Update: Assessing the evolutionary trajectory of the Apaporis caiman (Caiman crocodilus apaporiensis, Medem 1955) via mitochondrial molecular markers

Abstract

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.

Caiman tales: new enlightenments about species conservation risks

“…The existence of C.crocodilus southwestern Amazon and upper Branco River lineages were also represented and stated to be different from other C.crocodilus lineages with obvious differentiation in this study [4]. Nevertheless, a following publication in 2022 showed a phylogenetic analysis of this subspecies via utilising mtDNA materials, cytb and cytochrome c oxidase subunit I (COI), to construct the phylogenic tree (Figure 4) [8]. The samples were collected from the basin with 40 specimens.…”

“…A sister clade to the C.yacare labelled as X collected from Peru showed a divergence time approximate 4.5-5 myr. On the other hand, clade B embraced three lineages (6,7,8), while they were considered to be C.c.crocodilus model lineages. The divergence time of this clade was not as diverse as that of clade A since the highest divergence time was only ~1.5-2 myr, indicating relatively recent divergence events.…”

“…Otherwise, a monophyletic clade of C.crocodilus cannot be achieved since it includes the C.yacare within it, making C.crocodilus a paraphyletic group. 6), Atlantic coast (7) and Amazon (8).…”

“…Unfortunately, the molecular support for species delimitation is limited and the recent genetic analysis reveals many underestimated cryptic species within the genus Caiman [5]. Publications from the last decade confirmed the existence of this complexity of taxonomic relationships in the Caiman genus through utilising genetic analysis methods and quantitative sampling approaches [4,[6][7][8][9]. Additionally, evidence suggest that the Caiman composes more than just three species, most of which are under evaluation for the protection status and the habitat destruction [6][7][8][9].…”

“…Publications from the last decade confirmed the existence of this complexity of taxonomic relationships in the Caiman genus through utilising genetic analysis methods and quantitative sampling approaches [4,[6][7][8][9]. Additionally, evidence suggest that the Caiman composes more than just three species, most of which are under evaluation for the protection status and the habitat destruction [6][7][8][9]. This is believed to be a feasible approach to protecting them more efficiently to facilitate the protection of workers and researchers to perform protective activities of each lineage.…”