Managing Polyploidy in Ex Situ Conservation Genetics: The Case of the Critically Endangered Adriatic Sturgeon (Acipenser naccarii)

Abstract

While the current expansion of conservation genetics enables to address more efficiently the management of threatened species, alternative methods for genetic relatedness data analysis in polyploid species are necessary. Within this framework, we present a standardized and simple protocol specifically designed for polyploid species that can facilitate management of genetic diversity, as exemplified by the ex situ conservation program for the tetraploid Adriatic sturgeon Acipenser naccarii. A critically endangered endemic species of the Adriatic Sea tributaries, its persistence is strictly linked to the ex situ conservation of a single captive broodstock currently decimated to about 25 individuals, which represents the last remaining population of Adriatic sturgeon of certain wild origin. The genetic variability of three F1 broodstocks available as future breeders was estimated based on mitochondrial and microsatellite information and compared with the variability of the parental generation. Genetic data showed that the F1 stocks have only retained part of the genetic variation present in the original stock due to the few parent pairs used as founders. This prompts for the urgent improvement of the current F1 stocks by incorporating new founders that better represent the genetic diversity available. Following parental allocation based on band sharing values, we set up a user-friendly tool for selection of candidate breeders according to relatedness between all possible parent-pairs that secures the use of non-related individuals. The approach developed here could also be applied to other endangered tetraploid sturgeon species overexploited for caviar production, particularly in regions lacking proper infrastructure and/or expertise.

Genetic profile analysis of aquaculture Russian sturgeon (Acipenser gueldenstaedtii) – implications for restocking measures

“…Our own results show that 67% of loci have a tetrasomic profile, 8% are octasomic, and 17% are disomic. AnacE4 was shown to be tetrasomic for Acipenser naccarii (Bonaparte, 1836) in case of Congiu et al (2011) while our results for A. gueldenstaedtii showed a maximum number of alleles per locus of 3. The data suggests that there is a high degree of transition from an octaploid state to a tetraploid one and that the genome for A. gueldenstaedtii has a low degree of functional diploidization.…”

Validation of 12 species-specific, tetrasomic microsatellite loci from the Russian sturgeon, Acipenser gueldenstaedtii, for genetic broodstock management

“…Jenneckens et al (2001) suggested to estimate the number of allele copies on the basis of peak heights and areas in the electropherograms as exemplified by the microsatellite locus LS-39 in the Siberian sturgeon Acipenser baerii. However, this approach seems not to be fully reliable: Congiu et al (2011) found that the four peaks of a complete heterozygous genotype did not always show the expected same height in Adriatic sturgeon, and the same discrepancy was observed in the present study of Russian sturgeon (data not shown). Instead, Congiu et al (2011) proposed a band sharing approach for which microsatellite data were considered as presence/absence of bands, disregarding the number of alleles present in each individual.…”

“…However, this approach seems not to be fully reliable: Congiu et al (2011) found that the four peaks of a complete heterozygous genotype did not always show the expected same height in Adriatic sturgeon, and the same discrepancy was observed in the present study of Russian sturgeon (data not shown). Instead, Congiu et al (2011) proposed a band sharing approach for which microsatellite data were considered as presence/absence of bands, disregarding the number of alleles present in each individual. Another and probably more convenient solution of the problem is provided by software specifically designed for the analyses of (allo-)tetraploid microsatellite loci: TETRASAT (Markwith et al 2006), TETRA (Liao et al 2008), and ATETRA (Van Puyvelde et al 2010).…”

“…However, they have limitations in the light of the present development of sequencing technologies (Putman and Carbone 2014) that are underlined by their utilization in polyploid organisms (Dufresne et al 2014;Meirmans et al 2018). Although microsatellites might be displaced by single nucleotide polymorphisms (SNPs) for sturgeon conservation in future (Ogden et al 2013), their suitability for the management of a captive broodstock of another tetraploid sturgeon species, the critically endangered Adriatic sturgeon Acipenser naccarii, could clearly be demonstrated (Congiu et al 2011).…”

Transcriptome sequencing and de novo annotation of the critically endangered Adriatic sturgeon

“…Sturgeons (order: Acipenseriformes, infraclass: Chondrostei) are a very ancient fish group distributed in the Palearctic hemisphere with about 25 species, most of which are considered to be on the brink of extinction [1]. Their conservation importance has led to the inclusion of all the species in the red list of the International Union for the Conservation of Nature (IUCN) and to commercial restrictions under the Convention for International Trading of Endangered Species (CITES).…”