Morelet's Crocodile Research Articles

Variation in the Diet of Hatchling Morelet's Crocodile (Crocodylus moreletii) in the Wild.

The relationship between diet and behavior is essential to understanding an animal's strategies to obtain food, considering ontogenical changes. In reptiles, there is a relationship between the length of the individual and the size of the prey it consumes. Studies have focused on the ontogenetic changes in reptile diets from hatchling to adult, but only a few studies have focused on the transition from hatchling to juvenile. We aimed to describe and analyze the composition, variation, diversity, and overlap in the diet of hatchling Morelet's crocodiles (Crocodylus moreletii) for three size intervals during the hatchling-juvenile transition. We captured 31 hatchling Morelet's crocodiles in an urbanized lagoon in Tabasco. We performed stomach-flushing to determine the diet. Additionally, we estimated the volume, frequency of occurrence, and relative importance of diet items and analyzed the relationship between prey type and the total length of the individuals. The diversity of the hatchling prey suggests a generalist diet. We observed two items not previously described in the diet of hatchling crocodiles. In addition, we found differences in diet between the initial and final size intervals, as increases in the length of prey appeared that they did not consume when they were hatchlings. Our results contribute new information to the dietary changes that occur during the hatchling-juvenile transition.

Length and weight of farmed young Morelet's crocodiles (Crocodylus moreletii) as predictors of their future size

The aim of the study was to determine the earliest time at which the future size (length and weight) of farmed Morelet's crocodiles (Crocodylus moreletii) can be accurately predicted, to establish selection criteria in these individuals. A total of 8040 crocodiles (7394 males and 646 females) hatched from artificially incubated eggs were included. In each crocodile the total length and weight were measured on days 1, 132, 248, 364, 500, 616, 750, and 878 of age. On day 878 crocodiles were classified into five size groups: runt (RT), small (SL), medium (MM), large (LG), and extra-large (EL). The association between evaluations for length and weight, the correlation between length and weight in each measurement, and the differences in length and weight between assessments and sex were determined. Analysis from day 132 through day 878 included both sexes together. Neither length nor weight on day one correlated (> 0.40) with any subsequent evaluation. There was no difference among groups (P > 0.05) between length on day one and size on day 878. Difference was found between length on day 132 and size on day 878 in RT (P < 0.05), and between length on days 248, 364, 616, and 750 and size on day 878 in all the groups (P < 0.05). Difference was found between weight on day one and size on day 878 only in SL (P < 0.05), and between weight on days 132, 248, 364, 616, and 750 and size on day 878 in all the groups (P < 0.05). The size farmed Morelet's crocodiles will have at 878 days can be predicted with weight at 132 and length at 248 days. Use of the ranges of the size groups as selection criteria for growth will allow selecting the future smallest and largest individuals early in the production cycle and to enhance sustainable management of this species.

Effectiveness of Morelet's crocodile as a bioindicator of metal pollution and metallothionein response to spatial variations of metal exposure

• Significant differences for mercury between the factors tissue:site were detected. • Significant differences for zinc between the factors tissue:site were detected. • Metallothioneins in blood plasma were detected in all sites but in erythrocytes detection frequency was lower than 20%. Several studies have assessed the potential of crocodylians as bioindicators of environmental contamination. In this study, the Morelet's crocodile ( Crocodylus moreletii ) was used as a bioindicator of metal pollution across five locations in southeastern Mexico classified as having high, medium, and low anthropogenic impact. Total length and sex were determined for each animal and concentrations of metals and metallothioneins (MTs) were determined by using non-destructive tissues. Mercury (Hg) concentrations in crocodile blood and scutes generally exhibited a decreasing pattern from the higher impacted site to the lower impacted site ( x 2 (14) = 185.42, p < 0.001), suggesting that concentrations in these samples are sensitive enough to identify difference in the bioavailability of Hg within crocodile populations. The highest concentrations were detected in scutes from Laguna Guerrero (Hg = 0.60 ± 0.217 µg/g w.w.) and Nichupté-Bojorquez (Cd = 14.99 ± 2.95 µg/g w.w., Cu = 58.66 ± 11.29 µg/g w.w., Zn = 80.86 ± 80.54 µg/g w.w.). MTs in blood plasma were detected at all sites (27.48 ± 4.78 µg/mL) but was low in erythrocytes detection frequency, suggesting this latter fraction may not be useful for MTs analysis. In general, our study supports the utility of crocodiles as bioindicators of xenobiotic metal pollution. However, it is necessary for such studies to perform assays for specific MT isoforms and the effective concentrations of metals bound to this protein, and to determine metal concentrations in multiple environmental matrices from the sites under evaluation.

Stress responses in captive Crocodylus moreletii associated with metal exposure

Environmental pollution by metals has repercussions on wildlife health. It is known that some metals can have an influence on the neuroendocrine stress response, and at the same time, metals have pro-oxidant effects that can overwhelm the antioxidant system and cause oxidative stress. This study evaluates the association of metals with neuroendocrine stress activity and biomarkers of oxidative stress in 42 captive female Morelet's crocodiles (Crocodylus moreletii). We measured five metals of ecotoxicological importance (Hg, Cd, Pb, Cu and Zn), and three biomarkers of the oxidative stress response in the liver: glutathione (GSH) and glutathione disulfide (GSSG) as markers for antioxidant system and thiobarbituric acid reactive substances (TBARS) for oxidative damage. We also measured one biomarker of the neuroendocrine response to stress: corticosterone (B) in blood plasma. The mean ± SD concentrations of metals in the liver expressed in μg/g (dw) were: Cd: 0.004 ± 0.003, Hg: 0.014 ± 0.019, Cu: 0.017 ± 0.013, Zn: 0.043 ± 0.035, Pb: 0.16 ± 0.256. The mean ± SD of GSH was 0.42 ± 0.35 nmol/mg protein, the mean ± SD of GSSG was 0.24 ± 0.20 nmol/mg protein, the mean ± SD concentrations of TBARS were 0.36 ± 0.21 nmol/mg protein, and the mean ± SD of B was 393.57 ± 405.14 pg/mL. Hg presented a significant negative relationship with corticosterone. Cd had a negative relationship with both GSH and GSSG; meanwhile, Zn showed a negative relationship with TBARS levels, could be a protective element against hepatic oxidative damage. Finally, B had negative relationship with oxidative damage. The connection found between Hg and the neuroendocrine stress response, as well as the correlations of Cd and Zn with oxidative damage and antioxidant activity should be studied further, given their toxicological importance and implications for the conservation of C. moreletii and other crocodilians.

Effectiveness of Morelet's Crocodile as a Bioindicator of Metal Pollution and Metallothionein Response to Spatial Variations of Metal Exposure

Effectiveness of Morelet's Crocodile as a Bioindicator of Metal Pollution and Metallothionein Response to Spatial Variations of Metal Exposure

Assessment of wildlife crime in a high-biodiversity region of Mexico

Wildlife crime, including illegal harvesting, poaching, use, and trade, is a global issue. While studies on wildlife crimes have been performed on a global scale, it is also essential to assess their impact on native species at national scales. Investigating illegal activities involves analyzing law enforcement and seizure data, especially in areas with high biodiversity. In this study, we analyzed the effects of wildlife crime on native wild vertebrates of Oaxaca, southern Mexico, from 2004 to 2018. We used data from law enforcement by Mexican authorities on activities that affect vertebrates: trafficking, illegal possession, exploitation, breaking of hunting laws, permit breaches, and illegal scientific collecting. Oaxaca has a high incidence of wildlife crime, and illegal trading accounts for 38 % of wildlife law violations (62 % are other illegal activities). In addition, 8047 specimens of 226 species were seized during the study period, of which 54 % are considered endangered in Mexico or worldwide. Reptiles accounted for the highest number of individual specimens, while birds recorded the greatest range of species. The main species seized were green iguana (Iguana iguana), black iguana (Ctenosaura pectinata), Morelet's crocodile (Crocodylus moreletii), olive ridley turtle (Lepidochelys olivacea), orange-fronted parakeet (Aratinga canicularis), and white-tailed deer (Odocoileus virginianus). Many of these seizures were made close to roads. Our results support the understanding that illegal trade reports are underestimates. This study allows us to have a greater understanding of the real magnitude of the problem. We hope this research will inform policies and strategies to combat the illegal activities that affect wildlife in regions with high biodiversity.

Using regression tree analysis to determine size class intervals and sexual dimorphism in the Morelet's crocodile Crocodylus moreletii

Assignment of Morelet's crocodile Crocodylus moreletii individuals into size groups or classes based on ecological and morphological similarities has not yet been associated with species‐specific ontogeny related changes. Age or size of first reproductive behavior is not precisely known for C. moreletii, but differences in allometric patterns and relative cranial size between juveniles and adults might be used as an indicator of sexual maturity. In this study, a regression tree analysis was used to investigate the relationship between age and body size in 1266 crocodiles by using both simple and generalized linear models, with gender and origin (captivity or wild) as factors. Total length (TL), snout–vent length (SVL) and cranial length (CL) were used as predictor variables and the logarithm of body mass as the response variable. Four length intervals with well‐defined thresholds (514, 899 and 1497 mm of TL) were established using all three predictors (TL, SVL and CL). Relationship between SVL and TL was described, and a strong positive relationship (r2 = 0.98), unaffected by crocodile gender, was observed. The observed CL–TL and CL–SVL relationships were also positive but significantly different between males and females (p &lt; 0.001) and length interval classes (p = 0.01). These results suggest that our estimated size thresholds seem to correspond to important ontogenetic changes in C. moreletii and that sexual maturity is closely related to size in this species, where sexual dimorphism in body length occurs, particularly in large individuals (size group IV).

Phylogenomics reveals novel relationships among Neotropical crocodiles (Crocodylus spp.)

Extant species in the order Crocodylia are remnants of an ancient lineage of large-bodied archosaur reptiles. Despite decades of systematic studies, phylogenetic relationships among members of the genus Crocodylus (true crocodiles) in the Neotropics are poorly understood. Here we estimated phylogenomic relationships among the four extant Crocodylus species in the Americas. Species-tree reconstructions using genotypic data from 17,538 SNPs collected for 33 individuals spanning six Crocodylus species (four ingroup and two outgroup) revealed novel relationships for all Neotropical species. For the first time, C. acutus, the American crocodile, was recovered as monophyletic when individuals from Antillean and continental populations were analyzed together. Our results also contradict previous inferences based on mitochondrial DNA data and a limited number of nuclear markers by robustly grouping Morelet's crocodile (C. moreletii) as the sister species to C. acutus, suggesting a novel phylogeographic hypothesis for the group. The present study punctuates the importance of using nuclear genome-wide information and representative sampling for resolving phylogenetic relationships, especially in broadly distributed species and those with complex evolutionary histories.

Nest-site selection and nest size influence the incubation temperature of Morelet's crocodiles.

In oviparous tetrapods, the nesting-site selection by females is related to the habitat characteristics, which influences nest incubation temperature. Females can directly influence the incubation temperature by choosing certain construction materials or by building nests of different sizes. There are few studies focusing on these aspects in crocodilians that build mound nests. The aim of this study was to determine whether the nest size, its exposure to solar radiation, and the environmental temperature influence the incubation temperature of Morelet's crocodile (Crocodylus moreletii) nests. Artificial nests of two sizes (small and large) were constructed with similar characteristics to natural nests and placed in two locations differing in exposure to solar radiation (shaded and sunny). We used temperature and relative humidity data loggers to record the incubation temperature inside each nest every hour during the species' natural nesting period. Likewise, we recorded the ambient temperature every hour where the experiments were set up with temperature data loggers. We found that nest size and its exposure to solar radiation affected the incubation temperature, with smaller nests in shaded locations having lower incubation temperatures than larger nests in sunny locations. We discuss the importance of nest-site selection and maintenance behaviour of the mound nest by female crocodiles on the incubation temperature of the nest.

Record of Haementeria acuecueyetzin (Oceguera-Figueroa, 2008) in Morelet's Crocodiles from Quintana Roo, Mexico

Herein, we present the first Mexican record of Morelet's crocodile, Crocodylus moreletii, as a host for the proboscis-bearing leech, Haementeria acuecueyetzin. From November 2004 to October 2017, we captured 111 crocodiles during spotlight surveys in lagoons of the Dziuche ejido, municipality of Jose Maria Morelos, Quintana Roo, Mexico. Twenty-one (18.9%) individuals had leeches identified as H. acuecueyetzin. It is the first report of H. acuecueyetzin for the State of Quintana Roo, Mexico, and the northernmost record of the species. This is also the second case of leech parasitism in C. moreletii. Haementeria acuecueyetzin likely parasitize a large array of vertebrates, and its role as a potential vector of blood parasites in C. moreletii requires further investigation.

Distribution of metals in tissues of captive and wild Morelet's crocodiles and the potential of metallothioneins in blood fractions as a biomarker of metal exposure.

The distribution of Hg, Cd, Cu, and Zn in keratinized tissues, blood fractions, and excretory organs, and MTs in blood fractions and excretory organs was determined in captive, semicaptive, and wild Morelet's crocodiles and they were compared to select the most useful non-destructive tissues for the monitoring of metal exposure and to assess the potential of MTs as a biomarker. Our results indicate blood plasma, claws, and caudal scutes altogether are suitable tissues for xenobiotic metals exposure, with concentrations in blood plasma being an indicator of recent exposure, whereas concentrations in claws and caudal scutes are indicators of chronic exposure. Results in keratinized tissues suggest they are an important detoxification strategy in crocodiles, and claws presented the highest concentrations of metals in both captive (Hg=0.44±0.23μgg-1, Cd=11.10±5.89μgg-1, Cu=45.98±23.18μgg-1, Zn=124.75±75.84μgg-1) and wild populations (Hg=1.31±0.32μgg-1, Cd=26.47±21.15μgg-1, Cu=191.75±165.91μgg-1, Zn=265.81±90.62μgg-1). Thus, they are an appropriate tool for assessing metal exposure in populations where scutes clipping as a marking technique is not allowed, and their collection is less complicated than with other tissues. MTs are a suitable biomarker in blood plasma, whereas in erythrocytes detoxification processes might depend on hemoglobin, rather than MTs. Future studies should consider the implementation of these tools for the monitoring of wild populations.

Correlation between increased postpubertal phallic growth and the initiation of cranial sexual dimorphisms in male Morelet's crocodile.

While puberty is an animal commonality, little is known of its timing or process in crocodylians. Males copulate with an intromittent phallus that has a distinct glans morphology which directly interacts with the female cloaca, putatively effecting effective semen transfer and ultimately increased fecundity. Here we present, during the Morelet's crocodile lifecycle, a well-defined body length (65 cm snout-vent length) inflection point that marks a subsequent increase of phallic glans growth rates. Putatively, this postpubescent growth produces a copulatory-effective phallus. While not as robust of a trend as snout-vent length, this growth inflection concomitantly begins with a body condition index (CI = BM/SVL3 ) between 2.0 and 2.5 and is most distinct above a CI of 2.5. Also, in males, this 65 cm size threshold also aligns with the initiation of more robust growth in caniniform alveoli associated with prominent maxillary and mandibular teeth. This inflection was not observed in females, thus marking a sexual dimorphism that begins to present with the onset of puberty. This bodily manifestation of puberty other than those changes observed in the reproductive tracts is a novel observation for crocodylians and lays a foundation for further study among species of how changing endocrine signaling within sexually maturing males may also influence a broader range of secondary sex characteristics.

Expression of the Sox9, Foxl2, Vasa, and TRPV4 genes in the ovaries and testes of the Morelet's crocodile, Crocodylus moreletii.

The Sox9 gene is important for determining sex in vertebrates, as well as for maintaining testis morphology and fertility during adult life. In the same way, Vasa is an important gene for the maintenance of the germinal lineage and has been highly conserved throughout evolution, as it is expressed in germ cells of both vertebrates and invertebrates. In the particular case of crocodiles, the expression of Sox9 during gonadal morphogenesis and in the testes of 3-month-old Alligator mississippiensis has been studied. However, it is interesting to carry out studies on other species of crocodiles in relation to their particular mechanism for sex determination influenced by temperature. In this work, we investigated the expression of the Sox9, Vasa, Foxl2, and TRPV4 genes in the ovaries and testes of 5-year-old juvenile crocodiles from Crocodylus moreletii. As expected, Sox9 expression was found in males, but surprisingly, it was also found in females. For the first time, the expression of Vasa was reported in spermatogonia, oogonia, and oocytes of 5-year-old crocodiles. Foxl2 is important for the development and maintenance of the ovary during adult life in vertebrates; moreover, Foxl2 protein and transcripts are both highly expressed in the ovaries compared to the testes. A possible upstream regulator of the Sox9 gene in reptiles has not yet been discovered; as such, the expression of the TRPV4 ion channel was evaluated. The TRPV4 ion channel was expressed in the cytoplasm of Sertoli and follicular cells and was therefore proposed as a possible regulator of SOX9.

High Levels of Heavy Metals in Scutes and Eggs of Morelet's Crocodiles (Crocodylus moreletii) from Northeast Mexico

We evaluated the concentrations of three heavy metals (cadmium, chromium, lead) in eggs and caudal scutes of nesting female Crocodylus moreletii in El Carpintero Lagoon, Tamaulipas, Mexico, in the months of May to August 2013. Samples were processed and analyzed based on the method of flame atomic absorption spectrophotometry at the Centro de Investigacion and Tecnologia en Saneamiento Ambiental (CITSA). Our results showed the presence of cadmium, chromium, and lead in both caudal scutes and eggs. The three heavy metals showed values in nesting females of 20.3, 5.0, and 28.0 mg kg-1, respectively. We observed significant differences in levels of cadmium and lead among nests but not with levels of chromium. The variations in heavy metal concentrations in eggs suggest that extrinsic and intrinsic factors simultaneously affect crocodiles during the reproductive season. Our levels were high compared with other species of crocodilians and are above thresholds established by Mexican pollution laws.

Mercury and metallothioneins in blood fractions and tissues of captive Morelet's crocodiles in Quintana Roo, Mexico

Even though studies of heavy metals and their relation with metallothioneins (MTs) in reptile tissues have been conducted, research on heavy metals and MTs in organs and blood fractions of crocodylians is limited. To date there are no studies on the distribution of MTs in organs and their relation with mercury (Hg), or the concentration of MTs in plasma and erythrocytes of crocodylians. In order to understand the role of MTs in crocodiles, our aim was to assess the detoxification mechanisms for exposure to metals in Morelet's crocodile (Crocodylus moreletii) by using two biomarkers (Hg and MTs) in blood fractions and tissues, and comparing them with concentrations between two populations of crocodiles, one previously wild and currently captive (Theme Park) and another raised in a Wildlife Management Unit (WMU). The caudal scutes from the Theme Park showed higher concentrations of Hg than those from the skin in the WMU samples, and significant negative relationships were observed between the total length (TL) and Hg in the scutes. The significant negative relationship between Hg and hemoglobin (Hb) may be due to disorders in the oxidation process and even denature of this protein, while the positive trend observed between MTs and Hb is consistent with the detoxifying functions and the protection against oxidative damage. This study is the first to report Hg in the erythrocytes of crocodylians and the use of MTs for testing the potential of these biomarkers as a tool to assess Hg exposure in crocodile's habitats.

Organochlorine Pesticide Residues in Caudal Scutes of Belize Morelet's Crocodiles (Crocodylus moreletii)

Abstract Historically, Belize has used large quantities of organochlorine (OC) pesticides for agriculture and disease-vector control, yet few tools exist for noninvasive assessment of OC contaminant loads in Belize wildlife. Crocodile caudal (tail) scutes are clipped as a marking technique in wildlife management programs and may also have utility as a minimally invasive, nonlethal technique to assess contaminant burden. We collected caudal scutes from 96 Morelet's Crocodiles in Belize over 2 yr to analyze scute tissues for OCs and to compare the observed OC concentrations among different scute tissue (fat, cartilage, and muscle) and among crocodiles of different age classes, sexes, and collection locations. Organochlorines of the DDT-type subclass were detected in 72 of 96 crocodiles, with methoxychlor detected in all 72 scutes containing OCs and p,p-DDE, p,p'-DDT, and p,p-DDD detected in 54, 47, and 20 scute samples, respectively. Organochlorines were more-frequently detected in scutes of adult crocodile...

External injuries of Morelet's crocodile Crocodylus moreletii in Campeche, Mexico.

Analysis of external injuries in captive and free-ranging Morelet's crocodiles Crocodylus moreletii was performed in the northern wetlands of Campeche, Mexico. From March to September of 2007, a total of 52 free-ranging and 51 captive Morelet's crocodiles were studied. Captive crocodiles presented significantly more injuries. Sixteen free-ranging crocodiles presented some type of lesion, mostly superficial abrasions. Nineteen captive crocodiles presented lesions, mostly incisions from agonistic interactions. Overall, the injuries with highest prevalence were the incisions. The tail was the most frequently injured body region. Injuries were more common in adults than in other size classes. Conversely, the presence of lesions caused by the parasite Paratrichosoma spp. was greater in crocodiles captured in the coastal channels (mangrove habitat). The information presented here is important to understand some of the effects of individual interactions and to foresee and manage the consequences of conservation and management activities of crocodile populations.

Usefulness of oxidative stress biomarkers evaluated in the snout scraping, serum and Peripheral Blood Cells of Crocodylus moreletii from Southeast Campeche for assessment of the toxic impact of PAHs, metals and total phenols

In this study, we assessed the effects of inorganic and organic pollutants [As, Cu, Fe, Mn, Pb, Zn, PAHs (11 compounds) and total phenols] from a panel of biomarkers [O2, H2O2, thiobarbituric acid reactive substances (TBARS), carbonyl proteins (RCO), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and total cytochrome P450 activities] evaluated in the Snout Scraping (SS), Serum (S) and Peripheral Blood Cells (PBC) of the Morelet's crocodile (Crocodylus moreletii) inhabiting the reference locality (Lake Mocu) and polluted locality (Champoton River) using Principal Component Analysis (PCA). In male crocodiles from the reference site, only H2O2 in PBC was related to levels of fluoranthene on the Keel of Caudal Scales (KCS), but, in females, no association was detected. In contrast, a sex-linked response was detected in specimens from the polluted locality. Levels of benzo[a]pyrene, benzo[a]anthracene, chrysene, pyrene, phenanthrene, acenaphthene, Zn, Cu, and Pb in KCS of the female crocodil were related to the oxidative stress biomarkers on PBC, incluing the total CYP450 activity and levels of O2, H2O2 in serum. However, in male crocodiles, the oxidative stress in SS and in the serum (TBARS, RCO, CAT, GPx), and SOD in PBC was related to As, Pb, Cu, Fe, and benzo[a]pyrene water concentrations and to the burdens of As, Fe, Mn, indeno[1,2,3cd]pyrene in KCS. These results confirm the usefulness of minimal or non-invasive methods of evaluating the oxidative stress response for the environmental monitoring program on the wild Morelet's crocodile that is subject to special protection in Mexican guidelines.

Similarity of Crocodilian and Avian Lungs Indicates Unidirectional Flow Is Ancestral for Archosaurs

Patterns of airflow and pulmonary anatomy were studied in the American alligator (Alligator mississippiensis), the black caiman (Melanosuchus niger), the spectacled caiman (Caiman crocodilus), the dwarf crocodile (Osteolaemus tetraspis), the saltwater crocodile (Crocodylus porosus), the Nile crocodile (Crocodylus niloticus), and Morelet's crocodile (Crocodylus moreletii). In addition, anatomy was studied in the Orinoco crocodile (Crocodylus intermedius). Airflow was measured using heated thermistor flow meters and visualized by endoscopy during insufflation of aerosolized propolene glycol and glycerol. Computed tomography and gross dissection were used to visualize the anatomy. In all species studied a bird-like pattern of unidirectional flow was present, in which air flowed caudad in the cervical ventral bronchus and its branches during both lung inflation and deflation and craniad in dorsobronchi and their branches. Tubular pathways connected the secondary bronchi to each other and allowed air to flow from the dorsobronchi into the ventrobronchi. No evidence for anatomical valves was found, suggesting that aerodynamic valves cause the unidirectional flow. In vivo data from the American alligator showed that unidirectional flow is present during periods of breath-holding (apnea) and is powered by the beating heart, suggesting that this pattern of flow harnesses the heart as a pump for air. Unidirectional flow may also facilitate washout of stale gases from the lung, reducing the cost of breathing, respiratory evaporative water loss, heat loss through the heat of vaporization, and facilitating crypsis. The similarity in structure and function of the bird lung with pulmonary anatomy of this broad range of crocodilian species indicates that a similar morphology and pattern of unidirectional flow were present in the lungs of the common ancestor of crocodilians and birds. These data suggest a paradigm shift is needed in our understanding of the evolution of this character. Although conventional wisdom is that unidirectional flow is important for the high activity and basal metabolic rates for which birds are renowned, the widespread occurrence of this pattern of flow in crocodilians indicates otherwise. Furthermore, these results show that air sacs are not requisite for unidirectional flow, and therefore raise questions about the function of avian air sacs.

Effect of nesting environment on incubation temperature and hatching success of Morelet's crocodile (Crocodylus moreletii) in an urban lake of Southeastern Mexico

Incubation temperature is an important aspect in terms of biological performance among crocodiles, and several controlled experiments have demonstrated a significant relationship between incubation temperature, success in hatching and survival of hatchlings. However, a few studies have tested these relationships in the wild. The objective of this study was to determine the relationship of nest characteristics and environment (hatch year, nest basal area and height, clutch size, distance to shore line, and vegetation cover), to incubation temperature and hatching success among Morelet's crocodile (Crocodylus moreletii). The study was carried out during the nesting seasons of Morelet's crocodile, from 2007 to 2009 in the Laguna de Las Ilusiones, an urban lake located in Villahermosa, Tabasco, Mexico. We physically characterized 18 nests and inserted a temperature data logger in each nest chamber. At the end of the nesting season and prior to hatching, we recovered the crocodile eggs and data loggers and calculated hatching success, under laboratory conditions. We related the environmental variables of the nest with the mean and fluctuation (standard deviation) of nest temperature, using linear models. We also related the environmental variables affecting the nest, to mean nest temperature and fluctuation in incubation temperature and to hatching success, using linear models. Although we found differences in incubation temperature between nests, mean incubation temperature did not differ between years, but there were differences in nest thermal fluctuation between years. The mean incubation temperature for 11 nests (61.1%) was lower than the suggested Female–Male pivotal temperature (producing 50% of each sex) for this species, and all hatchlings obtained were males. There were no differences in clutch size between years, but hatching success varied. Our study indicates that hatching success depends on certain environmental variables and nest conditions to which the eggs are subjected, including season, nest size and clutch size. We also discuss the importance of the fluctuation of incubation temperature on hatching success and sex determination.