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Population genetic structure of Morelet’s and American crocodiles in Belize: hybridization, connectivity and conservation

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Abstract

Hybridization can influence the evolutionary potential of wild species and can be especially detrimental where one species is abundant, and the other much rarer. In Belize, the Morelet’s crocodile (Crocodylus moreletii) primarily inhabits inland freshwater lagoons, lakes and rivers, whereas the less abundant American crocodile (Crocodylus acutus) is more prevalent among the offshore cayes and atolls. Both species are historically sympatric along the brackish coastline, but it is unclear if admixture between the two is affecting genetic integrity of the species. We investigated the extent of interspecific hybridization across Belize using genomic variants identified using double digest restriction-site associated DNA sequencing (ddRADseq). Five groups of genetically pure C. moreletii were identified, two of which were inland, including the protected Chiquibul National Park. Two groups of genetically pure C. acutus were identified, one on northern offshore islands, and a second along the southern coastline. Hybrids were only identified along the central-southern coastline and were in close geographic proximity to coastal purebreds. Based on these results, we suggest that the central-southern coastline represents a hybrid zone, while the inland areas and offshore islands that harbour only genetically pure populations may benefit from conservation prioritisation.

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Data availability

Raw sequence data are available at via the NCBI Sequence Read Archive (BioProject PRJNA931141). Code and files are available at https://doi.org/10.5281/zenodo.7604944.

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Acknowledgments

We thank the Belize Forest Department for providing fieldwork research permits. We thank staff and volunteers of the Crocodile Research Coalition for support during fieldwork and sample preparation. We thank the following NGOs and landowners for sampling permissions and support: Belize Audubon Society, Belize Aquaculture Limited, Cardelli Shrimp Farm, Sarteneja Alliance for Conservation and Development, Friends for Conservation and Development, Programme for Belize, Toledo Institute for Development and Environment. We thank Míra Procházka of Krokodýl Zoo Protivín (Czech Republic) and Shaun Foggett of Crocodiles of the World (UK) for samples. We thank Jane Coghill and Christy Waterfall of the University of Bristol Genomics Facility for sequencing support. This research was conducted under the following permits: Belize Forest Department research permits [Reference Numbers WL/1/1/1645) and WL/2/1/17(30)]. Samples were shipped to the University of Bristol for processing, as per export and import license regulations, assigned under transport class B (low risk biological material): UN 3373. A permit to export forest products was issued by the Belize Forest Department for C. moreletii [Permit Number: WL/2/7/17 (58)] and C. acutus [Permit Number: FD/WL/7/19(31)]. CITES export and import permits were issued for C. moreletii (Export Permit Number: 6292, import permit number: 569648/01) and C. acutus (Export Permit Number: 08055, Import Permit Number: 584955/01).

Funding

This study was funded by IUCN-SSC Crocodile Specialist Group's Student Research Assistance Scheme, European Croc Network (ECN), Feral – Wild Animal Project.

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Authors and Affiliations

  1. School of Biological Sciences, University of Bristol, Life Sciences Building, Tyndall Avenue, Bristol, BS8 1TQ, UK

    Clare J. Wilkie, Gareth Jones & Martin J. Genner

  2. Crocodile Research Coalition, Placencia, Belize

    Marisa Tellez

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  1. Clare J. Wilkie
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  2. Marisa Tellez
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  4. Martin J. Genner
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Contributions

Study conception and design, all authors. Research design and preparation, CW, MT and GJ. Supervision, GJ and MJG. Fieldwork, MT. Laboratory work and data analyses, MJG and CW. First manuscript draft, CW. Completion and approval of final manuscript, all authors.

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Correspondence to Clare J. Wilkie or Martin J. Genner.

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Wilkie, C.J., Tellez, M., Jones, G. et al. Population genetic structure of Morelet’s and American crocodiles in Belize: hybridization, connectivity and conservation. Conserv Genet 25, 585–590 (2024). https://doi.org/10.1007/s10592-023-01590-7

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