Genetic diversity and cryptic population re-establishment: management implications for the Bojer’s skink (Gongylomorphus bojerii)

Understanding genetic structure and diversity underpins the management of isolated populations. Small populations confined to islands may require effective genetic management for population persistence due to inbreeding and reduced genetic diversity. Endemic to the offshore islands of mainland Mauritius, the Bojer’s skink (Gongylomorphus bojerii) has previously been managed as two genetic units due to divergence between populations to the north and south-east. In 2009, a few individuals were discovered on the south-eastern island Ile de la Passe (IDLP), an island within its former range where the species was believed to have gone extinct. This island was later supplemented with translocations from other south-eastern islands, but individual geographic origin and the genetic consequences of these translocations remains unknown. Demographic population history and translocation events were reconstructed using a suite of microsatellite markers and the mitochondrial DNA cytochrome b gene, assessing two northern and three south-eastern populations to infer the geographic origin of the IDLP individuals, and to assess the population’s genetic diversity and structure. Although IDLP showed significant differentiation from all other populations, all analyses indicated a south-eastern origin, possibly founded by a single gravid female. Subsequent translocations have so far failed to ameliorate IDLP’s genetic diversity. In addition, admixture analysis was used to track translocation and gene-flow in IDLP. We recommend using additional translocations from other south-eastern islands to further genetically support IDLP. Our study highlights the need to clarify cryptic population structure and utilise post-translocation genetic monitoring among similarly managed populations, particularly endangered island populations.