We investigated the types of endosymbionts present in Dreissena mussels in Lake Ohrid, Republic of Macedonia,
and characterized their intensity, prevalence, location, and host impact. Considering the taxonomic uncertainty
of many Balkan dreissenid populations, accurate host identity was considered a very high priority. Our
efforts using both morphological and molecular approaches confirmed the identity of all mussels examined to
be Dreissena stankovici. Key external shell characteristics of D. stankovici are its possession of a: 1) a carina,
2) a convex posterior ventral surface, and 3) a sharp dorsal longitudinal ridge that is distinctively-peaked in
most specimens and slightly convex to almost straight immediately posterior to its peak. Nucleotide sequence
data were successfully generated for 67 Lake Ohrid Dreissena. For each mussel, sequences were obtained for at
least 1 of the following 3 DNA loci: mitochondrial gene 16S rRNA, nuclear gene 28S rRNA, and mitochondrial
gene cytochrome c oxidase subunit I (COI). Remarkably little intraspecific variation was observed in our data
matrices for these 3 gene regions, and we interpreted this, in combination with BLAST searches of the NCBI
database, as strong evidence that the specimens examined were all conspecific D. stankovici. Specimens of
Dreissena polymorpha and Dreissena rostriformis bugensis were used for comparison purposes in both morphological
and molecular analyses.
This is the first study documenting the endosymbiont community in D. stankovici. This dreissenid population in
Lake Ohrid appears to have a rich endosymbiont assemblage, ranging from commensals to parasites, and is comprised
primarily of ciliates (Conchophthirus, Hypocomagalma, Ophryoglena, and Sphenophrya), trematodes
(Echinostomatidae and Phyllodistomum), and intracytoplasmic prokaryote infections. One of the most interesting
findings of our study was how similar this endosymbiont assemblage was to that reported from European
D. polymorpha populations. This perhaps should not be unexpected, however, since D. stankovici and D. polymorpha
are considered sister taxa with divergence estimated at only several million years ago.