This project describes various aspects of the breeding ecology and behaviour of the brown falcon Falco berigora, a common but poorly study Australian raptor. In particular it examines (a) the main influences on reproductive success; (b) tests predictions of theories proposed to explain the evolution and maintenance of sexual size dimorphism (RSD; females the larger sex) in raptors; and (c) investigates sex allocation patterns in the light of current sex ratio and parental investment theory. The study was conducted between July 1999 and June 2002 approximately 35 km southwest of Melbourne, at the Western Treatment Plant (WTP), Werribee (38°0’S 144°34’E) and surrounds, a total area of approximately 150 km2.¶ · In all plumage and bare part colouration of 160 free-flying falcons was described. The majority of variation in these characters could be attributed to distinct age and/or sex differences as opposed to previously described colour ‘morphs’.¶ · Nestling chronology and development is described and formulae based on wing length derived for determining nestling age. An accurate field-based test for determining nestling sex at banding age is also presented.¶ · Strong sex role differentiation was apparent during breeding; typical of falcons females performed most parental duties whilst males predominantly hunted for their brood and partner. Based on observations of marked individuals, both sexes of brown falcons aggressively defended mutual territories throughout the year, with just 10% of each sex changing territories during the entire study period. Males performed territorial displays more frequently than females, the latter rarely displaying alone.¶ · The diet of the population as a whole was very broad, but within pairs both sexes predominantly specialised on either lagomorphs, small ground prey (e.g. house mice Mus musculus), small birds, large birds or reptiles, according to availability.¶ · Reproductive parameters such as clutch size and the duration of parental care were constant across all years, however marked annual differences in brood size and the proportion of pairs breeding were evident.¶ · Age was an important influence upon reproductive success and survival, with immature birds inferior to adults in both areas. However, interannual differences were by far the most influential factor on breeding success and female survival. Heavy rain downpours were implicated as the main determinant of reproductive success and adult female mortality in a population largely devoid of predation or human interference.¶ · Female-female competition for territorial vacancies was intense; larger adult females were more likely to be recruited and once breeding fledged more offspring. In contrast, male recruitment and breeding success was unrelated to either body size or condition indices, although smaller immature males were more likely to survive to the next breeding season. This directional selection is consistent only with the predictions of the intrasexual competition hypothesis.¶ · Despite marked RSD (males c. 75% of female body mass), throughout the nestling phase female nestlings did not require greater quantities of food than their male siblings. However, female parents fed their last-hatched sons but not daughters, resulting in the complete mortality of all last-hatched female offspring in focal nests. Given last-hatched nestlings suffered markedly reduced growth rates and female, but not male, body size is important in determining recruitment patterns, the biased allocation amongst last-hatched offspring is likely to reflect differing benefits associated with investing in small members of each sex, consistent with broad-scale Trivers-Willard effects. Recruitment patterns support this, with surviving last-hatched females, in contrast to males, unable to gain recruitment into the breeding population upon their return to the study site.¶ Thus selection appears to act at the nestling, immature and adult stages to maintain RSD in the focal population. Larger females were favoured in the nestling phase, at recruitment and once breeding had greater reproductive success. In contrast, selection favoured a reduction or maintenance of immature male size as smaller birds had a greater chance of survival in the year following recruitment than their larger counterparts; thereafter male size was unimportant. Together, this directional selection favouring increased female competitive ability is consistent only with the predictions of the intrasexual competition hypothesis, which appears the most probable in explaining the maintenance and perhaps evolution of RSD in raptors.

In nature, environments are often variable and heterogeneous influencing ecological and evolutionary processes. This thesis focus on how animals interact with their environment and how that affects the reproductive decisions they make. Using empirical data collected from wild collared flycatcher populations, experiments and molecular approaches I try to unveil some of these relationships and the evolutionary, ecological and conservation implications of these findings are discussed. Firstly, collared flycatchers were shown to use breeding densities of their own and other species using similar resources when assessing costs and benefits associated to breeding in specific habitats. However, species will vary in how informative they are, and the worst competitor – with whom you overlap most in resources needs – also provides the best source of information. Collared flycatcher parents will also benefit differentially from investments in sons and daughters due to habitat characteristics and dispersal differences between the sexes. Here, I show that they will produce more of the sex that will give the highest expected fitness return given the environment they are in. These results also provide a reciprocal scenario to Clark's (1978) classical study of sex ratio adjustment in relation to local resource competition (LRC), as more of the natal philopatric sex is produced when LRC is low. Secondly, the effect of elaborated ornaments on paternity in the socially monogamous collared flycatcher was shown to be of more importance in areas where the intensity of intra- and intersexual conflicts are expected to be elevated. Hence, ornamentation by environmental interactions determines paternity, illustrating that sexual selection through extra-pair paternity is context dependent. Finally, even though the collared flycatcher populations that this thesis is based on have been studied on their breeding grounds for more then 25 years, we know little of where they are when they are not breeding. Here, stable isotope signatures in winter-grown feathers suggests that they may spend their winter with their breeding ground neighbours and do so repeatedly over years. Differences between breeding populations at this small scale should have many impactions for evolutionary and ecological processes as it will, for example, determine with whom individuals interact throughout their life.

The allocation of resources to male or female progeny, or to male or female reproductive function more generally, is one of the most important life history decisions a sexually reproducing individual must ever make. Sex determination is thus a fundamental process, yet the mechanisms which control it are surprisingly diverse. In this thesis, I examine sex determination in the plant species Mercurialis annua L. (Euphorbiaceae). I assess the mechanism of sex determination operating in dioecious and androdioecious populations of M. annua and also investigate the conservation and evolution of sex-determining mechanisms across the annual mercury clade, the lineages of which display exceptional variation in sexual system. First, using crosses, I establish that sex in dioecious M. annua is controlled by a single-locus genetic mechanism, consistent with recent work that identified a single male-linked DNA marker in the species. My search for new sex-linked genes revealed none, however, suggesting that M. annua possesses at most a small non-recombining region around sex-determining loci. Why many dioecious plants lack heteromorphic sex chromosomes is still poorly understood and I consider explanations for this. I extend my investigation by comparing genetic diversity between loci that differ in their linkage to the sex-determining locus. I find a single male-linked marker to possess significantly lower diversity than autosomal loci, but no difference in the diversity of partially sex-linked and non-sex-linked genes. I also assess the conservation of a sex-linked marker among annual mercury lineages and conduct crosses between lineages to examine the conservation of sex determination. My findings indicate a conserved mechanism of single-locus genetic sex determination and I consider the role polyploidisation and hybridisation have played in sexual system evolution and the modification of sex-determining mechanisms in the clade. Finally, I assess the presence of environmental sex determination in androdioecious M. annua, concluding that although male frequency is not influenced by growing density, a degree of sexual lability exists in the lineage.

Les femelles parasitoïdes exploitant un agrégat d’hôtes doivent ajuster leurs comportements en fonction des facteurs environnementaux auxquels elles sont soumises, dont la présence de compétiteurs dans l’environnement. L’objectif de cette étude est de mesurer les impacts de la compétition sur les stratégies d’exploitation d’agrégats chez deux espèces de parasitoïdes non agressives. Les espèces Trichogramma pintoi et T. minutum (Hymenoptera : Trichogrammatidae), des parasitoïdes d’œufs de lépidoptères, furent utilisées et leurs temps de résidence dans l’agrégat, leurs mécanismes de prise de décision et le sexe des descendants alloués furent mesurés en l'absence de compétition et en situation de compétition directe et indirecte, intra- et interspécifique. Trichogramma pintoi privilégie une stratégie générale basée uniquement sur la qualité perçue de l’agrégat. À l’inverse, T. minutum privilégie une stratégie adaptée au type de la compétition (directe ou indirecte) et à la nature des compétiteurs (intra ou interspécifiques), sans égards à la qualité de l’agrégat. La distinction de ces deux stratégies amène des perspectives de recherche intéressantes sur les impacts de la compétition à l’échelle du paysage, et est d’un intérêt certain pour ceux voulant améliorer l’efficacité des programmes et des élevages de masse utilisés en lutte biologique. / Female parasitoids must adjust their behavior in response to different environmental factors when foraging for hosts. One of the most important factors they must cope with is the presence of competitors in their environment. The objective of this study is to measure the effects competition has on the foraging strategies of non-aggressive parasitoids. We used the species Trichogramma pintoi and T. minutum (Hymenoptera: Trichogrammatidae), two egg parasitoids of lepidoteran species. We measured patch residence times, patch-leaving mechanisms and progeny sex allocation of females foraging alone, and of females foraging under direct or indirect, intra- or interspecific competition. Trichogramma pintoi females favoured a general strategy entirely based on the perceived quality of the patch, whereas T. minutum females favoured a strategy that was adapted to the type of competition (direct or indirect) and to the nature of the competitors (intra- or interspecific) they were subjected to, with no regards for the quality of the patch. The distinction between these two strategies brings forth interesting research opportunities regarding the effects of competition at the landscape level, and should be of interest for biological control practitioners wishing to increase the efficacy of biological control programs and of commercial mass rearings.

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