The reasons behind the absence of the prawn Palaemon adspersus and the presence of P. squilla in rockpools and on bare sand bottoms were studied. Some maximal abundances in different habitats are given. Introduction experiments into natural and artificial rockpools and measurements of tolerance towards low oxygen levels showed that nocturnal hypoxia excluded P. adspersus which was significantly more sensitive to oxygen depletion. Respiration rates measured by the closed-bottle method showed no interspecific difference. On bare sand bottoms P. aspersus was probably excluded by predators, since predator exclusion experiments in cages and predator inclusion experiments in containers showed that P. adaspersus was more vulnerable to predation than P. squilla.The costs for being able to cope with a wide array of habitat in P. squilla are probably balanced by the benefits of access to habitats such as intertidal rockpools, very shallow bottoms and deeper sand bottoms. Tolerance towards abiotic factors extends its habitat range upwards into shallower waters, and tolerance towards biotic factors, i.e. predation, extends it downwards.

An assumption central to many tests of statistical association between two variables is the null expectation of zero association. Here, we draw attention to the fact that in many published tests of mass-dependent mass loss in breeding birds, this assumption has been violated. We show that a correct null hypothesis can be derived by using resampling methods, and analyse three data sets (two previously published) from passerine birds to illustrate the approach. Our results show, that under a correct null hypothesis, the biological interpretation of the previously published results is reversed-initially heavy birds do actually lose less mass (relative to their weight) than the initially light birds.

Many snake populations contain moderate to high frequencies of individuals with ventral scale anomalies, which are often associated with duplicated or fused vertebrae and ribs and are known to impair locomotion and growth. In an attempt to test whether such anomalies may influence survival, we examined their frequency among cage-reared juvenile adders, Vipera berus, and wild-caught individuals that presumably had been exposed to natural selection. Midbody ventral scale anomalies were significantlyless frequent among snakes exposed to selection than among cage-reared juveniles in one of three populations studied, indicating that they might indeed reduce survival. Furthermorem, idbody anomalies wereless common among large than among small wild-caught individuals, although not significantly so. The association between anomalies among captive mothers and their offspring was very weak, indicating low heritability of this trait. This low heritability might explain why scale anomalies are common in adder populations in spite of the apparent selection against anomalous individuals. We also found the proportion of anomalous offspring to increase with litter size, suggesting a trade-off between number and quality of young.

The theory of reinforcement predicts that natural selection against the production of unfit hybrids favours traits that increase assortative mating. Whether culturally inherited traits, such as bird song, can increase assortative mating by reinforcement is largely unknown. We compared songs of pied (Ficedula hypoleuca) and collared flycatchers (F. albicollis) from two hybrid zones of different ages with songs from allopatric populations. Previously, a character divergence in male plumage traits has been shown to reinforce premating isolation in sympatric flycatchers. In contrast, we find that the song of the pied flycatcher has converged towards that of the collared flycatcher (mixed singing). However, a corresponding divergence in the collared flycatcher shows that the species differences in song characters are maintained in sympatry. Genetic analyses suggest that mixed song is not caused by introgression from the collared flycatcher, but rather due to heterospecific copying. Circumstantial evidence suggests that mixed song may increase the rate of maladaptive hybridization. In the oldest hybrid zone where reinforcement on plumage traits is most pronounced, the frequency of mixed singing and hybridization is also lowest. Thus, we suggest that reinforcement has reduced the frequency of mixed singing in the pied flycatcher and caused a divergence in the song of the collared flycatcher. Whether a culturally inherited trait promotes or opposes speciation in sympatry may depend on its plasticity. The degree of plasticity may be genetically determined and accordingly under selection by reinforcement.

A sexual conflict over levels of parental care occurs in most animals with biparental care, and studies of sexual differences in levels of parental care have usually focused on its intra-annual fitness consequences. We investigated inter-annual fitness consequences of a sexual difference in timing of feather replacement (moult) in collared flycatchers (Ficedula albicollis). In this study, males overlapped reproduction and moult more often than females, they also initiated their moult at an earlier stage of breeding than females. Females mated to males with a moult-breeding overlap had significantly lowered survival chances than females mated with males initiating moult after breeding. Furthermore, females mated with moulting males risked a lowered future fecundity in terms of a delayed start to breeding in the following season. However, early moulting males achieved a similar reproductive success as males initiating moult after breeding. Likewise, male survival probability to the following breeding season did not differ between early and late moulting individuals, nor was there any evidence that males gained or lost in future mating advantages by moulting early. These results show not only that a sexual conflict over timing of moult may operate, but also that it can impose severe fitness consequences, in terms of reduced future fecundity and survival probability, upon the 'losing' sex.

We manipulated brood sizes of 132 pairs of the collared flycatcher to investigate whether or not an investment in reproduction was traded against an investment and timing of the post-nuptial moult. Our manipulations did not affect the probability of moult-breeding overlap in males, and there was no effect on their moult scores at fledging time of the young. Males and young birds initiated moult earlier than females and old birds, respectively. Very few females started moulting during the period of nestling care. Reproductive success in terms of recruitment rate of fledglings was independent of parental moult stage during reproduction, which indicates that the manipulation did not induce a trade-off between moult and post-fledging care. Furthermore, the survival probability of adults was independent of brood size manipulations and their moult stage at fledging time. Thus, our brood size manipulations showed no evidence for a trade-off between reproductive and moult investments in the collared flycatcher.

Virtually all diurnal birds have tetrachomatic vision based on four different colour receptors. As a result, birds are potentially able to perceive their environment in twice as many colours as humans and four times as many colours compared to most other mammals, which are dichromatic. In addition to the spectrum visible to humans, birds are able to detect ultraviolet (UV) light. Signals with a UV component have been shown to be important to birds both in foraging and colour signalling. Because of the superior colour discrimination of the avian eye, UV sensitivity, but especially owing to its tetrachromacy, we cannot know what birds look like to those that matter, i.e. other birds.

In my thesis I describe a new molecular method with which it is possible to identify the vision system of birds only using a small amount of DNA, without the need to keep or sacrifice the animal. It thereby facilitates large screenings, including rare and endangered species. The method has been used to increase the number of species with identified vision system type from 19 to 66. I show that raptors and songbirds have different vision systems, giving songbirds the possibility of a secret channel for colour signalling, and that male songbirds in coniferous forest take advantage of this to be significantly more cryptic to raptors than to females songbirds. I show that gulls have gained a vision system enabling them to detect the UV signals of fish when the fish swim close to the surface.

Even though we tend to be rather self-satisfied with the quality of our colour vision, we are colour-blind when compared to birds. My work shows that human colour vision is inadequate for judging animal coloration, and that there is much more going on in bird colour signalling than meets our eye.

Arctic charr (Salvelinus alpinus) were tested for aggressive behavior using intruder tests, before and after 2 days of dyadic social interaction. Following social interaction, half of the dominant and half of the subordinate fish were given l-DOPA (10 mg/kg, orally), whereas the remaining dominant and subordinate fish were given vehicle. One hour following drug treatment, the fish were tested for aggressive behavior again in a third and final intruder test, after which blood plasma and brain tissue were sampled for analysis of plasma cortisol concentrations and brain levels of monoamines and monoamine metabolites. Subordinate fish showed a reduction in the number of attacks launched against the intruder, as well as an increase in attack latency, as compared to prior to dyadic social interactions. Social subordination also resulted in an elevation of brain serotonergic activity. Fish receiving l-DOPA prior to the final intruder test showed shorter attack latency than vehicle controls. Drug treatment was a stressful experience and vehicle controls showed elevated plasma cortisol levels and longer attack latency as compared to before treatment. l-DOPA-treated fish showed lower plasma levels of cortisol and lower serotonergic activity in certain brain areas than vehicle controls. These results suggest that l-DOPA counteracts the stress-induced inhibition of aggressive behavior, and at the same time inhibits stress-induced effects on brain serotonergic activity and plasma cortisol concentrations.

When individuals receive different returns from their reproductive investment dependent on mate quality, they are expected to invest more when breeding with higher quality mates. A number of studies over the past decade have shown that females may alter their reproductive effort depending on the quality/attractiveness of their mate. However, to date, despite extensive work on parental investment, such a differential allocation has not been demonstrated in fish. Indeed, so far only two studies from any taxon have suggested that females alter the quality of individual offspring according to the quality/attractiveness of their mate. The banggai cardinal fish is an obligate paternal mouth brooder where females lay few large eggs. It has previously been shown that male size determines clutch weight irrespective of female size in this species. In this study, I investigated whether females perform more courtship displays towards larger males and whether females allocate their reproductive effort depending on the size of their mate by experimentally assigning females to either large or small males. I found that females displayed more towards larger males, thereby suggesting a female preference for larger males. Further, females produced heavier eggs and heavier clutches but not more eggs when paired with large males. My experiments show that females in this species adjust their offspring weight and, thus, presumably offspring quality according to the size of their mate.

Female reproductive decisions have been suggested to be highly influenced by mate quality. I have studied whether offspring quality may be adjusted by females to match the attractiveness of males and how strong control females have over their reproductive investment focusing on egg size. This was done in the Banggai cardinalfish (Pterapogon kauderni), a sex-role reversed obligate paternal mouthbrooder where males invest heavily into reproduction. As this species is suitable for both laboratory experiments and field studies it is an ideal candidate for the study of reproductive investment.

Mating was size-assortative and both males and females benefited from pairing with large partners. However, male size determined the reproductive output of a pair. Females courted large males more intensively and produced larger, but not fewer eggs when mated to large males as compared to small males. Further, this matching of egg size to mate attractiveness may be fast. Female courtship behaviours contained honest information regarding both clutch weight and egg maturity, traits that may be highly important for male mate choice. Surprisingly, males played an important part in territory defence suggesting relatively equal sex-roles in this species. Also, this species showed stable group structures which may be important for the evolution of female plasticity in reproductive investment due to high variance in quality of available mates.

This thesis suggest that females have a remarkable control over their reproductive investments and that male quality may be highly influential on reproductive decisions regarding offspring quality. Furthermore, it suggest that sexual selection may have strong effects on the evolution of egg size and parental care on a whole.

Size can have strong effects on reproductive success in both males and females, and in many species large individuals are preferred as mates. To estimate the potential benefits from mate choice for size in both sexes, I studied the effects of the size of each sex on the reproductive output of pairs of Banggai cardinalfish, Pterapogon kauderni, a sexually monomorphic obligate paternal mouthbrooder. When pairs were allowed to form freely, a size-assortative mating pattern was observed and larger pairs had a higher reproductive output as determined by total clutch weight and egg size. To separate the potential benefits from mate choice for size for each sex, I subsequently used these pairs to form reversed size-assortative pairs, that is, the largest male paired to the smallest female and vice versa. I found a positive correlation between male size and clutch size: relatively heavier clutches were found in pairs where females were given a larger male. This suggests that the size of the male influences clutch weight. For egg size, however, the size of both sexes seemed important. The study reveals the benefits of mutual mate choice on size in this species: larger females provide larger eggs and larger males can brood heavier clutches. Furthermore, these results suggest that females differentially allocate resources into the eggs according to the size of the mate.

In a field experiment, we studied how levels of aggression in males and females in established pairs of the Banggai cardinalfish were influenced by the sex of an experimentally introduced individual larger and more attractive than its resident counterpart. Contrary to previous studies on other cardinalfish species, and contrary to expectations in a sex role reversed species, the male was the main aggressor towards an intruder. Moreover, residents were more aggressive towards an intruder of the same sex as themselves. Furthermore, even though females often courted introduced, larger males, no intruder managed to take over the partnership of any resident. We suggest that our findings imply relatively equal sex roles in the Banggai cardinalfish and we discuss the evolution of sex specific territory defence and its significance in the Banggai cardinalfish as well as the implications of such behaviour in the interpretations of sex roles in general.

The commercial fishery for coral reef fish for the aquarium trade has begun to change, at least in some parts of the world, from destructive methods such as cyanide and dynamite fishing to less-destructive methods such as hand-net fishing. However, data on the effects on wild populations of such relatively nondestructive methods is nonexistent. The Banggai cardinalfish (   Pterapogon kauderni ) is a paternal mouthbrooder living in groups of 2–200 individuals in the proximity of sea urchins (   Diadema setosum ). This fish has limited dispersal abilities because it lacks a pelagic larval phase, and it is believed to be endemic to the Banggai archipelago off the east coast of Sulawesi, Indonesia. Since its rediscovery in 1995, the Banggai cardinalfish has become a popular aquarium fish, and thousands have been exported—mainly to North America, Japan, and Europe. To study the effects of the aquarium trade fishery on wild populations of the Banggai cardinalfish, we performed a field study in which we quantified density, age distribution ( quantified as the ratio of numbers of juveniles to adults ) and habitat quality ( i.e., sea urchin density ) at eight sites in the Banggai archipelago. Through interviews with local fishers, we estimated the fishing pressure at each site and related this to data on fish density. We found a marginally significant negative effect of fishing pressure on density of fish and significant negative effects on group size in both sea urchins and fish. We did not find any effect of fishing on fish size structure. To our knowledge this is the first study to compare sites under different amounts of fishing pressure that has demonstrated the negative effects of the aquarium trade on wild populations of reef fish, despite the widespread use of relatively nondestructive fishing methods.

To test whether females can change their egg investment according to the different attractiveness ( i.e. size as measured by standard length, L_s) of a new mate after eggs have already matured in response to an earlier mate, female Banggai cardinalfish Pterapogon kauderni were first allowed to produce eggs for small (unattractive) or large (attractive) males. Then, when spawning was initiated, but prior to actual spawning, their partner was switched to either a significantly larger or a significantly smaller partner, respectively. A strong positive correlation between egg size and days until spawning with the second male was found for the females initially paired to a small and then a large male. Within a few days, these females apparently increased their egg size to match the attractiveness of their new male. No correlation between days until spawning and egg size in females initially paired to a large and then a small male, however was found, so apparently females were unable to adjust egg size in response to a decrease in mate attractiveness. Consequently, it is suggested that females can increase their egg size investment even after the onset of egg maturation and that this change can be quite rapid.

Comparative studies of the genetic architecture of different types of traits were initially prompted by the expectation that traits under strong directional selection (fitness traits) should have lower levels of genetic variability than those mainly under weak stabilizing selection (nonfitness traits). Hence, early comparative studies revealing lower heritabilities of fitness than nonfitness traits were first framed in terms of giving empirical support for this prediction, but subsequent treatments have effectively reversed this view. Fitness traits seem to have higher levels of additive genetic variance than nonfitness traits — an observation that has been explained in terms of the larger number loci influencing fitness as compared to nonfitness traits. This hypothesis about the larger functional architecture of fitness than nonfitness traits is supported by their higher mutational variability, which is hard to reconcile without evoking capture of mutational variability over many loci. The lower heritabilities of fitness than nonfitness traits, despite the higher additive genetic variance of the former, occur because of their higher residual variances. Recent comparative studies of dominance contributions for different types of traits, together with theoretical predictions and a large body of indirect evidence, suggest an important role of dominance variance in determining levels of residual variance for fitness-traits. The role of epistasis should not be discounted either, since a large number of loci increases the potential for epistatic interactions, and epistasis is strongly implicated in hybrid breakdown.

Natural selection may act in different directions during different life-history stages, or in different directions on different classes of individuals. Antagonistic selection of this kind may be an important mechanism by which additive genetic variation for quantitative traits is maintained, and can prevent populations or species reaching local adaptive peaks. This paper reports the results of a study of viability selection on morphological traits of nestling collared flycatchers Ficedula albicollis. Analyses performed without knowledge of the sex of nestlings suggested that no selection was occurring on these traits. However, using molecular sex identification with the avian CHD gene, it is shown that selection acts in different directions on male and female body size from fledging to breeding, apparently favouring relatively small males and large females. The results suggest that differential selection on male and female nestlings may contribute to purely phenotypic sexual size dimorphism in this species. These findings highlight the potential of newly developed molecular sexing techniques to reveal the consequences of an individual's gender for many aspects of its life history in taxa where gender cannot be determined on the basis of external appearance.

Quantitative genetic theory predicts that evolution of sexual size dimorphism (SSD) will be a slow process if the genetic correlation in size between the sexes is close to unity, and the heritability of size is similar in both sexes. However, there are very few reliable estimates of genetic correlations and sex-specific heritabilities from natural populations, the reasons for this being that (1) offspring have often been sexed retrospectively, and hence, selection acting differently with respect to body size in the two sexes between measuring and sex identification can bias estimates of SSD; and (2) in many taxa, parents may be incorrectly assigned to offspring either because of assignment errors or because of extrapair paternity. We used molecular sex and paternity identification to overcome these problems and estimated sex-specific heritabilities and the genetic correlation in body size between the two sexes in the collared flycatcher, Ficedula albicollis. After exclusion of the illegitimate offspring, the genetic correlation in body size between the sexes was 1.00 (SE = 0.22), implying a severe constraint on the evolution of SSD in this species. Furthermore, sex-specific heritability estimates were very similar, indicating that neither sex will be able to evolve faster than the other. By using estimated genetic parameters, together with empirically derived estimates of sex-specific selection gradients, we further demonstrated that the predicted selection response in female tarsus length is displaced about 200% in the opposite direction from that to be expected if there were no genetic correlation between the sexes. The correspondence between the biochemically estimated rate of extrapair paternity (about 15 % of the young) and that estimated from the "heritability method" (11%) was good. However, the estimated rate of extrapair paternity with the heritability method after exclusion of the illegitimate young was 22%, adding to increasing evidence that factors other than extrapair paternity (e.g., maternal effects) may be resposible for the commonly observed higher mother- offspring than father-offspring resemblance.

1. Although the importance of adequate fat deposits for migrating birds has long been recognized, little is known about causes of intraspecific variation in the size of energy reserves. 2. We studied individual variation in visible fat reserves, body size, state of health and nutrition among autumn migrating Goldcrests Regulus regulus. 3. Birds showing signs of infectious/inflammatory diseases (high red blood cell sedi- mentation rate) or anaemia (low packed red blood cell volume) had significantly smaller fat stores than birds lacking these signs. However, no differences in fat reserves or health state were detected in relation to stage of post-juvenile moult. 4. These results suggest that the ability to deposit fat in the face of an energetically demanding migration may be affected by an individual's state of health.

The effect of natural brood size variation on offspring quality was studied in a blue tit (Parus caeruleus) population on the island of Gotland in the Baltic Sea. Offspring quality, measured as nestling body mass at day 13 post-hatch, declined significantly with increasing brood size, as did offspring structural body size (tarsus length). A quantitative genetic analysis revealed a high heritability of tarsus length, but also that the shorter tarsi of young from larger broods represented a negative environmental deviation from the genotypic values of their parents. Similarly, positive environmental deviations in tarsus length were found in small broods. Nestling mortality increased with increasing brood size, and smaller and lighter nestlings suffered higher mortality between day 13 and 20 post-hatch. These findings, together with those of previous studies showing that the survival prospects of malnutritioned passerine young are greatly reduced, provide evidence for a trade-off between the quantity and quality of young under non-manipulative conditions.

Interspecific competition for nest sites between tits (Parus spp.) and Collared Flycatchers (Ficedula albicollis) was responsible for the death of 23 flycatchers during one breeding season. Eighteen (78%) of the killed flycatchers were males, and nineteen (83%) of the kills took place in nest boxes occupied by Great Tits (Parus major), and two (9%) in boxes occupied by Blue Tits (P. caeruleus). The number of casualties in different plots increased with increasing proportion of nest boxes occupied by tits (r = 0.76), and decreased with increasing density of nest boxes (r = -0.43). The number of casualties equalled up to 17% of all flycatcher individuals breeding in a given plot, indicating that interspecific competition for nest sites may constitute a significant source of adult mortality in the Collared Flycatcher population studied.

1. The hypothesis that mass reduction in breeding passerines results from energeticstress was evaluated using data on body mass changes in female blue tits Paruscaeruleus.

2. In accordance with both the adaptive adjustment and the physiological stresshypotheses, females with experimentally enlarged broods lost more mass than femalesrearing reduced or control broods. However, the ability to allocate energy to selfmaintenance(as measured by the regrowth rate of a tail feather removed duringincubation) was negatively correlated with the amount of lost body mass.

3. In one of the study years, loss of body mass was more pronounced among smallfemales, suggesting that larger females are better able to cope with poor food conditionsduring breeding.

4. In a poor-weather year, 30% of the females deserted their clutches, comparedwith 8% in a good year. Females that deserted their clutches before hatching weresignificantly lighter during incubation than non-deserters, indicating that good bodycondition is important for successful reproduction.

5. In one year young females lost more mass than older females and therefore theability to maintain adequate body condition in the face of energetic stress appears tobe age-dependent.

6. Taken together, these results suggest that mass loss in breeding blue tits is, to somedegree, attributable to energetic stress, although we have not ruled out the possibilitythat flight cost reductions may help explain the phenomenon.

Traditionally, females have been considered to be strictly monogamous. Today, we know that females in the majority of species actively seek out and mate with several males. Trying to understand female preferences, including what benefits mate choice entails, has been the focus of intense research during the last decades. Females can gain both direct (e.g. access to better territories or paternal care) and indirect (i.e. genetic) benefits. The aim of this thesis is to further our understanding of the female reproductive strategies in the ruff, Philomachus pugnax (Aves, Scolopacidae). The ruff is a lekking wader, where males gather on leks to display to females that come there to mate. Males do not provide any paternal care to the offspring. Lekking systems are ideal for studying indirect benefits of female choice, as females do not gain any direct benefits from males.

Females mated with several males and 50% of the broods were fathered by at least two males. The level of genetic similarity between two parents has previously been shown to be an important source of variation in offspring fitness. Males that were less closely related to the female fathered more offspring in broods with multiple paternity, such that females that mated multiply gained in terms of receiving more outbred offspring. There did not, however, appear to be an overall female preference for less closely related males. There are two genetically determined male reproductive strategies in the ruff, that differ in behaviour and morphology. There was no evidence for females taking male strategy into account when choosing a partner.

Female post-fertilisation strategies may also influence fitness, e.g. through differential investment in eggs, gender of the offspring and choice of breeding habitat. Females allocated sex in a non-random manner dependent upon body condition, such that females in good condition had more daughters.

Females were found to nest in higher than average vegetation and in areas with higher than average abundance of insects, factors likely to influence predation rates on both eggs and young, as well as foraging opportunities for the precocial young. Further, females were faithful to their previous breeding site and usually nested within meters of their previous nest. Hatching success did not, however, affect a female’s decision to return or not.

This thesis integrates the fields of sexual selection, parental investment and sex role theory by investigating mutual mate choice and mate competition in the sex role reversed deep snouted pipefish Syngnathus typhle (Pisces: Syngnathidae) through a series of laboratory experiments. In S. typhle, the female transfers her eggs to the male's brood pouch where they are nourished and oxygenated for about a month, when the male gives birth to the independent fry.

Mate choice was found to be adaptive. Both sexes benefited from mating with preferred partners in terms of increased offspring viability and got larger, or faster growing, offspring when mating with large fish. Females were also shown to prefer males with thicker brood pouches. Thus, females, the more competitive sex, had multiple preferences. Both male and female choice behaviour was found to be flexible and influenced by available information on partner quality. In addition, males, but not females, copied the mate choice of consexuals.

Both sexes were found to take their own quality in relation to surrounding competitors into account when deciding whether to display to potential partners. Male-male competition was found to influence both the mate choice of males and, potentially, overrule the mate choice of females. Males did not compete as intensely as females, nor did they use their sexual ornament in this context as females do. Rather, the ornament was used in interactions with females, and males that displayed more received more eggs.

The findings in this thesis emphasise the importance of not viewing mate choice and competition as opposite behaviours, but rather to apply a dynamic approach in mate choice studies, integrating choice and competition in both sex