Surveillance for evidence of West Nile virus (WNV) infection in Morelet’s crocodiles (Crocodylus moreletii) was conducted in Campeche State, Mexico, in 2007. Sera from 62 crocodiles (32 free-ranging and 30 captive) were assayed for antibodies to WNV by epitope-blocking enzyme-linked immunosorbent assay. Antibodies to WNV were detected in 13 (41%) wild and nine (30%) captive crocodiles, and the overall antibody prevalence was 35%. Although evidence of WNV infection in captive crocodiles has been reported in Mexico, we provide the first evidence of WNV exposure in wild crocodiles in Mexico.

When backcrosses are fertile, interbreeding between endangered taxa can lead to the admixture of gene pools under threat. One such case pertains to the Mesoamerican crocodile Crocodylus moreletii, a species which shows strong signatures of both recent hybridisation and historic intogression with the American crocodile C. acutus across large parts of its range. In the present paper, we use RAD-seq derived SNPs (4980 nuclear and seven mtDNA loci) to demonstrate that C. moreletii populations inhabiting the region of Calakmul in central Yucatan (Mexico) are rather unaffected by hybridization, despite being surrounded by coastal areas where pervasive admixture has previously been documented. All (based on fastSTRUCTURE) and 96% (based on NGSadmix) of 84 genotyped individuals from 18 sampled waterbodies (locally termed aguadas) were free from nuclear introgression of C. acutus DNA at at threshold of 0.95. Seven individuals (8%) possessed a C. acutus mtDNA haplotype, five of which were derived from two adjacent, rather peripheral aguadas. Spatial inferences based on a DAPC and fineRADstructure further showed that the region of Calakmul is inhabited by three genetic clusters spanning across a set of distinct aguadas each. Taken together, our findings reveal that central Yucatan contains the currently largest documented stronghold of C. moreletii populations only marginally affected by introgression, which has major implications for the conservation management of this important flagship species.