Effect of the Central American Isthmus on gene flow and divergence of the American crocodile (Crocodylus acutus)

Novel island species elucidate a species complex of Neotropical crocodiles

The evolutionary history of Neotropical crocodiles has remained elusive. They inhabit a broad geographic range with populations spanning from coastal, inland, and insular locations. Using a selection of natural insular, coastal, and one inland population of C. acutus, coastal C. moreletii, and the single surviving population of C. rhombifer, we discovered a remarkable genetic diversity for the group. Moreover, geometric morphometric results of skull shapes shows that these crocodylus species span a morphological cline. We recovered a high genetic differentiation between C. moreletii, C. rhombifer, and five clusters of C. acutus. The genetic and geographic differences among the C. acutus clusters were used to suggest these may be a species complex. Several ecological, morphological and genetics traits are identified in the well-studied populations from Banco Chinchorro and Cozumel islands off the Mexican Yucatan Peninsula to support discrete species designations for these populations. This work suggests the presence of rapid, recent evolution of several cryptic Crocodylus species throughout the Neotropics.

Pleistocene sea level changes and crocodile population histories on the Isthmus of Panama: A comment on Avila-Cervantes et al. (2020)

Avila-Cervantes et al. proposed that glacial-interglacial sea level changes played an important role in the evolutionary and demographic histories of the crocodile Crocodylus acutus on the Isthmus of Panama. However, the study used erroneous sea level proxy data that produced flawed paleogeographic reconstructions. We present new paleogeographic reconstructions and review the timing of, and proposed mechanisms behind, the demographic events estimated by Avila-Cervantes et al.. With the data currently available, we find little evidence to support the hypothesis that sea level changes drove population demographic events in crocodiles on the Isthmus. Alternative hypotheses, including changing climate and habitat suitability, are equally valid and should be considered along with well-supported sea level models.