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Phylogeny and phylogeography of the cave bivalve Congeria kusceri, with an outline for its endangerment in Croatia

Congeria kusceri Bole 1962 is the only stygobitic bivalve in the world. It is also the only surviving species of the genus Congeria which was widespread in the tertiary. Its current distribution is quite disjunct. Mitochondrial 16S rRNA and COI and nuclear ITS and 18S rRNA markers were employed to examine the position of the genus within the family Dreissenidae as well as to infer the relations between different populations. Our results support Congeria being the third extant genus of the family Dreissenidae as previous studies suggested. Within Congeria, two main phylogeographical groups were found: one encompassing Markov ponor (Lika region) and Suvaja (northern Bosnia) populations, and another comprising all southern Dalmatian and Hercegovinian populations. Uncorrected genetic distances (P) between them were up to 1.7 %, and 8.8 %, for 16S rRNA and COI marker, respectively. In contrast to the relatively low level of genetic divergence between populations within second group (maximal P values being 0.5 % for 16S rRNA and 1.4 % for COI), genetic distances between Markov Ponor and Suvaja amounted to 1.0 % and 4.3 % for 16S rRNA and COI, respectively. These results are in congruence with biogeographical data since Markov ponor and Suvaja are several hundred kilometres away and hidrologically isolated from the rest of the localities. The species is recorded in a total of fifteen localities in Croatia, but at most sites only shells were found. Live populations were documented in only five sites, but the surveys in 2008 revealed that the two populations disappeared. In addition to being strictly protected by the Croatian law, the species is listed in the Annexes II and IV of the Habitats Directive. Nevertheless, two out of three remaining populations could be facing serious destruction if not extinction in the near future. All this led to the enlistment of Congeria kusceri in the Red list of Croatian cave fauna in the IUCN category CR.

cave; bivalve; Dinarides; Congeria; IUCN

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