GENETIC AND GENOMIC INVESTIGATIONS FOR THE CONSERVATION OF STURGEONS

The order of Acipenseriformes is one of the most endangered taxa. One paddlefish species and another sturgeon species have been recently declared respectively ‘Extinct’ and ‘Extinct in the Wild’ according to the IUCN Red List’s assessment. Of the remnant twenty-five species, twenty are classified either as ‘Endangered’ or ‘Critically Endangered’ while the last five are stated as ‘Vulnerable’. Therefore, these populations require timely and adequate conservation plans both in situ and ex situ that need to be informed by relatedness analysis and genetic variability characterization. The present Ph.D. thesis will mainly focus on the Adriatic sturgeons (Acipenser naccarii), a tetraploid species endemic to the Adriatic region, and historically present in the Po Rivers and its tributaries. Intending to preserve the highest possible level of genetic variability in future generations the farmed progenies (F1), now mature, need to be allocated to their parents of wild origin (F0) to identify groups of sibs and to inform breeding plans. To this purpose, microsatellite loci will be used as they still be the best markers to study polyploid species. However, before applying microsatellite markers to parental allocations, the segregation patterns at these loci need to be previously assessed. In fact, different possible inheritance patterns are possible in tetraploids, namely disomic and tetrasomic. A similar microsatellite-based relatedness analysis was then applied to another sturgeon species on the brink of extinction, the Chinese sturgeon (Acipenser sinensis), to estimate the minimum breeders’ number that participated in the only significant breeding event occurs in the last 10. Even in this case microsatellite loci, resulted to be powerful molecular markers for parental inferences, allowing to estimate an approximative number of 10 males and 10 females remaining for this species. The Adriatic sturgeon was also included in a PRIN project called ENDEMIXIT (https://endemixit.com/) whose aim is to apply conservation genomics to five endangered Italian endemics. Given the possibility to perform controlled reproductions, this species was selected to test in vivo the potentiality and weakness of genomic mutation load predictions, evaluating the relations between the load of bioinformatically identified deleterious mutations and the offspring fitness of selected parents. Another relevant contribution of genetics to the management of captive stocks is the development of suitable markers for the identification of interspecific hybrids which are frequently occurring in captive stocks due to the promiscuity between aquaculture for commercial production and aquaculture for conservation. To develop a new category of multilocus markers (MIPs, Multi-locus Intron Polymorphisms) that allow the detection of multi-species contribution also in hybrids after the first generation, the possibility to use the polymorphisms of intronic regions was explored. This study followed a more general investigation on Teleosts in which thanks to the numerous available genomes, a highly transferable panel of primers for intronic regions amplification was identified and a protocol for simultaneous amplification followed by sequencing on Illumina platform was optimized. Introns proved to be promising markers at both species and population levels in different teleost species. For this reason, the same approach was applied to sturgeons. MIPs markers designed for sturgeons promise to be highly versatile with many possible applications from individuals to populations levels in detecting differentiation signals. An important tool for the analyses of genetic diversity in situ and ex situ conservation plans, and the identification of species and hybrids to contrast the illegal trade of surgeons’ derived products.