Nematode burdens and variation in morphological characteristics were assessed in eighty-eight animals from three host species (Apodemus sylvaticus, Apodemus flavicollis, and Myodes glareolus) from eight localities in Serbia. In total, 15 species of nematodes were identified, and the overall mean parasite species richness (IndPSR) was 1.61 per animal (1.98 in A. flavicollis, 1.43 in M. glareolus, and 0.83 in A. sylvaticus). Furthermore, the studied host species significantly differed in individual parasite load (IndPL) and in the following morphological characters: spleen mass, body condition index (BCI), and body mass. We aimed to analyze the relationship between the burden of intestinal nematodes, on one hand, and the body conditions of the host and its capability to develop immune defends on the other. Spleen mass was considered as a measure of immune response. In all host species, larger animals with a better condition (higher BCI) were infected with more parasites species (IndPSR), while parasite load was not related to BCI. Only in A. flavicollis were males significantly larger, but females of the same sizes were infected with more parasite species. This female-biased parasitism is contrary to the theoretical expectation that males should be more parasitized, being larger, more active, with a wider home range. Although the spleen size was significantly correlated with body condition and body mass, IndPSR was not related to spleen mass in any studied species, but in M. galareolus, we found that a smaller spleen was related to higher infection intensity (IndPL).

B chromosomes (Bs) are supernumerary to the standard chromosome set, from which they prevalently derive. Variation in numbers both among individuals or populations and among cells within individuals is their constant feature. Leisler’s bat Nyctalus leisleri (Kuhl, 1817) is one of only four species of Chiroptera with detected Bs. Four males of N. leisleri were collected from two localities on the territory of Serbia and cytogenetically analysed. All animals had Bs with interindividual variability ranging from two to five heterochromatic micro Bs. The highest number of Bs was detected in this species. Among mammals, Rodentia and Chiroptera are orders with the largest number of species, but Bs frequently appear in rodents and rarely in chiropterans. Possible explanations for this difference are offered.

Background Haemosporidian parasites of the genus Polychromophilus infect bats worldwide. They are vectored by obligate ectoparasitic bat flies of the family Nycteribiidae. Despite their global distribution, only five Polychromophilus morphospecies have been described to date. The two predominant species, Polychromophilus melanipherus and Polychromophilus murinus, are broadly distributed and mainly infect miniopterid and vespertilionid bats, respectively. In areas where species from different bat families aggregate together, the infection dynamics and ability of either Polychromophilus species to infect other host families is poorly characterized. Methods We collected 215 bat flies from two bat species, Miniopterus schreibersii and Rhinolophus ferrumequinum, which sometimes form mixed clusters in Serbia. Miniopterus schreibersii is known to be frequently infected with P. melanipherus, whereas R. ferrumequinum has been observed to be incidentally infected with both Polychromophilus species. All flies were screened for Polychromophilus infections using a PCR targeting the haemosporidian cytb gene. Positive samples were subsequently sequenced for 579 bp of cytochrome b (cytb) and 945 bp of cytochrome oxidase subunit 1 (cox1). Results Polychromophilus melanipherus DNA was detected at six out of nine sampling locations and in all three examined bat fly species collected from M. schreibersii (Nycteribia schmidlii, n = 21; Penicillidia conspicua, n = 8; Penicillidia dufourii, n = 3). Four and five haplotypes were found for cytb and cox1, respectively. Evidence for multiple Polychromophilus haplotypes was found in 15 individual flies. These results point to a high diversity of P. melanipherus parasites in Miniopterus hosts and efficient transmission throughout the study area. A single Phthiridium biarticulatum bat fly collected from R. ferrumequinum screened positive for P. melanipherus, but only yielded a partial cox1 sequence fragment. Nevertheless, this result suggests that secondary hosts (both bat and fly species) are regularly confronted with this parasite. Conclusions The results of this study provide new insights into the prevalence and distribution of Polychromophilus parasites in European bats and their nycteribiid vectors. The use of bat flies for the non-invasive investigation of Polychromophilus infections in bat populations has proven to be efficient and thus represents an alternative for large-scale studies of infections in bat populations without the need to invasively collect blood from bats. Graphical Abstract

Background Hydatigera (Cestoda: Taeniidae) is a recently resurrected genus with the description of a new species, Hydatigera kamiyai, a cryptic entity within the Hydatigera taeniaeformis species complex. Rodents are intermediate hosts and correct taxonomic identification of H. taeniaeformis sensu lato (s.l.) species is difficult without the use of molecular methods. The aim of this study was to identify and explore the genetic diversity of Hydatigera and other taeniid species. Methods Ten different small mammals species (856 individuals) (Rattus rattus, three Apodemus, three Arvicolinae and three Soricidae species) were examined from 2013 to 2023. Captured animals were visually examined for cysts and visible lesions. Two markers were used for amplification and sequencing: cox1 and 12S rDNA. Results Molecular analysis of cysts and visible lesions revealed four taeniid species: Hydatigera kamiyai, H. taeniaeformis sensu stricto (s.s.), Taenia martis and T. crassiceps. Hydatigera kamiyai was found in Apodemus flavicollis, A. agrarius, Microtus arvalis and Crocidrua leucodon, while H. taeniaeformis s.s. is registered in R. rattus. Hydatigera kamiyai cox1 sequences clustered with European populations and showed at least 25 nucleotid differences compared to Asian, African, Australian and one of our isolates of H. taeniaeformis s.s acquired from a rat, followed by large sequence distances (9.4% to 12.9%), indicating clear molecular distinction of two species. Conclusions This is one of the few mitochondrial gene-based studies performed after the description of cryptic entities within the Hydatigera taeniaeformis s.l. complex and represents a valuable contribution to understanding of genetic diversity, host suitability and geographic distribution of these tapeworm species. Also, our study provides an important basis of molecular data from this part of Europe for further studies. We emphasize the importance of additional studies of intermediate hosts, especially rats from Europe and Apodemus spp. and voles from Asia and Africa. Graphical abstract