Browsing by Subject "Couleur"

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    Host-Parasite Arms Races and Rapid Changes in Bird Egg Appearance
    (2012) Spottiswoode, Claire N; Stevens, Martin
    Abstract Coevolutionary arms races are a powerful force driving evolution, adaptation, and diversification. They can generate phenotypic polymorphisms that render it harder for a coevolving parasite or predator to exploit any one individual of a given species. In birds, egg polymorphisms should be an effective defense against mimetic brood parasites and are extreme in the African tawny-flanked prinia (Prinia subflava) and its parasite, the cuckoo finch (Anomalospiza imberbis). Here we use models of avian visual perception to analyze the appearance of prinia and cuckoo finch eggs from the same location over 40 years. We show that the two interacting populations have experienced rapid changes in egg traits. Egg colors of both species have diversified over time, expanding into avian color space as expected under negative frequency-dependent selection. Egg pattern showed signatures of both frequency-dependent and directional selection in different traits, which appeared to be evolving independently of one ano...
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    The effect of dust obscuration in RR Telescopii on optical and IR long-term photometryand Fe II emission lines
    (2006) Kotnik-Karuza, D; Friedjung, M; Whitelock, P A; Marang, F; Exter, K; Keenan, F P; Pollacco, D L
    Aims. Infrared and optical photometric and spectroscopic observations of the symbiotic nova RR Tel are used to study the effects and properties of dust in symbiotic binaries containing a cool Mira component, as well as showing obscuration events of increased absorption, which are typical for such Miras. Methods. A set of photometric observations of the symbiotic nova RR Tel in different wavelength bands - visual from 1949 to 2002 and near-infrared (JHKL) from 1975 to 2002 - are presented. The variability due to the normal Mira pulsation was removed from the JHKL data, which were then compared with the American Association of Variable Star Observers' (AAVSO) visual light curve. The changes of the Fell emission line fluxes during the 1996-2000 obscuration episode were studied in the optical spectra taken with the Anglo-Australian telescope. Results. We discuss the three periods during which the Mira component was heavily obscured by dust as observed in the different wavelength bands. A change in the correlations of J with other infrared magnitudes was observed with the colour becoming redder alter JD 2 446 600. Generally, J-K was comparable, while K-L was larger than typical values for single Miras. A distance estimate of 2.5 kpc, based on the IR data, is given. A larger flux decrease for the permitted than for the forbidden Fe II lines, during the obscuration episode studied, has been found. There is no evidence for other correlations with line properties, in particular with wavelength, which suggests obscuration due to separate optically thick clouds in the outer layers. Conclusions.