Synthetic progestins are steroid hormones, which are not only part of the hormonal contraceptives, but they are also used to treat a number of health problems in human. Due to the widespread use of progestin-based drugs, their residues are being found in wastewaters, from where they also enter into the wastewater treatment plants and surface waters. The aim of this thesis was to assess whether the synthetic progestin etonogestrel affects the secondary sexual characteristics and gonad histology of Endler´s guppy (Poecilia wingei). During the experiment, males and females were separately exposed to 3.2 and 320 ng.l-1 etonogestrel for 34 days. A group of fish reared in pure water (K) and group of fish reared in pure water containing the solvent dimethylsulfoxide (KS) served as controls. At the end of the test, all the fish were photographed to capture any color changes. Then the fish were sacrificed and fixed in 10 % buffered formalin solution for morphometric and histological analysis. Fish samples taken for morphometric analysis were photographed using QuickPHOTO MICRO 2.3 software and individual morphometric parameters were measured on the images taken. Fish sample processing for histological analysis included decalcification, dehydration, and pouring of the samples into paraffin blocks. Then paraffin blocks were cut with the thickness of about 4.5 um, resulting slides were stained with hematoxylin and eosin. Histological changes of the gonads were determined on the histological samples prepared in this way. In females exposed to both concentrations of etonogestrel occurrence of color spots was observed. Color spots are characteristic for male and in females indicate masculinization. In addition, females exposed to 320 ng.l-1 etonogestrel showed a change in anal fin morphometry to a gonopodium-like structure (modified anal fin of males serving as helping copulatory organ), a sign also suggesting masculinization. Furthermore, exposure of etonogestrel in both lower and higher concentration of etonogestrel reduced number of mature oocytes in the ovaries, and their occurrence decreased with increasing concentration. In males exposed to both concentrations of etonogestrel a smaller ratio of the length of 4th ray to the length of 6th ray of gonopodium was found. In addition, at concentration of etonogestrel 320 ng.l-1 a greater ratio of the length of 6th ray to body length and extension of length of 6th ray was observed. Although there were no changes, which would indicate hypermasculinization, these changes could have a negative impact on reproduction, or sexual selection by the female. Etonogestrel exposure had no effect on the normal development of testes, because predominantly mature spermatophores were found in males of all treatment groups. Based on these findings, we can say that etonogestrel, like other progestins, represents a real risk to fish if it occures in aquatic environment at concentrations reaching units of ng.l-1.

[Truncated abstract]Judgements of physical attractiveness are thought to reflect evolved preferences for a high quality mate. The central aim of this thesis was to investigate the hypothesis that female preferences are adaptations for finding good quality mates and that faces and bodies signal honest information about mate quality. To date, most human mate preference studies have examined face or body attractiveness alone, and many have created stimuli using computer graphic techniques. Throughout these studies, I endeavoured to maximise the biological relevance of my studies by incorporating both face and body attractiveness, and using photographs of individual participants. Most research on attractiveness has focused on faces or bodies separately, while our preferences have evolved based on both seen together. A fundamental requirement of studying face and body attractiveness independently is that there is no interaction between the two. My first study confirmed that the face and body did not interact when an overall attractiveness judgment was made. I also investigated the independent contributions of rated attractiveness of the face and the body to ratings of overall attractiveness. Face and body attractiveness each made significant independent contributions to overall attractiveness in males and females. For both sexes, facial attractiveness predicted overall attractiveness more strongly than did body attractiveness, and this difference was significant in males. ... This study indicates that although current levels of T covary with male mating success, this effect may not be mediated by women's preferences for visual cues to T levels conveyed in static face or body features. The fourth study in this thesis investigated the phenotype-linked fertility hypothesis, which proposes that females obtain reliable information on male fertility from male expression of sexual traits. A previous study of Spanish men reported that facial attractiveness was positively associated with semen quality. I aimed to determine whether this effect was widespread by examining a large sample of Australian men. I also extended my study to determine whether cues to semen quality are provided by components of attractiveness: masculinity, averageness, and symmetry. I found no significant correlations between semen quality parameters and attractiveness or attractive traits. While male physical attractiveness may signal aspects of mate quality, my results suggest that phenotype-linked cues to male fertility may not be generalised across human populations. Together, these studies challenge current methodologies and theories of preferences for secondary sexual traits as honest signals of mate quality. The findings show that it is important to study human mate preferences in biologically relevant contexts, for example by using photographs of both faces and bodies, to maximise the real life application of results. In addition, the findings suggest that male attractiveness does not signal cues to testosterone or semen quality, although testosterone is associated with mating success. The implications of these findings and possible avenues for future research are discussed.