Article

Molecular analyses confirming the introduction of nile crocodiles, crocodylus niloticus laurenti 1768 (Crocodylidae), in southern Florida, with an assessment of potential for establishment, spread, and impacts

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Abstract

Abstract.—The state of Florida, USA, has more introduced herpetofauna than any other governmental region on Earth. Four species of nonnative crocodilians have been introduced to Florida (all since 1960), one of which is established. Between 2000–2014 we field-collected three nonnative crocodilians in Miami-Dade County, Florida, and one in Hendry County, Florida. We used DNA barcoding and molecular phylogenetics to determine species identification and native range origin. Also, we described diet, movement, and growth for one crocodile. Our molecular analyses illustrated that two of the crocodiles we collected are most closely related to Nile Crocodiles (Crocodylus niloticus) from South Africa, suggesting this region as a source population. We, thus, documented the first known introduction of C. niloticus in Florida. Two, and possibly three of the introduced crocodiles shared the same haplotype, suggesting they are likely from the same introduction pathway or source. One animal was captured, measured, marked, and released, then recaptured 2 y later allowing us to calculate growth rate (40.5 cm/y) and movement. The most likely route of travel by waterway (i.e., canal) illustrates that this animal traveled at least 29 km from its original capture site. One crocodile escaped from a facility in Hendry County, Florida, and survived in 1,012 ha of semi-wild habitat for three to four years, confirming that this species can survive in southern Florida.

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... Florida harbors the highest diversity of established nonindigenous reptile species in the world, with three turtles, 50 lizards, five snakes, and one crocodilian, most of which arrived through the commercial pet trade (Krysko et al., 2011. Over the last few decades, an increasing number of exotic crocodilian species has been registered in Florida, including Caiman crocodilus, Crocodylus niloticus, Paleosuchus palpebrosus, Paleosuchus trigonatus, and Mecistops cataphractus (Krysko et al., 2011;Rochford et al., 2016). However, only Ca. crocodilus is established in Florida (Ellis, 1980;Krysko et al., 2019). ...
... Recent molecular phylogenetic studies have revealed substantial cryptic lineage diversity within Crocodylia, some of which have been or will likely be recognized as distinct species within Caiman (Roberto et al., 2020), Osteolaemus, Mecistops (Shirley et al., 2014), Crocodylus (Hekkala et al., 2011), and Paleosuschus (Muniz et al., 2018;Bittencourt et al., 2019). Rochford et al. (2016) also employed similar tools to identify introduced individuals of Crocodylus in southern Florida as Cr. niloticus, most likely of South African origins, while previous to this study it was thought the introduced species was the morphologically similar Crocodylus suchus. ...
... Outside its' natural range, C. niloticus have been wild-caught and genetically confirmed in southern Florida, USA most likely as either released pets or zoological escapees (Rochford et al. 2016). Rochford et al. (2016) raise concerns about the potential risk of human-crocodile conflicts as well as the potential for hybridization with the indigenous C. acutus population. ...
... Outside its' natural range, C. niloticus have been wild-caught and genetically confirmed in southern Florida, USA most likely as either released pets or zoological escapees (Rochford et al. 2016). Rochford et al. (2016) raise concerns about the potential risk of human-crocodile conflicts as well as the potential for hybridization with the indigenous C. acutus population. Neither risk has so far been realised. ...
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Since the last Crocodilus niloticus assessment in 1996, genetic analysis confirmed two lineages of African Crocodylus, namely C. niloticus and C. suchus (Schmitz et al. 2003, Hekkala et al. 2011, Shirley et al. 2015). This assessment takes account of this recent information and only considers the range of C. niloticus (see the distirbution map and the Geographic Range section: 26 countries in southern and eastern Africa). This range represents the majority of habitat and populations on which previous continent-wide assessments of the Nile Crocodile were based. Despite some evidence of localised population declines (Ottley et al. 2008, Fergusson 2010, Bourquin and Leslie 2011, Combrink et al. 2011, Ferreira and Pienaar 2011, Calverley and Downs 2014, Marais 2014, Behangana et al. 2017), C. niloticus (sensu novo) generally remains widespread and as the population has not significantly changed, the assessment LC remains the same. West African populations constituting C. suchus are likely depleted and less numerous and will be assessed separately.
... En un estudio reciente se han localizado en Florida, Estados Unidos, entre dos y tres cocodrilos de Nilo (Crocodylus niloticus). Esto supone una amenaza para los cocodrilos de Florida por la introgresión genética, y se recomienda que siga siendo estudiado por si pudiera haber más de estos cocodrilos y por su impacto (Rochford et al., 2016). 68 situación actual de los grandes depredadores terrestres ...
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Se analiza la distribución y en algunos casos abundancia de los grandes depredadores a nivel mundial, así como 3 de estos grandes depredadores en México y algunos temas como etnobiología, y el papel de los zoos en la conservación
... En un estudio reciente se han localizado en Florida, Estados Unidos, entre dos y tres cocodrilos de Nilo (Crocodylus niloticus). Esto supone una amenaza para los cocodrilos de Florida por la introgresión genética, y se recomienda que siga siendo estudiado por si pudiera haber más de estos cocodrilos y por su impacto (Rochford et al., 2016). 68 situación actual de los grandes depredadores terrestres ...
... Case studies from other tropical systems, including the dramatic if poorly understood shift in community structure and lake trophic ecology observed in Lake Victoria following its colonization by Nile perch (Lates niloticus), should serve as a clear warning of the implications of introducing apex predators (Ogutu-Ohwayo, 1990). This trend perhaps reached a new level with the recent discovery of Nile crocodiles (Crocodylus niloticus) in southern Florida (Rochford et al., 2016). ...
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Reliable recovery of the 5'''' region of the cytochrome c oxidase 1 (COI) gene is critical for the ongoing effort to gather DNA barcodes for all fish species. In this study, we develop and test primer cocktails with a view towards increasing the efficiency of barcode recovery. Specifically, we evaluate the success of polymerase chain reaction amplification and the quality of resultant sequences using three primer cocktails on DNA extracts from repre- sentatives of 94 fish families. Our results show that M13-tailed primer cocktails are more effective than conventional degenerate primers, allowing barcode work on taxonomically diverse samples to be carried out in a high-throughput fashion.
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ABSTRACT The use of simple terms to articulate ecological concepts can confuse ideological debates and undermine management efforts. This problem is particularly acute in studies of nonindigenous species, which alternatively have been called ‘exotic’, ‘introduced’, ‘invasive’ and ‘naturalised’, among others. Attempts to redefine commonly used terminology have proven difficult because authors are often partial to particular definitions. In an attempt to form a consensus on invasion terminology, we synthesize an invasional framework based on current models that break the invasion process into a series of consecutive, obligatory stages. Unlike previous efforts, we propose a neutral terminology based on this framework. This ‘stage-based’ terminology can be used to supplement terms with ambiguous meanings (e.g. invasive, introduced, naturalized, weedy, etc.), and thereby improve clarity of future studies. This approach is based on the concept of ‘propagule pressure’ and has the additional benefit of identifying factors affecting the success of species at each stage. Under this framework, invasions can be more objectively understood as biogeographical, rather than taxonomic, phenomena; and author preferences in the use of existing terminology can be addressed. An example of this recommended protocol might be: ‘We examined distribution data to contrast the characteristics of invasive species (stages IVa and V) and noninvasive species (stages III and IVb)’.
Article
Relationships of the newly discovered dwarf crocodiles from Mauritania were inferred from mitochondrial 12S sequences. Specimens from 13 different Crocodylus niloticus populations (from East Africa, West Africa and Madagascar) were compared. Additional representatives of the genus Crocodylus (one from Africa and one from Australia), the African genus Osteolaemus and the South American alligatorid Paleosuchus palpebrosus (as outgroup) were included in the analysis. Maximum-likelihood and Bayesian analyses yielded relationships that were strikingly different from currently prevailing phylogenetic hypotheses. Both analyses consistently revealed two groups, one consisting of the monophyletic West- and Central African populations and the other of a paraphyletic group containing the East African and Madagascan populations. High genetic divergence between those groups indicates separation on the species level. Furthermore ‘C’ cataphractus is clearly shown not to be a member of the genus Crocodylus. The resulting nomenclatural changes are discussed. To cite this article: A. Schmitz et al., C. R. Palevol 2 (2003).
Article
Nile crocodiles (Crocodylus niloticus) are one of the few dangerous predators regularly found outside protected wildlife areas. This is particularly so in northeastern Namibia where an extensive network of rivers and wetlands coupled with successful conservation measures has allowed crocodile populations to flourish since uncontrolled exploitation ended over three decades ago. This area is predominantly communal land characterized by numerous subsistence communities dependent on river and wetland resources. In recent years, the combination of a growing human population and resurgent crocodile populations has resulted in considerable conflict between humans and crocodiles. The principle objective of this study was to quantify the impact of crocodiles on rural livelihoods. Data were obtained from existing records and through community surveys on the lower Kavango, Chobe and Kwando rivers and upper Zambezi River. Existing estimates suggest an annual loss of 255 domestic cattle per year for northeastern Namibia whilst community survey estimates suggest a substantially greater annual loss of 6864 cattle per year. Community surveys also revealed conflict between crocodiles and artisinal fishermen, with an estimated 71 500 fishing nets damaged by crocodiles per year. Human-crocodile conflict in Namibia may have greater impacts than previously assumed, and may undermine conservation and development objectives.
Article
When the American Crocodile (Crocodylus acutus) was declared endangered in 1975, scant data were available for making management decisions. Results of intensive studies conducted during the late 1970s and early 1980s by the National Park Service, Florida Game and Fresh Water Fish Commission, and Florida Power and Light Company resulted in an optimistic outlook for crocodiles. However, new issues face crocodiles today. Florida and Biscayne bays have undergone changes that have caused concern for the health of these ecosystems. The purpose of this paper is to review results of monitoring programs for C. acutus that have been used as a basis for consideration of reclassification of this endangered species and for restoration of its endangered ecosystem. More crocodiles and nests occur in more places today than in 1975. The maximum number of nesting females in Florida has increased from 20 in 1975 to 85 in 2004, and the number of concentrations of nesting effort from two to four. This evidence supports the proposed reclassification of the American Crocodile from endangered to threatened. However, crocodiles are still threatened by modification of habitat because of development adjacent to crocodile habitat and will benefit from restored freshwater flow into estuaries. As crocodiles continue to increase in number and expand into new areas, interactions with humans will occur more frequently. The challenge of integrating a recovering population of the American Crocodile with an ever-increasing use of coastal areas by humans will be the final challenge in successful recovery of this once critically endangered species.
Article
(1) In a study of the population ecology of the Nile crocodile at Ngezi, Zimbabwe, animals were measured, and thermal and feeding data collected during a 3-year mark-recapture experiment. (2) Juvenile growth was confined to the hot season and physical condition declined in the cool season. Large animals grew in irregular spurts. (3) Low cool-season growth was attributed to the physiological affects of temperature on feeding. Juvenile body temperatures equilibrated with the water to which they returned at night and were therefore as high as 30 degrees C in the hot season, but fell to 15 degrees C in the cool. Animals of all sizes basked in the sun, but only for short periods in the cool season did body temperatures exceed 25 degrees C and therefore approach temperatures efficient for digestion. Juveniles were more often seen feeding and were more replete in the hot season. Hatchlings were able to grow at lower temperatures than older animals. (4) On the basis of size, it was impossible to assign juveniles to accurate age-classes after 3 years, and growth curves resulting from the estimation of individual ages by skeletochronology were more accurate than those constructed from growth data. (5) Because growth was slow, females took approximately 30 years to reach sexual maturity. The growth rate of males declined more slowly than that of females and thus they attained larger sizes. (6) At a size of 600 mm snout-vent length, the diet of juveniles changed from a predominance of insects to fish and birds and a concurrent reversal of several important allometric relationships of the head was believed to be an adaptation for the efficient capture of prey of an increasing size. A fundamental change of home range behaviour also occurred in these animals and the abruptness of the dietary transition may partly reflect a change in prey availability.
Article
The American crocodile was declared endangered in the United States in 1975. At that time 75% of the remaining crocodile nests were in Everglades National Park, in Florida Bay. In 1980, the National Park Service established a crocodile sanctuary in northeastern Florida Bay to protect nesting and nursery habitat. In 1985, a monitoring program, focused on nesting, growth, and survival, was established to evaluate the effects of modified water deliveries on crocodiles in Florida Bay. The number and range of crocodile nests increased between 1970 and 1995, but nesting success decreased slightly. Nests on artificial substrates in the Greater Flamingo-Cape Sable area accounted for most of the increase in nests. Nests on artificial substrates were more prone to predation by raccoons. At least 1.5% of marked hatchlings survived for more than 12 mo, and growth rates were variable. Detailed information on growth and survival of crocodiles is still lacking. It is no longer a question of whether crocodiles with survive in Florida Bay, but how ecosystem restoration and management can be applied to improve conditions for crocodiles.
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Silvopasture, which combines trees, forages, and shrubs with livestock operations, has potential for limiting phosphorus runoff, sequestering atmospheric carbon dioxide, and improving habitat for wildlife. This study estimates the public demand for these environmental services in south-central Florida's Lake Okeechobee watershed using a stated preference approach. The results from a random parameter logit model reveal that households would pay US$30.24–71.17 per year for 5 years for these environmental benefits. These estimates provide a basis for formulating policies to promote silvopasture practices in the Lake Okeechobee watershed.
Article
The Nile crocodile (Crocodylus niloticus) is an ancient icon of both cultural and scientific interest. The species is emblematic of the great civilizations of the Nile River valley and serves as a model for international wildlife conservation. Despite its familiarity, a centuries-long dispute over the taxonomic status of the Nile crocodile remains unresolved. This dispute not only confounds our understanding of the origins and biogeography of the 'true crocodiles' of the crown genus Crocodylus, but also complicates conservation and management of this commercially valuable species. We have taken a total evidence approach involving phylogenetic analysis of mitochondrial and nuclear markers, as well as karyotype analysis of chromosome number and structure, to assess the monophyletic status of the Nile crocodile. Samples were collected from throughout Africa, covering all major bioregions. We also utilized specimens from museum collections, including mummified crocodiles from the ancient Egyptian temples at Thebes and the Grottes de Samoun, to reconstruct the genetic profiles of extirpated populations. Our analyses reveal a cryptic evolutionary lineage within the Nile crocodile that elucidates the biogeographic history of the genus and clarifies long-standing arguments over the species' taxonomic identity and conservation status. An examination of crocodile mummy haplotypes indicates that the cryptic lineage corresponds to an earlier description of C. suchus and suggests that both African Crocodylus lineages historically inhabited the Nile River. Recent survey efforts indicate that C. suchus is declining or extirpated throughout much of its distribution. Without proper recognition of this cryptic species, current sustainable use-based management policies for the Nile crocodile may do more harm than good.
Article
There is a surprising lack of genetic data for the Cuban crocodile (Crocodylus rhombifer), especially given its status as a critically endangered species. Samples from captive individuals were used to genetically characterize this species in comparison with other New World crocodilians. Partial mitochondrial sequence data were generated from cyt-b (843 bp) and the tRNA(Pro)- tRNA(Phe)-D-loop region (442 bp). Phylogenetic analyses were performed by generating maximum parsimony, maximum likelihood, and Bayesian-based topologies. In addition, in an effort to identify species-specific alleles, ten polymorphic microsatellite loci were genotyped. Distance and model-based clustering analyses were performed on microsatellite data, in addition to a model-based assignment of hybrid types. Both mitochondrial and nuclear markers identified two distinct C. rhombifer genetic sub-clades (alpha and beta); and microsatellite analyses revealed that most admixed individuals were F(2) hybrids between C. rhombifer-alpha and the American crocodile (C. acutus). All individuals in the C. rhombifer-beta group were morphologically identified as C. acutus and formed a distinct genetic assemblage. J. Exp. Zool. 309A:649-660, 2008. (c) 2008 Wiley-Liss, Inc.
Article
High-throughput data production has revolutionized molecular biology. However, massive increases in data generation capacity require analysis approaches that are more sophisticated, and often very computationally intensive. Thus, making sense of high-throughput data requires informatics support. Galaxy (http://galaxyproject.org) is a software system that provides this support through a framework that gives experimentalists simple interfaces to powerful tools, while automatically managing the computational details. Galaxy is distributed both as a publicly available Web service, which provides tools for the analysis of genomic, comparative genomic, and functional genomic data, or a downloadable package that can be deployed in individual laboratories. Either way, it allows experimentalists without informatics or programming expertise to perform complex large-scale analysis with just a Web browser.
Article
The increase in the number of large data sets and the complexity of current probabilistic sequence evolution models necessitates fast and reliable phylogeny reconstruction methods. We describe a new approach, based on the maximum- likelihood principle, which clearly satisfies these requirements. The core of this method is a simple hill-climbing algorithm that adjusts tree topology and branch lengths simultaneously. This algorithm starts from an initial tree built by a fast distance-based method and modifies this tree to improve its likelihood at each iteration. Due to this simultaneous adjustment of the topology and branch lengths, only a few iterations are sufficient to reach an optimum. We used extensive and realistic computer simulations to show that the topological accuracy of this new method is at least as high as that of the existing maximum-likelihood programs and much higher than the performance of distance-based and parsimony approaches. The reduction of computing time is dramatic in comparison with other maximum-likelihood packages, while the likelihood maximization ability tends to be higher. For example, only 12 min were required on a standard personal computer to analyze a data set consisting of 500 rbcL sequences with 1,428 base pairs from plant plastids, thus reaching a speed of the same order as some popular distance-based and parsimony algorithms. This new method is implemented in the PHYML program, which is freely available on our web page: http://www.lirmm.fr/w3ifa/MAAS/.