Cryptic diversity of Keratella cochlearis – genetical, morphological and demographic aspects

Biodiversity is under threat in recent decades, with many natural habitats irreversibly disappearing due to global warming and human activity. Our perception of species loss highly depends on an accurate species estimate. However, occurrence of cryptic species (i.e. distinct species that are impossible or difficult to distinguish based on their morphology) hinders a correct assessment of biodiversity. Cryptic species have been described for rotifers of the class Bdelloidea and Monogononta. Rotifers of the class Monogononta are widespread in freshwater lakes all over the world and can serve as model organisms for speciation and adaptation. The main aim of this thesis was to investigate and describe the genetic diversity of one of the most common freshwater rotifer - Keratella cochlearis - in relation to its morphological variability. Beside the assessment of genetic diversity, a detailed study of K. cochlearis life cycle and reproductive strategy was performed. The results of the first study demonstrated that based on the cytochrome c oxidase subunit 1 (COI) gene different putative evolutionary significant units (ESU; a.k.a. cryptic species) can be delimited in Keratella cochlearis (I). Based on morphology, two ESUs can be delimited from the other six ESUs found. We also reported on co-occurrence of different putative ESUs of K. cochlearis in the same lakes, and presented the first SEM pictures of K. cochlearis females showing some detailed morphological characteristics. Life histories and demographic parameters differences between various haplotypes of K. cochlearis were determined in the second study (II). Several differences between life history traits and demographic parameters of haplotypes were found corroborating their status as cryptic species and demonstrating that genetic diversity of K. cochlearis is also reflected in demographic diversity. Additionally, morphologically deformed females occurring during the life table experiment were documented and photographed for the first time in this species. Moreover, the first case of an amphoteric female (producing both males and females) in K. cochlearis was reported. In the third study (III), mitonuclear discordance in three rotifer species complexes was assessed. Mitonuclear discordance hinders the assessment of species delimitation based on only one gene (single-locus). Discordance between mitochondrial and nuclear phylogenies was reported for three rotifer species complexes (K. cochlearis, Polyarthra dolichoptera, Synchaeta pectinata) with different levels of discordance between the mitochondrial COI and the nuclear ITS gene. The results corroborated the previous description of two ESUs in K. cochlearis. During our studies on K. cochlearis males, we developed a method to film zooplankton in general and rotifers specifically (IV). We connected a commercial single-lens reflex camera to a microscope and presented an affordable system with widely available components for filming. In filming male-female interactions of Brachionus angularis, our film showed a thread-like structure linking male and female. However, the purpose of this structure remained unclear. In conclusion, this PhD provided evidence for a high genetic and morphological diversity of K. cochlearis. Existence of a species complex of K. cochlearis was corroborated by mitochondrial and nuclear genetic information. This high genetic diversity in K. cochlearis was reflected to some extent in life histories and morphology. First videos of K. cochlearis males and of B. angularis males interaction with females were presented