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

Abstract

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 southeast. In 2009, a few individuals were discovered on the southeastern 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 southeastern 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 southeastern 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 southeastern 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 southeastern 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.

Non‐invasive sampling reveals low mitochondrial genetic diversity for an island endemic species: The critically endangered Grenada Dove Leptotila wellsi

“…This is not uncommon in island species and populations have been known to successfully recover from a very small number of individuals (Copsey et al., 2018), for example, the Pink Pigeons went from nine or 10 individuals in 1990 to 446 in 2011 (Swinnerton et al., 2004), the Echo Parakeet Psittacula eques went from as low as 12 individuals in the 1990s to more than 500 in 2010 (Raisin et al., 2012) and the Rodrigues Warbler Acrocephalus rodericanus started with approximately 17 individuals in 1979 and grew to more than 3000 in 2010 (Copsey et al., 2018; Showler et al., 2002). Additional isolated populations may be useful for rescue measures and to protect against localised extinction (du Plessis et al., 2019; Frankham et al., 2019; Grant et al., 2001); however, reliable information and regular assessment of genetic variability are essential for conservation decisions and to monitor whether new populations are successfully established (Gregory et al., 2012).…”

“…The data from this study revealed unique genetic variation at one locality (Perseverance) suggesting additional habitat protection at this site is important for conserving genetic diversity in this species (Tarr & Fleischer, 1999). Re‐introduction of the Grenada Dove to dry forest in its northern historic range, using individuals from both Mt Hartman and Perseverance, could also be beneficial as geographically separate populations are not only important for promoting genetic diversity (du Plessis et al., 2019; Gregory et al., 2012; Major et al., 2021) but also in safeguarding against natural disasters such as hurricanes. Given recent habitat loss on Grenada, availability of suitable habitat on the island for establishing new populations is limited and would likely result in additional isolated populations (Prugh et al., 2008; Rusk et al., 2008).…”

“…Carrying out genetic diversity assessment using nuclear markers, which are inherited from both parents, would avoid these issues; however, this was not possible in this study because of the type and degraded nature of the samples (Peters et al, 2019). ASRs are a key component in understanding species' demography and biology (Bosque & Pacheco, 2019;Donald, 2007;Székely et al, 2014) and therefore further investigation into the sex ratio, such as the banding programme proposed in Bolton et al (2015), could be critical for the survival of this critically endangered species.…”

“…Skewed sex ratios may not be the result of unequal production of the sexes at birth but could be the result of differential adult survival rates where one sex is at higher risk of predator-based mortality or more susceptible to parasites and disease (Bosque & Pacheco, 2019;Székely et al, 2014). There have been a number studies on ASR in bird populations which have revealed, for example, that a male skew is frequently seen in threatened species (Donald, 2007) as well as species with small ranges and island species (Venables & Brooke, 2015).…”

How diverse are national banking systems? An analysis on banking business models, profitability, and riskiness

“…Human beings can affect the genetic structure of populations by introducing or removing barriers and obstacles and preventing or facilitating gene flows. Nevertheless, isolation prevents genetic diversity (which would contribute to the creation of new populations, strategic for conservation) and facilitates inbreeding (du Plessis et al, ). Regulatory activity works in a similar fashion when pushing institutions toward increasing degrees of legal integration and strategic standardization.…”