Out with the old, introgression with the new: Signals of ancient and
recent admixture in hybridizing Mesoamerican crocodiles
(Crocodylus acutus x Crocodylus moreletii)
Abstract
A central aim of conservation is to preserve existing biodiversity and
understand the ecological and evolutionary processes that support it.
Inter- and intra-specific hybridization in wildlife has been recognized
as a common and naturally occurring phenomenon that facilitates species
adaptation and evolution. However, hybridization still constitutes one
of the most challenging problems for legal protection and species
management due to its perceived biological risk, lack of regulatory
oversight, and different case-by-case impacts. When considering rare or
threatened hybridizing species with unequal legal protection, management
strategies risk being inaccurate or unsuccessful unless contextualized
with an informed understanding of the species’ genetic and evolutionary
backgrounds. We investigated hybridization dynamics and genetic
diversity of American crocodiles (Crocodylus acutus) and Morelet’s
crocodiles (Crocodylus moreletii) from Belize to ascertain whether
genetic exchange through admixture displayed signs of evolutionary
significance. Using genomic reduced representation (3RAD) datasets from
242 wild crocodile samples, we found evidence of population structure
among C. acutus, as well as ancient bidirectional gene flow that had
occurred between C. acutus and C. moreletii. Notably, we also found
evidence of high levels of recent admixture along the coastal Crocodylus
populations in areas with extensive habitat modification due to human
impact. These findings as well as a discovered disconnect between
morphological and genetic species assignments used to identify
populations have implications for conservation management practices and
suggest a range of additional genetic investigations to understand the
natural and anthropogenic role of hybridization in large long-lived
tropical predators that span marine and terrestrial ecosystems.