Ligula intestinalis (Linnaeus, 1758) is a tapeworm parasite with a worldwide distribution that uses a wide variety of fish species as its second intermediate host. In the present study, we investigated the prevalence and population genetic structure of plerocercoids of L. intestinalis in five common cyprinoid species, roach Rutilus rutilus (Linnaeus), freshwater bream Abramis brama (Linnaeus), white bream Blicca bjoerkna (Linnaeus), bleak Alburnus alburnus (Linnaeus), and rudd Scardinius erythrophthalmus (Linnaeus), collected in six water bodies of the Czech Republic (Milada, Most, Medard, Jordán, Římov and Lipno). Of the six study sites, the highest frequency of parasitism was recorded in Lake Medard (15%). The overall prevalence rate among the species was as follows: roach > rudd ≥ freshwater bream > bleak > white bream. Two mitochondrial genes (cytb and COI) were used to compare the population genetic structure of parasite populations using selected samples from the five fish species. The results of the phylogenetic analysis indicated that all populations of L. intestinalis were placed in Clade A, previously identified as the most common in Europe. At a finer scale, haplotype network and PCoA analyses indicated the possible emergence of host specificity of several mtDNA haplotypes to the freshwater bream. Moreover, pairwise Fixation indices (FST) revealed a significant genetic structure between the parasite population in freshwater bream and other host species. Parasite populations in roach not only showed the highest rate of prevalence but also depicted a maximum number of shared haplotypes with populations from bleak and rudd. Our results suggest that recent ecological differentiation might have influenced tapeworm populations at a fine evolutionary scale. Thus, the differences in prevalence between fish host species in different lakes might be influenced not only by the parasite's ecology, but also by its genetic diversity.
Fish species exhibit different preferences and are segregated according to a set of physical habitat conditions. We documented microhabitat preferences on the three dimensions (substrate type, water depth, current velocity) for two native species: the stream catfish, Trichomycterus corduvense and the eel catfish, Heptapterus mustelinus. The study was conducted on the Anizacate River in a semiarid region of Córdoba Province located in central Argentina. We established one transect perpendicular to flow at the downstream end of each study site with subsequent parallel transects spaced at 5 m intervals throughout the length of the study site. Fish collections and habitat measurements were made in 1 m2-quadrates at 3 m-intervals along each transect. We quantified available microhabitats and estimated the proportion used by both fish species through suitability curves, niche breadth and Shoener ́s overlap formula. Current velocity is the key factor that distinguishes microhabitat use between T. corduvense and H. mustelinus. The former species is acting as a velocity specialist whereas the latter could be considered as a generalist. In spite of the trophic competition between these species, spatial partitioning may be promoting coexistence of H. mustelinus and T. corduvense in Anizacate River.