Crocodylus Acutus Research Articles

The crocodile that crossed an ocean

The study of a forgotten crocodile skull collected in Libya back in 1939 suggests that the extinct Crocodylus checchiai may be the link between the Nile and the American crocodiles. This discovery would support the hypotheses of crocodiles’ journey across the ocean from Africa to America. - submission by Massimo Delfino

Nest temperature assessment in an American crocodile (Crocodylus acutus) population on the central coast of Oaxaca, Mexico.

The temperatures at which eggs of crocodilians are incubated plays an important role in embryo survival, rate of embryonic development and sex definition. The aim of this study was to assess the nest temperatures of an American crocodile (Crocodylus acutus) population on the central coast of Oaxaca state in Mexico. The fieldwork was carried out from February to June 2018at Palmasola Lagoon, Oaxaca. Ten natural nests of C. acutus were carefully excavated to determine clutch size. When putting the eggs back in the nests, we placed a data logger in the center of the egg mass to determine the temperature parameters in the nest chamber environment, as well as the variation in temperature during the incubation period. All nests were revisited to count the number of hatched eggs (NHE) and to determine the hatching success (HS), along with the duration of the incubation period (IP). Hatching success was 89.04%. The mean clutch size in the American crocodile nests was 30.7±7.83 eggs (ranging from 17 to 46 eggs), and the mean incubation period was 77.6±5.89 days. The mean nest incubation temperature throughout the reproductive season was significantly different among nests. Based on the average temperature during the middle third of the incubation period, the nests should have produced both sexes, but with a higher proportion of males. This study tried to elucidate the impact of nest temperatures during the incubation period on embryo survival, as well as hatchling sex ratio in a local climate on the central coast of Oaxaca.

American crocodiles (Crocodylus acutus) as restoration bioindicators in the Florida Everglades.

The federally threatened American crocodile (Crocodylus acutus) is a flagship species and ecological indicator of hydrologic restoration in the Florida Everglades. We conducted a long-term capture-recapture study on the South Florida population of American crocodiles from 1978 to 2015 to evaluate the effects of restoration efforts to more historic hydrologic conditions. The study produced 10,040 crocodile capture events of 9,865 individuals and more than 90% of captures were of hatchlings. Body condition and growth rates of crocodiles were highly age-structured with younger crocodiles presenting with the poorest body condition and highest growth rates. Mean crocodile body condition in this study was 2.14±0.35 SD across the South Florida population. Crocodiles exposed to hypersaline conditions (> 40 psu) during the dry season maintained lower body condition scores and reduced growth rate by 13% after one year, by 24% after five years, and by 29% after ten years. Estimated hatchling survival for the South Florida population was 25% increasing with ontogeny and reaching near 90% survival at year six. Hatchling survival was 34% in NE Florida Bay relative to a 69% hatchling survival at Crocodile Lake National Wildlife Refuge and 53% in Flamingo area of Everglades National Park. Hypersaline conditions negatively affected survival, growth and body condition and was most pronounced in NE Florida Bay, where the hydrologic conditions have been most disturbed. The American crocodile, a long-lived animal, with relatively slow growth rate provides an excellent model system to measure the effects of altered hydropatterns in the Everglades landscape. These results illustrate the need for continued long-term monitoring to assess system-wide restoration outcomes and inform resource managers.

Sperm kinematic subpopulations of the American crocodile (Crocodylus acutus).

There has been very limited use of computer assisted semen analysis (CASA) to evaluate reptile sperm. The aim of this study was to examine sperm kinematic variables in American crocodile (Crocodylus acutus) semen samples and to assess whether sperm subpopulations could be characterized. Eight ejaculates (two ejaculates/male) from four sexually mature captive crocodiles were obtained. An ISAS®v1 CASA-Mot system, with an image acquisition rate of 50 Hz, and ISAS®D4C20 counting chambers were used for sperm analyses. The percentages of motile and progressively motile spermatozoa did not differ among animals (P > 0.05) but there was a significant animal effect with regards to kinematic variables (P < 0.05). Principal component (PC) analysis revealed that kinematic variables grouped into three components: PC1, related to velocity; PC2 to progressiveness and PC3 to oscillation. Subpopulation structure analysis identified four groups (P < 0.05), which represented, on average, 9.8%, 32.1%, 26.8%, and 31.3% of the total sperm population. Males differed in the proportion of sperm in each of the kinematic subpopulations. This new approach for the analysis of reptile sperm kinematic subpopulations, reflecting quantifiable parameters generated by CASA system technology, opens up possibilities for future assessments of crocodile sperm and will be useful in the future development of assisted reproduction for these species.

A 4.1 m male American Crocodile

A 4.1 m male American Crocodile

Effect of the Central American Isthmus on gene flow and divergence of the American crocodile (Crocodylus acutus).

The final formation of the Central American Isthmus (CAI) about 3.5 million years ago altered global ocean circulation, connected North and South America terrestrial biotas, and established the Caribbean Sea. The nature of this event creates a natural scenario to test vicariance, divergence, and speciation by allopatry. Studies have shown the effect of the CAI on marine and terrestrial species, but none have examined a large-bodied amphibious taxon. We used RAD sequencing on populations of the American crocodile (Crocodylus acutus) to study the genomic variation of C. acutus on both sides of the CAI, infer its demographic history, and measure the effect of the opening of the Panama Canal. Our results showed three genomic clusters: (1) Caribbean and the Panama Canal, (2) Pacific coast, and (3) Coiba island. The estimated divergence times between the Caribbean and Pacific populations are about 20,000 years ago, which is younger than the formation of the CAI, coinciding with the Last Glacial Maximum. We hypothesize the glacial/interglacial cycles facilitated gene flow between the Caribbean and Pacific crocodile populations after the formation of the CAI, masking any genomic divergence the CAI may have caused. There is no evidence of gene flow associated with the opening of the Panama Canal.

Major hurricanes affect body condition of American crocodile Crocodylus acutus inhabiting Mexican Caribbean islands

Recent models suggest that anthropogenic global warming will lead to an increase in the number of major hurricanes, which have strong effects on ecosystems and may modify animal population characteristics. The goal of this study was to assess the body condition of American crocodiles Crocodylus acutus of Cozumel and Banco Chinchorro islands, Mexico, and use it as a tool to better understand short- and long-term effects of hurricanes on crocodilian populations. Changes in body condition (Fulton’s K) of 392 crocodiles, captured between 2003 and 2015, were assessed and analyzed in response to a major hurricane through different environmental factors. Differences among populations and size classes, and between sexes, together with seasonal variation, were also evaluated. The body condition of crocodiles was generally good, with better condition for Banco Chinchorro, suggesting that these populations and the ecosystems they inhabit are healthy. Body condition for hatchlings and adults was higher than for other classes, with adults exhibiting the best condition. Body condition of Banco Chinchorro individuals varied seasonally, responding to reproductive events and environmental parameter fluctuations. We also found that C. acutus body condition is sensitive to the passage of tropical cyclones, most likely through their effects on salinity, temperature, and prey availability. Tropical cyclones have a 2fold effect on populations. In the short-term, crocodile health is negatively affected by disturbance, while the species seems to maintain and improve its body condition over the longer term. An increase in strong tropical cyclone frequency could impede the recovery of populations, while causing a continual decrease in crocodile body condition.

Individual identification patterns as a monitoring strategy for American crocodiles: Tayrona National Natural Park as a study case

Abstract Population numbers of the American crocodile in Colombia have shown an increasing trend during the last decades. However, the lack of monitoring programs has restricted our understanding about this species’ ecology, limiting the ability to develop sound conservation plans. We assessed the effectiveness and robustness of the Individual Identification Pattern Recognition (IIPR) method for remotely monitoring American crocodile populations based on photographs taken by researchers, tourists, locals, and employees at the Tayrona National Natural Park (TNNP). We catalogued a total of 97 events from 2008 to 2020; 34.02% of which were suitable to analyze using IIPR. We identified eight individuals across 33 events that required only 4.71 ± 1.70 transverse scute lines to obtain complete identification, with the lowest levels of variation in the post occipital and nuchal regions compared with the dorsal area. The probabilities of repeating both the most and least common patterns found in the TNNP were 1.88 × 10−6 and 1.81 × 10−12, respectively, and the probabilities of repeating the same pattern of each individual identified ranged between 48.73 × 10−11 and 15.24 × 10−8. Animals B and C were continuously identified between 2012 and 2020 along the Arrecife beach coastline, whereas animals A, H, E, and F were occasionally registered between 2008 and 2019 at the Cañaveral beach. Overall, the IIPR method looks as a promising tool for monitoring American crocodile populations in the TNNP albeit some improvements in data collection that must be done to increase the number of useful events and analysis quality.

Tracking a voyager: mitochondrial DNA analyses reveal mainland-to-island dispersal of an American crocodile (Crocodylus acutus) across the Caribbean

Abstract Conservation efforts have allowed American crocodile (Crocodylus acutus) populations to recover to the point that dispersal movements are beginning to be documented. The environmental authority of San Andres Island in Colombia reported, for the first time, the arrival of two C. acutus from unknown localities in 2012 and 2018. The former was sacrificed, and the latter was captured and kept in captivity to determining its potential origin. We used wildlife forensics to establish the origin of the animal that arrived in 2018 based on two mitochondrial genes (COI and Cytb). Additionally, five other samples from Tayrona National Natural Park (TNNP), and Salamanca Island Road Park (SIRP) were sequenced for molecular attribution of these populations to the currently described lineages. Phylogenetic and phylogeographic analyses showed that the American crocodile found in San Andrés belongs to a continental evolutionary lineage endemic to Colombia, showing also a strong genetic similarity with animals from SIRP. Thus, the most likely origin for this individual was not the nearest continental area but somewhere around the central Colombian Caribbean, located ~700 km from the island. We discuss the implication of our findings in the systematics and conservation of the species and the potential of mitochondrial DNA analysis to identify such migrants.

Analysis of the Interactions Between Humans and Crocodiles in Costa Rica

The habitat of crocodiles (Crocodylus acutus) and caimans (Caiman crocodilus) has been subjected to pressure due to human expansion. Habitat reduction, coupled with the simultaneous growth of the crocodile population, increases the number of interactions between crocodiles and humans. There is currently no official and systematized interactions database, but it is necessary to know the magnitude and nature of the interactions and establish management measures. The objective of the work was to systematize and evaluate the interactions between crocodiles and humans in Costa Rica. Historical information was collected from several sources. A total of 99 records, dated between 1990–2017, were found from press reports and the Integrated System for Processing Environmental Complaints of the Ministry of Environment and Energy (SITADA). The Fire Department recorded 123 events in 2017. All Fire Department records corresponded to encounters or sightings. Of the SITADA incident records, 35.4% were non-fatal, 27.3% were fatal, 21.2% were encounters and sightings, and the remaining 16.1% were miscellaneous situations. Most interactions occurred during the day, a fact potentially explained by human behavior of being in bodies of water or on adjacent shoreline while the sun is out. Most interactions occurred in the Central Pacific, followed by the Caribbean and then the South Pacific. The information available is brief but allows to establish management measures. The country needs to create a national database of interactions and to encourage individuals to report their interactions. Further research should continue to analyze the data for trends with the goal of building recommendations to prevent an increase in negative interactions.

Differences in distress: Variance and production of American Crocodile (Crocodylus acutus) distress calls in Belize.

Acoustic communication of American Crocodiles (Crocodylus acutus) is relatively understudied. Our overall aim was to determine the acoustic structure of wild American Crocodile distress calls, distinguish call differences among size classes (hatchling, juvenile, sub‐adult, and adult), and investigate call production on a gradient of human disturbance. American Crocodile distress calls have strong frequency modulation and are comprised of multiple harmonics in a downsweeping pattern. Measured parameters (total duration, first quartile duration, maximal frequency, first quartile frequency, end frequency, slope of first quartile, slope of last quartiles) differed significantly among size classes (p < .05). Hatchling distress calls are higher in frequency and strongly modulated, whereas calls produced by sub‐adults and adults showed little modulation, are lower in frequency, and have greater overall duration. Proportion of crocodiles that produced distress calls during capture differed by size class and sampling location, particularly adult distress calls which are reported here to be produced with undocumented frequency. We determined that American Crocodiles of all size classes produce distress calls at varying rates among study sites. Our results demonstrate that American crocodiles produce distress call more frequently at sites with higher anthropogenic activity. Measured call parameters of juveniles and hatchling American crocodiles also varied among sites in relation to human disturbance. Calls recorded at sites of high anthropogenic impact have increased duration and less modulation which may adversely affect response to emitted distress calls. Proportional and call parameter variances suggest anthropogenic activity as a driver for increased call production and alteration of call parameters at high human‐impacted sites.

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.

Egg predation and vertebrates associated with wild crocodilian nests in Mexico determined using camera-traps

ABSTRACT Interactions between species and individuals can determine their survival in the wild. Most of the time these relationships are difficult to study in situ by direct observation. However, technology can help collect these data with minimal impact on animals’ behaviour. Egg stage is certainly the most vulnerable life stage in crocodilians, but few studies have focused on animal species visiting crocodilian nests and associated egg predation. Herein, we use camera-traps in four Mexican states (Chiapas, Oaxaca, Jalisco, Tabasco) to determine vertebrate species and egg predators associated with wild nests of Caiman crocodilus chiapasius, Crocodylus acutus and Crocodylus moreletii. We recorded 72 species of vertebrates at nesting sites and obtained the first photographic evidence of crocodilian egg predation by Caracara cheriway, Cuniculus paca, Didelphis virginiana and Procyon lotor. We also identified commensalism, cooperation, and predation as types of interactions within observed nesting areas, which indicates the importance of crocodilian nesting areas for other wild vertebrates. Finally, we found that crocodilian egg predation depends on species richness present in the area of study, as well as crocodilian size.

Ancient skull could be ‘missing link’ between African and American crocodiles

Ancient skull could be ‘missing link’ between African and American crocodiles

Old African fossils provide new evidence for the origin of the American crocodiles

Molecular and morphological phylogenies concur in indicating that the African lineages formerly referred to Crocodylus niloticus are the sister taxon the four Neotropical crocodiles (Crocodylus intermedius, C. moreleti, C. acutus and C. rhombifer), implying a transoceanic dispersal from Africa to America. So far the fossil record did not contribute to identify a possible African forerunner of the Neotropical species but, curiously, the oldest remains referred to the African C. niloticus are Quaternary in age, whereas the oldest American fossils of Crocodylus are older, being dated to the early Pliocene, suggesting that another species could be involved. We re-described, also thanks to CT imaging, the only well-preserved topotipic skull of Crocodylus checchiai Maccagno, 1947 from the late Miocene (Messinian) African site of As Sahabi in Libya. As previously suggested on the basis of late Miocene material from Tanzania, C. checchiai is a valid, diagnosable species. According to our phylogenetic analyses, C. checchiai is related to the Neotropical taxa and could be even located at the base of their radiation, therefore representing the missing link between the African and the American lineages.

High levels of population genetic differentiation in the American crocodile (Crocodylus acutus).

The American crocodile (Crocodylus acutus) is a widely distributed species across coastal and brackish areas of the Neotropical region of the Americas and the Greater Antilles. Available information on patterns of genetic differentiation in C. acutus shows a complex structuring influenced by interspecific interactions (mainly hybridization) and anthropogenic actions (mostly historical hunting, recent poaching, habitat loss and fragmentation, and unintentional translocation of individuals). In this study, we used data on mitochondrial DNA control region and 11 nuclear polymorphic microsatellite loci to assess the degree of population structure of C. acutus in South America, North America, Central America and the Greater Antilles. We used traditional genetic differentiation indices, Bayesian clustering and multivariate methods to create a more comprehensive picture of the genetic relationships within the species across its range. Analyses of mtDNA and microsatellite loci show evidence of a strong population genetic structure in the American crocodile, with unique populations in each sampling locality. Our results support previous findings showing large degrees of genetic differentiation between the continental and the Greater Antillean C. acutus. We report three new haplotypes unique to Venezuela, which are considerably less distant from the Central and North American haplotypes than to the Greater Antillean ones. Our findings reveal genetic population differentiation between Cuban and Jamaican C. acutus and offer the first evidence of strong genetic differentiation among the populations of Greater Antillean C. acutus.

Status and Conservation of Crocodylus acutus at a Naval Base in Aragua State, Venezuela

We present the conservation status and ecological characteristics (distribution, habitat preference, reproduction, population size, and structure) of an American Crocodile (Crocodylus acutus) population associated with the naval base “TN Tomas Vega” in Turiamo Bay, Aragua state, Venezuela. The sheltered coastal habitats, with freshwater or brackish water, as San Miguel River of Turiamo Bay, provide essential nursery habitats for hatchling American Crocodiles. During the breeding season, we looked for signs of nesting activity; however, because of continuous military exercises in the area, it is currently not known where nesting occurs. Based upon spotlight surveys of 6.7 km of survey routes, the resident American Crocodile population of Turiamo Bay was estimated at 38 American Crocodiles. Of this population, 6 sightings were classified as eyeshine only, 11 as class I, 14 as class II, 6 as class III, and 1 as class IV, exhibiting differential habitat association according to the size class. Encounter rates were highest in the brackish lagoon and low in the west coast and the San Miguel River, possibly because of the activities of the naval base causing evasive behavior by American Crocodiles. Our results indicate the C. acutus population in Turiamo Bay has been relatively stable in the past few years. However, it is important to accurately estimate the population size of C. acutus and protect the nesting and nursery habitats. Therefore, we recommend continuation of the population studies and involvement of environmental organizations to regulate anthropogenic activities in Turiamo Bay.

Analysis of the population dynamics of the endangered American crocodile, Crocodylus acutus in Paramillo National Natural Park

Few studies have been conducted on the population dynamics of crocodiles, especially in the Neotropics. This is the first study to provide data on the population dynamics of the threatened American crocodile (Crocodylus acutus (Cuvier, 1807)) in Paramillo National Natural Park. Twenty-four survey routes of 22km each were studied, and a total of 733 sightings was recorded. During the study period (from October 2014 to March 2016), the population remained stable and experienced slight growth (λ=1.049±0.428). Offspring production by the adults II stage was the most sensitive contribution (17.05), whereas the permanence of this adult stage was the demographic process that contributed the most to population growth (0.653). However, an 18% decrease in adults II would jeopardise long-term population viability and lead to a high probability of quasi-extinction, with under 300 individuals over the next 30 years. Thus, despite the apparent stability of this population, we suggest that it be considered a key target for future conservation efforts. Additionally, we recommend that this species continue to be listed as endangered in Colombia and not be modified in the CITES Appendix I.

Crocodylus acutus (American crocodile) bite marks on a nest data logger.

Several data loggers deployed to monitor temperature and humidity of Crocodylus acutus (American crocodile) nests in South Florida could not be located after hatching. One badly damaged data logger was retrieved, providing insight into the possible fate of the others. Using a taphonomic approach, we identified numerous indentations, consistent with crocodylian bite marks, and inconsistent with potential mammalian or squamate bites. It seems most likely that the data logger was damaged by the nesting C. acutus rather than during attempted nest predation. Estimated bite forces for reproductive age, female C. acutus exceed the predicted material properties of the data logger’s housing, suggesting that the bites were exploratory in nature. We suggest that data loggers be removed prior to hatching or permit remote data storage.

Shifts in hatching date of American crocodile (Crocodylus acutus) in southern Florida.

Globally temperature of marine environments is on the rise and temperature plays an important role in the life-history of reptiles. In this study, we examined the relationship between sea surface temperature and average date of hatching for American crocodiles (Crocodylus acutus) over a 37-year period at two nesting sites, Everglades National Park and Florida Power and Light Turkey Point Power Plant site in southern Florida. Our results indicate that hatch dates are shifting 1.5 days earlier every two years and at half that rate for the Turkey Point site, and with every 1°C degree increase in temperature, hatching occurs about 10 days earlier in the Everglades and 6 days earlier at Turkey Point. Our results on shifting hatch dates for American crocodiles provide further details about the impacts of temperature change on crocodile life history and suggest that increased temperature may affect their phenology.