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Abstract Parthenogenesis, or virgin birth, describes a mode of reproduction where an egg develops into an offspring without fertilization, and is observed across various vertebrate taxa, excluding mammals. Obligate parthenogenesis, found in around 100 vertebrate species and 1000 invertebrate species, is relatively rare. Conversely, facultative parthenogenesis, where females can reproduce both sexually and parthenogenetically, is observed in some vertebrates, including elasmobranchs. Notably, this phenomenon in elasmobranchs is mainly documented in captivity, allowing for detailed long-term observation. Specifically, this study reports the first case of facultative parthenogenesis in the common smooth-hound shark Mustelus mustelus, a species classified by IUCN as endangered. Here we show that the juvenile M. mustelus were born through parthenogenesis, exhibiting homozygosity at each genetic marker, consistent with terminal fusion automixis. Remarkably, this finding reveals that parthenogenesis can occur annually in these sharks, alternating between two females, and conclusively excludes long-term sperm storage as a cause. Consequently, this enhances our understanding of parthenogenesis in elasmobranchs and highlights the reproductive flexibility of M. mustelus. Overall, these results contribute to our broader understanding of reproductive strategies in elasmobranchs, which could inform conservation efforts for endangered species.

In the fresh waters of Sardinia (Italy), the non-indigenous crayfish species Procambarus clarkii has been reported from 2005, but, starting from 2019, there have been several reports of a new non-indigenous crayfish in southern and central areas of this Mediterranean island, and its morphology suggests that this species may be the marbled crayfish Procambarus virginalis. Forty-seven individuals of this putative species were analyzed, using the mitochondrial gene Cytochrome c Oxidase subunit I as molecular marker to identify this crayfish and investigate the level of genetic variability within the recently established population. Phylogenetic and phylogeographic analyses were carried out on a dataset including sequences from the Sardinian individuals and from all congenerics available in GenBank. Results showed that the new Sardinian crayfish belong to the species P. virginalis. All the sequences belonging to P. virginalis from European countries are identical, with only few exceptions found among Sardinian individuals. In conclusion, this paper highlights the occurrence of a new further alien species in the Sardinian fresh waters, which are already characterized by the high presence of non-indigenous species.