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Reproductive isolation occurring at the gamete level is called gametic isolation and almost always prevents gene flow between unrelated species and (to some extent) between closely related species or subspecies. The hybrid zone of the house mouse (HMHZ), which was formed by contact and interbreeding of two subspecies, the Western European house mouse (M. m. domesticus) and the Eastern European house mouse (M. m. musculus) provides a usefull model for the study of speciation processes involving gametic isolation. The probability of sperm competition within the female reproductive tract is high in the house mouse because high levels of sexual promiscuity (in 20˗40 % of all reproductive cycles) have been observed in this species. Thus, the reproductive isolation at gametic level may be determined both by the phenotypic characteristics of sperm (the ability to outcompete heterospecific sperm in the process of sperm- sperm competition) and by the preference of the sperm of conspecific males in the female reproductive tract (cryptic female choice). In my Ph.D. thesis I tested the degree of affinity of male and female gametes reciprocally between the both subspecies of M. musculus and the phylogenetically more distant species M. spretus, which is characterized by a higher degree of promiscuity. Although a...

Singing is important for communication in birds. Some species of birds copy singing from other species. This heterospecific copying of singing is common especially in closely related bird species, and is usually called mixed singing in such cases. Mixed singing is often asymmetric, when only one species of the pair copies a song of the congener. The meaning of mixed singing is not well explained yet. The most common mechanism is probably an error during the learning phase of singing, but in some cases mixed singing can be adaptive. In my master's thesis I deal with the evolutionary meaning of mixed singing in two closely related passerine species - Common nightingale (Luscinia megarhynchos) and Thrush nightingale (Luscinia luscinia). These species co-occur in secondary contact zone in central and eastern part of Europe. Only Thrush nightingale which is larger and probably a more dominant species, exhibits mixed singing. In playback experiments in Common nightingale I studied a possible adaptive meaning of mixed singing in relation to interspecific communication. I tested the differences in behavioural and vocal response of Common nightingales to three types of stimuli: pure singing of Common nightingale, pure singing of Thrush nightingale and mixed singing of Thrush nightingale. The tested males...

The male gametes (sperms) are under strong sexual selection and are therefore very diverse in their morphology and often differ even amongst closely related species. Sperms are thus assumed to play very important role in reproductive isolation between species, due to their fast evolution in morphology. In my master thesis, I have studied the possible role of sperm morphology divergence in reproductive isolation in two sister species of passerine birds, the common nightingale (Luscinia megarhynchos) and the thrush nightingale (L. luscinia). The areas of these species overlap in secondary contact zone running across central and Eastern Europe, where they occasionally hybridize. I have compared sperm morphology of males of both species originating in allopatric and sympatric localities as well as interspecies hybrids. The results showed significant differences in total sperm length which is approximately 20 % longer in the common nightingale. That is caused by great interspecies divergence in midpiece (containing mitochondria) length. Interspecific hybrids showed sperms with intermediate length but despite expectations completely morphologically normal. This outcome corresponds with observed fertility in F1 hybrid males. What I consider to be an essential finding is a significant divergence in head...

Hybrid sterility plays a key role in reproductive isolation during evolution of species. The mechanisms responsible for hybrid sterility are relatively well understood in organisms with heterogametic males, such as drosophila or mouse but are largely unknown in organisms with heterogametic females (e.g. birds). Studies on reproductive isolation in birds takes place in natural hybrid zones, instead of captivity. Hybrid sterility preferentially affects the heterogametic sex, males in mammals (XY) and females in birds (ZW), according to Haldane's rule. This leads to reduced introgression in sex chromosomes and mitochondrial DNA compared to autosomal DNA. The purpose of this thesis is to summarize known information on hybrid sterility and its expression in two models of interspecies hybridization: flycatchers and nightingales. Additionally, this thesis contains also a practical part, which compares morfology of sperms of two species of nightingales. Powered by TCPDF (www.tcpdf.org)

The contact zone between subspecies of house mouse Mus musculus musculus and Mus musculus domesticus is one of the most intensively studied hybrid zones. It is also due to extensive introgression of the Y chromosome of M. m. musculus subspecies to the genetic background of M. m. domesticus. One theory of the origin of the introgression explains it by intragenomic conflict between the sexes. With a set of variable microsatellite markers on the Y chromosome, I have examined the validity of this theory by simple approaches revealing the history of the introgression area. It turned out that overly big variability of our markers makes the revelation of this theory impossible. Our markers have been found suitable for use in the analysis of population structure of house mouse. Thanks to them, we can identify migrants between localities and estimate the level of closeness of the population structure in relation to migrants from the neighborhood. Populations in our analysis proved to be relatively closed and resistant to the influx of migrants. Despite the conclusions of previous research where the dispersion of males ran up to one kilometer, I have discovered a relatively large number of migrations to a distance of thirty kilometers. Keywords Mus musculus musculus, Mus musculus domesticus, Y chromosome,...

In this elaborate the methods that are used for studying the hybrid zone of Bombina bombina and B. variegata were summarized. The principals, advantages and disadvantages of these methods are mentioned.