal capacity, reaching efficiencies greater than 70%. The positive correlation observed between volumetric organic load and organic matter removal efficiency indicates that acclimated biomass has a greater capacity to treat effluents with high levels of organic load. Research implications: Biomass acclimatization is essential to improve the efficiency of biological treatment in slaughterhouse effluents, reducing its environmental impact and the need for costly treatments. Value/originality: This study proposes a more sustainable and efficient solution for the treatment of slaughterhouse wastewater, highlighting the importance of biomass acclimatization.

Preliminary changes in the humoral and cellular response of shrimp Litopenaeus vannamei during the acclimatization to different salinity

In Nayarit Mexico, the shrimp Litopenaeus vannamei (Boone, 1931) is one of the most widely used species grown on farms, due to its tolerance to a wide range of salinity, probably caused by salinity decreased in the shrimp ponds during rainy season from 35 to 5 practical salinity units (psu) The purpose of this work was to evaluate the response of shrimp to the acclimatization process during both decreasing salinity (10 psu, 7 psu, 5 psu and 2 psu) and its gradual increase (2 psu, 5 psu, 7 psu and 10 psu). The variables determined were, hemocyanin concentration, total count, and differential count of hemocytes in juvenile shrimp. Shrimp clotting time from both experiments was not altered. Hemocyanin increased significantly (P <0.05) with the reduction of salinity while hemocytes tended to decrease as salinity decreased, and to increase when salinity increased. Hyaline hemocytes showed a higher percentage when salinity increased, showing significant differences (P <0.05) in shrimp from both experiments. Finally, the acclimatization process did not affect survival, and the differences between the determined variables could be related to the decrease in salinity.

ROS as Signaling Molecules to Initiate the Process of Plant Acclimatization to Abiotic Stress.

During their life cycle, plants constantly respond to environmental changes. Abiotic stressors affect the photosynthetic and respiratory processes of plants. Reactive oxygen species (ROS) are produced during aerobic metabolism and play an important role as regulatory mediators in signaling processes, activating the plant's protective response to abiotic stress and restoring "oxidation-reduction homeostasis". Cells develop normally if the rates of ROS production and the ability to neutralize them are balanced. To implement oxidation-reduction signaling, this balance must be disrupted either by an increase in ROS concentration or a decrease in the activity of one or more antioxidant systems. Under abiotic stress, plants accumulate excessive amounts of ROS, and if the ROS content exceeds the threshold amount dangerous for living organisms, it can lead to damage to all major cellular components. Adaptive resistance of plants to abiotic stressors depends on a set of mechanisms of adaptation to them. The accumulation of ROS in the cell depends on the type of abiotic stress, the strength of its impact on the plant, the duration of its impact, and the recovery period. The aim of this review is to provide a general understanding of the processes occurring during ROS homeostasis in plants, oxidation-reduction processes in cellular compartments in response to abiotic stress, and the participation of ROS in signaling processes activating adaptation processes to abiotic stress.

Environmental determinants of venom variability in captive scorpions: A comprehensive analysis of diet, temperature, and humidity effects

This study examines the effects of environmental conditions on venom production in four prevalent scorpion species in Morocco: Androctonus amoreuxi, Androctonus mauretanicus, Buthus mardochei, and Scorpio maurus. The research focuses on how climatic factors such as temperature, humidity, and diet—specifically mealworm consumption—affect physical parameters including size and weight, and ultimately venom yield. We conducted a comprehensive investigation involving the capture, acclimatization, and systematic venom extraction from 480 scorpions. Our findings indicate considerable variations in venom volumes, with Scorpio maurus showing a reduced yield compared to Androctonus amoreuxi. Key determinants of venom production were identified as humidity and dietary intake, pointing to significant implications for interspecific diversity and acclimatization processes. These insights have crucial implications for medical and pharmaceutical applications, emphasizing the need for species-specific husbandry protocols to optimize venom extraction for therapeutic use.

Two critical membranes. How does the chloroplast envelope affect plant acclimation properties?

Chloroplasts play a pivotal role in the metabolism of leaf mesophyll cells, functioning as a cellular hub that orchestrates molecular reactions in response to environmental stimuli. These organelles contain complex protein machinery for energy conversion and are indispensable for essential metabolic pathways. Proteins located within the chloroplast envelope membranes facilitate bidirectional communication with the cell and connect essential pathways, thereby influencing acclimation processes to challenging environmental conditions such as temperature fluctuations and light intensity changes. Despite their importance, a comprehensive overview of the impact of envelope-located proteins during acclimation to environmental changes is lacking. Understanding the role of these proteins in acclimation processes could provide insights into enhancing stress tolerance under increasingly challenging environments. This review highlights the significance of envelope-located proteins in plant acclimation.

Morphophysiological adaptations and fragrance profile analysis of two relocated orchid species

This study investigates the morpho-physiological adaptations and fragrance profiles of 2 relocated orchid species, Cattleya aclandiae x Brassavola Little star (V1) and Dendrobium var. Meesangnil (V2), following their translocation from Nagercoil to Coimbatore, India. The research aims to elucidate the mechanisms underlying successful acclimatization of these fragrant orchids to a new environment, with implications for horticulture, conservation and therapeutic applications. Comprehensive analyses were conducted on vegetative growth parameters, flowering characteristics, physiological responses and volatile organic compound (VOC) profiles. Morphological assessments revealed distinct adaptive strategies between the 2 species, with Dendrobium exhibiting superior vertical growth (39.13 cm) and leaf production (9 leaves/plant), while Cattleya developed larger leaves (30.483 cm length, 7.178 cm breadth) and longer internodes (5.061 cm). Flowering characteristics also differed significantly, with Cattleya demonstrating earlier spike emergence and floret opening. Physiological analyses using a CI-340 Handheld Photosynthesis System showed higher photosynthetic rates, transpiration rates and stomatal conductance in Dendrobium, suggesting a more resource-acquisitive strategy. Gas chromatography-mass spectrometry (GC-MS) analysis identified unique VOC profiles for each species, with 30 compounds detected in both varieties, including notable compounds such as n-Hexadecanoic acid, Octadecanoic acid and beta-Sitosterol. The study also explored potential applications in therapeutic horticulture, highlighting the diverse sensory and educational value of these orchid species. This comprehensive analysis of morphological, physiological and biochemical adaptations provides valuable insights into orchid acclimation processes and their potential for conservation and horticultural applications, contributing to our understanding of plant adaptability in the face of environmental changes and offering a foundation for future studies on orchid biology, ecology and therapeutic uses.

Genotype-specific responses to in vitro drought stress in myrtle (Myrtus communis L.): integrating machine learning techniques.

Myrtle (Myrtus communis L.), native to the Mediterranean region of Türkiye, is a valuable plant with applications in traditional medicine, pharmaceuticals, and culinary practices. Understanding how myrtle responds to water stress is essential for sustainable cultivation as climate change exacerbates drought conditions. This study investigated the performance of selected myrtle genotypes under in vitro drought stress by employing tissue culture techniques, rooting trials, and acclimatization processes. Genotypes were tested under varying polyethylene glycol (PEG) concentrations (1%, 2%, 4%, and 6%). Machine learning (ML) algorithms, including Gaussian process (GP), support vector machine (SVM), Random Forest (RF), and Extreme Gradient Boosting (XGBoost), were utilized to model and predict micropropagation and rooting efficiency. The research revealed a genotype-dependent response to drought stress. Black-fruited genotypes exhibited higher micropropagation rates compared to white-fruited ones under stress conditions. The application of ML models successfully predicted micropropagation and rooting efficiency, providing insights into genotype performance. The findings suggest that selecting drought-tolerant genotypes is crucial for enhancing myrtle cultivation. The results underscore the importance of genotype selection and optimization of cultivation practices to address climate change impacts. Future research should explore the molecular mechanisms of stress responses to refine breeding strategies and improve resilience in myrtle and similar economically important crops.

Efficient in-vitro regeneration protocol for large-scale propagation of Aloe vera (L.) Burm.f.

Aloe vera a medicinal shrub, is used in pharmaceuticals and cosmetics due to its therapeutic properties, but its male sterility and self-incompatibility make seed-based reproduction challenging. The current investigation provides a detailed account of a refined in-vitro regeneration process, discussing direct and indirect organogenesis techniques. Shoot multiplication, callus formation, organogenesis in callus culture, and rooting were all evaluated in the Murashige and Skoog (MS) medium employing several plant growth regulators (PGRs). BAP (N6-benzyl amino purine) alone at 3.5 mg/l was the most effective treatment for rapid shoot multiplication and the healthiest shoot quality in direct shoot proliferation. It was shown that a combination of 2.0 mg/l Kn (Kinetin) and 1.0 mg/l NAA (1-naphthalene acetic acid) was most responsive for regeneration in callus culture, whereas 2.5 mg/l 2,4-D (2,4-dichloro phenoxy acetic acid) produced the most profuse regenerative callusing. In addition, plantlets treated with 1.5 mg/l IBA (indole-3-butyric acid) in-vitro produced the highest and longest roots, contributing to a 94 % survival rate during the subsequent acclimatization process. Moreover, regeneration efficiency via direct and indirect channels is also briefly discussed. This research has the potential to enhance the efficiency, precise application of appropriate PGRs needed for the mass production of Aloe vera at various stages of in-vitro culture.

Acclimatisation process of biogas production from tofu industrial wastewater using biofilter in anaerobic baffled reactor (ABR)

A biofilter is a simple technology used in an anaerobic baffled reactor (ABR) to keep biological solids (inoculum) from being easily carried by the inlet substrate and to shorten the hydraulic retention time (HRT). The principle of a biofilter is to form a biofilm on the packed bed of the biofilter in ABR so that it contains immobilised microorganisms. This study aims to know the performance of the biofilter reactor on biogas production during the acclimatisation process. The results show biofilters shorten the HRT and effectively remove pollutants, increasing biogas production and methane quality. The total solid content decreases by around 44 %, from 0.38 % to 0.17 %. The biogas production during acclimatisation was 1806.41 L and COD removal was 95 %. The biogas composition of CH4 was 58.05 %, CO2 38.23 %, and N2 3.2 %. This study provides preliminary findings for further studies on the use of tofu wastewater as a biogas feedstock with different concentrate substrates, which is very useful for sustainability activities and improving the industry to become green.

The effect of several growth regulators and biostimulant on biochemical and physiological changes in acclimation of micropropagated Echinacea purpurea Moench. ‘Raspberry Truffle’

Micropropagation is currently one of the primary methods for plant propagation, known for its efficiency in producing disease-free and vigorous plants. However, the final stage of this—acclimatization, is critical due to the transfer from a controlled in vitro environment to an external one. To reduce mortality and alleviate acclimation stress, plant growth regulators (PGRs) or biostimulants can be employed. This study investigated the effects of exogenously sprayed PGRs: 0.001 mg L−1 abscisic acid (ABA), 0.001 mL L−1 brassinolide (BL), 0.001 mL L−1 24-epibrassinolide (24-epiBL), and 0.3 mL L−1 biostimulant Goteo on the physiological and biochemical responses of Echinacea purpurea ‘Raspberry Truffle’ plantlets during the acclimation process. The effects of treatments at various acclimation stages on chlorophyll (chl) and carotenoids content, hydrogen peroxide (H2O2), catalase (CAT), malondialdehyde (MDA), free amino acids, soluble proteins, total soluble sugar and reduced soluble sugars were tested in this research. The results confirmed changes in biochemical parameters, including an increase in chlorophyll and carotenoids in the acclimatization period where the highest level obtained by BL spraying. A decline in stomatal conductance was also observed, where ABA influenced the most on drop. It was also recorded the decrease in H2O2 and MDA concentration. CAT activity increased, especially with biostimulant treatment. We recorded an increase in total soluble proteins along acclimatization. Goteo affected the most on morphology parameters, ABA, BL and 24-epiBL increased acclimatization efficiency. Our studies indicate that potentially the most effective substances in the acclimatization of E. purpurea ‘Raspberry Truffle’ are brassinosteroids and ABA.

Populations of the Caucasus as an object for studying the process of adaptation to conditions of high-altitude hypoxia

The work examines the main mechanisms responsible for the process of acclimatization of the population of high mountain regions to the conditions of hypobaric hypoxia. The purpose of this review is to describe the pathways of genetic, epigenetic and physiological control in the adaptation of indigenous populations of highlands to reduced barometric pressure and oxygen tension in the environment. It has been shown that populations living in different high-mountain regions demonstrate different ways of adaptation in response to a decrease in the partial pressure of oxygen in the inspired air. The changes that occur in the body in response to stressful conditions are extremely diverse. These include changes in the respiratory, cardiovascular, hematological systems and cellular adaptation. In this review, we examine genomic variations leading to evolutionary adaptation to life at high altitudes, gene expression, pathophysiological and metabolic features, and long-term adaptation in various high-altitude populations. We also consider the peoples of the Caucasus as one of the most promising populations for further study of complex adaptation mechanisms.

A novel stepwise salinity acclimation method to improve the survival of freshwater microalgae Haematococcus lacustris in seawater salinity.

Freshwater microalga Haematococcus lacustris rich in astaxanthin, as a supplemental live diet can directly supply natural astaxanthin to the aquaculture organisms, except marine aquaculture organisms, since H. lacustris cannot tolerate seawater salinity. The objective of the present study is to provide a salinity acclimation method that allows H. lacustris to survive and accumulate astaxanthin with the aim of developing a novel supplemental live diet for marine aquaculture organisms. H. lacustris cultured in freshwater was subjected to different stepwise salinity acclimation processes (two-, three-, and four-shift). As the controls, H. lacustris was exposed to five constant salinities conditions (0, 0.05, 0.075, 0.3, and 0.6M NaCl, respectively). Among the controls, almost all cells in the 0.3M and 0.6M NaCl conditions died immediately. In contrast, H. lacustris in the stepwise salinity acclimation processes survived in 0.6M NaCl (equivalent to seawater salinity of 35 psu), showing the highest living-cell proportion (50.0%) and astaxanthin yield (0.72mg·L-1) in the four-shift. The present study first demonstrated that H. lacustris tolerated seawater salinity through a stepwise acclimation process, proving a new strategy to supply live microalgal diets rich in natural astaxanthin for marine aquaculture.

Experimental evolution reveals that males evolving within warmer thermal regimes improve reproductive performance under heatwave conditions in a model insect.

Climate change is increasing mean temperatures, and intensifying heatwaves. Natural populations may respond to stress through shorter-term acclimation via plasticity and/or longer-term inter-generational evolution. However, if the pace and/or extent of thermal change is too great, local extinctions occur; one potential cause in ectotherms is identified to be the heat-liability of male reproductive biology. Recent data from several species, including the beetle Tribolium castaneum, confirmed that male reproductive biology is vulnerable to heatwaves, which may constrain populations. However, such reproductive-damage may be overestimated, if there is potential to adapt to elevated mean temperatures associated with climate change via evolution and/or acclimation. Here, we tested this to evaluate whether pre-exposures could improve heatwave tolerance (adaptation or acclimation), by experimentally evolving Tribolium castaneum populations to divergent thermal regimes (30 °C vs. 38 °C). Findings across assays revealed that relative to 30 °C-regime males, males from the 38 °C regime, maintained constantly at 8 °C warmer for 25 generations, displayed an increase; (i) in post heatwave (42 °C) reproductive fitness by 55%, (ii) survival by 33%, and (iii) 32% larger testes volumes. Unexpectedly, in the acclimation assay, warm-adapted males' post-heatwave survival and reproduction were best if they experienced cool developmental acclimation beforehand, suggesting a cost to adapting to 38 °C. These results help progress knowledge of the potential for survival and reproduction to adapt to climate change; trait specific adaptation to divergent thermal regimes can occur over relatively few generations, but this capacity depended on the interaction of evolutionary and thermal acclimatory processes.

Elucidating light and temperature-dependent signalling pathways from shoot to root in rice plants: Implications for stress responses.

The main aim of this work was to better understand how the low temperature signal from the leaves may affect the stress responses in the roots, and how the light conditions modify certain stress acclimation processes in rice plants. Rice plants grown at 27°C were exposed to low temperatures (12°C) with different light intensities, and in the case of some groups of plants, only the leaves received the cold, while the roots remained at control temperature. RNA sequencing focusing on the roots of plants grown under normal growth light conditions found 525 differentially expressed genes in different comparisons. Exposure to low temperature led to more down-regulated than up-regulated genes. Comparison between roots of the leaf-stressed plants and whole cold-treated or control plants revealed that nitrogen metabolism and nitric oxide-related signalling, as well as the phenylpropanoid-related processes, were specifically affected. Real-time PCR results focusing on the COLD1 and polyamine oxidase genes, as well as metabolomics targeting hormonal changes and phenolic compounds also showed that not only cold exposure of the leaves, either alone or together with the roots, but also the light conditions may influence certain stress responses in the roots of rice plants.

PHB And Its Role In Salt Acclimatization In Halotolerant Azotobacter Salinestris Species

Poly β-hydroxybutyrate (PHB) are important storage compounds of carbon and energy. Bacteria usually produce PHB apparently in response to the limitation of an essential nutrient and conditions of physiological stress. Therefore, it is assumed that the function of PHB is to serve as an available carbon repository when bacteria face carbon limitation, supporting their survival. Recent findings indicate that PHB plays a protective role against stress-like conditions such as thermal and oxidative shock. The objective of the review is to look at the role of PHB in the salt acclimation process. Salinity is considered to be the most serious abiotic stress affecting crop productivity. It is an active process, spreading globally and a reason for land degradation. Several strategies have been assumed to be used in order to deal with soil salinity. Salt tolerant plant growth promoting rhizobacteria (ST- PGPR) used as a biofertilizer has known to increase the crop yield under stressed condition. Azotobacter salinestris species is known to tolerate 8% salt concentration and can be studied as a model organism to understand the role of PHB in salt acclimatization. Thus, a sustainable approach under saline condition.

Lab-Scale Treatment of Anaerobic Co-Digestion Liquor from Kitchen Waste, Human Feces, and Municipal Sludge Using Partial Nitritation-Anammox Process

Effective nitrogen removal from anaerobic co-digestion is a major challenge to achieving dual-carbon goals. This study explored the acclimatization process of a lab-scale two-stage partial nitritation and anammox process of a stepwise increase in the percentage of raw anaerobic co-digestion liquor from kitchen waste, human feces, and municipal sludge in a venous industrial park in China, which has not been reported yet. Under limited dissolved oxygen (below 0.5 mg/L) and high ammonia levels (200–1500 mg/L), based on adjusting aeration rates, partial nitritation rapidly started up in 50 days. After acclimatization, partial nitritation still performed efficiently and stably, with the final total nitrogen loading rate (TNLR) of 1.24 ± 0.09 gN/L/d, nitrite accumulation rate of 99 ± 4%, and ratio of eff. nitrite/ammonia of 1.32 ± 0.13. In the anammox process, the final total nitrogen removal efficiency, total nitrogen removal rate, and TNLR reached 94 ± 5%, 1.27 ± 0.03 gN/L/d, and 1.36 ± 0.05 gN/L/d, respectively. Chemical oxygen demand (COD) was also reduced in both reactors, with COD removal rates of 0.7 gCOD/L/d in the partial nitritation and 0.4 gCOD/L/d in the anammox process. Overall, the PNA system demonstrated its feasibility in adapting to high ammonia, salinity, and iron levels, when treating anaerobic co-digestion liquor, particularly regarding resource recovery in venous industrial parks.

Physiological and molecular responses of 'Hamlin' sweet orange trees expressing the VvmybA1 gene under cold stress conditions.

Overexpression of VvmybA1 transcription factor in 'Hamlin' citrus enhances cold tolerance by increasing anthocyanin accumulation. This results in improved ROS scavenging, altered gene expression, and stomatal regulation, highlighting anthocyanins' essential role in citrus cold acclimation. Cold stress is a significant threat to citrus cultivation, impacting tree health and productivity. Anthocyanins are known for their role as pigments and have emerged as key mediators of plant defense mechanisms against environmental stressors. This study investigated the potential of anthocyanin overexpression regulated by grape (Vitis vinifera) VvmybA1 transcription factor to enhance cold stress tolerance in citrus trees. Transgenic 'Hamlin' citrus trees overexpressing VvmybA1 were exposed to a 30-day cold stress period at 4°C along with the control wild-type trees. Our findings reveal that anthocyanin accumulation significantly influences chlorophyll content and their fluorescence parameters, affecting leaf responses to cold stress. Additionally, we recorded enhanced ROS scavenging capacity and distinct expression patterns of key transcription factors and antioxidant-related genes inthe transgenic leaves. Furthermore, VvmybA1 overexpression affected stomatal aperture regulation by moderating ABA biosynthesis, resulting in differential responses in a stomatal opening between transgenic and wild-type trees under cold stress. Transgenic trees exhibited reduced hydrogen peroxide levels, enhanced flavonoids, radical scavenging activity, and altered phytohormonal profiles. These findings highlighted the role of VvmybA1-mediated anthocyanin accumulation in enhancing cold tolerance. The current study alsounderlines the potential of anthocyanin overexpression as a critical regulator of the cold acclimation process by scavenging ROS in plant tissues.

Does deacclimation reverse the changes in structural/physicochemical properties of the chloroplast membranes that are induced by cold acclimation in oilseed rape?

Winter crops acquire frost tolerance during the process of cold acclimation when plants are exposed to low but non-freezing temperatures that is connected to specific metabolic adjustments. Warm breaks during/after cold acclimation disturb the natural process of acclimation, thereby decreasing frost tolerance and can even result in a resumption of growth. This phenomenon is called deacclimation. In the last few years, studies that are devoted to deacclimation have become more important (due to climate changes) and necessary to be able to understand the mechanisms that occur during this phenomenon. In the acclimation of plants to low temperatures, the importance of plant membranes is indisputable; that is why the main aim of our studies was to answer the question of whether (and to what extent) deacclimation alters the physicochemical properties of the plant membranes. The studies were focused on chloroplast membranes from non-acclimated, cold-acclimated and deacclimated cultivars of winter oilseed rape. The analysis of the membranes (formed from chloroplast lipid fractions) using the Langmuir technique revealed that cold acclimation increased membrane fluidity (expressed as the Alim values), while deacclimation generally decreased the values that were induced by cold. Moreover, because the chloroplast membranes were penetrated by lipophilic molecules such as carotenoids or tocopherols, the relationships between the structure of the lipids and the content of these antioxidants in the chloroplast membranes during the process of the cold acclimation and deacclimation of oilseed rape are discussed.

Adaptive integumentary features of beef cattle raised on afforested or non-shaded tropical pastures

We aimed to analyze the seasonal acclimatization process of Nelore and Canchim cattle raised on two production systems (non-shaded, NS, and integrated crop-livestock-forest, ICLF), based on the dynamics of the morphological and functional attributes of the hair coat and skin during winter and summer. The study was conducted in Brazil, in a low-altitude tropical climate region. A completely randomized 2 × 2 factorial design was adopted as follows: two production systems (NS and ICLF), two breeds (Nelore and Canchim) in a longitudinal structure, with measurements repeated over time through two stations (winter and summer). The experimental animals consisted of 32 Nelore (Bos indicus) and 32 Canchim (5/8 Bos taurus × 3/8 Bos indicus) bulls. The animals were equally distributed between two intensive rotational grazing systems. In both breeds, the hair coat was significantly thicker in winter but longer in summer, which increased epidermal protection. The Nelore bulls had shorter, wider, and thicker hairs, which are attributes that promote heat loss via conduction. The Canchim bulls showed significantly lower hair density and higher epithelium distance to sweat glands, which resulted in higher core temperature and respiratory rate. In turn, Nelore bulls had higher serum concentrations of triiodothyronine and lower serum concentrations of cortisol. However, Canchim bulls more frequently and intensely activated their thermoregulatory system and markedly adjusted their hair coat and hair features to reduce heat gain, especially in summer. Therefore, the anatomical plasticity and functional integumentary characteristics of Nelore and Canchim bulls reflect their acclimatization to tropical conditions.