title: Genetic and morphological evidence of a geographically widespread hybrid zone between two crocodile species, Crocodylus acutus and Crocodylus moreletii.
abstract: Hybrid zones represent natural laboratories to study gene flow, divergence and the nature of species boundaries between closely related taxa. We evaluated the level and extent of hybridization between Crocodylus moreletii and Crocodylus acutus using genetic and morphological data on 300 crocodiles from 65 localities. To our knowledge, this is the first genetic study that includes the entire historic range and sympatric zone of the two species. Contrary to expectations, Bayesian admixture proportions and maximum-likelihood estimates of hybrid indexes revealed that most sampled crocodiles were admixed and that the hybrid zone is geographically extensive, extending well beyond their historical region of sympatry. We identified a few geographically isolated, nonadmixed populations of both parental species. Hybrids do not appear to be F1 s or recent backcrosses, but rather are more likely later-generation hybrids, suggesting that hybridization has been going on for several to many generations and is mostly the result of natural processes. Crocodylus moreletii is not the sister species of C. acutus, suggesting that the hybrid zone formed from secondary contact rather than primary divergence. Nonadmixed individuals from the two species were distinguishable based on morphological characters, whereas hybrids had a complex mosaic of morphological characters that hinders identification in the wild. Very few nonadmixed C. acutus and C. moreletii populations exist in the wild. Consequently, the last nonadmixed C. moreletii populations have become critically endangered. Indeed, not only the parental species but also the naturally occurring hybrids should be considered for their potential conservation value.
authors.affiliation: Departamento de Ecología de la Biodiversidad, Instituto de Ecología, Universidad Nacional Autónoma de México, Ap. Postal 70-275, Ciudad Universitaria, México, DF, 04510, México.|Posgrado en Ciencias Biológicas, Universidad Nacional Autónoma de México, Coyoacán, México, DF, 04510, México.
authors.forename: Gualberto
authors.initials: G
authors.lastname: Pacheco-Sierra
authors.affiliation: Department of Biology and Ecology Center, Utah State University, Logan, UT, 84322, USA.
authors.forename: Zachariah
authors.initials: Z
authors.lastname: Gompert
authors.affiliation: Programa Crocodylia, COMAFFAS AC, Chiapa de Corzo, Chiapas, 29066, México.
authors.forename: Jerónimo
authors.initials: J
authors.lastname: Domínguez-Laso
authors.affiliation: Departamento de Ecología de la Biodiversidad, Instituto de Ecología, Universidad Nacional Autónoma de México, Ap. Postal 70-275, Ciudad Universitaria, México, DF, 04510, México.
authors.forename: Ella
authors.initials: E
authors.lastname: Vázquez-Domínguez
mesh_terms: D000489:Alligators and Crocodiles / Q000235:genetics*; D000818:Animals; D001499:Bayes Theorem; D017691:Caribbean Region; D003247:Conservation of Natural Resources; D056727:Endangered Species; D005828:Genetics, Population; D005838:Genotype; D060851:Gulf of America; D006824:Hybridization, Genetic; D016013:Likelihood Functions; D018895:Microsatellite Repeats; D061350:Sympatry
keywords: Mexico; crocodilia; hybridization; introgression; microsatellites; reptiles