Abstract. Most colonially breeding animals occupy colonies that range in size from a few pairs to thousands of individuals, but the causes of colony size variation are largely unknown. Three general hypotheses are: (1) that variation in colony size is maintained by fluctuating selection via spatial and temporal changes in fitness associated with different colony sizes; (2) that colony formation reflects heterogeneity in habitat, with some sites having resources to support more individuals than others; and (3) that individuals assess the presence or annual reproductive success of current colony residents at each site and aggregate preferentially at high-quality sites. These hypotheses make predictions about how consistent colony size should be across sites and among years. We examined temporal and spatial variability of colony size for .200 Cliff Swallow (Petrochelidon pyrrhonota) colony sites in western Nebraska across a 30-year period. A colony's substrate type, annual population size in the study area, and whether the nesting season was relatively warm or cool, influenced average annual colony size. While some Cliff Swallow colony sites hosted perennially large colonies and others perennially small ones, between-year variability in colony size at most sites was high. Annual colony size distributions were relatively stable over 30 years and provided no evidence for long-term directional changes in colony size. The only ecological characteristic that was strongly associated with Cliff Swallow colony size at a site was the type of nesting substrate, with bridges tending to have larger colonies and being more frequently occupied than other substrates. Some sites showed annual changes in colony size consistent with the birds' basing their choice of colony on the presence or success of conspecifics, but many sites did not conform to a pattern expected if coloniality is a by-product of traditional aggregation. Colony size in Cliff Swallows was temporally and spatially unpredictable when viewed across the 30 years of this study. Each of the three hypotheses to explain size variation may have applied at certain sites, but the pattern of colony size variability leant the most support to the hypothesis that fluctuating selection on group size maintains colonies of widely different sizes.

ABSTRACT. The effort expended on reproduction may entail future costs, such as reduced survival or fecundity, and these costs can have an important influence on life-history optimization. For birds with precocial offspring, hypothesized costs of reproduction have typically emphasized nutritional and energetic investments in egg formation and incubation. We measured seasonal survival of 3856 radio-marked female Mallards (Anas platyrhynchos) from arrival on the breeding grounds through brood-rearing or cessation of breeding. There was a 2.5-fold direct increase in mortality risk associated with incubating nests in terrestrial habitats, whereas during brood-rearing when breeding females occupy aquatic habitats, mortality risk reached seasonal lows. Mortality risk also varied with calendar date and was highest during periods when large numbers of Mallards were nesting, suggesting that prey-switching behaviors by common predators may exacerbate risks to adults in all breeding stages. Although prior investments in egg laying and incubation affected mortality risk, most relationships were not consistent with the cost of reproduction hypothesis; birds with extensive prior investments in egg production or incubation typically survived better, suggesting that variation in individual quality drove both relationships. We conclude that for breeding female Mallards, the primary cost of reproduction is a fixed cost associated with placing oneself at risk to predators while incubating nests in terrestrial habitats.RÉSUMÉ. L'effort investi à la reproduction peut avoir une incidence sur les coûts futurs -comme un faible taux de survie ou de fertilité -et ces coûts peuvent grandement influencer l'optimisation du cycle biologique. Chez les oiseaux dont les jeunes sont nidifuges, les coûts hypothétiques de la reproduction sont surtout liés aux efforts nutritionnel et énergétique investis dans la formation des oeufs et à l'incubation. Dans le cadre de cette étude, nous avons mesuré le taux de survie saisonnier de 3 856 Canards colverts (Anas platyrhynchos) femelles munies d'un émetteur radio, de leur arrivée sur les aires de nidification jusqu'à ce que l'élevage des jeunes soit complété ou jusqu'à l'échec de la nidification. Le taux de mortalité était de 2,5 fois plus élevé chez les femelles qui couvaient leurs oeufs en milieu terrestre, tandis qu'il a était à son plus bas niveau saisonnier au moment de l'élevage des jeunes en milieu aquatique. Le taux de mortalité a aussi varié en fonction de la date : il était à son maximum au moment où de nombreux Canards colverts nichaient, ce qui laisse croire que le changement de proies dans la diète des prédateurs communs pourrait exacerber le risque de mortalité chez les femelles à toutes les étapes de la nidification. Même si les efforts investis dans la ponte et l'incubation ont eu un effet sur le taux de mortalité, la plupart des relations n'étaient pas conformes aux prédictions de l'hypothèse des coûts de la reproduction; les femelles qui ont grandement investi dans la production d'oeufs ...

Genomewide association studies may offer the best promise for genetic mapping of complex traits. Such studies in outbred populations require very densely spaced single-nucleotide polymorphisms. In recently founded population isolates, however, extensive linkage disequilibrium (LD) may make these studies feasible with currently available sets of short tandem repeat markers, spaced at intervals as large as a few centimorgans. We report the results of a genomewide association study of severe bipolar disorder (BP-I), using patients from the isolated population of the central valley of Costa Rica. We observed LD with BP-I on several chromosomes; the most striking results were in proximal 8p, a region that has previously shown linkage to schizophrenia. This region could be important for severe psychiatric disorders, rather than for a specific phenotype.

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Farm to School (FTS) programs are increasingly popular as methods to teach students about food, nutrition, and agriculture by connecting students with the sources of the food that they eat. They may also provide opportunity for farmers seeking to diversify market channels. Food service buyers in FTS programs often choose to procure food for school meals directly from farmers. The distribution practices required for such direct procurement often bring significant transaction costs for both school food service professionals and farmers. Analysis of data from a survey of Vermont farmers who sell directly to school food services explores farmers' motivations and distribution practices in these partnerships. A two-step cluster analysis procedure characterizes farmers' motivations along a continuum between market-based and socially embedded values. Further bivariate analysis shows that farmers who are motivated most by market-based values are significantly associated with distribution practices that facilitate sales to school food services. Implications for technical assistance to facilitate these sales are discussed.