Mark Webster’s research while affiliated with University of Chicago and other places

The spectacled caiman (Caiman crocodilus) is currently considered to be a species complex due to the relatively high morphological and molecular diversity expressed across its range. One of the populations of interest, inhabiting the Apaporis River (Colombia), was described based on skull features as an incipient species (C. c. apaporiensis) and has been treated by some authors as a full species. Recent molecular work challenged this hypothesis, because relatively low mitochondrial molecular differentiation was found between the morphologically described Apaporis caiman and C. crocodilus (s.s.) Amazonian populations. Here, we present an update on the topic based on a larger molecular sample size and on analysis of expanded geometric morphometric data that include six newly collected skulls. Morphometric data support the existence of previously recognized morphotypes within the complex in Colombia and demonstrate that the newly collected material can be assigned to the classic Apaporis caiman morphotype. However, our expanded genetic analysis fails to find appreciable mitochondrial molecular divergence of the Apaporis caiman population from the C. c. crocodilus population (COI-CytB: Amazon Peru 0.17 ± 0.06%, CytB-only: Caquetá River Colombia 0.08 ± 0.07%). The Apaporis caiman is interpreted to be a phenotypically distinct member of the cis-Andean C. crocodilus metapopulation that has not yet achieved (or may not be undergoing at all) appreciable genetic differentiation. Thus, it should not be considered a fully independent evolutionary lineage, nor given full species rank.