Genetic structure of red-handed howler monkey populations in the fragmented landscape of Eastern Brazilian Amazonia

Abstract

We genotyped 15 microsatellite loci in order to evaluate the effects of habitat fragmentation, caused by flooding of the Tucuruí reservoir, on the genetic structure of Alouatta belzebul in eastern Amazonia. The analysis included two populations sampled in 1984, representing both margins of the Tocantins river, and three populations sampled 18 years later. Minimal differences in the diversity levels between present-day (Ho = 0.62-0.69 and A(R) = 6.07-7.21) and pre-flooding (Ho = 0.60-0.62 and A (R) = 6.27-6.77) populations indicated there was no significant loss of genetic variability, possibly because of successful management strategies applied during the flooding. The changes observed were limited to shifts in the composition of alleles, which presumably reflect the admixture of subpopulations during flooding. Given this, there were significant differences in the Rst values (p = 0.05) in all but one between-site comparison. Both present-day and original populations showed a deficit of heterozygotes, which suggests that this may be typical of the species, at least at a local level, perhaps because of specific ecological characteristics. The relatively large number of private alleles recorded in all populations may be a consequence of the Wahlund effect resulting from population admixture or a process of expansion rather than the loss of rare alleles through genetic drift. Additionally, the levels of genetic variability observed in this study were higher than those reported for other species of Neotropical primates, suggesting good fitness levels in these A. belzebul populations. Regular genetic monitoring of remnant populations, especially on islands, should nevertheless be an integral component of long-term management strategies.

Keywords: Alouatta belzebul; Amazonia; conservation; genetic structure; habitat fragmentation.

Figure 1

Map of the study area based on satellite imagery, showing the Tucuruí reservoir (center) and the sampling localities mentioned in the text. The Tocantins river (in black) runs south-north. In the surrounding matrix, darker gray areas are forest, while lighter coloration indicates pasture or plantations. A includes LB02 = Germoplasma Island in 2002, representing the left bank of the Tocantins post-flooding, B includes RB85 = Base 4 in 1985, representing the right bank prior to flooding, RB02 = Base 4 in 2002, representing the right bank post-flooding, and RB02B = Cornélio Island in 2002, an isolated post-flooding right bank population, C includes LB85 = Base 3 in 1985, representing the left bank prior to flooding of the reservoir.