Caiman Crocodilus Research Articles

Mass transfer modeling during wet salting of caiman meat (Caiman crocodilus yacare) at different brine temperatures

Caiman meat is considered exotic and its consumption has significantly increased due to its nutritional quality. This study aimed to evaluate the kinetics of water content (WC) and salt content (SC) at different temperatures (1, 5, 10 and 15 °C) and to evaluate the use of mathematical models to predict the mass transfer kinetics until equilibrium conditions during the wet salting of caiman tail fillets. Moisture and chloride analyses were performed throughout the wet salting process. Four models (Peleg; Weibull; Zugarramurdi and Lupín; Diffusion) were tested to predict WC and SC kinetics in caiman tail fillets subjected to wet salting. The increase in the temperature resulted in a reduction (P < 0.05) in WC and an increase (P < 0.05) in SC. Nonlinear effects on WC and SC kinetics were observed between the different temperatures evaluated. Furthermore, the effective diffusion coefficients (Dw and Ds) increased (P < 0.05) with increasing temperature. Peleg, Weibull, Zugarramurdi and Lupín, and the Diffusion model satisfactorily represented WC and SC rates throughout the process. The kinetic behavior of the parameters of the models corroborated the effects of temperature on those parameters. Peleg was the best model for predicting WC and SC kinetics, and Zugarramurdi and Lupín was the best for predicting the equilibrium conditions of the process (WC∞ SC∞), all parameters which can be used to describe the mass transfer kinetics during wet salting of caiman tail fillets.

Phylogeographical analysis and phylogenetic inference based on the cytochromebgene in the genusCaiman(Crocodylia: Alligatoridae) in Central and South America

AbstractThe genus Caiman is one of the most taxonomically conflicted among crocodilians. Caiman crocodilus has four subspecies: Caiman crocodilus crocodilus, Caiman crocodilus fuscus, Caiman crocodilus chiapasius and Caiman crocodilus apaporiensis, but some studies recognize Caiman yacare as a subspecies of C. crocodilus or as a C. crocodilus–C. yacare complex. In Argentina, Caiman latirostris and C. yacare are present and included in sustainable use programmes, although they have hardly been studied at the genetic level. The present study had two main objectives: (1) to study the genetic diversity, structure and phylogeny of C. yacare and C. latirostris in Argentina; and (2) to perform a phylogenetic analysis of the genus Caiman throughout its entire distribution. The results show high haplotype diversity for both species but low nucleotide diversity for C. latirostris. Phylogenetic analysis shows a clear separation between both species but, surprisingly, a well-differentiated clade belonging to the Chaco region was observed. The phylogenetic analysis exhibited clades made up of the sequences of each Caiman species, with some inconsistencies: in the clade of C. crocodilus, one sequence of C. yacare is included, and one clade is observed including sequences from C. c. fuscus and C. c. chiapasius. These data indicate the need to undertake interdisciplinary studies to clarify the taxonomic status of these crocodilian species.

Phylogenetic and phylogeographic insights on Trans-Andean spectacled caiman populations in Colombia

Context Spectacled caiman (Caiman crocodilus) is a species complex with at least eight phylogenetic lineages distributed across Central and South America. However, several populations remain unstudied, which limits a clear understanding of the relationship among lineages as well as whether all hidden diversity has been unveiled. Aim We analysed the molecular variation of spectacled caiman populations inhabiting the Colombian Trans-Andean range based on cytochrome oxidase I (COI) and cytochrome B (CytB) mitochondrial markers. Methods We performed phylogenetic and population genetic analysis to identify phylogeographic patterns and verify genetic variation across Trans-Andean spectacled caiman by using a dataset of 78 individuals from 15 localities across Colombia. Results Haplotype accumulation curve estimated that our sample sizes recovered 82.68% of all unique haplotypes. Analysis of molecular variance showed that most of the genetic variation across the Trans-Andean samples collected can be explained by macro basins (49.85%), 32.45% by localities and 17.70% by intra-specific variation within populations. Conclusions Our study confirmed that high nucleotide diversity is present in Colombian Trans-Andean spectacled caiman populations, the absence of a genetically distinguished lineage in the Choco region, as suggested by morphologic analysis, and the presence of only one molecularly well distinguished group (C. c. fuscus sensu stricto) in the in the Colombian Trans-Andean region.

What is the potential for extirpating spectacled caiman from Comprehensive Everglades Restoration Plan projects in South Florida?

What is the potential for extirpating spectacled caiman from Comprehensive Everglades Restoration Plan projects in South Florida?

Nutritional properties of spectacled caiman (Caiman yacare) meat marketed as part of a wildlife management strategy in the Beni river basin

We determined the nutritional quality of yacare meat (Caiman yacare) in the Beni river basin. Commercial cut samples were obtained from the tails of four males harvested as part of a management plan implemented in the Tacana Indigenous Territory. This plan guarantees long-term sustainability of caiman hunting. pH analysis, the Eber test, and the ammoniacal nitrogen test suggest that the meat was of good quality, processed properly, and free of contamination. Nutritional analyses suggest that yacare meat is a healthy alternative for human consumption, as it has a high protein value (23.02 g/100g) and low fat concentration (0.67g/100g). Yacare meat has a high concentration of minerals such as phosphorus (227.53 g) and calcium (11.84 g), both beneficial for memory and cardiovascular health. Caiman meat can be considered as a valuable nutritional supplement in human diets both in urban and rural areas

Landscape features affect caiman body condition in the middle Araguaia River floodplain

AbstractLandscape modifications often undermine habitat suitability for species’ persistence, with initial effects observed through the physiological responses of individuals and populations. However, some landscape features can allow tolerant wildlife species to persist in human‐modified landscapes, but they are still overlooked. Across distinct agricultural landscapes, we assessed landscape features affecting the body condition (estimate through scaled mass index ‐ SMI) of Caiman crocodilus (Crocodylia, Alligatoridae) in human‐modified landscapes of the Araguaia floodplain, central Brazil. We used a spatial Bayesian model averaging approach to determine the effects of landscape attributes, ectoparasites, tail damage and severe body injuries on caiman body condition. We found that caimans had higher SMI in anthropogenic (ditches and artificial ponds) than natural habitats (lakes or rivers). Overall, caiman SMI was negatively associated with wetland cohesion (an aggregation and connectivity metric). Otherwise, landscape composition did not influence caiman SMI. Further, ectoparasites and body injuries did not affect SMI, whereas tail damage negatively affected SMI. Our findings underscore that caiman populations can adapt to artificial wetlands and irrigated rice fields, provided they incorporate natural and semi‐natural habitat patches that enhance environmental heterogeneity, prey availability, and waterbody availability and connectivity.

Molecular Characterization of Salmonella spp. Isolates from Wild Colombian Babilla (Caiman crocodilus fuscus) Isolated In Situ.

Salmonella enterica is a pathogen capable of colonizing various environments, including the intestinal tract of different animals such as mammals, birds, and reptiles, which can act as carriers. S. enterica infection induces different clinical diseases, gastroenteritis being the most common, which in some cases, can evolve to septicemia and meningitis. Reptiles and amphibians have been reported as a reservoir of Salmonella, and transmission of the pathogen to humans has been documented. This study aimed to determine the presence of virulence genes and characterize the genotypic antibiotic resistance profile in Salmonella strains isolated from Caiman crocodilus fuscus obtained in situ (natural habitat) in Prado, Tolima, Colombia in a previous study and stored in a strain bank in our laboratory. Fifteen Salmonella strains were evaluated through endpoint PCR to determine the presence of resistance genes and virulence genes. The genes blaTEM, strB, and sul1 were detected in all the strains that confer resistance to ampicillin, streptomycin, and sulfamethoxazole, as well as the virulence genes invA, pefA, prgH, spaN, tolC, sipB, sitC, pagC, msgA, spiA, sopB, sifA, lpfA, csgA, hilA, orgA, iroN, avrA, and sivH, indicating the possible role of babilla (Caiman crocodilus fuscus) as a carrier of multidrug-resistant bacteria.

Nuclei and tracts in the pretectum and associated tegmentum of crocodiles.

In all vertebrates, the pretectum and associated tegmentum arise from prosomere 1, but the adult derivatives of these embryonic regions are not well defined in reptiles-especially in crocodiles, the reptilian group most closely related to birds. Despite its importance in vision and visuomotor behavior, descriptions of the pretectum in crocodiles are brief and photographs are lacking. To fill this gap in knowledge, the pretectum and associated tegmentum were examined in two crocodilians, Caiman crocodilus and Alligator mississippiensis, using a variety of histological stains in all three traditional planes of section. These observations were compared with similar studies in other reptiles and birds. These comparisons were hampered by differences in nomenclature and limited data. Nevertheless, pretectal nuclei in receipt of retinal input in crocodiles, other reptiles, and birds were the most easily identified when compared with the present analysis. Despite identifying the traditional nuclei comprising the pretectum of crocodiles, other areas remain to be characterized. Nevertheless, knowledge gained from this description will aid further investigations of this brain region in crocodiles and other reptiles as well as provide a reference for developmental studies in crocodiles.

First Isolation of Yarrowia lipolytica in a Granulomatous Pneumonia of a Spectacled Caiman, Caiman crocodilus Linnaeus, 1758.

Contrary to humans, candidiasis is a rare infection in animals. However, in reptiles, candidiasis can cause gastrointestinal, cutaneous, or rarely systemic infections in stressed animals. The infections due to Yarrowia lipolytica have been increasingly described in human medicine, and hundreds of cases are reported, comprised of granulomatous lung lesions. Herein, granulomatous pneumonia of a spectacled caiman, Caiman crocodilus, was described, and the presence of Y. lipolytica in the lesion was confirmed through histopathology, microbiologic cultures, and molecular methods. The cause of death of the spectacled caiman was ascribed to bacterial shock septicemia consequentially to a traumatic lesion. However, in the right lung, several nodules containing white exudate were evidenced. At mycological and molecular analyses, Y. lipolytica was evidenced, and the histological finding confirmed the presence of a Candida infection in the lung granulomatous lesions. The comparison of ITS sequences with 11 Yarrowia spp. isolates, recently described in green sea turtles, and with a human strain was conducted, and the whole genome of a strain isolated in the spectacled caiman was sequenced. Even though Y. lipolytica is considered a non-pathogenic yeast and has been rarely described in animals, it seems to cause granulomatous lesions in reptiles as in humans.

Update: Assessing the evolutionary trajectory of the Apaporis caiman (Caiman crocodilus apaporiensis, Medem 1955) via mitochondrial molecular markers

Abstract The spectacled caiman (Caiman crocodilus) is currently considered to be a species complex due to the relatively high morphological and molecular diversity expressed across its range. One of the populations of interest, inhabiting the Apaporis River (Colombia), was described based on skull features as an incipient species (C. c. apaporiensis) and has been treated by some authors as a full species. Recent molecular work challenged this hypothesis, because relatively low mitochondrial molecular differentiation was found between the morphologically described Apaporis caiman and C. crocodilus (s.s.) Amazonian populations. Here, we present an update on the topic based on a larger molecular sample size and on analysis of expanded geometric morphometric data that include six newly collected skulls. Morphometric data support the existence of previously recognized morphotypes within the complex in Colombia and demonstrate that the newly collected material can be assigned to the classic Apaporis caiman morphotype. However, our expanded genetic analysis fails to find appreciable mitochondrial molecular divergence of the Apaporis caiman population from the C. c. crocodilus population (COI-CytB: Amazon Peru 0.17 ± 0.06%, CytB-only: Caquetá River Colombia 0.08 ± 0.07%). The Apaporis caiman is interpreted to be a phenotypically distinct member of the cis-Andean C. crocodilus metapopulation that has not yet achieved (or may not be undergoing at all) appreciable genetic differentiation. Thus, it should not be considered a fully independent evolutionary lineage, nor given full species rank.

Relationships between stable isotopes and trace element concentrations in the crocodilian community of French Guiana.

Trace elements in the blood of crocodilians and the factors that influence their concentrations are overall poorly documented. However, determination of influencing factors is crucial to assess the relevance of caimans as bioindicators of environmental contamination, and potential toxicological impact of trace elements on these reptiles. In the present study, we determined the concentrations of 14 trace elements (Ag, As, Cd, Cr, Co, Cu, Fe, Hg, Pb, Mn, Ni, Se, V, and Zn) in the blood of four French Guiana caiman species (the Spectacled Caiman Caiman crocodilus [n = 34], the Black Caiman Melanosuchus niger [n = 25], the Dwarf Caiman Paleosuchus palpebrosus [n = 5] and the Smooth-fronted Caiman Paleosuchus trigonatus [n = 20]) from 8 different sites, and further investigated the influence of individual body size and stable isotopes as proxies of foraging habitat and trophic position on trace element concentrations. Trophic position was identified to be an important factor influencing trace element concentrations in the four caiman species and explained interspecific variations. These findings highlight the need to consider trophic ecology when crocodilians are used as bioindicators of trace element contamination in environmental studies.

Population Ecology and Human Disturbance Effects on Two Caiman Species in the Southern Brazilian Amazon

Although caiman populations are being conserved in some protected areas, they face threats related to human pressure, which may ultimately influence their distribution, abundance, and behavior. In this study, we investigated the population ecology (encounter rate, size structure, sex ratio, and injury frequency) and the effects of human disturbance on Melanosuchus niger and Caiman crocodilus populations in Cantão State Park, southern Brazilian Amazon, Central Brazil. We assessed human pressure on both populations, testing the human disturbance–abundance and human disturbance–size structure relationships. We sampled waterbodies within (lakes) and adjacent to (river) protected areas via nocturnal surveys and captures. Human pressure in the river was assessed and categorized via transects with low, medium, and high levels of disturbance. Our results indicate that C. crocodilus was more abundant than M. niger, with populations of both species mainly composed of juvenile males. We also observed that injuries were more prevalent in juveniles and males. Human disturbance negatively affected C. crocodilus abundance, but no effect was found for M. niger. We found no significant effect of human disturbance on size structure for either species; however, the response for each species differed. Snout–vent length (SVL) decreased with increasing human pressure level in the C. crocodilus population, whereas M. niger showed a greater SVL at higher human pressure levels. Our results suggest that human disturbance related to boat traffic, pollution, riverine population, land use, and human activities negatively influence crocodilian populations in their distribution through a distance–abundance relationship. Additionally, the proximity of settlements and accessibility to protected areas are factors related to human disturbance and should be considered in government decisions and the management of protected areas by environmental agencies. Our results improve our understanding caiman population responses to human disturbance.

Characterization of Jaguar Utilization Distributions in the Brazilian Pantanal

Jaguars (Panthera onca) have been eradicated from 50% of their historical range across Mexico, Central America, and South America. The Brazilian Pantanal in west-central Brazil represents a stronghold of core habitat for the species and is an important site for conservation. Habitat in the Pantanal is threatened largely due to expanding human activity causing habitat loss and fragmentation, making remaining habitat vitally significant. This study seeks to characterize the utilization distributions of jaguars in the area to better understand the habitat use and spatial ecology of a threatened species. GPS locations taken from 13 jaguars were used to calculate estimates of kernelhomesrangesatthe50% (core range)and 95% (home range)isopleth levels. These ranges were used to quantify habitat use in relation to land cover types. Patterns of distribution heavily followed waterways, perhaps following that of their main prey,caimans(Caiman crocodilus yacare). Wetlands were the most heavily utilized among all jaguars at the 95% home range followed by grasslands. However, at the 50% core range level there was a shift in greater utilization of forest habitat over grassland. Additionally, females generally had smaller home ranges than that of males and exhibited less overlap between home ranges(27 km2) than between male home ranges(217 km2) – a key indicator of female spatial avoidance.

Effect of gamma irradiation on the quality characteristics of frozen yacare caiman (Caiman crocodilus yacare) meat

This study investigated the effect of gamma irradiation (0, 3 and 5 kGy) on the quality characteristics of yacare caiman (Caiman crocodilus yacare) meat under typical storage and commercialization conditions (−18 °C for 150 days). The overall quality characteristics (texture profile, TBARS values, water-holding capacity and cooking loss) of the irradiated samples were not significantly affected (P > 0.05) during frozen storage. However, irradiation promoted the formation of volatile compounds from lipid oxidation known to be important markers in meat odor, particularly hexanal, pentanal and 1-hexanol, in samples treated with 5 kGy after 150 days of frozen storage. The results obtained indicate the need for further research to determine the effect of the doses tested on the sensory attributes of yacare caiman meat.

Physiological stress response in free-living Amazonian caimans following experimental capture.

When captured, free-living crocodilians respond by hyperstimulation of the hypothalamic-pituitary-adrenal (HPA) axis, which triggers a cascade of downstream events of physiological stress. We examined these responses in two unstressed, and stressed Amazonian caimans, Caiman crocodilus and Melanosuchus niger. Plasma corticosterone levels increased in both stressed caiman species. In M. niger, the levels of this hormone increased 5.2-fold compared with the basal range values, while in C. crocodilus this was only 1.7-fold. After stress, M. niger needed more than 6 h to return its corticosterone levels to basal range values, whereas in C. crocodilus just 0.5 h was enough. Downstream events were characterized by an increase in glucose levels, which is associated with corticosterone increments. Excessive muscle activity resulted in increased plasma lactate content in both species. Lactate levels were also related to plasma calcium concentration, possibly due to the buffering capacity for preventing lactic acidosis. Clearance of excessive lactate load was faster in M. niger (0.5 h) than in C. crocodilus (more than 6 h). Although both caiman species respond in the same way to capture, the amplitude and duration of activation of the HPA axis are different. M. niger may be potentially more sensitive to acute stress than C. crocodilus. On the other hand, C. crocodilus needs more time to recover from the lactic acid load. Our experiment provides a useful diagnostic tool for management and conservation programs, as well as evaluating the impacts of tourism and recreational capture on caimans in the Amazon.

A draft genome sequence of the common, or spectacled caiman Caiman crocodilus

The common, or spectacled, caiman Caiman crocodilus is an abundant, widely distributed Neotropical crocodilian exhibiting notable morphological and molecular diversification. The species also accounts by far for the largest share of crocodilian hides on the global market, with the C. crocodilus hide trade alone valued at about US$86.5 million per year. We obtained 239,911,946 paired-end reads comprising approximately 72 G bases using IlluminaTM sequencing of tissue sampled from a single Caiman crocodilus individual. These reads were de-novo assembled and progressively aligned against the genomes of increasingly related crocodilians; liftoff was used to annotate the draft C. crocodilus genome assembly based on an Alligator mississipiensis (a confamilial species) annotation. The draft assembly has been submitted to the National Center for Biotechnology Information and both assembly and annotation are currently available for review at doi.org/10.5281/zenodo.4755063

Population status of the American crocodile, &lt;em&gt;Crocodylus acutus&lt;/em&gt; (Reptilia: Crocodylidae) and the spectacled caiman, &lt;em&gt;Caiman crocodilus&lt;/em&gt; (Reptilia: Alligatoridae) in the Costa Rican North Caribbean

Along the Costa Rican Caribbean shoreline, it is possible to find two species of crocodilians, the American crocodile (Crocodylus acutus) and the spectacled caiman (Caiman crocodilus). This region can be divided geographically into three subregions: North, Central, and South Caribbean. We conducted this research in the North Caribbean, between October 6, 2018 and August 31, 2019. Specifically, we worked in the area lying between the Jalova Station of the Tortugero National Park (TNP) and Agua Dulce Lake situated in the northern tip of Machuca Island, at the mouth of the Colorado River inside the Barra del Colorado National Wildlife Refuge (BACORE), which includes other connecting wetlands as well (Sierpe River, Samay Lake). Overall, this study area had an approximate extension of 408 km2 characterized by large, wide and deep canals, as well as wetlands, meanders, and adjacent lakes. The sampling was performed along 10 segments that varied in length from 7.5 km up to 29.49 km, located in the nearby zones of TNP and BACORE. In these zones, nightly counts were carried out using dazzling lamps. Individuals of C. acutus and C. crocodilus were classified into eight and six body size classes, respectively (both with 50 cm intervals). A relative abundance of 0.55 crocodiles and 1.37 caimans per linear kilometer was estimated during these spotlight surveys. The capture of 39 caimans let us to estimate a ratio of 30 males to 9 females (3.3:1 M:F). In stark contrast, only 1 male and 1 female crocodile were captured. A total of 85 C. acutus and 205 C. crocodilus were observed. Regarding the number of caiman sightings in the TNP, a statistically significant difference was found (Χ2=5.62, p≤0.05) for the distribution by sizes between the zones of BACORE and TNP, whereas no such difference was found for C. crocodilus sightings (Z=–1.22, p≥0.222). Some segments had a higher probability of caiman occurrence than did others in the surveys performed during the monitoring period (X2=8.36, p≤0.05), especially the Jalova-Sierpe River, Caño Negro-Tortuguero, and Tortuguero-Samay Lake (Tortuguero subarea) segments. Ninety percent of the sightings occurred in the BACORE zone, and this was significantly different (Χ2=7.34, p≤0.026) from the studied subareas. The number of crocodile sightings in the Colorado River segment was significantly different and higher than the other segments (X2=7.28, p≤0.05). There was a significant statistical difference among the sizes in all areas of study (X2=5.529, p≤0.026). The abundance of C. acutus and C. crocodilus in the north Caribbean part is lower than in the central Caribbean part of Costa Rica, where this species could use the resources available in more urbanized areas.

Molecular characterization of the spectacled caiman (Caiman crocodilus) in the upper Magdalena River basin, Colombia: Demographic and phylogeographic insights

Maintenance of high levels of genetic diversity is crucial for the recovery of overexploited species and gaining knowledge of genetic diversity of natural populations is crucial to define effective conservation strategies. Spectacled caimans (Caiman crocodilus) were unsustainably exploited for decades in Colombia causing drastic population reductions with unknown effects on genetic structure. We molecularly characterized three spectacled caiman populations from the upper Magdalena River basin (UMRB), analyzing them within the context of the trans-Andean C. c. fuscus sensu stricto lineage, assessing nucleotide and genetic diversity, demographic history, and phylogeography at different scales. Seventeen of the 23 mitochondrial haplotypes currently described for Colombia are present in the UMRB, showing high levels of genetic diversity even when compared with the trans-Andean region (uncorrected genetic distances 0.00-0.87%). Mutational steps between closest haplotypes ranged from one to four while the most differentiated haplotypes were separated by 19 mutational steps across the whole trans-Andean region. Distribution of pairwise nucleotide differences and raggedness tests showed unimodal patterns of mismatch distribution curves fitting the sudden expansion model. Average time since demographic expansion for UMRB, Colombia, and trans-Andean region were inferred as 10,540, 7,591, and 7,071 years before present, respectively, placing the latest expansion close to the Pleistocene-Holocene boundary. Intriguingly, samples from Tolima were overall more related to those collected from Panama and Costa Rica (0.34 ± 0.15%) than the ones collected across Choco (0.45 ± 0.15%), Cauca (0.70 ± 0.09%), and Nariño (0.60 ± 0.14%) departments. We discuss our genetic findings in the context of the management policies carried out in the country during the last decades (unsustainable and sustainable use, and population restocking), evaluating the implications of these events for the genetic integrity and conservation of the species.

Effects of the Belo Monte hydro-electric-dam complex on crocodilians in the Xingu River, Brazilian Amazonia

Abstract The Belo Monte hydroelectric dam on the Xingu River has the third largest generating capacity of any hydroelectric dam in the world. We conducted surveys of crocodilians (Caiman crocodilus, Paleosuchus trigonatus) by boat in the Xingu River at the site of the dam prior to (2013-2015), and after filling (2016-2017). While the number of C. crocodilus sighted decreased with increasing water level, there was no difference in numbers prior to, and after reservoir filling. The number of P. trigonatus was unaffected by both water level prior to and after reservoir filling. Reservoir filling had little effect on the number of crocodilians using the forest around the Xingu River reservoir. Most crocodilians seen in forest surveys were P. trigonatus, both before and after reservoir filling, but C. crocodilus was recorded occasionally in the forest. It seems that most Amazonian crocodilians are sufficiently generalist to adapt to the new conditions created by the construction of dams, at least in the short-term. However, there may be long-term collateral effects on crocodilian populations from dams, due to as deforestation and improved access for hunters.

New insights into the allosteric effects of CO2 and bicarbonate on crocodilian hemoglobin.

Crocodilians are unique among vertebrates in that their hemoglobin (Hb) O2 binding is allosterically regulated by bicarbonate, which forms in red blood cells upon hydration of CO2. Although known for decades, this remarkable mode of allosteric control has not yet been experimentally verified with direct evidence of bicarbonate binding to crocodilian Hb, probably because of confounding CO2-mediated effects. Here, we provide the first quantitative analysis of the separate allosteric effects of CO2 and bicarbonate on purified Hb of the spectacled caiman (Caiman crocodilus). Using thin-layer gas diffusion chamber and Tucker chamber techniques, we demonstrate that both CO2 and bicarbonate bind to Hb with high affinity and strongly decrease O2 saturation of Hb. We propose that both effectors bind to an unidentified positively charged site containing a reactive amino group in the low-O2 affinity T conformation of Hb. These results provide the first experimental evidence that bicarbonate binds directly to crocodilian Hb and promotes O2 delivery independently of CO2. Using the gas diffusion chamber, we observed similar effects in Hbs of a phylogenetically diverse set of other caiman, alligator and crocodile species, suggesting that the unique mode of allosteric regulation by CO2 and bicarbonate evolved >80-100 million years ago in the common ancestor of crocodilians. Our results show a tight and unusual linkage between O2 and CO2 transport in the blood of crocodilians, where the build-up of erytrocytic CO2 and bicarbonate ions during breath-hold diving or digestion facilitates O2 delivery, while Hb desaturation facilitates CO2 transport as protein-bound CO2 and bicarbonate.