Genetic Diversity and Population Structure of the Threatened Giant Arapaima in Southwestern Guyana: Implications for Their Conservation
Information on population genetic structure and connectivity among populations is essential for the implementation of effective conservation and management strategies for threatened species. The giant Arapaima is one of the most heavily exploited and threatened freshwater fishes in Guyana. Using nuclear microsatellite markers and mitochondrial (mtDNA) sequences (partial 16S rRNA gene, tRNA-Leu gene, and ND1 gene), we evaluated the genetic structure of Arapaima from the Essequibo and Branco (i.e., Amazon) river basins in Guyana. Both markers showed low genetic diversity compared to previously reported studies of Arapaima from the Amazon. Only two mtDNA haplotypes were recovered in Guyana that differed in a single nucleotide position. One was novel and restricted to the Branco basin; the other had previously been reported from the Amazon but, in this study, was restricted to the Essequibo basin. Surprisingly, STRUCTURE analysis of microsatellite markers grouped Arapaima from Guyana into three distinct clusters; one was again restricted to the Branco basin, while the other two were sympatric at multiple sites in the Essequibo basin. This is the first time genetically distinct groups of Arapaima have been found in sympatry at multiple sites. Results have important implications for management of Arapaima and conservation of their genetic diversity.
(A) South America showing natural distribution of Arapaima (dark boundary) and our study area in Guyana (black box, indicated by arrow; modified from Castello and Stewart, 2010). (B) Map of southwestern Guyana showing enlarged study area and sampling locations (approximately 4°N, 58°W) for Arapaima: (a) Pirara, (b) Karanambu, (c) Rewa, (d) Apoteri, and (e) Iwokrama; see Table 1 for precise localities for each lake sampled. The double arrow with asterisk marks area of possible faunal interchange between Pirara and Essequibo basins during exceptionally wet years, and short arrows indicate a series of rapids and low waterfalls along the Essequibo River that might allow downstream movement but inhibit upstream movement of Arapaima. Sites a and b fall within savanna habitat and are on opposite sides of the Amazon-Essequibo drainage divide; sites c, d, and e occur within rainforest habitat. Pie charts illustrate proportions of individuals at each site that belong to the three clusters identified in the STRUCTURE analysis (dark gray = C1; gray = C2; and light gray = C3). (C) The bar graph generated by the STRUCTURE program with sites arranged to match geographic position on the map, and within each Essequibo basin site, individual fish are represented by bars arranged according to clusters identified by that analysis (colors as in Fig. 1B).
Mean posterior probability LnP(D) values (circles) per clusters (K) and delta K analysis (squares) of LnP(D); values were generated, respectively, by STRUCTURE (Pritchard et al., 2000) and by STRUCTURE HARVESTER (Earl and von Holdt, 2012).
Contributor Notes
Associate Editor: R. E. Reis.