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The monozoic tapeworm Caryophyllaeus laticeps has been characterized by five markedly different morphotypes largely corresponding to different fish hosts. Recently, the most distinct morphotype 4 from the common nase Chondrostoma nasus was studied in more details resulting in description of a new species Caryophyllaeus chondrostomi. The molecular study based on mitochondrial cox1 and ribosomal lsrDNA did not reveal any interspecific differences between C. laticeps and C. chondrostomi and did not provide any molecular support for recognition of these two species. In the current study, six polymorphic microsatellite markers were applied in order to detect molecular differences between the two species and to provide molecular evidence of validity of C. chondrostomi. While all six microsatellite loci were amplified in different geographic populations of C. laticeps, only two of them provided the amplification product in C. chondrostomi. Results on the Bayesian analysis assigned C. chondrostomi and all geographic populations of C. laticeps to distinct clusters. Neither any close relationships among C. laticeps populations nor specific position of C. chondrostomi were revealed. Contrary, the results of the principal coordinate analysis revealed striking genetic separation of C. chondrostomi with no overlaps with any of the C. laticeps population or morphotype. Caryophyllaeus chondrostomi very probably underwent morphological divergence as a result of ongoing speciation, but this process has not yet been accompanied by sufficient genetic divergence. In this particular case, microsatellites were proved to be better molecular discriminative markers than rDNA and mtDNA.

Major histocompatibility complex class II (MHC II) is an essential molecule triggering the adaptive immune response by the presentation of pathogens to helper T cells. The association between individual MHC II variants and various parasites has become a frequent finding in studies of vertebrate populations. However, although bird ectoparasites have a significant effect on their host's fitness, and the host's immune system can regulate ectoparasitic infections, no study has yet investigated the association between MHC II polymorphism and ectoparasite infection in the populations of free-living birds. Here, we test whether an association exists between the abundance of a chewing louse (Myrsidea nesomimi) and MHC II polymorphism of its hosts, the Galápagos mockingbirds (Mimus). We have found that the presence of two MHC II supertypes (functionally differentiated clusters) was significantly associated with louse abundance. This pattern supports the theory that a co-evolutionary interaction stands behind the maintenance of MHC polymorphism. Moreover, we have found a positive correlation between louse abundance and heterophil/lymphocyte ratio (an indicator of immunological stress) that serves as an additional piece of evidence that ectoparasite burden is affected by immunological state of Galápagos mockingbirds.

Atractolytocestus tenuicollis (Li, 1964) Xi, Wang, Wu, Gao et Nie, 2009 is a monozoic, non-segmented tapeworm of the order Caryophyllidea, parasitizing exclusively common carp (Cyprinus carpio L.). In the current work, the first molecular data, in particular complete ribosomal internal transcribed spacer 2 (ITS2) and partial mitochondrial cytochrome c oxidase subunit I (cox1) on A. tenuicollis from Niushan Lake, Wuhan, China, are provided. In order to evaluate molecular interrelationships within Atractolytocestus, the data on A. tenuicollis were compared with relevant data on two other congeners, Atractolytocestus huronensis and Atractolytocestus sagittatus. Divergent intragenomic copies (ITS2 paralogues) were detected in the ITS2 ribosomal spacer of A. tenuicollis; the same phenomenon has previously been observed also in two other congeners. ITS2 structure of A. tenuicollis was very similar to that of A. huronensis from Slovakia, USA and UK; overall pairwise sequence identity was 91.7-95.2%. On the other hand, values of sequence identity between A. tenuicollis and A. sagittatus were lower, 69.7-70.9%. Cox1 sequence, analysed in five A. tenuicollis individuals, were 100 % identical and no intraspecific variation was observed. Comparison of A. tenuicollis cox1 with respective sequences of two other Atractolytocestus species showed that the mitochondrial haplotype found in Chinese A. tenuicollis is structurally specific (haplotype 4; Ha4) and differs from all so far determined Atractolytocestus haplotypes (Ha1 and Ha2 for A. huronensis; Ha3 for A. sagittatus). Pairwise sequence identity between A. tenuicollis cox1 haplotype and remaining three haplotypes followed the same pattern as in ITS2. The nucleotide and amino acide (aa) sequence comparison with A. huronensis Ha1 and Ha2 revealed higher sequence identity, 90.3-90.8% (96.9% in aa), while lower values were achieved between A. tenuicollis haplotype and Ha3 of Japanese A. sagittatus-75.2 % (81.9 % in aa). The phylogenetic analyses using cox1, ITS2 and combined cox1 + ITS2 sequences revealed close genetic interrelationship between A. tenuicollis and A. huronensis. Independently of a type of analysis and DNA region used, the topology of obtained trees was always identical; A. tenuicollis formed separate clade with A. huronensis forming a closely related sister group.