Genetic diversity and population structure in the endangered giant otter, Pteronura brasiliensis

Abstract

We assessed levels of genetic diversity and investigated patterns of population structure in three remnant populations of the endangered giant otter, Pteronura brasiliensis, using microsatellite loci. All populations displayed moderate to low levels of heterozygosity and allelic richness (H O 0.56-0.57, A R 4.00-5.15) and effective population sizes were low (N E 10.8-54) although only the Iténez population exhibited the signature of a genetic bottleneck. Population structure analyses revealed a pattern in which the populations of the Upper Amazon, Orinoco and Essequibo drainages comprised partially differentiated segments of a northern South American metapopulation, whereas the population of the Iténez appeared isolated. The observed patterns are congruent with previous mitochondrial DNA analysis which suggested the Iténez and northern South American groups constitute two evolutionary significant units. The results presented here should be considered in planning future policies aiming to manage the recovery of the giant otter across its range.

Advances in the study of giant otter (Pteronura brasiliensis): ecology, behavior, and conservation: a review

“…However, data obtained by Pickles et al (2012) presented little evidence of bottleneck despite the population collapse due to widespread hunting for pelts between 1940 and 1975. According to the authors during this harvest period about 65000 giant otters were killed, corresponding to three or four generations of giant otters. Four reasons were presented by Pickles et al (2012) to explain the lack of bottleneck signature and the retention of moderate genetic diversity: 1) the fur hunting period, while extensive, left multiple locally isolated pockets of otter packs, 2) the vagile nature of transient male giant otters maintained a degree of contact among dispersed packs, 3) reduced density effects following cessation of hunting may have encouraged recolonization of river systems from which the species was extirpated, and 4) the long generation time of the giant otter may have buffered the attrition of genetic diversity.…”

“…Pickles et al (2012) also investigated patterns of population structure in those phylogeographic groups previously described and the data suggest a degree of reproductive isolation between the Iténez (Bolivia) population and the populations of northern South America.…”

“…Four reasons were presented by Pickles et al (2012) to explain the lack of bottleneck signature and the retention of moderate genetic diversity: 1) the fur hunting period, while extensive, left multiple locally isolated pockets of otter packs, 2) the vagile nature of transient male giant otters maintained a degree of contact among dispersed packs, 3) reduced density effects following cessation of hunting may have encouraged recolonization of river systems from which the species was extirpated, and 4) the long generation time of the giant otter may have buffered the attrition of genetic diversity. Nevertheless, further work investigating contemporary and historical levels of genetic diversity in the eastern and southern parts of the otter's distribution, where the species is severely reduced, should be conducted to determine the actual effect of the past hunting pressures on the genetic diversity of P. brasiliensis (Pickles et al, 2012).…”

“…Hydroelectric dams: While hydroelectric dams may present major threats for giant otters (Pickles et al, 2012), there are still limited data to accurately evaluate the effects caused by these infrastructure elements on giant otter populations. As stated earlier, judging by the number of giant otter groups identified in only 10% of the Balbina hydroelectric lake (at least 35 groups present) it seems that in some instances such man-made lakes can sustain viable populations of giant otters .…”

“…According to Pickles et al (2012) despite giant otter populations recovering in parts of their range, the species remains patchily distributed and it is unlikely that gene flow is currently occurring among the populations of northern South America (Amazonas, Orinoco and Guianas). Therefore, the authors recommend the re-establishment and maintenance of the complex pattern of connectivity within this metapopulation allowing the dispersal of the species via corridors among the Orinoco, Amazon and Guianas (Pickles et al, 2012).…”