Crocodylus Acutus Research Articles

Population status of the American crocodile, Crocodylus acutus (Reptilia: Crocodilidae) and the caiman, Caiman crocodilus (Reptilia: Alligatoridae), in the Central Caribbean of Costa Rica

American crocodile (Crocodylus acutus)(Reptilia:Crocodilidae) and caiman (Caiman crocodilus)(Reptilia:Alligatoridae) population status, in the Costarican Central Caribbean. Two species of crocodilians have been described in Costa Rica, american crocodile (Crocodylus acutus: Cuvier 1807), and caiman (Caiman crocodilus: Linnaeus 1758). In Costa Rica, data has been generated on both species, but populations in the Pacific have received more attention from researchers; due to the fact that the Pacific slope has a greater development, which brings greater social pressure on the attention of the incidents generated by the encounter between humans and crocodiles. This study, performed during 2017, was done in an area of approximately 400 km2, characterized by having a wide and dense network of water courses, which includes the Matina, Pacuare, Reventazón and Parismina rivers. In these rivers, an average of 25 kilometers were traveled from the coastline up stream to the interior of the territory, including the Tortuguero canals, and other water bodies that connect these rivers, as well as in the most important lagoons and secondary channels. Three repetitions were made per segment. A population of 1084 caimans and 503 crocodiles is estimated; for a relative abundance of 8.64 and 2.80 ind/Km respectively. Speaking of caimans, up to 12% of individuals of reproductive age were observed, while for crocodiles that number was only 2%. The presence of both species in the different places studied, turned out to be significantly different for crocodiles and for caimans (Kruskal-Wallis, p≤0,000). Likewise, the size distribution is similar for crocodiles reported in all environments (Kruskal-Wallis, p≤0.15), while for caimans it indicates that there is a different distribution for sizes, according to the environment in which they are found (Kruskal -Wallis, p≤0,000), with a bias against of the Pacuare and Matina rivers. It was possible to estimate a sex ratio of 1.25 and 0.83 males to females, in crocodiles and caimans respectively, with 9 and 11 captures in that same order, in individuals of recruits, juvenile and subadult sizes. The Matina River and the Jalova Lagoon are the two main sites for the observation of crocodiles, their abundances are lower than those reported for the Pacific of Costa Rica, in whereas caimans, with a more homogeneous distribution throughout the sampling area, have a relative abundance considerably more than that reported in Honduras (2.2 ind/km), but lower than the 12.5 reported forLa Rambla de Sarapiquí, in the Northern Zone of Costa Rica.

Metal Contamination Hotspots in the Everglades

Left: shell casings at a site in the Everglades. Top right: Megan Bruce operating an atomic absorption flame emission spectrophotometer. Bottom right: J. Matt Hoch and Bruce collecting samples at a site in the Everglades. The Everglades ecosystem of South Florida may appear to be a wild, untouched landscape. However, there is a long history of human impacts—from attempts to drain the river of grass in the 1920s to pollution from agricultural and urban development and the introduction of invasive plants and animals. Currently, there are large-scale efforts to restore water flow and habitat in this unique ecosystem, but human impacts—both small and large—are still apparent. J. Matthew Hoch, Associate Professor in the Department of Marine and Environmental Sciences at Nova Southeastern University, conducts research in the Everglades. He says that during outings with a field course, the group noticed areas that are illegally used for firearm target practice. These unregulated illegal shooting ranges are littered with bullet casings and other trash. Hoch and his students wondered if these shooting ranges were contaminated with metal—from the soil and water to the plants and animals—and Hoch and co-author Megan Bruce decided to investigate further. The results of this initial survey were recently published in the Journal of Environmental Quality (https://doi.org/10.2134/jeq2018.08.0319). In 2017, Hoch and colleagues took survey samples at sites in the Everglades ecosystem. They sampled water, sediment, plants, and invertebrates and tested for lead, copper, and aluminum. Samples were collected at two unregulated shooting sites, three reference sites in the Everglades that did not show evidence of ammunition accumulation, and at a regulated shooting range. The samples revealed that the unregulated shooting areas are contaminated by copper and lead. The levels of lead and copper in the sediment at the unregulated sites were greater than the reference sites and similar to the levels found at the regulated shooting range. Lead levels in plants were also greater at the unregulated sites compared with the reference sites. Additionally, the average lead levels in grass shrimp at target sites was 416.1 µg/g compared with levels averaging 18.9 µg/g at the reference sites. This initial work documents the contamination associated with these unregulated target practice areas and leads to new questions. Hoch and his lab recently obtained grant funding to purchase new equipment that will enable them to do more in-depth analyses. He would like to do a more detailed sampling of plants and animals to test for bioaccumulation of lead and copper in the food chain that may originate at these sites. Understanding how these metals move through the ecosystem is important considering the Everglades ecosystem is critical habitat for many threatened and endangered species, including the Florida panther, American crocodile, wood stork, and snail kite. The problems with illegal firearm use go beyond contamination as these areas can pose a risk to other people using public lands who are unaware of the existence or exact location of these illicit shooting ranges. For example, Hoch described how during this study, a fisherman was accidentally killed by target shooters at one of the study sites. In the western U.S., target shooters have also started wildfires on public land, resulting in damage to structures and costly firefighting efforts. View the Journal of Environmental Quality article, “Metal Contamination Hotspots at Unregulated Firearm Target Shooting Sites in the Everglades” at: https://doi.org/10.2134/jeq2018.08.0319. It will likely take a combination of efforts, including education and increased law enforcement, to reduce illegal target practice on public land in the Everglades and on other sites across the U.S. Increasing law enforcement presence can be expensive, but it is probably the most effective strategy. After the shooting accident mentioned earlier, Hoch says a law enforcement agent was stationed near the target shooting site. This resulted in a decrease in target shooting at the site and suggests that increased law enforcement presence can reduce these activities on public land.

Influence of salinity on relative density of American crocodiles (Crocodylus acutus) in Everglades National Park: Implications for restoration of Everglades ecosystems

The status of the American crocodile (Crocodylus acutus) has long been a matter of concern in Everglades National Park (ENP) due to its classification as a federal and state listed species, its recognition as a flagship species, and its function as an ecosystem indicator. Survival and recovery of American crocodiles has been linked with regional hydrological conditions, especially freshwater flow to estuaries, which affect water levels and salinities. We hypothesize that efforts to restore natural function to Everglades ecosystems by improving water delivery into estuaries within ENP will change salinities and water levels which in turn will affect relative density of crocodiles. Monitoring ecological responses of indicator species, such as crocodiles, with respect to hydrologic change is necessary to evaluate ecosystem responses to restoration projects. Our objectives were to monitor trends in crocodile relative density within ENP and to determine influences of salinity on relative density of crocodiles. We examined count data from 12 years of crocodile spotlight surveys in ENP (2004–2015) and used a hierarchical model of relative density that estimated relative density with probability of detection. The mean predicted value for relative density (λ) across all surveys was 2.9 individuals/km (95% CI: 2.0–4.2); relative density was estimated to decrease with increases in salinity. Routes in ENP’s Flamingo/Cape Sable area had greater crocodile relative density than routes in the West Lake/Cuthbert Lake area and Northeast Florida Bay areas. These results are consistent with the hypothesis that restored flow and lower salinities will result in an increase in crocodile population size and provide support for the ecosystem management recommendations for crocodiles, which currently are to restore more natural patterns of freshwater flow to Florida Bay. Thus, monitoring relative density of American crocodiles will continue to be an effective indicator of ecological response to ecosystem restoration.

The Cuban Crocodile (Crocodylus rhombifer) from Late Quaternary Underwater Cave Deposits in the Dominican Republic

Late Quaternary fossils representing a locally extinct population of the Cuban crocodile (Crocodylus rhombifer) are reported from two underwater caves in the Dominican Republic. A large fossil sample of C. rhombifer, from Oleg's Bat Cave near Bavaro in the southeastern Dominican Republic, consists of four nearly complete skulls, numerous isolated cranial elements and mandibles, and more than 100 postcranial bones representing most of the skeleton. These fossils were collected from a completely submerged portion of the cave at a depth of 11 m and about 100 m from the nearest entrance. A skull, mandibles, and two vertebrae of a Cuban crocodile were also found in a second cave called Ni-Rahu, northeast of Santo Domingo.We identify the fossil crocodile skulls from the Dominican Republic as Crocodylus rhombifer because they share the following characters with modern skulls of C. rhombifer from Cuba (as well as fossil skulls from Cuba, the Bahamas, and Cayman Islands): short, broad, and deep rostrum; large orbits; convex nasals along the midline (midrostral boss); prominent swelling on the lacrimals anterior and medial to the orbits; low but obvious ridges extending anteriorly from the lacrimals to the nasals and posteriorly from the lacrimals to the prefrontals and frontals, outlining a distinct diamond- or rhomboid-shaped structure; strongly concave interorbital region and cranial roof; high, narrow ridges on the internal margins of the orbits, extending from the prefrontals to the frontals and posteriorly to the postorbitals; prominent ridges along the lateral margins of the cranial roof on the postorbitals and squamosals, terminating as noticeable protuberances on the posterolateral corners of the squamosals; premaxillary/maxillary suture on the palate essentially horizontal or transverse to the long axis of the skull at the level of the first maxillary tooth; 13 teeth in the maxilla.Certain aspects of the ecology and anatomy of living Crocodylus rhombifer in Cuba, and carbon isotope data from fossil crocodile bones from both the Dominican Republic and the Bahamas, indicate that the Cuban crocodile is a terrestrially adapted predator. The fossil deposits in Oleg's Bat Cave and other underwater caves in the Dominican Republic lack freshwater vertebrates, such as fish and turtles, but contain abundant samples of hystricognath rodents, small ground sloths, and other terrestrial vertebrates, including large land tortoises, that apparently were the primary prey of the crocodiles. Bats are abundant in the fossil deposits in Oleg's Bat Cave, and may have been an additional food source. Bone collagen from a tibia of C. rhombifer from Oleg's Bat Cave yielded an AMS radiocarbon date of 6460 ±30 ryrBP (equivalent to 7320 to 7430 cal yrBP). The chronology for the local extinction of C. rhombifer in Hispaniola is currently unknown, except to document the presence of this species in the eastern Dominican Republic in the early Holocene. Radiocarbon dates and historical records confirm that Cuban crocodiles survived into the period of European colonization (post-1492) in the Bahamas and on Grand Cayman. The only species of crocodile currently found in Hispaniola, the American crocodile (C. acutus), occurs in coastal marine habitats and in two inland brackishwater lakes: Lago Enriquillo in the Dominican Republic and the nearby Etang Saumâtre in Haiti. C. acutus has no fossil record in Hispaniola or elsewhere in the West Indies, suggesting that this species may be a very recent (late Holocene) immigrant in the Antillean region. Crocodylus rhombifer has one of the most limited geographic ranges of any living crocodylian species, known only from freshwater swamps in south-central Cuba and the Isla de Juventud (Isla de Pinos) off the southwestern coast of Cuba. Locally extinct or extirpated populations of C. rhombifer from fossil deposits in the Dominican Republic, Grand Cayman, and the Bahamas document a considerably wider distribution for this spe

Genetic evidence supports a distinct lineage of American crocodile (Crocodylus acutus) in the Greater Antilles.

Four species of true crocodile (genus Crocodylus) have been described from the Americas. Three of these crocodile species exhibit non-overlapping distributions—Crocodylus intermedius in South America, C. moreletii along the Caribbean coast of Mesoamerica, and C. rhombifer confined to Cuba. The fourth, C. acutus, is narrowly sympatric with each of the other three species. In this study, we sampled 113 crocodiles across Crocodylus populations in Cuba, as well as exemplar populations in Belize and Florida (USA), and sequenced three regions of the mitochondrial genome (D-loop, cytochrome b, cytochrome oxidase I; 3,626 base pair long dataset) that overlapped with published data previously collected from Colombia, Jamaica, and the Cayman Islands. Phylogenetic analyses of these data revealed two, paraphyletic lineages of C. acutus. One lineage, found in the continental Americas, is the sister taxon to C. intermedius, while the Greater Antillean lineage is most closely related to C. rhombifer. In addition to the paraphyly of the two C. acutus lineages, we recovered a 5.4% estimate of Tamura-Nei genetic divergence between the Antillean and continental clades. The reconstructed paraphyly, distinct phylogenetic affinities and high genetic divergence between Antillean and continental C. acutus populations are consistent with interspecific differentiation within the genus and suggest that the current taxon recognized as C. acutus is more likely a complex of cryptic species warranting a reassessment of current taxonomy. Moreover, the inclusion, for the first time, of samples from the western population of the American crocodile in Cuba revealed evidence for continental mtDNA haplotypes in the Antilles, suggesting this area may constitute a transition zone between distinct lineages of C. acutus. Further study using nuclear character data is warranted to more fully characterize this cryptic diversity, resolve taxonomic uncertainty, and inform conservation planning in this system.

How to estimate population size in crocodylians? Population ecology of American crocodiles in Coiba Island as study case

AbstractReliable estimates of crocodylian population size are desirable for both understanding the ecology and natural history of species and developing sound conservation and management plans. However, choosing appropriate methods to estimate population numbers can be difficult due to the paucity of comprehensive analyses regarding their effectiveness, robustness, and applicability. We estimated the American crocodile population size in the southern tip of Coiba Island, Panama, using both spotlight surveys (Messel's and King's visible fraction estimations) and mark–recapture (POPAN formulation–superpopulation) methods. We assessed and compared the outcomes of these methods with the overall capture record for the study area from 2009 to 2013, evaluating their applicability, accuracy, strengths, and limitations. Using historical and current capture data, we defined a minimum population size of ~112 non‐hatchling animals in our study area, which was larger than both Messel's (19.00 ± 7.50 individuals) and King's (25.71 ± 7.25 individuals) population size estimates, revealing that these latter approaches clearly underestimate population numbers. We estimated a total population size that range between 147 and 257 individuals based on POPAN formulation grouping the data by sex and age groups as the most plausible population size of the American crocodile population in this area at the time. We analyzed and discussed sources of bias in population size estimations for all methods used in the present study, providing recommendations to minimize errors and improve estimations. Finally, we analyzed and compared population ecology attributes obtained in our study with what have been reported in other insular and coastal areas across the American crocodile range, increasing knowledge about the ecology of the species.

Insights into the introduction history and population genetic dynamics of the Argentine black-and-white tegu (Salvator merianae) in Florida.

Invasive species are a major threat to global biodiversity. The US state of Florida is especially susceptible to the spread of exotic reptiles due to its subtropical climate, disturbed habitats, and robust pet trade. The Argentine black-and-white tegu (Salvator merianae) is a large, omnivorous lizard currently established in two different regions of Southern Florida. These two populations pose potential threats to sensitive ground nesting species such as gopher tortoises, American crocodiles, and migratory birds. At present, the introduction histories of these populations and the degree to which they are connected by gene flow are largely unknown. To address these issues, we genotyped S. merianae from Hillsborough and Miami-Dade Counties at ten microsatellite loci to assess intrapopulation genetic diversity, the degree of gene flow between populations, and compare the plausibilities of several potential introduction scenarios. Our results indicate that both populations have low genetic diversity [mean number of effective alleles across loci in both populations = 2.09 and are highly differentiated from each other (GST = 0.170; G″ST = 0.545)]. In addition, our results suggest that these populations underwent a bottleneck event prior to their divergence. We discuss what our results suggest about the histories of Florida's invasive tegu populations, as well as how they inform ongoing management strategies.

Ancestral Hybridization Yields Evolutionary Distinct Hybrids Lineages and Species Boundaries in Crocodiles, Posing Unique Conservation Conundrums

Interspecific hybridization can lead to adaptation and speciation, especially in the context of recent radiations. The emblematic Crocodylus (true crocodiles) is the most broadly distributed, ecologically diverse, and species-rich crocodylian genus. Nonetheless, their within-species evolutionary processes are poorly resolved mainly due to their potential for hybridization. Notably, the evolutionary outcomes when hybridization is ancient and involves long-lived species, like crocodiles, remain largely unexplored. Here, we evaluate the genomic admixture between the American (Crocodylus acutus) and the Morelet’s (Crocodylus moreletii) species, and demonstrate that this hybridization system challenges the definition of species boundaries and poses a triple conservation conundrum: what has been recognized as C. acutus is actually two distinct species, therefore its taxonomic reassessment is needed; we identified two evolutionary distinct hybrids lineages, which are genetically discernible from the parental species; the remaining C. moreletii populations evidence its likely extinction as a species and/or evolution via hybridization. Hence, the crocodiles’ distinct species and hybrids lineages warrant recognition and need urgent conservation efforts.

FOOTFALL PATTERN OF A BOTTOM-WALKING CROCODILE (CROCODYLUS ACUTUS)

Abstract Drone footage of a large American crocodile bottom walking in shallow coastal water off Costa Rica was used to estimate oblique pace and stride lengths and pace angulations from autopodial touchdowns. The crocodile's pes stride lengths were longer but more variable than expected for an individual of comparable size high-walking on land, due in part to punting locomotion, but also to wave action moving the reptile's body. Pace angulations were also larger than expectations for a crocodile high walking on land. These features are also seen in fossil trackways, suggesting that trackways ascribed to “swimming” crocodylomorphs might better be characterized as made by bottom walking and punting reptiles.

Food habits and ontogenetic dietary partitioning of American crocodiles in a tropical Pacific Island in Central America

AbstractStudies on food habits are fundamental to understanding the ecology of a species and its interactions with the community to which it belongs. Among crocodylians, diet affects a variety of biological, physiological, and behavioral characteristics. However, despite having one of the largest distributions across the Americas, some aspects of Crocodylus acutus’ natural history remain poorly studied, particularly in insular areas. We characterized American crocodiles’ food habits in Coiba Island, Panama, assessing ontogenetic dietary variation and dietary overlap by age group and size. We captured and collected stomach content samples from 49 individuals from four transects from March to December 2013. From these samples, we could taxonomically identify three phyla, four subphyla, eight classes, 11 orders, 17 families, 14 genera, and 12 species as prey items. However, not all samples could be identified to the lowest taxon (species), having most of them identified only to family level. Large juveniles had the largest proportion of prey items and subadults the largest proportion of gastroliths and vegetal content. Percent occurrence per major categories (insects, arachnids, crustaceans, fish, reptiles, birds, and mammals) showed crustaceans and insects as the most prominent groups of prey items on this island. Overlapping group analysis showed a reduction in the consumption of invertebrates (crustaceans and insects) as individuals aged. However, these items were the most common throughout all American crocodiles sampled. Dietary overlap analyses showed a likely ontogenetic dietary partitioning with high overlap (>60%) between small and large juveniles and low overlap (<30%) among small juveniles, subadults, and adults. To date, 71 species have been reported as prey items for American crocodiles. However, relying on prey items identified only to genus, we had at least 97 prey items. Thus, C. acutus can be defined as generalist with a broad spectrum of prey inhabiting all types of habitats and having all types of consumption classifications. Overall, American crocodiles inhabiting coastal areas present some differences in both dietary composition and structure with those dwelling inland and freshwater habitats as well as an interindividual diet variation, which reflects the plasticity and adaptability of C. acutus to a variety of conditions.

Variation in home range size and patterns in adult female American crocodiles Crocodylus acutus

Variation in home range size and patterns in adult female American crocodiles Crocodylus acutus

Contributions to the nutrition of the American crocodile Crocodylus acutus (Cuvier, 1807) in captivity

In this work we evaluated the essential amino acid profile of muscle Crocodylus acutus and calculated their chemical score of main proteins used in their diet in captivity. The separation and identification of amino acids was carried out by high performance liquid chromatography coupled to a fluorescence detector. The calculation of chemical score was obtained by dividing the value of each essential amino acid between the same amino acid of the reference protein. The lowest value of the relationships is the chemical score. The amino acids present in greater quantities in the tail muscle are glutamic acid, lysine and leucine (16.96, 9.84 and 8.87 g amino acid per 100 g of protein, respectively), whereas histidine, methionine and tryptophan (2.99, 2.93 and 0.59 g amino acid per 100 g of protein) were the lowest. The chemical score obtained results showed that the proteins of animal origin, preferably marine fish and supplemented with terrestrial animals ingredients, including beef liver appear to be the most effective. The incorporation of plant proteins in diets for C. acutus does not appear as a viable alternative due to deficiencies in several essential amino acids such as methionine, lysine and threonine. amino acids, chemical score, protein, crocodile, feeding, diet.

Scute Patterns as an Individual Identification Tool in an American Crocodile (Crocodylus acutus) Population on Coiba Island, Panama

Abstract Identification of individuals based on morphological patterns is a strategy used primarily in human forensics that has also been applied successfully in several wildlife scenarios. To date, no study has evaluated the potential of these techniques on American Crocodiles (Crocodylus acutus). We assessed whether the dorsal scute number and pattern of 110 American Crocodiles captured from the wild on Coiba Island, Panama could be used for individual recognition. We estimated scute variation using the number and position of scutes, testing both a binary and a coded assessment for scute presence and pattern, respectively. We analyzed scute patterns using 21 transverse scute lines (TSL) including the three most prominent scutes present on each side of the vertebral column axis. We found significant differences in the number of scutes per TSL and longitudinal scute lines (LSL) by individual. Based on both the binary and coded analyses, we identified all American Crocodiles assessed at the individual leve...

Estimación poblacional del cocodrilo americano (Crocodylus acutus) en el Parque Nacional Lagunas de Chacahua, Oaxaca, México

This study was conducted from November 2013 to June 2014 with the aim of estimating the population of American crocodile (Crocodylus acutus) in the Lagunas de Chacahua National Park (PNLCh). The field work consisted in surveys during three consecutive nights each month on several localities. The recorded encounter rates (ER) obtained by transect lines ranged from 2.3 (Zapotalito) to 33.4 (Palmarito) ind/km. The locality Palmarito showed the most representative population structure, while Zapotalito presented the lowest percentage of sightings. Significant differences were found per month in the abundance with age class respect to the frequency of crocodile use of the environments, as well as a significant interaction between month, habitat and age class. The total population estimated by transect lines fluctuated between 2.8 and 47.9 individuals. The greater abundance of individuals occurred in Palmarito (47.9±0.4individuals), while the lowest was found in Zapotalito (2.8±0.3individuals). The first approximations on population ecology and the current status of the American crocodile in the PNLCh are provided in this research and represent the basis of population monitoring in future years for the administration of this Mexican protected site.

Variation in crocodilian dorsal scute organization and geometry with a discussion of possible functional implications.

Dermal ossifications, including osteoderms, are present in many vertebrates and are frequently interpreted as a defense against predators. Nevertheless, osteoderms remain ubiquitous in adult crocodilians while being absent in hatchlings, even though adults rarely experience predation. In other biological systems, increased variation, particularly fluctuating asymmetry, have proven useful for identifying biological structures likely to have evolved under relaxed selection, which in turn may inform their function. Therefore, using the keratinous scutes as proxies for the underlying osteoderm morphology, I investigated the average intraspecific variability of geometry and fluctuating asymmetry in dorsal scutes in five species of crocodilians. I first tested for differences in variability of scute length and width, then for differences in bilateral fluctuating asymmetry of scute number, before finally investigating scute distribution patterns for each species compared to hypothetical rectangular and hexagonal scute arrangements. The American crocodile, Crocodylus acutus, shows significantly more asymmetry than other species, which is consistent with relaxed selection on osteoderms in this species. A suspected decrease in intraspecific aggression within Crocodylus acutus, in conjunction with the inferred relaxed selection, suggests that, in general, crocodilian osteoderms function primarily as defensive armor in aggressive encounters with conspecifics. The smooth-fronted caiman, Paleosuchus trigonatus, exhibits increased variation in scute dimensions linked to the mediolateral offset of osteoderms in adjacent rows, possibly resulting in a more rigid carapace. Unfortunately, comparative data on crocodilian behavior, physiology, and development is extremely limited and restricts the ability to explore other potential explanations for the patterns observed, highlighting the need for more research on rare and cryptic crocodylians.

Life histories and conservation of long-lived reptiles, an illustration with the American crocodile (Crocodylus acutus).

Successful species conservation is dependent on adequate estimates of population dynamics, but age-specific demographics are generally lacking for many long-lived iteroparous species such as large reptiles. Accurate demographic information allows estimation of population growth rate, as well as projection of future population sizes and quantitative analyses of fitness trade-offs involved in the evolution of life-history strategies. Here, a long-term capture-recapture study was conducted from 1978 to 2014 on the American crocodile (Crocodylus acutus) in southern Florida. Over the study period, 7,427 hatchlings were marked and 380 individuals were recaptured for as many as 25 years. We estimated survival to be strongly age dependent with hatchlings having the lowest survival rates (16%) but increasing to nearly 90% at adulthood based on mark-recapture models. More than 5% of the female population were predicted to be reproductive by age 8 years; the age-specific proportion of reproductive females steadily increased until age 18 when more than 95% of females were predicted to be reproductive. Population growth rate, estimated from a Leslie-Lefkovitch stage-class model, showed a positive annual growth rate of 4% over the study period. Using a prospective sensitivity analysis, we revealed that the adult stage, as expected, was the most critical stage for population growth rate; however, the survival of younger crocodiles before they became reproductive also had a surprisingly high elasticity. We found that variation in age-specific fecundity has very limited impact on population growth rate in American crocodiles. We used a comparative approach to show that the original life-history strategy of American crocodiles is actually shared by other large, long-lived reptiles: while adult survival rates always have a large impact on population growth, this decreases with declining increasing growth rates, in favour of a higher elasticity of the juvenile stage. Crocodiles, as a long-lived and highly fecund species, deviate from the usual association of life histories of "slow" species. Current management practices are focused on nests and hatchling survival; however, protection efforts that extend to juvenile crocodiles would be most effective for conservation of the species, especially in an ever-developing landscape.

Trackways of the American Crocodile (Crocodylus acutus) in Northwestern Costa Rica: Implications for Crocodylian Ichnology

ABSTRACTWe documented trackways of free-living Crocodylus acutus on beaches at the mouths of Tamarindo and Ventanas estuaries, Costa Rica. Our crocodiles had estimated total lengths of 1–3 meters or more. Manus prints have five digits, with digits I–III bearing claw marks. Pes prints have four digits, with claw marks on digits I–III. The pes is plantigrade. Claws generally dig into the substrate. Apart from claw marks, digit I and the heel of the pes are usually the most deeply impressed parts of footprints. Trackways are wide-gauge. Pes prints are usually positioned just behind ipsilateral manus prints of the same set and may overlap them. Manus and pes prints angle slightly outward with respect to the crocodile's direction of movement. Claw-bearing digits of both the manus and pes may create curved, concave-toward-the-midline drag marks as the autopodium is protracted. The tail mark varies in depth and clarity, and in shape from nearly linear to markedly sinuous. Sometimes the tail mark hugs the trackway midline, but sometimes it is closer to, or even cuts across, prints of one side. American crocodile footprints and trackways are similar to those observed in other extant crocodylian species, indicating substantial trackway conservatism across the group.

Morphological diversity of the American crocodile (Crocodylus acutus) in the Yucatán Peninsula

Recent evidence suggests that morphological divergence of the American crocodile (Crocodylus acutus) occurred in Greater Antilles under conditions of prolonged isolation and hybridization with the Cuban crocodile (C. rhombifer). We investigated morphological diversity in C. acutus in the coastal zone of the Yucatan Peninsula, where isolation and hybridization have also been reported. We compared the relationships among various morphological traits between insular and coastal populations. Our results suggest morphological diversity in the region, which is possibly related to population isolation and mechanical constraints imposed by differences in diet. A broad-snouted morphotype appears typical of island populations. Hybridization could also cause morphological variation, but its importance in this case remains to be confirmed. Sexual dimorphism of the American crocodile in the region appears to be less pronounced than for other crocodilians. We also provide population-specific size estimation models for two populations (Banco Chinchorro and Cozumel) to improve future monitoring.

FROM EGGS TO HATCHLINGS: NEST SITE TAPHONOMY OF AMERICAN CROCODILE ( CROCODYLUS ACUTUS ) AND BROAD-SNOUTED CAIMAN ( CAIMAN LATIROSTRIS )

Abstract: Nesting behaviors of extant vertebrates can serve as taphonomic models for interpreting extinct archosaurian reproduction. Past studies have examined birds with open nests and nest-bound young and tortoises with buried nests and precocial young. Here we taphonomically describe nesting sites of two crocodylians, American crocodile (Crocodylus acutus) at Turkey Point, Florida and broad-snouted caiman (Caiman latirostris) from Santa Fe and Chaco provinces, Argentina. Surveys focused on eggshell abundance, orientation, and distribution and nest modification of successfully hatched nests. American crocodiles excavate triangular or semi-circular depressions into their nest during hatching. Maximum depths of these parent-assisted hatching traces ranged from 20–45 cm, with a breadth of 50–80 cm. Eggshell orientations outside these excavated pits favored concave down (53.1–80.0%). Broad-snouted caiman constructed mound nests of predominantly plant debris in forested areas with organic rich soil or on veg...

Detection of a synthetic sex steroid in the American crocodile (Crocodylus acutus): Evidence for a novel environmental androgen

Endocrine-disrupting contaminants (EDC's) are well known to alter sexual differentiation among vertebrates via estrogenic effects during development, particularly in organisms characterized by temperature-dependent sex determination. However, substances producing androgenic effects typically lack potency when tested in laboratory settings and are virtually unstudied in field settings. Here, we assay levels of a synthetic androgen, 17α-methyltestosterone (MT), in a heavily male-biased population of American crocodiles in the Tempisque River Basin of Costa Rica based on the recent hypothesis that this chemical is an EDC in developing crocodilian embryos. The presence of MT was documented in all field-collected samples of egg yolk and in plasma of all age classes in among population of crocodiles. Hatchlings exhibited higher plasma MT concentrations (102.1 ± 82.8 ng/mL) than juveniles (33.8 ± 51.5) and adults (25.9 ± 20.8 ng/mL). Among populations, crocodiles captured in the Tempisque River (62.9 ± 73.7 ng/mL) were higher in MT concentration than those from Tarcoles (13.3 ± 11.4 ng/mL) and negative controls (0.001 ± 0.0002 ng/mL). A mechanism for the bio-transport of MT and its subsequent effects is proposed.