<p>Chemical signals are the most widely used form of sexual communication throughout the living world. However, there is in general little knowledge about what these signals actually communicate. The role of chemical signals, i.e. pheromones, in sexual behaviour has traditionally been seen as restricted to mate attraction and species recognition. This thesis reviews the evidence for pheromones as indicators of mate quality, and then investigates three important factors for mate quality signals – individual variation, heritability and cost – by using the male pheromone of the lekking fruit fly <i>Drosophila grimshawi</i> as a model.</p><p>The experiments presented indicate that the pheromone of <i>D. grimshawi</i> has multiple functions, and that these functions vary with social context. Thus, with regard to females, the pheromone seems to act mainly as a species/mate recognition signal, since females show little preference for the amount of pheromone deposited by a male. Moreover, males invest less in pheromone production when subjected to females as compared to when subjected to rival males. However, the pheromone seems to be costly in production since males that invest much in pheromone deposition has a shorter lifespan. This suggests a function for the pheromone in male-male interactions. Males can distinguish their own pheromone depositions from those of a strange male, and also discriminate between pheromone depositions from one and two strange males. This might give them the ability to assess the size of a lek and the competitive capacities of rivals, information that should be useful when optimizing sexual behaviour.</p><p>In conclusion, the pheromone seems to act as an honest mate/competitor quality signal in some social contexts, and as a non-costly species/mate recognition signal in other. In addition, I show for the first time that a chemical signal has differential fitness costs, and that an insect is able to distinguish between individual odour signatures.</p>

<p>This thesis focuses on the evolutionary interactions between birds and a parasite, the mosquito-borne Sindbis virus (Togaviridae, <i>Alphavirus</i>). In conclusion, the results show that the Sindbis virus is widespread among birds, and that the fitness of infected hosts may be reduced by the virus. Furthermore, viruclearance ability was revealed by male plumage traits, and viraemia was related to hormonal- and social status.</p><p>The distribution of Sindbis virus infections among passerine birds was examined in five areas in Sweden. Almost all species tested were infected, and three species of thrushes weridentified as the main hosts. In a series of experimental infections, greenfinches (<i>Carduelis chloris</i>) kept in aviaries were used ahosts. First, the behavioural consequences of an infection were investigated. During the infection, birds tended to reduce thespontaneous locomotion activity, and when escaping from a simulated predator attack, infected birds had reduced take-off spee Furthermore, when comparing virus clearance rate between male greenfinches, I found that males with large yellow tail ornaments hafaster virus clearance rates as compared to those with smaller ornaments. Thus, male virus clearance ability was honestly revealed by the size of an ornament. Moreover, males with experimentally elevated testosterone levels experienced a delayed, but not increased viraemia as compared to controls. When the relationship between male social ranand viraemia was examined, I found no evidence that high-ranked males suffered reduced rank during the infection. Nevertheless, viraemipatterns of males were related to their social rank, so that low-ranked birds had a delayed viraemia as compared to high-ranked birds. </p>

This thesis focuses on the evolutionary interactions between birds and a parasite, the mosquito-borne Sindbis virus (Togaviridae, Alphavirus). In conclusion, the results show that the Sindbis virus is widespread among birds, and that the fitness of infected hosts may be reduced by the virus. Furthermore, viruclearance ability was revealed by male plumage traits, and viraemia was related to hormonal- and social status. The distribution of Sindbis virus infections among passerine birds was examined in five areas in Sweden. Almost all species tested were infected, and three species of thrushes weridentified as the main hosts. In a series of experimental infections, greenfinches (Carduelis chloris) kept in aviaries were used ahosts. First, the behavioural consequences of an infection were investigated. During the infection, birds tended to reduce thespontaneous locomotion activity, and when escaping from a simulated predator attack, infected birds had reduced take-off spee Furthermore, when comparing virus clearance rate between male greenfinches, I found that males with large yellow tail ornaments hafaster virus clearance rates as compared to those with smaller ornaments. Thus, male virus clearance ability was honestly revealed by the size of an ornament. Moreover, males with experimentally elevated testosterone levels experienced a delayed, but not increased viraemia as compared to controls. When the relationship between male social ranand viraemia was examined, I found no evidence that high-ranked males suffered reduced rank during the infection. Nevertheless, viraemipatterns of males were related to their social rank, so that low-ranked birds had a delayed viraemia as compared to high-ranked birds.

Chemical signals are the most widely used form of sexual communication throughout the living world. However, there is in general little knowledge about what these signals actually communicate. The role of chemical signals, i.e. pheromones, in sexual behaviour has traditionally been seen as restricted to mate attraction and species recognition. This thesis reviews the evidence for pheromones as indicators of mate quality, and then investigates three important factors for mate quality signals – individual variation, heritability and cost – by using the male pheromone of the lekking fruit fly Drosophila grimshawi as a model. The experiments presented indicate that the pheromone of D. grimshawi has multiple functions, and that these functions vary with social context. Thus, with regard to females, the pheromone seems to act mainly as a species/mate recognition signal, since females show little preference for the amount of pheromone deposited by a male. Moreover, males invest less in pheromone production when subjected to females as compared to when subjected to rival males. However, the pheromone seems to be costly in production since males that invest much in pheromone deposition has a shorter lifespan. This suggests a function for the pheromone in male-male interactions. Males can distinguish their own pheromone depositions from those of a strange male, and also discriminate between pheromone depositions from one and two strange males. This might give them the ability to assess the size of a lek and the competitive capacities of rivals, information that should be useful when optimizing sexual behaviour. In conclusion, the pheromone seems to act as an honest mate/competitor quality signal in some social contexts, and as a non-costly species/mate recognition signal in other. In addition, I show for the first time that a chemical signal has differential fitness costs, and that an insect is able to distinguish between individual odour signatures.

Natural and sexual selection and sexual conflict are forces shaping the evolution of reproductive behaviour, while constrained by factors like environment, physiology and life-history trade-offs. Parental care is costly both in terms of time and energy. In fish, filial cannibalism is a strategy for caring males to compensate for some of the energy loss. Human impact like eutrophication also alters the basics for animals living in that environment. It is fundamental to any species to adjust its behaviour to a changing environment. Studying sand goby males, I found trade-offs both regarding parental care allocations, like ventilation vs. predator defence, and investment in present vs. future reproductive success. Paternal sand gobies exposed to water with low oxygen levels increased their fanning effort but did not compensate by eating more eggs, even though an increased current parental effort should affect future reproductive success negatively. Investigating if patterns of filial cannibalism change with time of season, I found no correlation. Theory predicts that it should pay more to eat eggs early, when future mating potential is higher than late in the season. However, as early hatching fry are likely to gain higher fitness through larger size the next breeding season, this may provide an opposing selection pressure. In species with male care the only way a female can affect the level of post-spawning care is by choosing a good mate. A female preference to spawn in nests that already contain eggs of other females has been interpreted as a means to avoid filial cannibalism through a dilution effect or to decrease the costs of search time. Yet, in my study females did not avoid filial cannibalism by preferring large clutches to small ones. Oxygenation of the eggs might be a key factor, since both large and small females preferred spawning in nests with small clutches. Thus, as in most animals, trade-offs clearly govern the reproductive behaviour of sand gobies.

The evolutionary goal of individuals is reproduction and sexual selection favours traits improving reproductive success. When males invest less than females in offspring, males have potentially a higher reproductive rate than females. This typically results in sex-specific reproductive strategies of male-male competition and female choice of mating partner. Under polyandry, sexual selection can continue after copulation as sperm competition and cryptic female choice. This thesis focuses on male and female pre- and post-copulatory reproductive strategies in the promiscuous red junglefowl, Gallus gallus ssp., and its domestic subspecies the domestic fowl, Gallus gallus domesticus. Males impose high re-mating rates on females, which triggers female resistance in copulations. In addition, when sexual harassment increases, females re-mate at times of day when male mating propensity is lower, to avoid intense sexual harassment. Males allocate sperm supplies differentially according to (i) variation in female polyandry and own competitive ability, (ii) earlier sperm investment in a female, and (iii) female reproductive quality, signalled by female comb size. Males also perform ‘aspermic’ copulations (i.e. copulations with no semen transfer), which inhibit polyandry and in turn reduce sperm competition. In mating opportunities with relatives, males do not avoid inbreeding. However, females avoid inbreeding before copulation through kin recognition and after copulation by selecting against related males’ sperm. These results show that selection on males to re-mate at higher rates than females and copulate indiscriminately according to partner relatedness, trigger counteracting female responses, creating the potential for sexual conflict over fertilisation. Teasing apart pre- and post-copulatory strategies and the contribution of each sex therefore becomes crucial in order to understand the evolution of reproductive strategies and the mechanisms affecting paternity.

Competition over mating opportunities is a conspicuous characteristic of animal behaviour. In many butterfly species the males establish territories in places advantageous for encountering females. This thesis addresses questions about how territoriality has evolved and is maintained in butterflies. The studies have been conducted using the speckled wood butterfly, Pararge aegeria, as a model species. Males of P. aegeria are found in sunspots on the forest floor (paper I-V), on the lookout for females visiting the sunspots. However, males are only found in sunspots above a certain size (paper III). This behavior is maintained by a mating success advantage, where using large sunspots instead of small sunspots as perching areas generates a higher reproductive output (paper I). The mating success asymmetry is not explained by female choice or by a female preference for large sunspots per se (paper I, V), but rather the large sunspot facilitates visual performance of perching males and improves flight pursuit and interception of females (paper III). Winners of territorial contests gain sole ownership of large sunspot territories, while losers search for a new suitable sunspot territory (paper I, II &amp; IV) or use smaller, suboptimal sunspots as perching sites (paper II). Territorial contests between P. aegeria males are not settled due to an obvious morphological/physiological asymmetry (paper I). Rather, variation in resource value and motivational asymmetries are important for settling contests (paper IV). A majority of male-female interactions (paper V) and matings (paper I) are initiated by a perching male detecting and intercepting a flying female. Furthermore, females can affect their chances of being detected by a perching male by behaving more conspicuously (paper V). This thesis highlights the role of female behaviour, variation in resource value and motivation asymmetries to understand the evolution of territoriality in butterflies.

In this thesis, different genetic tools are used to investigate pre- and postzygotic barriers to gene exchange and their role in speciation in the pied flycatcher (Ficedula hypoleuca) and the collared flycatcher (F. albicollis). This species complex consists of four genetically distinct clades that apparently diverged in allopatry (I). Sequencing of introns from autosomal and Z-linked genes from the two species reveals signs of selection on the Z-chromosome. Sexual selection acting on Z-linked genes might explain this pattern (II). By using large-scale genotyping of single nucleotide polymorphisms (SNPs), introgression is observed at autosomal- but not Z-linked loci, mostly from the pied- to the collared flycatcher. Male plumage characters and genes involved in hybrid fitness are largely mapped to the Z-chromosome (III). By studying mate choice of female hybrids I show that there is a link between female preferences and the Z chromosome (IV). The rate of introgression in island versus clinal hybrid zones is consistent with regional differences in hybrid fertility. Asymmetric gene flow from allopatry on the islands may oppose reinforcement, leading to introgression and a partial breakdown of postzygotic isolation. Adaptive introgression may explain the high rate of introgression observed at one of the genetic markers (V). For late breeding female collared flycatchers it appears to be adaptive to use pied flycatchers as social fathers but conspecific males as genetic fathers. Additionally, females in mixed species pairs may reduce hybridization costs by producing an excess of male hybrid offspring that are more fertile than females (VI). In conclusion, the Z-chromosome appears to play a major role in flycatcher speciation. Sexual selection and reinforcement are important mechanisms in the divergence of these birds. However, gene flow from allopatry, introgression of adaptive genes and adaptive hetrospecific pairing by late breeding collared flycatcher females may work in the opposite direction.

Eco-evolutionary dynamics integrates the reciprocal interactions betweenecology and evolution. These two branches of biology traditionally assumethe other as static for simplicity. However, increasing evidence shows thatthis simplification may not always hold because ecology and evolution canoperate in similar timescales. This thesis theoretically explores how thereciprocal interactions may influence ecological and evolutionary outcomesin four different eco-evolutionary contexts.Many species of non-social animals live in groups. Aggregating ingroups often has both benefits and costs that depend on group size. Thanksto the benefits of aggregation, population growth likely depends positivelyon population density when it is small. This phenomenon, the Allee effect,has been hypothesized to explain the evolution of aggregation behavior. Ifind that the Allee effect alone does not lead to the evolution whenpopulation dynamics is explicitly accounted for. Some other mechanisms,such as frequent needs for colonizing new patches or anti-aggregation,should be invoked to explain why aggregation behavior could evolve.Phenotypic plasticity is the ability of a genotype to express distinctphenotypes when exposed to different environments. Although it is oftenshown to be adaptive and not costly, highly plastic organisms are rare. Paststudies demonstrated some potential reasons. I test another possibility; costsmay arise from sexual selection because highly plastic individuals may beless preferred as a mate. I show that, even in the absence of the direct cost ofplasticity, the level of plasticity remained low at intermediate strengths ofassortative mating. This pattern is robust across wide ranges of parametervalues.Ecological speciation occurs when ecologically divergent selectionbetween environments causes reproductive isolation between divergingsubpopulations. Several verbal models of ecological speciation emphasizethe roles of phenotypic plasticity in promoting speciation. The complexprocesses involved in speciation, however, are difficult to be evaluated byverbal accounts. I quantitatively test the proposed idea in a mechanisticmodel of ecological speciation in the presence and absence of plasticity. Ifind conditions under which plasticity can promote or hinder ecologicalspeciation. Plasticity facilitates speciation by producing a gap in thedistributions of expressed phenotypes, which serves as a barrier to gene flowin an assortatively mating population.Ecosystem ecology and evolutionary biology are the least integratedfields in ecology and evolution. Natural selection operating at the individuallevels on traits governing ecosystem functions may affect ecosystemproperties, which may feedback to individuals. I reviewed this idea anddemonstrate the feedback loop by using a simple consumer-resource model.

Sex ratio theory suggests that the strength of intersexual selection will increase as a population more male-biased; reflecting increased selectivity in mate choice. Populations of pond turtle have varying adult sex ratios, in painted turtles (Chrysemys picta), reported sex ratios range from female biased (1:3) to male biased (3:1). I investigated the effect of sex ratio on male reproductive success (quantified as “fertilization success”) in painted turtles. I examined the mating system of painted turtles in a female-biased population using microsatellite paternity analysis, relating variation in male fertilization success to male phenotype and offspring survival, employed ex situ behavioural observation to clarify the mechanism behind the variation in male fertilization success and used agent-based modeling to simulate the effects of changing sex ratio, population density and proportions of male phenotype on male fertilization success. Small males contributed sperm to a greater number of clutches than did larger males, but were not more likely to reproduce in a season than larger males. There was no offspring fitness advantage related to male body size and no relationship between male claw length and fertilization success. Large male painted turtles courted at a higher frequency than small males. I found no relationship between male courtship behavior and claw length. Females showed no preference for males of any phenotype. Agent-based simulations were based on the distribution of best fit from the observed data; an amalgam of two Poisson distributions, each with its own probability of success and proportional representation in the final distribution. Increased female sex ratio bias, increased population density and increased proportions of “more successful” males all increased the mean and variance of male fertilization success, based on increased encounter rate among turtles. Small and large male painted turtles enjoy different fertilization success. It is uncertain whether this difference is based on active female choice, cryptic female choice, sperm competition or a combination of factors. Sex ratio simulations predict the opposite result as that predicted by sex ratio theory. These contrary results should be compared to simulations manipulating choosiness and field data from painted turtle populations to clarify mechanisms influencing male reproductive success.