Lek mating systems, in which males aggregate at traditional sites to display for females that attend primarily for the purpose of fertilisation, are characterised by large inequalities in male mating success, and intense competition between males. It seems paradoxical, therefore, that males of one genus of lek mating manakins, <I>Chiroxiphia </I>(Aves: Pipridae), cooperate in dual-male displays for females. The benefits of this cooperation appear virtually unilateral, especially as males are not closely related. However, benefits to subordinates are offset in time, and relate primarily to ascent to dominance status. I studied the behaviour of Long-tailed Manakins <I>Chiroxiphia linearis</I> at a long-terms study site at Monteverde, Costa Rica, to investigate the physiological control of delayed breeding in subordinate males. The results presented here form a background to that study, and address issues relating to the roles of inter-and intrasexual selection in determining male mating success, the reproductive strategies employed by males, and the role of plumage in the establishment of dominance. Methods included the monitoring of male displays and female visitation at nine principal leks, and the gathering of morphological and plumage data, and blood samples from captured birds. Male mating success was determined by a combination of intra- and intersexual selection. Males at each lek form an orderly queue for dominant status, which among top-ranking males is linear. Only the dominant male, with rare exceptions, had access to mating opportunities. Females appear to discriminate between male queues on the basis of dual-male phenotypes relating to display performance.

I examine the CO₂ response of the nematode <i>C. elegans. </i>This species inhabits rotting material, which typically has a broad CO₂ concentration range. I show that well-fed <i>C. elegans</i> avoid CO₂ levels greater than 0.5%. Animals can respond to changes in CO₂ levels in seconds. Responses to CO₂ do not reflect avoidance of acid pH but appear to define a new sensory response. Sensation of CO₂ is promoted by the cGMP-gated ion channel subunits TAX-2 and TAX-4. TRPV (transient receptor potential vanilloid-type) channels appear to play only a minor role in CO₂ avoidance. The transmembrane guanylate cyclase <i>daf-11</i> is required to promote CO₂ avoidance off food, but not on food. CO₂ avoidance is promoted by DAF-11 activity in the AWB neurons, which express <i>tax-2</i> and <i>tax-4.</i> Starvation strongly suppresses CO₂ avoidance. Robust CO₂ avoidance in well-fed animals requires inhibition of the DAF-16 forkhead transcription factor by the insulin-like receptor DAF-2. Although starvation activates DAF-16, <i>daf-16</i> alone is not responsible for starvation-induced suppression of CO₂ avoidance. Interestingly, exposure to hypoxia (<1% O₂) also suppresses CO₂ avoidance, via activation of the hypoxia inducible transcription factor, HIF-1. The <i>npr-1 215V</i> allele of the naturally polymorphic neuropeptide receptor <i>npr-1</i>, besides inhibiting avoidance of high O₂ in feeding <i>C. elegans</i>, also promotes avoidance of high CO₂. NPR-1 215V acts in the ASE neurons to promote CO₂ avoidance. <i>C. elegans </i>integrates competing CO₂ and O₂ sensory inputs such that either the CO₂ or the O₂ response dominates. Food and allelic variation at NPR-1 determine which response dominates. To identify <i>C. elegans</i> CO₂ receptors, I performed an EMS mutagenesis screen for carbon <i>d</i>ioxide <i>a</i>voidance <i>d</i>efective (Cdad) mutants. One Cdad isolate, <i>db130, </i>revealed a novel H377E missense mutation in the <i>C. elegans</i> Protein Kinase B orthologue, <i>akt-1.</i>

The thesis pursues two themes: The first investigate neophilia, innovation and social learning in captive callitrichid monkeys (family <i>Callitrichidae</i>) and guppy fish (<i>Poecilia reticulata</i>). The second explores the application of innovation and social learning theory and research findings to conservation techniques, especially reintroduction. The thesis relies on data collected in a zoo-based study where groups of callitrichids were exposed to novel extractive foraging tasks and also on data collected from laboratory studies of novel foraging behaviour in the guppy. The use of both primates and fish allow a broader range of issues to be addressed than could be tackled with a single model system. The callitrichid study reports intergeneric, age and enclosure type differences in neophilia, innovation and social learning, but no such sex differences. The same study examine the processes that lead to social learning but finds little evidence for directed social learning, although other forms of social learning are observed, namely localised stimulus enhancement. Laboratory studies of guppies reveal an influence of positive frequency-dependent social learning, or conformity, upon the spread of novel foraging behaviour. Fish experiments also examine the relative weighting of asocial and social information by manipulating the cost of reliance upon individual information relative to social information, in the process confirming the findings of theoretical models. The implications of the thesis’ findings for innovation and social learning research and also for conservation and reintroduction techniques are highlighted.

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To determine if evolution to polar water temperatures has altered the way in which Antarctic marine organisms adapt to changing temperature, protein metabolism, growth and ATP allocation were examined in the Antarctic teleost <i>Harpagifer antarcticus, </i>and compared with data from two temperate teleosts, <i>Lipophrys pholis </i>and <i>Parablennius gattorugine.</i> The energetic cost of protein synthesis in the Antarctic limpet, <i>Nacella concinna</i>, was similar to that measured in other non-polar ectotherms, and unaffected by acclimation temperature. The rate of protein synthesis in <i>H. antarcticus </i>was unaffected by temperature between -1 and +3°C, and was significantly lower than in <i>L. pholis</i> held at the same temperature. Growth rates in <i>H. antarcticus </i>were significantly lower and protein metabolism less efficient than in <i>L. pholis</i>. Tissue specific protein synthesis rates varied in a similar manner to that reported in other studies, while the effects of temperature were again markedly reduced in the Antarctic species when compared with the temperate species. Protein metabolism in the examined Antarctic species is considerably less efficient than in the temperate species, suggesting that slow growth rates reported in Antarctic species may not only be the result of a variable food supply, but also biochemical constraints on growth efficiency. There were significant differences in how temperature affected the oxygen consumption allocated to major hepatocyte energy consuming processes in <i>H. antarcticus </i>and <i>P. gattorugine.</i> The effects of temperature were less pronounced in <i>H. antarcticus, </i>however proton leak increased significantly with falling temperature in <i>H. antarcticus</i>, but not <i>P. gattorugine.</i> Increased proton leak in <i>H.antarcticus</i> at low temperatures may be a mechanism to reduce oxidative damage.

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