Dinâmica e estrutura populacional do jacaré-açu (Melanosuchus niger) na Amazônia

Abstract

Melanosuchus niger is one of the 23 species of Crocodylia order. Receives the popular name of black caiman due to its predominant color, averaging four meters for males and 2.8 for females. It is distributed in the entire Amazon and can be found in the rivers of the Amazon basin and those that drain to the Atlantic coast. It is found in the backwaters of rivers and especially in lakes and wetlands. The species was abundant, but due to commercial hunting during 1930-1980, came close to being extinct. However, with government protection and conservation strategies, their populations has recovered considerably. Some works on the structure and genetic diversity have been developed, obtaining partial results due to restricted sample. In this study, we try to cover the largest possible area of species distribution, and through the use of a mitochondrial marker cytochrome b (Cytb) and SNPs markers (Single Nucleotide Polymorphisms), we analyzed the populations evaluating the genetic variability patterns, the structure of populations and tested the effect of rapids as a barrier to dispersion. Thus, 245 Cytb sequences from 17 localities were analyzed to calculate the rates of genetic diversity (H and π) and genetic equilibrium (Tajima´s D and Fu´s Fs). To determine the genetic structure, AMOVA was performed; Fst pairwise comparisons and Bayesian analysis were performed to determine the number of biological groups. Using next-generation sequencing (NGS), SNPs were developed with the ddRADseq methodology using 81 individuals from 10 localities. The results showed that there is a strong structure in black caiman populations determined by two factors: isolation by distance and presence of geographical barriers. Isolation by distance determines a pattern of diversity distribution West-East, represented mostly by the two most common haplotypes. The rapids of the rivers Araguaia, Branco and Madeira/Guaporé are barrier to the dispersion of the population, so the upstream populations must have colonized these areas prior to its formation, generating biological groups isolated. Testing the rapids on the Madeira River as a barrier, it was observed that they restrict gene flow, which is unidirectional (upstream to downstream the rapids). At a general level, M. niger populations are expanding, probably after a drastic reduction of size as that suffered in the past century. Finally, we proposed seven areas for conservation: for West, East and Centre areas, should be defined at least one operating unit for the management and conservation of the species; and for the other four areas, it was possible to define management units (MUs) to the population of the Araguaia, Guaporé, Uraricoera and Napo rivers.