This research investigated the effects of waterborne zinc (Zn) on the interactions between guppies, Poecilia reticulata (Peters), and Gyrodactylus turnbulli Harris, 1986, a monogenean parasite of its skin and fins. The first objective was to determine if sublethal concentrations of waterborne Zn (up to 240 mug/L added to artificial freshwater) exerted a concentration-dependent effect on the population dynamics of Gyrodactylus on isolated guppies. Whereas survival of uninfected fish was unaffected, mortality of infected fish increased linearly with increasing Zn concentration. In addition, the improved parasite population growth at concentrations up to 120 mug Zn/I suggested either that the elevated Zn promotes survival and/or reproduction of the parasite, or impairs host defense mechanisms. Analysis of lifetime survival and reproduction of individual parasites on and off the fish revealed Zn toxicity to the parasite as survival of detached parasites decreased linearly with increasing Zn concentration and parasite survival on the host was also lower at the highest Zn concentrations. Also, all morphological parameters decreased linearly in response both to increasing concentration and duration of exposure to waterborne Zn. The guppy epidermis responded rapidly to both infection and waterborne Zn, and the cumulative effects of these combined stressors were synergistic for epidermal thickness and mucous cell numbers, but antagonistic in terms of mucin composition. Both Zn and infection induced mucous production, but at elevated Zn concentrations and/or at high parasite burdens, the capacity for continued mucous production was apparently exceeded. I hypothesize that this condition is favorable for parasite survival because of the impaired host response; but unfavorable for host survival because of the high numbers of pathogenic parasites and the inability to control entry of Zn into host tissues. In conclusion, sublethal concentrations of waterborne Zn are more detrimental to the infected host than to the parasite.

The colour of guppies (Poecilia reticulata) evolves as a compromise between sexual selection (favouring conspicuousness) and natural selection (favouring crypsis). However, guppies live in a variety of habitats and with a variety of predators and consequently in a variety of selective environments. I investigated how habitat and predator's visual systems affect the evolution of colour. I used regressions to assess the importance of habitat features on the evolution of colour for 29 guppy populations. I then quantified the colour of guppies living in the presence and absence of two predators. The prawn predator is insensitive to orange light while the fish predator is insensitive to ultraviolet light. Habitat explained some variation in colour, but not in a consistent manner. Guppies living with the prawn were more orange and guppies living with the fish had more ultraviolet reflectance, providing evidence for the use of these aspects of colour as private signals.

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Contrary to traditional belief, the decisions that females make before, during and after mating shape its outcome and ultimately fitness. The aim of this thesis was to examine how females modify and adjust their mating decisions in line with social and environmental variability and how these directly and indirectly affect mating benefits. To address this aim I have formulated four main questions that correspond to chapters 2 to 6 in this thesis. Firstly I asked whether there was evidence for female choice being driven by mating benefits. More precisely, in chapter 2, I reviewed the literature in search of evidence for direct and indirect benefits in female choice among freshwater fish species. Direct mating benefits were defined as an increase in female’s reproductive success (number of offspring). Conversely, increases in offspring reproductive success were considered to be indirect benefits. The results showed that despite the multiple suggestions and the great amount of information available, to date there is still no evidence for both direct (increase of F1) or indirect (increase in F2) mating benefits, nor their influence in female mating decisions if freshwater fishes species. Furthermore, although polyandry occurred in more than 60% of the species reviewed, I was unable to confirm that polyandry was maintained because of indirect benefits. These findings justified the need to experimentally investigate the drivers of female mating decisions in freshwater fish species and lead to the questions addressed on chapters 5 and 6. For the experimental chapters 3-6 I used the Trinidadian guppy, Poecilia reticulata, as a model species. Their unique and remarkable ecological and biological characteristics coupled with easy maintenance in laboratory conditions make guppies an ideal species for behavioural studies. But in particular, the fact that guppies live in a promiscuous mating system where females despite being constantly harassed by males may be able to control paternity, makes guppies the ideal species to address my aims. The second question was how much were females in control of their mating decisions, and how social environment could limit these decisions. In particular, in chapter 3 I looked at how females adapt and adjust their mating decisions in line with extreme differences in population sex ratio. In chapter 4, I examined to what extent male sexual harassment affects female reproductive behaviours. Results from these two chapters indicated that female guppies have a remarkable reproductive plasticity that enable them to control their mating decisions. When faced with extreme differences in population sex ratio, female mating decisions were made in an optimal way that maximized the ratio of female reproductive benefits per investment. This translated into producing bigger offspring when in a strong female biased environment, than when in a male biased environment. Further, chapter 4 illustrated that female guppies can, despite high levels of male sexual harassment, be in control of their mating decisions. These two chapters demonstrated and have reinforced previous findings of the remarkable reproductive adaptation of female guppies to differences in the social environment. The third question I addressed was: do multiply mated females have greater direct or indirect benefits than single mated females? To answer this question I followed for the first time reproductive success of females over two generations. I measured fitness directly (number of F1 and F2) and took as well as multiple indirect measures of fitness components for two generations in search for evidence of direct and indirect mating benefits in explaining the maintenance of female multiple mating. The results of chapter 5 revealed that female guppies do not have a higher number of F1 and F2 from polyandry or either from mating with males possessing allegedly good quality traits. I, therefore, stressed the idea that potential differences in sexual selection pressure between laboratory and wild populations may influence the expression and intensity of mating benefits between thus explaining the difficulty of finding mating benefits. In my fourth and last question, I used a novel statistical approach based on the analysis of the dispersion in phenotypes, to look for potential alternative explanations for the prevalence of polyandry. The results of this analysis show offspring from multiple mated mothers were phenotypically more diverse than offspring from single mated mothers. Given the direct relationship between phenotypic diversity and potential fitness gains in stochastic systems, female guppies are likely to get greater benefits from mating with males with different phenotypes than with males with a particular sexual trait. This result provides an alternative explanation for the maintenance of polyandry in resource free systems. Overall the results of this thesis reinforce previous suggestions that female guppies are active participants in the mating process, and not necessarily limited to post-copulatory mechanisms of selection of sperm. It also showed the remarkable ability of females to adjust their reproductive investment in line with changes in the social conditions. Interestingly, my results contradict the commonly accepted assertion that females’ mating preference converges towards unique male sexual traits. This result stresses the need to look at alternative explanations to justify female mating decisions.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg in fulfillment of the requirement for the degree of Doctor of Philosophy JOHANNESBURG January 1996 / I investigated some evolutionary implications of female mate choice in a feral population of guppies (Poecllia reticultuai. I performed correlative and manipulative experiments to establish the relationship between female mate choice and other sexually selective forces including iutermale aggression and sneak copulation, and the exaggerated secondary sex characters (ornaments) of male guppies. Orange (carotenoid) ornamentation is the best predictor of male attractiveness and mating success, a relationship which held under manipulation. Black (melanin) is sometimes correlated with male mating success. Mnnipulatiug the black area of males reveals that it is important to male attractiveness, and this appears to be in the form of a signal amplifier of male orangeness. This is the fi.st experimental evidence for a visual signal amplifier. For both orange and black areas, the relationship between absolute area and fluctuating asymmetry is positive and significant, suggesting that neither is n signal of male condition. These results arc Interpreted in the context of theories of the evolution of multiple male ornaments. Females are able to express their preference for orange with the first mature male they ever encounter, uuggestlng an important role for genetic determination in female preferences. This is corroborated by high repeatability of female mate choice behaviour. Experience modifies a female's preferences as she is able to adjust her response to a male in relation to the ornamentation of (at least) the previous male she saw. Mate copying has no mensurable effect on the outcome of female mate choice decisions. / MT2016

Thesis (Ph. D.)--University of California, Riverside, 2009. / Includes abstract. Available via ProQuest Digital Dissertations. Title from first page of PDF file (viewed March 17, 2010). Includes bibliographical references. Also issued in print.

Environments are changing rapidly, which renders many local populations susceptible to extinction unless they can adapt to these changes. Studies of rapid adaptation commonly document the evolution of individual traits. Overall adaptation however, is a function of fitness itself, rather than the individual traits that contribute to fitness. Although numerous studies provide evidence for the evolution of specific traits on contemporary time scales, no published studies of wild animal populations have examined the evolution of a major fitness component following environmental change. My research demonstrates that an introduced population of guppies (Poecilia reticulata) has adapted to its new environment in less than ten years (13-26 generations). This adaptation consists of several phenotypic traits that have changed in the expected direction. Most critically, the introduced population now has higher survival than its ancestral source population when both are tested together in the introduction site. These results show that important components of fitness can evolve rapidly in populations, and that this evolution might influence the persistence of populations in the face of environmental change.

Guppies exhibit color based sexual dimorphism and females generally prefer the most colorful males. It has also recently been found that guppies possess a large opsin repertoire. As opsins are the receptors responsible for color vision, this ten gene repertoire might have contributed to the evolution of extravagant male coloration in this species. My study starts by characterizing the opsin repertoire of Jenynsia onca, a noncolorful relative of the guppy belonging to the family Anablepidae (sister group to Poeciliidae, of which the guppy is a member). A PCR based survey indicated that J. onca had a very similar opsin repertoire to the guppy; J. onca had nine genes including orthologs of all but one of the guppy opsins. To gain further insight into the origin of the guppy repertoire, a bioinformatics based survey of ray-finned fish opsins was undertaken. This revealed that large opsin repertoires are common in ray-finned fish and are the product of gene duplication events, spanning the age of the taxon Teleostei. Given that the large opsin repertoire of the guppy did not appear to be perfectly correlated with the evolution of color based sexual selection in this lineage, I turned to investigating the expression of this opsin repertoire. In situ hybridization was used to characterize the pattern of opsin expression across the surface of the retina of adult male and female guppies. In situ hybridization demonstrated that most opsin genes had distinct expression profiles. These expression patterns also indicated that sensitivity and discrimination in the dorsal retina might differ from the ventral retina; the ventral retina appears to be tuned to middle-wavelength light (green), while the dorsal retina is predicted to have exceptional wavelength discriminatory ability and broad spectral sensitivity. This expression data was then used to evaluate models of sexual selection in the context of the predicted visual capacity of the guppy. / Graduate