Grau de parentesco e relações sociais em ariranhas (Pteronura brasiliensis)

Abstract

Molecular analysis has revolutionized knowledge of the social systems of species. Giant otters are social animals who demonstrate strong cooperation between individuals of the same group, and studies based on behavioral observation suggeste that the group is composed of a dominant reproductive pair and their offspring from subsequent years, which do not reproduce. This study had as objectives (1) to establish a semi-invasive method of retrieving genetic samples (tissue) from wild giant otters; (2) to develop specific microsatellite markers from Pteronura brasiliensis; (3) to access the degree of relatedness within and between groups of giant otters in the southern Pantanal, Brazil. Biopsy darts allowed us to collect tissue samples with high DNA quality from a large number of giant otters (n=41). This method cost less and was less invasive than capture, and allowed for the choice of individual to be sampled. Twelve polymorphic loci of microsatellites specific to P. brasiliensis with high resolution for paternal analysis were isolated. DNA samples were opportunistically collected by means other than biopsy darts, for a total of 50 genotyped giant otters. All examined animals belonged to a unique population, indicating substantial gene flow on the scale examined. The nuclear variability found in the population of the Pantanal was within the observed range for giant otters in larger geographic scales as well as for other otter species. The giant otter groups were usually composed of an unrelated dominant pair and their close relatives. However, the degree of relatedness varied within the groups, contradicting the current knowledge that giant otter groups are formed exclusively by a dominant pair and their offspring. The ecological mechanisms that lead to high relatedness variance within giant otters groups it is unclear, but we believe that high migration rate of individuals across groups, extra-pair copulation and subordinate reproduction can play important roles, as they do in other apparently monogamous species.