Feather Gene Expression Elucidates the Developmental Basis of Plumage Iridescence in African Starlings.

Iridescence is widespread in the living world, occurring in organisms as diverse as bacteria, plants, and animals. Yet, compared to pigment-based forms of coloration, we know surprisingly little about the developmental and molecular bases of the structural colors that give rise to iridescence. Birds display a rich diversity of iridescent structural colors that are produced in feathers by the arrangement of melanin-containing organelles called melanosomes into nanoscale configurations, but how these often unusually shaped melanosomes form, or how they are arranged into highly organized nanostructures, remains largely unknown. Here, we use functional genomics to explore the developmental basis of iridescent plumage using superb starlings (Lamprotornis superbus), which produce both iridescent blue and non-iridescent red feathers. Through morphological and chemical analyses, we confirm that hollow, flattened melanosomes in iridescent feathers are eumelanin-based, whereas melanosomes in non-iridescent feathers are solid and amorphous, suggesting that high pheomelanin content underlies red coloration. Intriguingly, the nanoscale arrangement of melanosomes within the barbules was surprisingly similar between feather types. After creating a new genome assembly, we use transcriptomics to show that non-iridescent feather development is associated with genes related to pigmentation, metabolism, and mitochondrial function, suggesting non-iridescent feathers are more energetically expensive to produce than iridescent feathers. However, iridescent feather development is associated with genes related to structural and cellular organization, suggesting that, while nanostructures themselves may passively assemble, barbules and melanosomes may require active organization to give them their shape. Together, our analyses suggest that iridescent feathers form through a combination of passive self-assembly and active processes.

Management of Unicistic Ameloblastoma in a Young Patient: Reducing Social Consequences.

ABSTRACT: Ameloblastoma is an odontogenic tumor of significant clinical relevance, aggressive and locally invasive. Although the posterior region of the mandible is more frequently affected, lesions observed in the maxilla should receive special attention due to the risk of expansion to the nasal, paranasal and orbital structures. This report shows a successful case of a maxillary ameloblastoma treated by combining therapies in a young patient. The treatment strategy adopted to reduce and redefine the lesion dimensions enabled enucleation in a safe way, without destruction of adjacent noble structures. It also allowed complementary approach with peripheral ostectomy and sclerosing agent, efficiently, without evidence of recurrence or complications after 2 years.

Ecological generalism facilitates the evolution of sociality in snapping shrimps.

Evidence from insects and vertebrates suggests that cooperation may have enabled species to expand their niches, becoming ecological generalists and dominating the ecosystems in which they occur. Consistent with this idea, eusocial species of sponge-dwelling Synalpheus shrimps from Belize are ecological generalists with a broader host breadth and higher abundance than non-eusocial species. We evaluate whether sociality promotes ecological generalism (social conquest hypothesis) or whether ecological generalism facilitates the transition to sociality (social transition hypothesis) in 38 Synalpheus shrimp species. We find that sociality evolves primarily from host generalists, and almost exclusively so for transitions to eusociality. Additionally, sponge volume is more important for explaining social transitions towards communal breeding than to eusociality, suggesting that different ecological factors may influence the independent evolutionary origins of sociality in Synalpheus shrimps. Ultimately, our results are consistent with the social transition hypothesis and the idea that ecological generalism facilitates the transition to sociality.

The Evolution of Energetic Scaling across the Vertebrate Tree of Life.

Metabolism is the link between ecology and physiology-it dictates the flow of energy through individuals and across trophic levels. Much of the predictive power of metabolic theories of ecology derives from the scaling relationship between organismal size and metabolic rate. There is growing evidence that this scaling relationship is not universal, but we have little knowledge of how it has evolved over macroevolutionary time. Here we develop a novel phylogenetic comparative method to investigate how often and in which clades the macroevolutionary dynamics of the metabolic scaling have changed. We find strong evidence that the metabolic scaling relationship has shifted multiple times across the vertebrate phylogeny. However, shifts are rare and otherwise strongly constrained. Importantly, both the estimated slope and intercept values vary widely across regimes, with slopes that spanned across theoretically predicted values such as 2/3 or 3/4. We further tested whether traits such as ecto-/endothermy, genome size, and quadratic curvature with body mass (i.e., energetic constraints at extreme body sizes) could explain the observed pattern of shifts. Though these factors help explain some of the variation in scaling parameters, much of the remaining variation remains elusive. Our results lay the groundwork for further exploration of the evolutionary and ecological drivers of major transitions in metabolic strategy and for harnessing this information to improve macroecological predictions.

The evolution of eggshell cuticle in relation to nesting ecology.

Avian eggs are at risk of microbial infection prior to and during incubation. A large number of defence mechanisms have evolved in response to the severe costs imposed by these infections. The eggshell's cuticle is an important component of antimicrobial defence, and its role in preventing contamination by microorganisms in domestic chickens is well known. Nanometer-scale cuticular spheres that reduce microbial attachment and penetration have recently been identified on eggs of several wild avian species. However, whether these spheres have evolved specifically for antimicrobial defence is unknown. Here, we use comparative data on eggshell cuticular structure and nesting ecology to test the hypothesis that birds nesting in habitats with higher risk of infection (e.g. wetter and warmer) are more likely to evolve cuticular nanospheres on their eggshells than those nesting in less risky habitats. We found that nanostructuring, present in 54 of 296 analysed species, is the ancestral condition of avian eggshells and has been retained more often in taxa that nest in humid infection-prone environments, suggesting that they serve critical roles in antimicrobial egg defence.

Key ornamental innovations facilitate diversification in an avian radiation.

Patterns of biodiversity are often explained by ecological processes, where traits that promote novel ways of interacting with the environment (key innovations) play a fundamental role in promoting diversification. However, sexual selection and social competition can also promote diversification through rapid evolution of ornamental traits. Because selection can operate only on existing variation, the tendency of ornamental traits to constrain or enable the production of novel phenotypes is a crucial but often overlooked aspect of diversification. Starlings are a speciose group characterized by diverse iridescent colors produced by nanometer-scale arrays of melanin-containing organelles (melanosomes) that play a central role in sexual selection and social competition. We show that evolutionary lability of these colors is associated with both morphological and lineage diversification in African starlings. The solid rod-like melanosome morphology has evolved in a directional manner into three more optically complex forms that can produce a broader range of colors than the ancestral form, resulting in (i) faster color evolution, (ii) the occupation of novel, previously unreachable regions of colorspace, and ultimately (iii) accelerated lineage diversification. As in adaptive radiations, key innovations in ornament production can provide high phenotypic trait variability, leading to dramatic effects on the tempo and mode of diversification.

Carotenoid-dependent signals and the evolution of plasma carotenoid levels in birds.

Sexual selection has resulted in a wide array of ornaments used in mate choice, and such indicator traits signal quality honestly when they bear costs, precluding cheating. Carotenoid-dependent coloration has attracted considerable attention in this context, because investing carotenoids in coloration has to be traded off against its physiological functions; carotenoids are antioxidants and increase immunocompetence. This trade-off is hypothesized to underlie the honesty of carotenoid-dependent coloration, signaling the "handicap" of allocating carotenoids away from somatic maintenance toward sexual display. Utilizing recent advances in modeling adaptive evolution, we used a comparative approach to investigate the evolution of plasma carotenoid levels using a species-level phylogeny of 178 bird species. We find that the evolutionary optimum for carotenoid levels is higher in lineages that evolved carotenoid-dependent coloration, with strong attraction toward this optimum. Hence, carotenoids do not appear to be limiting, given that higher carotenoid levels readily evolve in response to the evolution of carotenoid-dependent coloration. These findings challenge the assumption that carotenoids are a scarce resource and thus also challenge the hypothesis that physiological resource value of carotenoids underlies honesty of carotenoid-dependent traits. Therefore, the comparative evidence suggests that other factors, such as the acquisition and incorporation of carotenoids, are involved in maintaining signal honesty.

The adaptive value of primate color vision for predator detection.

The complex evolution of primate color vision has puzzled biologists for decades. Primates are the only eutherian mammals that evolved an enhanced capacity for discriminating colors in the green-red part of the spectrum (trichromatism). However, while Old World primates present three types of cone pigments and are routinely trichromatic, most New World primates exhibit a color vision polymorphism, characterized by the occurrence of trichromatic and dichromatic females and obligatory dichromatic males. Even though this has stimulated a prolific line of inquiry, the selective forces and relative benefits influencing color vision evolution in primates are still under debate, with current explanations focusing almost exclusively at the advantages in finding food and detecting socio-sexual signals. Here, we evaluate a previously untested possibility, the adaptive value of primate color vision for predator detection. By combining color vision modeling data on New World and Old World primates, as well as behavioral information from human subjects, we demonstrate that primates exhibiting better color discrimination (trichromats) excel those displaying poorer color visions (dichromats) at detecting carnivoran predators against the green foliage background. The distribution of color vision found in extant anthropoid primates agrees with our results, and may be explained by the advantages of trichromats and dichromats in detecting predators and insects, respectively.

Tubal ectopic pregnancy: comparative management between pre and Covid-19 pandemic periods.

Objective: To evaluate whether there were differences in the presentation of patients with tubal ectopic pregnancy (EP) during the first year of the COVID-19 pandemic. Methods: We performed a retrospective cohort study of all cases of tubal EP between March 2019 and March 2020 (pre-pandemic) and between March 2020 and March 2021 (pandemic). We compared between these two groups the risk factors, clinical characteristics, laboratory data, sonographic aspects, treatment applied and complications. Results: We had 150 EP diagnoses during the two years studied, of which 135 were tubal EP. Of these, 65 were included in the pre-pandemic and 70 in the pandemic period. The prevalence of lower abdominal pain was significantly higher in the pandemic compared to the pre-pandemic period (91.4% vs. 78.1%, p=0.031). There was no significant difference in shock index, initial beta-hCG level, hemoglobin level at diagnosis, days of menstrual delay, aspect of the adnexal mass, amount of free fluid on ultrasound, and intact or ruptured presentation between the groups. Expectant management was significantly higher during the pandemic period (40.0% vs. 18.5%, p=0.008), surgical management was lower during the pandemic period (47.1% vs. 67.7%, p=0.023), and number of days hospitalized was lower in the pandemic period (1.3 vs. 2.0 days, p=0.003). Conclusion: We did not observe a significant difference in patient history, laboratory and ultrasound characteristics. Abdominal pain was more common during the pandemic period. Regarding treatment, we observed a significant increase in expectant and a decrease in surgical cases during the pandemic period.

In silico and in vitro assays suggests Congo red dye degradation by a Lentinus sp. laccase enzyme.

Laccase is a superfamily of ligninolytic enzymes known to degrade a wide variety of xenobiotics, including synthetic dyes. Congo Red (CR) has a diazo dye function, carcinogenic and mutagenic potential, and is currently applied in clinical analysis. The objective of this work was to produce and characterize the crude extract of Lentinus sp. in semi-solid fermentation (FSS) and perform in vitro and in silico studies to assess the potential of the crude extract to discolor the CR dye. Laccase activity was determined using ABTS as substrate and characterized. The in vitro discoloration was carried out using experimental design 22 at room temperature and monitored at 340 nm for 24h. Molecular docking and molecular dynamics simulations were performed between laccase and CR. The maximum laccase activity production was 29.63 U L-1 with six days of FSS. The optimal temperature and pH were 50 °C and 3.0, respectively. Discoloration of the CR dye was obtained only in tests containing CuSO4. Laccase formed stable complexes with the dye, presenting negative binding energy values ranging from -70.94 to -63.16 kcal mol-1 and the occurrence of seven hydrogen bonds. Molecular dynamics results showed the stability of the system (RMSD ranging from 1.0 to 2.5 Ä) and protein-ligand interaction along simulation. RMSF values pointed residues at the end of chains A (residues 300 to 305, 480 to 500) and B (residues 650 to 655 and 950 to 1000) as the most flexible regions of the laccase. This study highlighted the enzymatic action in the bioremediation of CR in vitro in agreement with the in silico simulations that demonstrate the enzyme potential.Communicated by Ramaswamy H. Sarma.

Psycho-physio-neurological correlates of qualitative attention, emotion and flow experiences in a close-to-real-life extreme sports situation: low- and high-altitude slackline walking.

It has been indicated that extreme sport activities result in a highly rewarding experience, despite also providing fear, stress and anxiety. Studies have related this experience to the concept of flow, a positive feeling that individuals undergo when they are completely immersed in an activity. However, little is known about the exact nature of these experiences, and, there are still no empirical results to characterize the brain dynamics during extreme sport practice. This work aimed at investigating changes in psychological responses while recording physiological (heart rate-HR, and breathing rate-BR) and neural (electroencephalographic-EEG) data of eight volunteers, during outdoors slackline walking in a mountainous environment at two different altitude conditions (1 m-low-walk- and 45 m-high-walk-from the ground). Low-walk showed a higher score on flow scale, while high-walk displayed a higher score in the negative affect aspects, which together point to some level of flow restriction during high-walk. The order of task performance was shown to be relevant for the physiological and neural variables. The brain behavior during flow, mainly considering attention networks, displayed the stimulus-driven ventral attention network-VAN, regionally prevailing (mainly at the frontal lobe), over the goal-directed dorsal attention network-DAN. Therefore, we suggest an interpretation of flow experiences as an opened attention to more changing details in the surroundings, i.e., configured as a 'task-constantly-opened-to-subtle-information experience', rather than a 'task-focused experience'.

Chemotherapy-induced acute kidney injury: epidemiology, pathophysiology, and therapeutic approaches.

Despite significant advancements in oncology, conventional chemotherapy remains the primary treatment for diverse malignancies. Acute kidney injury (AKI) stands out as one of the most prevalent and severe adverse effects associated with these cytotoxic agents. While platinum compounds are well-known for their nephrotoxic potential, other drugs including antimetabolites, alkylating agents, and antitumor antibiotics are also associated. The onset of AKI poses substantial risks, including heightened morbidity and mortality rates, prolonged hospital stays, treatment interruptions, and the need for renal replacement therapy, all of which impede optimal patient care. Various proactive measures, such as aggressive hydration and diuresis, have been identified as potential strategies to mitigate AKI; however, preventing its occurrence during chemotherapy remains challenging. Additionally, several factors, including intravascular volume depletion, sepsis, exposure to other nephrotoxic agents, tumor lysis syndrome, and direct damage from cancer's pathophysiology, frequently contribute to or exacerbate kidney injury. This article aims to comprehensively review the epidemiology, mechanisms of injury, diagnosis, treatment options, and prevention strategies for AKI induced by conventional chemotherapy.

Miraculin-based sweeteners in the protein-engineering era: an alternative for developing more efficient and safer products.

The current sweeteners available are very efficient in providing sweet taste. However, they are associated with several chronic diseases. Some glycoproteins, such as miraculins, are extremely interesting from a biotechnological point of view because they perform the bitter into sweet taste modifying function excellently, in addition to being safer as food. In contrast, purifying and synthesizing these proteins represents a major challenge for the food industry, as these proteins are large and complex molecules, which would make the final product expensive and economically unviable. In this context, emerging techniques from computational biology and molecular modelling have been promoting a remarkable revolution in protein bioengineering. Bioinspired peptides can provide many possibilities in sweeteners development through rational design. Once these peptides are smaller molecules than an entire protein, its synthesis on a large scale tends to be much easier and more economical, besides presenting a potential for better bioavailability in the organism. The techniques discussed here allow, through sophisticated pipelines and algorithms, to perform the rational design of mimetic peptides and with smaller size, which can carry out the activation of sweet taste of miraculins and to be more viable for industrial production. In this review, the premises and tools for the elaboration of synthetic peptides bioinspired in proteins with sweetening activity that mimic this action will be emphasized.Communicated by Ramaswamy H. Sarma.

Comparative homology of Pleurotus ostreatus laccase enzyme: Swiss model or Modeller?

Laccases stand out in the industrial context due to their versatile biotechnological applications. Although these enzymes are frequently investigated, currently, Pleurotus ostreatus laccase structural model is unknown. Therefore, this research aims to predict and validate a P. ostreatus laccase theoretical model by means of comparative homology. The laccase target's primary structure (AOM73725.1) was obtained from the NCBI database, the model was predicted from homologous structures obtained from the PDB (PDB-ID: 5A7E, 2HRG, 4JHU, 1GYC) using the Swiss-Model and Modeller, and was refined in GalaxyRefine. The models were validated using PROCHECK, VERIFY 3D, ERRAT, PROVE and QMEAN Z-score servers. Moreover, molecular docking between the laccase model (Lacc4MN) and ABTS was performed on AutoDock Vina. The models that were generated by the Modeller showed superior stereochemical and structural characteristics to those predicted by the Swiss Model. The refinement made it difficult to stabilize the copper atoms which are typical of laccases. The Lacc4MN model showed the interactions between the amino acids in the active site of the laccase and the copper atoms, thereby hinting the stabilization of the metal through electrostatic interactions with histidine and cysteine. The molecular docking between Lacc4MN and ABTS showed negative free energy and the formation of two hydrogen bonds involving the amino acids ASP 208 and GLY 268, and a Pi-sulfur bond between residue HIS 458 and ABTS, which demonstrates the typical catalytic functionality of laccases. Furthermore, the theoretical model Lacc4MN presented stereochemical and structural characteristics that allow its use in silico tests.Communicated by Ramaswamy H. Sarma.

Iridescent colour production in hairs of blind golden moles (Chrysochloridae).

Relative to other metazoans, the mammalian integument is thought to be limited in colour. In particular, while iridescence is widespread among birds and arthropods, it has only rarely been reported in mammals. Here, we examine the colour, morphology and optical mechanisms in hairs from four species of golden mole (Mammalia: Chrysochloridae) that are characterized by sheens ranging from purple to green. Microspectrophotometry reveals that this colour is weak and variable. Iridescent hairs are flattened and have highly reduced cuticular scales, providing a broad and smooth surface for light reflection. These scales form multiple layers of light and dark materials of consistent thickness, strikingly similar to those in the elytra of iridescent beetles. Optical modelling suggests that the multi-layers produce colour through thin-film interference, and that the sensitivity of this mechanism to slight changes in layer thickness and number explains colour variability. While coloured integumentary structures are typically thought to evolve as sexual ornaments, the blindness of golden moles suggests that the colour may be an epiphenomenon resulting from evolution via other selective factors, including the ability to move and keep clean in dirt and sand.

Identification of 1,2,3-triazole-phthalimide derivatives as potential drugs against COVID-19: a virtual screening, docking and molecular dynamic study.

In this work we aimed to perform an in silico predictive screening, docking and molecular dynamic study to identify 1,2,3-triazole-phthalimide derivatives as drug candidates against SARS-CoV-2. The in silico prediction of pharmacokinetic and toxicological properties of hundred one 1,2,3-triazole-phtalimide derivatives, obtained from SciFinder® library, were investigated. Compounds that did not show good gastrointestinal absorption, violated the Lipinski's rules, proved to be positive for the AMES test, and showed to be hepatotoxic or immunotoxic in our ADMET analysis, were filtered out of our study. The hit compounds were further subjected to molecular docking on SARS-CoV-2 target proteins. The ADMET analysis revealed that 43 derivatives violated the Lipinski's rules and 51 other compounds showed to be positive for the toxicity test. Seven 1,2,3-triazole-phthalimide derivatives (A7, A8, B05, E35, E38, E39, and E40) were selected for molecular docking and MFCC-ab initio analysis. The results of molecular docking pointed the derivative E40 as a promising compound interacting with multiple target proteins of SARS-CoV-2. The complex E40-Mpro was found to have minimum binding energy of -10.26 kcal/mol and a general energy balance, calculated by the quantum mechanical analysis, of -8.63 eV. MD simulation and MMGBSA calculations confirmed that the derivatives E38 and E40 have high binding energies of -63.47 ± 3 and -63.31 ± 7 kcal/mol against SARS-CoV-2 main protease. In addition, the derivative E40 exhibited excellent interaction values and inhibitory potential against SAR-Cov-2 main protease and viral nucleocapsid proteins, suggesting this derivative as a potent antiviral for the treatment and/or prophylaxis of COVID-19.Communicated by Ramaswamy H. Sarma.

Leishmanicidal and cytotoxic activity of essential oil from the fruit peel of Myrciaria floribunda (H. West ex Willd.) O. Berg: Molecular docking and molecular dynamics simulations of its major constituent onto Leishmania enzyme targets.

Cutaneous Leishmaniasis (CL) is a neglected disease characterized by highest morbidity rates worldwide. The available treatment for CL has several limitations including serious side effects and resistance to the treatment. Herein we aimed to evaluate the activity of essential oil from the peel of Myrciaria floribunda fruits (MfEO) on Leishmania amazonensis. The cytotoxic potential of MfEO on host mammalian cells was evaluated by MTT. The in vitro leishmanicidal effects of MfEO were investigated on the promastigote and intracellular amastigote forms. The ultrastructural changes induced by MfEO were evaluated by Scanning Electron Microscopy (SEM). The molecular docking of the major compounds δ-Cadinene, γ-Cadinene, γ-Muurolene, α-Selinene, α-Muurolene and (E)-Caryophyllene onto the enzymes trypanothione reductase (TreR) and sterol 14-alpha demethylase (C14DM) were performed. Our results showed that MfEO presented moderate cytotoxicity for Vero cells and macrophages. The MfEO inhibited the growth of promastigote and the survival of intracellular amastigotes, in a dose- and time- dependent way. The MfEO presented high selectivity towards amastigote forms, being 44.1 times more toxic for this form than to macrophages. Molecular docking analysis showed that the major compounds of MfEO interact with Leishmania enzymes and that δ-Cadinene (δ-CAD) presented favorable affinity energy values over TreR and C14DM enzymes, when compared with the other major constituents. Molecular dynamics (MD) simulation studies revealed a stable binding of δ-CAD with lowest binding free energy values in MMGBSA assay. Our results suggested that δ-CAD may be a potent inhibitor of TreR and C14DM enzymes. Communicated by Ramaswamy H. Sarma.

Association between performance on the Glittre ADL-test and the functional capacity of patients with HF: A cross-sectional study.

Background: The Weber classification based on peak VO2 is a well-established method for categorizing patients with heart failure (HF) regarding severity. However, other submaximal tests such as the Glittre ADL-Test have been gaining prominence in practice due to a coherent and more comprehensive correlation with limitations for performing activities of daily living in patients with heart failure.Objective: To investigate the correlation between the time required to perform the Glittre ADL-Test and the peak VO2 in patients with HF.Methods: A cross-sectional study conducted with 40 adult individuals (21 to 65 years) diagnosed with HF of all etiologies, with LVEF<50% and NYHA II and III.Results: The average time for performing the Glittre ADL-Test was 284.9 seconds, and a significant difference was found between Weber classification classes A and C (p = .01). Significant correlations with peak VO2 were also found (r = -0.424 - p < .01). Thirty (30) patients performed a second test, and the ICC found in the reproducibility analysis was 0.75 (95% CI 0.14-0.91) and p < .01.Conclusion: The Glittre ADL-Test was able to reflect the functional performance of individuals with HF, suggesting that it represents an evaluation tool which can be safely used in clinical practice.

What makes a feather shine? A nanostructural basis for glossy black colours in feathers.

Colours in feathers are produced by pigments or by nanostructurally organized tissues that interact with light. One of the simplest nanostructures is a single layer of keratin overlying a linearly organized layer of melanosomes that create iridescent colours of feather barbules through thin-film interference. Recently, it has been hypothesized that glossy (i.e. high specular reflectance) black feathers may be evolutionarily intermediate between matte black and iridescent feathers, and thus have a smooth keratin layer that produces gloss, but not the layered organization of melanosomes needed for iridescence. However, the morphological bases of glossiness remain unknown. Here, we use a theoretical approach to generate predictions about morphological differences between matte and glossy feathers that we then empirically test. Thin-film models predicted that glossy spectra would result from a keratin layer 110-180 nm thick and a melanin layer greater than 115 nm thick. Transmission electron microscopy data show that nanostructure of glossy barbules falls well within that range, but that of matte barbules does not. Further, glossy barbules had a thinner and more regular keratin cortex, as well as a more continuous underlying melanin layer, than matte barbules. Thus, their quasi-ordered nanostructures are morphologically intermediate between matte black and iridescent feathers, and perceived gloss may be a form of weakly chromatic iridescence.

Social environment affects testosterone level in captive male blue-black grassquits.

The challenge hypothesis proposes that testosterone (T) elevation above what is needed for breeding is associated with social factors, and males possibly modulate their hormonal response to variations in population density and sex ratio. We investigated the role of social environment in altering testosterone levels and aggression in a tropical, seasonally breeding grassquit (Volatinia jacarina). We exposed males to three social conditions during 1 year: all-males treatment (six males), mixed treatment (three males-three females), and paired treatment (one male-one female). We quantified aggressiveness among males and T plasma concentration for each individual in each treatment monthly. We found that more aggressive interactions occurred in the all-males treatment than in the mixed treatment. The data also revealed that, coincident with these behavioral changes, the patterns of T variation through time in each treatment were markedly different. The all-males treatment exhibited an early increase in T concentration, which was sustained for a lengthy period with two distinctive peaks, and subsequently declined sharply. The mixed treatment presented an intermediate pattern, with more gradual increase and decrease in T levels. At the other extreme, the paired treatment presented a later rise in T concentration. We conclude that the more competitive environment, with higher density of males, caused the early and higher elevation in T level, thus the presence of competitors may influence the decision of how much a male should invest in reproduction. We suggest that the male's perception of his social environment ultimately mediates hormonal production and alters his reproductive strategy.