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Testudines possess a rigid shell that influences the mechanics of the respiratory system. We studied respiratory mechanics in the terrestrial red-footed tortoise Chelonoidis carbonarius (Cryptodira), comparing juvenile individuals with a less ossified and more flexible carapace with adults with a well-ossified rigid shell. Combined with these ontogenetic differences, we analyzed respiratory system mechanics with animals in a supine and a prone position, as well as in the isolated lungs, to evaluate the impact of the viscera on breathing mechanics. To do so, we used established protocols to measure pulmonary volume (i.e. resting, VLr; and maximum, VLm), static (Cstat) and dynamic (Cdyn) compliance, and the work of breathing (W). We observed that isolated lungs displayed increased VLr, VLm, Cstat and Cdyn and decreased W. Additionally, pulmonary volume, compliance and W were affected by evaluated position, such as a smaller VLr in a supine position. Cdyn and W showed a volume dependency while frequency had less influence on these variables. At similar levels of ventilation, juveniles showed a lower W than adults when standardized by body mass, but similar W when standardized by VLr. Clear ontogenetic changes could be observed in breathing mechanics between juvenile and adult C. carbonarius. While these differences might largely be explained by variation in shell ossification, other explanations such as differences in visceral proportions or developmental degree of the post-pulmonary septum should also be taken into account.

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Large predators have disproportionate effects on their underlying food webs. Thus, appropriately assigning trophic positions has important conservation implications both for the predators themselves and for their prey. Large-bodied predators are often referred to as apex predators, implying that they are many trophic levels above primary producers. However, theoretical considerations predict both higher and lower trophic position with increasing body size. Nitrogen stable isotope values (δ15N) are increasingly replacing stomach contents or behavioral observations to assess trophic position and it is often assumed that ontogenetic dietary shifts result in higher trophic positions. Intraspecific studies based on δ15N values found a positive relationship between size and inferred trophic position. Here, we use datasets of predatory vertebrate ectotherms (crocodilians, turtles, lizards and fishes) to show that, although there are positive intraspecific relationships between size and δ15N values, relationships between stomach-content-based trophic level (TPdiet) and size are undetectable or negative. As there is usually no single value for 15N trophic discrimination factor (TDF) applicable to a predator species or its prey, estimates of trophic position based on δ15N in ectotherm vertebrates with large size ranges, may be inaccurate and biased. We urge a reconsideration of the sole use of δ15N values to assess trophic position and encourage the combined use of isotopes and stomach contents to assess diet and trophic level.

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Important foraging and nesting habitats for Caribbean green sea turtles (Chelonia mydas) exist within the Mesoamerican Reef System in the Mexican Caribbean. During the last 25 years, urban development and touristic activities have drastically increased in Quintana Roo, Mexico. Moreover, in the last decade, massive pelagic sargasso blooms have also afflicted this region; however, information about the biochemical responses of Caribbean green turtles to these inputs is absent. This study aimed to assess if the oxidative stress indicators in the red blood cells of green turtles are valuable biomarkers of the extent of the anthropic impact in this region. Persistent organic pollutants (POPs) were also measured in the plasma of free-living green turtles during 2015-2018 to characterize these habitats further. As biochemical biomarkers, the production rate of superoxide radical (O2•-), carbonylated protein content, and lipid peroxidation (TBARS) levels, and the activities of superoxide dismutase, glutathione S-transferase (GST), catalase, glutathione peroxidase were measured in erythrocytes. A 15 % occurrence of fibropapillomatosis (FP) was revealed, with tumor size being positively correlated with CAT activity in the affected individuals. A multivariate analysis embracing all oxidative stress markers discriminated green turtles between years of capture (p < 0.001), with those sampled during 2015 presenting the highest production of O2•- (p = 0.001), activities of GST (p < 0.001), levels of TBARS (p < 0.001) and carbonylated proteins (p = 0.02). These local and temporal biochemical responses coincided with the first massive Sargassum spp. bloom reported in the region. The results of this study corroborate the utility of the oxidative stress indicators as biomarkers of environmental conditions (sargasso blooms and POPs) in the green turtle as sentinel species.

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Home range is a fundamental characteristic of an animal natural history. The study of home range provides information on the sites where organisms forage for food, find shelter, or locate mates. Home range size and shape can change throughout the lifespan of an organism, during the year, or across seasons, driven by resource availability and the basic needs for each organism. For freshwater and semi-aquatic turtles, home range is greatly affected by water availability, humidity, and temperature throughout the year, nevertheless demographic factors such age and sex are also important determinants of home range size. In this study we estimated home range and dispersal movements for Kinosternon creaseri, Terrapene yucatana, and Rhinoclemmys areolata in a semi-tropical dry forest in central Yucatán. For a two-year period, turtles were surveyed using hoop traps and visual encounters. Twenty-one individuals (5-8 per species) were equipped with radio transmitters to track them across the landscape. Distances between relocations and home range were compared across species seasons, sex, and interactions of these variables. Monthly average movements were positively correlated with rain in the three species studied. Home range of R. areolata was larger than those of K. creaseri and T. yucatana. Home range of the three studied species were larger during the wet season. Home range overlap index within same species individuals was higher during the rainy than dry season, but overall overlap is low between and within species.

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Our study aimed to establish reference values for nesting females and compare them with those previously reported to understand olive ridley turtles' health status and contribute to long-term health assessment and monitoring in foraging and nesting areas from the state of Sinaloa, Mexico. In August and September 2018, morphometric data and biochemical profiles were collected from 33 nesting olive ridley turtles from Ceuta Beach Sanctuary (CBS) and 14 foraging female turtles captured at the foraging site, Navachiste Marine Area (NMA). Nesting turtles sampled had greater CCL (65.86 ± 1.70 cm) than those from the foraging area (61.54 ± 1.22) (p < 0.05). Regarding biochemical profiles, post-nesting turtles had higher packed cell volume (PCV), albumin, blood urea nitrogen (BUN), cholesterol, triglycerides, and calcium than turtles from the foraging area (p < 0.05). Phosphorus levels were higher in foraging turtles than in nesting turtles (p = 0.001), while the remaining parameters showed no significant differences. The present study describes for the first time the blood biochemical values of nesting turtles from the Ceuta Beach Sanctuary in southern Sinaloa, Mexico, similar to those of foraging turtles from the north of the state. The significant differences observed between the two analysis groups may be due to the energy reserves and reproductive and nesting activity of the nesting turtles, so the blood biochemistry values described in this study can be used as a standard reference blood value for the olive ridley turtle population of Sinaloa, Mexico.

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Future climate change scenarios project that the increase in surface temperatures will affect ocean temperatures, inducing shifts in marine biodiversity. Sea turtles are species that are particularly vulnerable to the effects of climate change because temperature is a factor that influences embryonic development. We collected clutches of olive ridley turtles from a mass-nesting beach in the Mexican Pacific, which were incubated in ex situ conditions. When the hatchlings emerged, we measured the body condition index-which evaluates the weight-length relationship-and swim thrust, both were considered traits associated with fitness, termed "fitness proxies," and evaluated the effects of incubation temperature, maternal effects, and paternity on these fitness proxies. The body condition index was correlated positively and significantly with the arribada month and temperature during the last third of the incubation period but showed an inverse relationship with the maternal effect. While swim thrust was positively correlated with the maternal effect and the arribada month, there was an inverse relationship with incubation temperature during the first third of the period. Paternity, whether single or multiple, did not have a significant effect on either fitness proxies; however, it may have effects on the average fitness of a population of hatchlings. These results underscore the need to expand research on the sublethal effects of high incubation temperatures on the adaptation and survival of sea turtles, particularly in scenarios of rapid climate change.

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Contamination in marine ecosystems is of the most critical threats to marine turtles. The identification of useful biomarkers to detect and monitor the physiological and clinical effects of pollutants on these populations will allow early detection of alterations (e.g., mutagenic damages) that could risk their viability or favor the development of diseases, thus threatening the biodiversity of these ecosystems and human population. This study is aimed at describing and quantifying nuclear anomalies in peripheral blood erythrocytes of green turtles (Chelonia mydas) from three distinct foraging areas in Mexico (Akumal, Xcalak, and Punta Herrero). We developed a novel morphological index that could be used as a biomarker to identify abnormal nuclei in peripheral blood erythrocytes. Here we describe for the first time in C. mydas, with a species-specific staining protocol, distinct nuclear abnormalities such as blebbed, lobed, notched, eight shape nuclei, and binucleated cells. These nuclear abnormalities were present in > 90 % of the subjects (n = 30). Moreover, 50 % of the organisms presented erythrocytes with micronuclei. The number of nuclear abnormalities did not correlate with size of the green turtles or differ between sites, or health status. We found a higher frequency of green turtles with nuclear abnormalities in the southern region (Punta Herrero and Xcalak) with the highest frequency of micronucleus and buds. The former could be associated to the constant exposure to chemical pollutants of oceanographic origin in the southern coast of Quintana Roo. Furthermore, the increasing anthropogenic pollution in Akumal could also explain the highest variability in the number of nuclear abnormalities presented in resident individuals. We propose that a long-term monitoring programs of green turtle populations in the Mexican Caribbean that include a micronucleus test could be a useful to determine possible mutagenic damage in these animals.

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Understanding how megaherbivores incorporate habitat features into their foraging behavior is key toward understanding how herbivores shape the surrounding landscape. While the role of habitat structure has been studied within the context of predator-prey dynamics and grazing behavior in terrestrial systems, there is a limited understanding of how structure influences megaherbivore grazing in marine ecosystems. To investigate the response of megaherbivores (green turtles) to habitat features, we experimentally introduced structure at two spatial scales in a shallow seagrass meadow in The Bahamas. Turtle density increased 50-fold (to 311 turtles ha-1 ) in response to the structures, and turtles were mainly grazing and resting (low vigilance behavior). This resulted in a grazing patch exceeding the size of the experimental setup (242 m2 ), with reduced seagrass shoot density and aboveground biomass. After structure removal, turtle density decreased and vigilance increased (more browsing and shorter surfacing times), while seagrass within the patch partly recovered. Even at a small scale (9 m2 ), artificial structures altered turtle grazing behavior, resulting in grazing patches in 60% of the plots. Our results demonstrate that marine megaherbivores select habitat features as foraging sites, likely to be a predator refuge, resulting in heterogeneity in seagrass bed structure at the landscape scale.

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We analyzed the influence of the season, the environment, and the sex, as well as the relation of body mass (BM) in the serum albumin (ALB), aspartate aminotransferase (AST), creatinine (C), creatine kinase (CK), phosphorus (P), total calcium (tCa), total protein (TP), urea (U), uric acid (UA), calcium:phosphorus ratio (Ca:P), and the globulin value (GV) of thirty individuals of Phrynops geoffroanus of the urban area of Cuiabá, Mato Grosso, Brazil. The modeling of biochemical parameters was performed using the Generalized Additive Models for Location, Scale and Shape (GAMLSS) to verify the influence of variables considered in this study on each of the biochemical parameters analyzed. The season influenced AST, CK, C, tCa, Ca:P and UA. The environment influenced tCa, Ca:P, U and UA. On the other hand, CK, tCa, P, Ca:P and U differed significantly between males and females. Regarding the BM, a relationship of this variable was observed with CK, C, tCa, P, U, UA and Ca:P. We concluded that the season, environment, sex, and body mass can influence the biochemical parameters of P. geoffroanus, and these factors should be routinely considered in the interpretation of laboratory results.

Analisou-se a influência da estação, do ambiente e do sexo, assim como a relação da massa corporal (BM) nos níveis sorológicos de albumina (ALB), aspartato aminotransferase (AST), creatinina (C), creatina quinase (CK), fósforo (P), cálcio total (tCa), sólidos totais (TS), ureia (U), ácido úrico (UA), relação cálcio:fósforo (Ca:P), e do valor da globulina (GV) de Phrynops geoffroanus da área urbana de Cuiabá, Mato Grosso, Brasil. A modelagem dos parâmetros bioquímicos foi realizada utilizando-se os modelos aditivos generalizados para locação, escala e forma (GAMLSS) para verificar a influência das variáveis consideradas neste estudo em cada um dos parâmetros bioquímicos analisados. A estação sazonal influenciou os níveis de AST, CK, C, tCa, Ca:P e UA. O ambiente foi capaz de influenciar tCa, Ca:P, U e UA. Por outro lado, CK, tCa, P, Ca:P e U diferiram significativamente entre machos e fêmeas. Em relação à BM, observou-se relação dessa variável com CK, C, tCa, P, U, UA e Ca:P. Concluiu-se que a estação sazonal, o ambiente, o sexo e a massa corporal são capazes de influenciar os parâmetros bioquímicos de P. geoffroanus e que esses fatores devem ser rotineiramente considerados na interpretação dos resultados laboratoriais.

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Tortoises of the genus Gopherus evolved in North America and have survived major environmental challenges in the past 40 million years. However, this genus now faces multiple anthropogenic threats, such as the introduction of invasive plant species. Buffelgrass (Cenchrus ciliaris) is considered one of the greatest threats to arid and tropical ecosystems, where gopher tortoises inhabit, because the grass displaces native flora and fauna. Modification of the environment as a result of this invasive plant portends an alteration of the available thermal landscape. The aim of this paper is twofold: 1) to evaluate the thermal quality of the primary habitat of Gopherus evgoodei (tropical deciduous forest [TDF], and 2) determine the potential thermal changes due to habitat modification by buffelgrass. First, we obtained data on body temperature of active tortoises in semi-captivity. Second, we measured the operative environmental temperature during 5 years at three sites south of Sonora, Mexico that support G. evgoodei: a) a pristine TDF (Conserved-TDF); b) a forest patch surrounded by introduced buffelgrass pasture (Partial-TDF); and c) an introduced buffelgrass pasture area (Buffel-Pasture). Our results demonstrate that the intact microhabitats within the TDF provide G. evgoodei with high thermal quality at both spatial and temporal scales. However modified habitat by buffelgrass had higher operative temperatures for G. evgoodei than TDF. The thermal quality of the sites disturbed with buffelgrass can exceed the thermal requirements of G. evgoodei by up to 25 °C. Finally, we discussed potential collateral effects of habitat modification by invasion by buffelgrass.

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Dendritic cells form the link between the innate and adaptative immune response, particularly on mucosal and epidermal surfaces. The Langerhans, an epidermal dendritic cell subpopulation, play a key role in the skin immune response across several species. Scarse immune cell subpopulations, including Langerhans-like cells, have been identified in endangered green turtles thereby complicating the understanding of the pathogenesis of diseases such as fibropapillomatosis, which induces skin tumours in this species worldwide. In biopsies from green turtle skin, we demonstrated that the polyclonal anti-human Langerin antibodies strongly stained a Langerin+ cell population in epidermal sheets, the suprabasal layer of the epidermis in cryosections and in cells from cytospin preparation of migration assays. The morphology of these cells was round to amoeboid in normal skin; however, in skin with ulcerative dermatitis, Langerin+ cells aggregated around ulcers and adopted a more pleomorphic morphology. To our knowledge, this is the first identification of Langerin+ cells with a molecular marker in a reptile species.

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Sex steroid hormones are critical in gonadal differentiation in turtles. The gonads are not the only organs responsible for producing these hormones during this phase. Mesonephros play an important role in steroidogenesis. The present study aimed to investigate the presence of steroidogenic cells in mesonephros of Podocnemis expansa during gonadal differentiation and to evaluate their morphology and ultrastructure. Ten embryos of P. expansa were collected from 5 nests on day 36 of incubation, during spawning period on an artificial beach. Embryos were extracted from eggs by slicing the shell and euthanized. They were dissected under a stereoscopic microscope to collect the gonad-mesonephro complex, in which were fixed and subsequently processed for light microscopy, immunohistochemistry and transmission electron microscopy analysis. During histological analysis was observed mesonephros has typical morphological structure. Immunohistochemistry showed immunoreaction to aromatase in cells of intertubular space. Confirming these findings, it was possible to observe a type of intertubular cell in several regions of mesonephro, being more predominant in region close to blood vessels, distal and proximal tubules. In ultrastructural analysis these cells were characterized by having a clear, large, and rounded nucleus with evident nucleolus and cytoplasm rich in electron-dense droplets. This study demonstrated for the first time the presence of cells with morphological, immunohistochemical and ultrastructural characteristics similar to steroid-producing cells in P. expansa mesonephrons, suggesting that this organ may contribute to gonadal differentiation in this species.(AU)

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Chelonians are considered good bioindicators of environmental quality. The assessment of the health status of chelonian populations in the Amazon is important because they are traditionally consumed in large numbers in riverine communities and sustainable use reserves. The present study aimed to evaluate the health of Podocnemis unifilis (Testudines, Podocnemididae) in an environmental protection area in the Amazon region in Brazil. We analyzed the biomarkers lipoperoxidation, carbonylation of proteins, occurrence of micronuclei and erythrocytic nuclear abnormalities, quantified metallothioneins, and evaluated mercury bioaccumulation. We generated pioneering data regarding biomarkers in wild Amazonian freshwater turtles. All biomarker responses did not vary significantly between the sexes. The occurrence of oxidative and genotoxic damage, as well as concentrations of metallothioneins was low compared to other studies. In addition, the bioaccumulation of mercury in the muscle of the animals was below the limit recommended for human consumption by the World Health Organization. Our results provide baseline data on mercury bioaccumulation and biomarker responses that can be useful for future comparisons with other freshwater turtles. The data also provide evidence that the sustainable exploitation of these turtles in the study area (Piagaçu-Purus Sustainable Development Reserve) does not pose a risk to local riverine communities, as the detected mercury concentrations are safe for human consumption. In this sense, our results highlight the importance of protected areas for the conservation of healthy turtle populations, at the same time ensuring the health of the human populations that use them as a food resource.(AU)

Quelônios são considerados bons bioindicadores da qualidade ambiental. A avaliação do estado de saúde de populações de quelônios na Amazônia também é importante porque estes animais são tradicionalmente consumidos em grandes quantidades em comunidades ribeirinhas e em reservas de uso sustentável. O presente estudo avaliou a saúde de Podocnemis unifilis (Testudines, Podocnemididae) em uma área de proteção ambiental da Amazônia no Brasil. Analisamos lipoperoxidação, carbonilação de proteínas, ocorrência de micronúcleos e anormalidades nucleares eritrocíticas, quantificamos metalotioneínas, e avaliamos a bioacumulação de mercúrio. Geramos dados pioneiros sobre biomarcadores em quelônios de água doce amazônicos silvestres. Todas as respostas aos biomarcadores não variaram significativamente entre os sexos. A ocorrência de danos oxidativos e genotóxicos, bem como as concentrações de metalotioneínas foram baixas em comparação a outros estudos. Adicionalmente, a bioacumulação de mercúrio no músculo dos animais ficou abaixo dos limites recomendados para consumo humano pela Organização Mundial de Saúde. Nossos resultados constituem um conjunto de dados de referência para bioacumulação de mercúrio e respostas de biomarcadores que podem ser úteis para futuras comparações com outros quelônios de água doce. Os dados também fornecem evidências de que a exploração sustentável desses quelônios na área de estudo (Reserva de Desenvolvimento Sustentável Piagaçu-Purus) não apresenta risco às comunidades ribeirinhas locais, já que as concentrações de mercúrio detectadas são seguras para o consumo humano. Nesse sentido, nossos resultados evidenciam a importância das áreas protegidas para a conservação de populações saudáveis de quelônios, concomitantemente assegurando a saúde das populações humanas que os utilizam como fonte alimentar.(AU)

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In this study, we applied multiple reaction monitoring (MRM)-profiling to explore the relative ion intensity of lipid classes in plasma samples from sea turtles in order to profile lipids relevant to sea turtle physiology and investigate how dynamic ocean environments affect these profiles. We collected plasma samples from foraging green (Chelonia mydas, n = 28) and hawksbill (Eretmochelys imbricata, n = 16) turtles live captured in North Pacific Costa Rica in 2017. From these samples, we identified 623 MRMs belonging to 10 lipid classes (sphingomyelin, phosphatidylcholine, free fatty acid, cholesteryl ester, phosphatidylserine, phosphatidylinositol, phosphatidylglycerol, phosphatidylethanolamine, ceramide, and triacylglyceride) and one metabolite group (acyl-carnitine) present in sea turtle plasma. The relative ion intensities of most lipids (80%) were consistent between species, across seasons, and were not correlated to body size or estimated sex. Of the differences we observed, the most pronounced was the differences in relative ion intensity between species. We identified 123 lipids that had species-specific relative ion intensities. While some of this variability is likely due to green and hawksbill turtles consuming different food items, we found indications of a phylogenetic component as well. Of these, we identified 47 lipids that varied by season, most belonging to the structural phospholipid classes. Overall, more lipids (n = 39) had higher relative ion intensity in the upwelling (colder) season compared to the non-upwelling season (n = 8). Further, we found more variability in hawksbill turtles than green turtles. Here, we provide the framework in which to apply future lipid profiling in the assessment of health, physiology, and behavior in endangered sea turtles.

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The Mesoamerican slider Trachemysvenusta is endemic to Central America and Southern Mexico. Several human-mediated disturbances, including habitat degradation and illegal hunting for food, have impacted its populations along the Usumacinta river basin. The extent to which these disturbances have affected the genetic diversity and population structure of T. venusta inhabiting the basin remains unresolved. To this end, we analyzed eight microsatellite markers in five wild populations of T. venusta from the middle and lower reaches of the basin as well as one captive population. Our results show high levels of genetic diversity for all analyzed populations, low F ST values, high gene flow and no genetic structure, indicating an absence of genetic differentiation across sites and, thus, a single panmictic population for the basin. Evidence of a genetic bottleneck was observed in two of the wild populations (and the captive one), indicating some impact from disturbances, whether from poaching or habitat fragmentation, despite the seemingly high connectivity of most populations. Results are discussed in terms of the relative importance of genetic parameters for the conservation of T. venusta, particularly in light of the importance of demographic stochasticity in local conditions undergoing rapid changes.

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Knowledge of feeding patterns of highly migratory species is critical for understanding their habitat use and informing the management of their populations. The Galapagos Islands are one of the most important nesting and feeding areas for green turtles (Chelonia mydas) across the tropical eastern Pacific, yet little is known about the feeding patterns of this species. The isotopic composition of different tissues has been used to gain insight into the trophic dynamics of mobile aquatic consumers whose trophic behavior is difficult to directly measure. To elucidate the temporal feeding patterns and isotopic niche sizes of Galapagos green turtles, stable isotope analyses were performed on multiple tissues (skin and carapace) collected at the two most important nesting areas in the archipelago: Bachas and Quinta Playa. The δ13 C and δ15 N signatures on the skin and carapace samples from 56 adult females revealed significant differences between tissues (p = .001 and p = .021, respectively) and nesting areas (p = .011 and p = .003, respectively). These differences suggest a shift from oceanic feeding grounds to neritic habitats before nesting. The carapace isotope values indicated an offshore feeding strategy and a greater isotopic niche (SEAc = 1.91‰2 ), whereas the skin isotope values represented an inshore feeding strategy with a narrower niche (SEAc = 1.37‰2 ), likely related to the consumption of specific coastal prey. Our results suggest that Galapagos green turtles feed across different habitats, and this information can be applied to improve the management of this endangered species.

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Esse estudo objetivou caracterizar o desenvolvimento e a diferenciação gonadal de Podocnemis unifilis em temperatura controlada de 32°C em incubadora artificial e com controle de umidade feito por um higrômetro interno. Foram realizadas análises macroscópicas, por microscopia de luz e por microscopia eletrônica de transmissão. O desenvolvimento gonadal foi agrupado em três etapas: células germinativas primordiais (CGP), estabelecimento da gônada indiferenciada e diferenciação gonadal. As CGP só foram visualizadas a partir do 7º dia de incubação, e se encontravam na região caudal do corpo do embrião, e entre os dias 9 e 11 de incubação foi possível observar a migração das CGP a partir do saco vitelínico em direção à região ventromedial do mesonefro. Com 20 dias de desenvolvimento, a gônada indiferenciada estava estabelecida, sendo identificadas duas regiões distintas: a região cortical externa, caracterizada pela presença de CGP, e a região medular interna, marcada por cordões sexuais primitivos. Nesse estudo, a diferenciação gonadal só ocorreu em testículo. A diferenciação teve início após 35 dias de incubação, com o início da organização dos cordões sexuais em túbulos seminíferos. As etapas de diferenciação gonadal foram semelhantes às de outras espécies de quelônios com determinação do sexo pela temperatura, no entanto, neste estudo, usando a temperatura pivotal descrita para a espécie, todos os indivíduos analisados diferenciaram-se em machos, sendo necessária, portanto, a realização de mais estudos com diferentes temperaturas.

This study aimed to characterize the development and gonadal differentiation of Podocnemis unifilis at a controlled temperature of 32° C in artificial incubator and with humidity control performed by an internal hygrometer. Macroscopic analyzes, light microscopy and transmission electron microscopy were performed. We grouped gonadal development into three stages: primordial germ cells (PGC), establishment of the undifferentiated gonad and gonadal differentiation. We only visualized the PGC from the 7th day of incubation, and in the caudal region of the embryo body; between days 9 and 11 of incubation we were able to observe the migration of the PGC from the viteline sac towards the ventromedial region of the mesonefro. At 20 days of development, the undifferentiated gonad was established and two distinct regions were identified: the external cortical region characterized by the presence of PGC, and the internal medullary region marked by primitive sexual cords. In this study, only gonadal differentiation occurred in the testicle. Gonadal differentiation began after 35 days of incubation with the beginning of the organization of sexual cords in the seminiferous tubules. The stages of gonadal differentiation were similar to those of other species of turtles with temperature determined sex, however in this study, using the pivotal temperature described for the species all the individuals analyzed were males, and it is there for necessary to carry out further studies using a higher incubation temperature.

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O aumento do conhecimento sobre a ecologia populacional das espécies de quelônios amazônicos é essencial para a recuperação e manutenção dos estoques naturais desses répteis. Neste estudo foi avaliada a influência de fatores hidroclimáticos sobre parâmetros populacionais e a condição corporal de Podocnemis expansa (Schweigger, 1812) em um trecho do Rio Formoso, sudeste da Amazônia brasileira, caracterizado pelo intenso uso das águas superficiais na irrigação de culturas agrícolas. O trabalho de campo ocorreu em três campanhas realizadas entre o final de julho e início de agosto dos anos de 2016, 2017 e 2018, totalizando um esforço amostral de 205 horas. Os indivíduos foram capturados por meio dos métodos de arrasto de rede, pesca com anzol e rede de espera; e os dados hidroclimáticos obtidos no site da Agência Nacional das Águas - ANA. Um total de 466 espécimes foi capturado e marcado, incluindo 47 machos adultos, 76 fêmeas adultas e 343 juvenis- revelando-se uma população composta predominantemente por juvenis (73,60%) e com razão sexual funcional desviada para as fêmeas (0,62:1). A redução no número de indivíduos das classes de tamanhos maiores e melhores condições corporais estiveram associadas, respectivamente, a uma maior vazão média do rio na estação seca e ao aumento da vazão no período chuvoso. Estudos futuros de longo prazo devem buscar aprofundar os conhecimentos sobre como fatores hidroclimáticos e as atividades agrícolas desenvolvidas na região afetam a demografia da espécie.

Evaluation of the influence of hydroclimatic factors on the population structure of Podocnemis expansa (Testudines: Podocnemididae) in Formoso River, southeastern Brazilian Amazon. It is essential to have more knowledge about the population ecology of Amazonian chelonian species in order to recover and maintain the natural stocks of these reptiles. This study assessed the influence of hydroclimatic factors on population parameters and the body condition of Podocnemis expansa (Schweigger, 1812) in a specific region of Formoso River, in the southeast of Brazilian Amazon rainforest, where there is an intense use of surface water for irrigation of agricultural crops. The fieldwork took place in three campaigns carried out between the end of July and the beginning of August in the years 2016, 2017 and 2018, with a total sample effort of 205 hours. The individuals were captured using the methods of net trawling, hook fishing and waiting net; and the hydroclimatic data obtained from the website of the Agência Nacional de Águas - ANA. A total of 466 specimens were captured and tagged, being 47 adult males, 76 adult females and 343 juveniles, demonstrating a population composed mostly of juveniles (73.60%) and with a deviated functional sex ratio for females (0.62:1). The reduction in the number of individuals of larger sizes and better body conditions were associated, respectively, with higher river flow average in the dry season and an increase in flow during the rainy period. Future long-term studies are necessary to deepen the knowledge about how hydroclimatic factors and agricultural activities developed in the region affect the demography of the species.

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O aumento do conhecimento sobre a ecologia populacional das espécies de quelônios amazônicos é essencial para a recuperação e manutenção dos estoques naturais desses répteis. Neste estudo foi avaliada a influência de fatores hidroclimáticos sobre parâmetros populacionais e a condição corporal de Podocnemis expansa (Schweigger, 1812) em um trecho do Rio Formoso, sudeste da Amazônia brasileira, caracterizado pelo intenso uso das águas superficiais na irrigação de culturas agrícolas. O trabalho de campo ocorreu em três campanhas realizadas entre o final de julho e início de agosto dos anos de 2016, 2017 e 2018, totalizando um esforço amostral de 205 horas. Os indivíduos foram capturados por meio dos métodos de arrasto de rede, pesca com anzol e rede de espera; e os dados hidroclimáticos obtidos no site da Agência Nacional das Águas - ANA. Um total de 466 espécimes foi capturado e marcado, incluindo 47 machos adultos, 76 fêmeas adultas e 343 juvenis- revelando-se uma população composta predominantemente por juvenis (73,60%) e com razão sexual funcional desviada para as fêmeas (0,62:1). A redução no número de indivíduos das classes de tamanhos maiores e melhores condições corporais estiveram associadas, respectivamente, a uma maior vazão média do rio na estação seca e ao aumento da vazão no período chuvoso. Estudos futuros de longo prazo devem buscar aprofundar os conhecimentos sobre como fatores hidroclimáticos e as atividades agrícolas desenvolvidas na região afetam a demografia da espécie.(AU)

Evaluation of the influence of hydroclimatic factors on the population structure of Podocnemis expansa (Testudines: Podocnemididae) in Formoso River, southeastern Brazilian Amazon. It is essential to have more knowledge about the population ecology of Amazonian chelonian species in order to recover and maintain the natural stocks of these reptiles. This study assessed the influence of hydroclimatic factors on population parameters and the body condition of Podocnemis expansa (Schweigger, 1812) in a specific region of Formoso River, in the southeast of Brazilian Amazon rainforest, where there is an intense use of surface water for irrigation of agricultural crops. The fieldwork took place in three campaigns carried out between the end of July and the beginning of August in the years 2016, 2017 and 2018, with a total sample effort of 205 hours. The individuals were captured using the methods of net trawling, hook fishing and waiting net; and the hydroclimatic data obtained from the website of the Agência Nacional de Águas - ANA. A total of 466 specimens were captured and tagged, being 47 adult males, 76 adult females and 343 juveniles, demonstrating a population composed mostly of juveniles (73.60%) and with a deviated functional sex ratio for females (0.62:1). The reduction in the number of individuals of larger sizes and better body conditions were associated, respectively, with higher river flow average in the dry season and an increase in flow during the rainy period. Future long-term studies are necessary to deepen the knowledge about how hydroclimatic factors and agricultural activities developed in the region affect the demography of the species.(AU)

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Esse estudo objetivou caracterizar o desenvolvimento e a diferenciação gonadal de Podocnemis unifilis em temperatura controlada de 32°C em incubadora artificial e com controle de umidade feito por um higrômetro interno. Foram realizadas análises macroscópicas, por microscopia de luz e por microscopia eletrônica de transmissão. O desenvolvimento gonadal foi agrupado em três etapas: células germinativas primordiais (CGP), estabelecimento da gônada indiferenciada e diferenciação gonadal. As CGP só foram visualizadas a partir do 7º dia de incubação, e se encontravam na região caudal do corpo do embrião, e entre os dias 9 e 11 de incubação foi possível observar a migração das CGP a partir do saco vitelínico em direção à região ventromedial do mesonefro. Com 20 dias de desenvolvimento, a gônada indiferenciada estava estabelecida, sendo identificadas duas regiões distintas: a região cortical externa, caracterizada pela presença de CGP, e a região medular interna, marcada por cordões sexuais primitivos. Nesse estudo, a diferenciação gonadal só ocorreu em testículo. A diferenciação teve início após 35 dias de incubação, com o início da organização dos cordões sexuais em túbulos seminíferos. As etapas de diferenciação gonadal foram semelhantes às de outras espécies de quelônios com determinação do sexo pela temperatura, no entanto, neste estudo, usando a temperatura pivotal descrita para a espécie, todos os indivíduos analisados diferenciaram-se em machos, sendo necessária, portanto, a realização de mais estudos com diferentes temperaturas.(AU)

This study aimed to characterize the development and gonadal differentiation of Podocnemis unifilis at a controlled temperature of 32° C in artificial incubator and with humidity control performed by an internal hygrometer. Macroscopic analyzes, light microscopy and transmission electron microscopy were performed. We grouped gonadal development into three stages: primordial germ cells (PGC), establishment of the undifferentiated gonad and gonadal differentiation. We only visualized the PGC from the 7th day of incubation, and in the caudal region of the embryo body; between days 9 and 11 of incubation we were able to observe the migration of the PGC from the viteline sac towards the ventromedial region of the mesonefro. At 20 days of development, the undifferentiated gonad was established and two distinct regions were identified: the external cortical region characterized by the presence of PGC, and the internal medullary region marked by primitive sexual cords. In this study, only gonadal differentiation occurred in the testicle. Gonadal differentiation began after 35 days of incubation with the beginning of the organization of sexual cords in the seminiferous tubules. The stages of gonadal differentiation were similar to those of other species of turtles with temperature determined sex, however in this study, using the pivotal temperature described for the species all the individuals analyzed were males, and it is there for necessary to carry out further studies using a higher incubation temperature.(AU)

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