Abstract
The genus Crocodylus comprises 12 currently recognized species, many of which can be difficult to differentiate phenotypically. Interspecific hybridization among crocodiles is known to occur in captivity and has been documented between some species in the wild. The identification of hybrid individuals is of importance for management and monitoring of crocodilians, many of which are Convention on International Trade in Endangered Species (CITES) listed. In this study, both mitochondrial and nuclear DNA markers were evaluated for their use in confirming a suspected hybrid zone between American crocodile (Crocodylus acutus) and Morelet’s crocodile (Crocodylus moreletii) populations in southern Belize where individuals and nests exhibiting atypical phenotypic features had previously been observed. Patterns observed in both phenotypic and molecular data indicate possible behavioural and ecological characteristics associated with hybridization events. The results of the combined analyses found that the majority of suspected hybrid samples represent crosses between female C. acutus and male C. moreletii. Phenotypic data could statistically identify hybrids, although morphological overlap between hybrids and C. moreletii reduced reliability of identification based solely on field characters. Ecologically, C. acutus was exclusively found in saline waters, whereas hybrids and C. moreletii were largely absent in these conditions. A hypothesized correlation between unidirectional hybridization and destruction of C. acutus breeding habitats warrants additional research.
Highlights
Crocodiles (Crocodylus spp.) hybridize readily in captivity [1,2,3,4,5], and hybridization is known or suspected to occur among wild populations of several sympatric species [6,7,8,9,10,11,12]
C. acutus was exclusively found in saline waters, whereas hybrids and C. moreletii were largely absent in these conditions
Analysis of mtDNA from individuals collected outside of areas of sympatry in Belize, as well as data published elsewhere [10,11,40,52], indicates that there are fixed, diagnostic, haplotypic differences between C. moreletii and C. acutus, which can be used as DNA barcodes
Summary
Crocodiles (Crocodylus spp.) hybridize readily in captivity [1,2,3,4,5], and hybridization is known or suspected to occur among wild populations of several sympatric species [6,7,8,9,10,11,12]. In Mexico, hybridization appears to occur primarily in coastal regions of sympatry [10,11], while in Belize hybrids were found at inland sites outside the distribution of C. acutus [8]. Hybridization between C. acutus and the endangered Cuban crocodile (Crocodylus rhombifer) has been determined to be much more extensive than previously assumed based on phenotypic data [12]
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