A research project on the morphological traits and genetic diversity of Bradypus torquatus, endemic to the Atlantic Forest, is being conducted as a collaborative study between the Laboratory of Biodiversity and Molecular Evolution (LBEM) at the Federal University of Minas Gerais and the MSc Program of Vertebrate Zoology at the Catholic University of Minas Gerais, both in Belo Horizonte, Minas Gerais, Brazil. This project focuses on the morphological, ecological and genetic aspects of this poorly known and endangered species, and aims to supply information to support measures for its conservation and management.

This study has targeted forest fragments where the largest populations of the species are expected to be found, in the Brazilian states of Bahia, Espírito Santo and Rio de Janeiro. Morphological data have been collected from 62 wild-caught specimens, and genetic sequences have been derived from the mitochondrial control region (D-loop) from 45 adult animals. These samples represent one population from southeastern Bahia, two populations from south-central Espírito Santo – one from the lowlands and one from the highlands – and one population from Rio de Janeiro.

The morphological analysis indicates that adult Bradypus torquatus are the largest of their genus; adult females are significantly larger than males and may reach weights of 10 kg or more. The shape of the mane shows a previously undetected pattern of sexual dimorphism, in which the mane is more conspicuous in males than in females. Sexual dimorphism was also found in the structure of the external genitalia of reproductively active animals; these differences are extremely subtle and almost impossible to distinguish without a great deal of experience. We also detected significant differences in size between individuals from warmer and colder regions, suggesting that populations have adapted morphologically to the temperatures of their local environments. Examination of the animals captured, especially recaptured adults, has improved our understanding of their biological and reproductive parameters. Maned sloths appear to reach maturity at about three years of age, which is a relatively short time for animals of their size and low metabolic rate. (For details see Lara-Ruiz and Chiarello, in press.)

Concerning the genetic analysis (Lara-Ruiz, unpublished data), sequences from the mitochondrial control region showed low levels of withinpopulation polymorphism, and indicated that most of the genetic diversity found in this species is due to differences between populations. Based on D-loop sequences, genetic distances calculated among populations from the different states were high (> 0.90), while the distance found between the two populations sampled from ES was less than 0.1. Accordingly, relations among haplotype lineages present a strong geographic agreement and a highly discontinuous divergence pattern. The observed patterns of low genetic variability and high genetic structuring – a lack of shared haplotypes between populations, indicating distinct genetic lineages – might result from historic barriers to gene flow and from the species' reduced capacity for dispersal. However, they may also reflect other processes, such as severe population reductions and subsequent recovery (genetic bottlenecks) and the differentiation of remnant populations. These facts accentuate the importance of monitoring animals in their remaining habitat, and also highlight the genetic dangers posed by uninformed translocations between isolated lineages in different states. These results emphasize the need to thoroughly investigate patterns of genetic variability using nuclear markers (a study already in progress) – and if emerging patterns are confirmed, it will further emphasize the need for careful genetic management to promote the recovery and maintenance of the genetic diversity of the surviving populations.