Genetic and viability assessment of a reintroduced Eurasian otterLutra lutrapopulation on the River Ticino, Italy

Abstract

On the River Ticino in northern Italy, a small number of captive Eurasian otters Lutra lutra, belonging to the European breeding programme for self-sustaining captive populations, were reintroduced in 1997, after the species had been declared locally extinct in the 1980s. We surveyed for otter signs in 2008, 2010, 2016–2017 and 2018, confirming the presence of what is probably a small population. To assess the abundance and viability of the population, we genotyped fresh spraints collected during the last two surveys, using 11 microsatellite markers, and modelled the population trend using Vortex. A minimum of six individuals were identified from 25 faecal samples. The analysis of mitochondrial DNA determined that the reintroduced otters share a transversion that is characteristic of the Asiatic subspecies Lutra lutra barang, confirming the contribution of the Asiatic subspecies to the genetic pool of the captive-bred founder population. Population size was consistent with the release of three pairs of otters and all models implied that the number of founders was too small to ensure the long-term survival of the population. Stochastic factors are therefore likely to threaten the success of this reintroduction.

Avoiding bias in estimates of population size for translocation management

“…In such cases, if managers believe the population is larger than it really is, they might miss a crucial window of opportunity to reinforce it, thereby averting possible establishment failure (Armstrong & Seddon, 2008; Panfylova et al, 2019) driven by stochastic demographic processes (Bubac et al, 2019; Clark et al, 2002; Converse et al, 2013; Griffith et al, 1989), dispersal (Moseby et al, 2014; Resende et al, 2021) or Allee effects (Allee, 1931; Armstrong & Wittmer, 2011; Courchamp et al, 1999). Even if the population persists without reinforcement, it may be at increased risk of longer term inbreeding depression and reduced adaptive potential driven by this and genetic drift (Balestrieri et al, 2021; Frankel, 1970; Frankham, 2005).…”

Faecal DNA-based genetic survey of a relict Eurasian otter (Lutra lutra) population (Sila Massif, S Italy)

“…Overall, genotyping success was relatively high compared to previous studies (e.g., 14%, Lanszki et al 2008;21%, Ferrando et al 2008;41%, Prigioni et al 2006a;43%, Vergara et al 2014;73% Janssens et al 2008), balancing sample size, which was rather low (N = 47 vs. 156, 124, 185, 127 and 117, Fig. 2 Distribution and sex (males: black; females: white; undetermined: gray) of genotyped otters on the rivers Savuto (A-7 individuals: 1 male, 3 females, 2 undetermined) and Lese-Lepre (B-6 individuals: 2 males and 4 females, of which one (Open triangle)recorded in all the sampling stations on the R. Lese) respectively), being inevitably affected by otter abundance (Balestrieri et al 2021). However, following Arandjelovic and Vigilant (2018), the number of spraints analysed was about three times the number of individuals expected to occur in the sampled river stretches.…”

“…The unicity of the Italian otter population will need to be carefully considered whenever planning translocations to enhance its recolonisation of the whole Peninsula, as the admixture of historically isolated populations may increase genetic diversity but also lead to outbreeding depression (Frankham et al 2017). Guidelines for translocations ask for the genetic assessment of both donor and recipient populations to prevent introgression between subspecies (see Balestrieri et al 2021 about the contribution of the Asiatic L. lutra barang to the genetic pool of otters reintroduced in northern Italy). While this study confirmed the spread of H10 in southern Italy, further studies are needed to highlight, through the analysis of museum specimens, the genetic structure of the extinct sub-population of the River Po catchment, as the recent expansion of the Austrian and French populations demonstrates the existence of corridors crossing the Alps (Giovacchini et al 2021).…”

“…Ongoing Eurasian otter (Lutra lutra) natural expansion, as well as reintroduction programs carried out across Europe (Wayre 1985;Fernández-Morán et al 2002;Koelewijn et al 2010;Balestrieri et al 2021), require a detailed evaluation of the genetic structure of the different populations to enhance genetic variability while preserving "unique" haplotypes (Weeks et al 2016).…”

Low but highly geographically structured genomic diversity of East Asian Eurasian otters and its conservation implications

“…In Europe, efforts at standardized surveying and monitoring have indicated that some local populations are gradually recovering from the brink of extinction (such as in Great Britain; Mason & Macdonald, 2004). Reintroduction programs have also successfully re‐established some local populations (e.g., Balestrieri et al., 2021). The sparse information available about East Asian otters indicates that they have also sharply declined in number since the 1950s (Conroy et al., 1998).…”