Fine-scale genetic analysis of the exploited Nile monitor (Varanus niloticus) in Sahelian Africa

Abstract

BackgroundOverexploitation of wildlife populations results in direct consequences, such as extinction and local extirpation, as well as indirect effects including genetic diversity loss and changes in genetic structure. A clear understanding of the underlying genetic patterns of harvested species is necessary for sustainable management. The Nile monitor (Varanus niloticus) is a commercially valuable species in the international leather industry, with the highest levels of exploitation concentrated throughout Sahelian Africa. In this study, we examined the fine-scale genetic patterns of V. niloticus populations in the Sahel, with the expectation that the genetic structure would correspond to riverine drainage basins. The analyses were based on genotypes at 11 microsatellite loci for 318 individuals, spanning three separate watersheds throughout the Sahel.ResultsOur analyses identified four genetic clusters throughout the region, one of which (the westernmost population) exhibited very high levels of genetic differentiation (FST = 0.47). Contrary to our expectation, the largest genetic break occurred within a single watershed, the Niger basin, rather than between watersheds. However, other localities displayed evidence of reduced gene flow between watershed boundaries. Across methods, the westernmost population exhibited lower estimates of Ne as well as lower levels of genetic diversity compared to the other inferred populations. While we did not detect evidence for recent population bottlenecks, our analyses indicated historic population declines around 1,000–1,800 years ago.ConclusionWe found that the underlying genetic structure of Varanus niloticus across Sahelian Africa reflects historic as well as present-day patterns of riverine drainages. The high degree of differentiation found for the westernmost population indicates the presence of a separate lineage, and should be taken into consideration when setting harvest limits. The historic population decline for two of the populations corresponds to a drastic expansion of an ancient human civilization in the region, suggesting that human exploitation of V. niloticus has a longer history than previously thought.Electronic supplementary materialThe online version of this article (doi:10.1186/s12863-015-0188-x) contains supplementary material, which is available to authorized users.

Molecular data from contemporary and historical collections reveal a complex story of cryptic diversification in the Varanus (Polydaedalus) niloticus Species Group

“…Additionally, the cryptic western lineage within V. niloticus exhibits genetic differentiation levels above those typically found between sister varanid species. In a fine-scale genetic analysis, Dowell et al (2015) similarly found a sharp genetic break between V. niloticus populations in western Mali and those farther east, with very little evidence of admixture despite no obvious current geographic barrier. The same study also found reduced genetic diversity levels within the western lineage compared to neighboring V. niloticus populations (Dowell et al, 2015).…”

“…acanthurus (Fitch et al, 2005) following the modifications of Dowell et al (2015). Fragment analysis was carried out on an ABI 3100 Genetic Analyzer (Applied Biosystems, Inc.) with GeneScan 500 LIZ size standard and genotypes were scored using GeneMarker (SoftGenetics).…”

Present and Future Suitability of the Lake Tana Biosphere Reserve (LTBR) in Ethiopia for the Nile monitor (Varanus niloticus) using the MaxEnt Mode

“…However, it seems very unlikely that a true interspeci c competition could occur between the two species as they remarkably differ in size and the area where they forage. Crocodiles entirely forage in aquatic habitats whereas Varanids prefer to both terrestrial and aquatic habitats with permanent water bodies to forage and open rooftops and streets to bask (Dowell et al 2015). Besides, Varanids inhabit a wide variety of habitats including woodland, dry savanna, scrub, evergreen thickets, swamps, mangroves, marshes, creeks, rivers, lakes and in disturbed areas near canals (Luiselli et al 1999).…”

“…Although the practice is not common in the Lake Tana Biosphere Reserve (LTBR), the species is being hunted in Sahelian Africa for its leather, food, pet trade and for some medical treatments (Ahmed et al 2018). Consequently, the species is listed under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES, Appendix II) (Dowell et al 2015). This study, therefore, has tried to estimate population size, identify potential hotspots, and model the spatiotemporal distribution of Nile monitor (Varanus niloticus) within the LTBR, Ethiopia.…”

Insights into the introduction histories and population genetic dynamics of the Nile monitor (Varanus niloticus) and Argentine black and white Tegu (Salvator merianae) in Florida.

“…A recent study by Dowell et al (2015) examined the fine-scale genetic patterns of V. niloticus populations in West Africa under varying levels of exploitation pressure, and represents the only population-level assessment of native V. niloticus populations. For the four discrete populations that were inferred from microsatellite data, both genetic diversity and effective population size estimates were larger than for the introduced populations examined here, displaying H e values between 0.328 -0.429, and N e estimates ranging from 10.9 -1,327.27, depending on the population and method of analysis .…”