Scapini F., Rossano C., Marchetti G.M. and Morgan. E. 2005.
The role of biological clock in sun compass orientation of free-running individual of Talitrus saltator
Animal Behaviour 69, 4:835-843.
The relationship between the angle of solar orientation and the circadian rhythm of locomotor activity in Talitrus saltator has been investigated using a ‘variable-drift’ paradigm. The circadian rhythms of individual sandhoppers were recorded in constant darkness before testing individually at a set time during the day. Differences in free-running period between individuals thus caused animals to be tested at different phase points in their circadian cycle, so that the angular measurements were distributed across the subjective scotophase and photophase. The association between sun orientation angle and circadian time was investigated using circular correlation statistics, and circular-circular regression models were constructed for comparison with the biometric data. The sun orientation angles were strongly dependent on time of day, suggesting that orientation and locomotor activity are regulated by the same time-keeping system. The model fitting the experimental data best is a sinusoidal one, and the distribution of angular orientation predicted on this basis followed closely that of the non-parametrically smoothed data. During the day this followed the arc of movement of the sun, with a phase delay of about 90o and the sign of the angle of orientation reverses around noon and midnight. The data are interpreted in terms of a mean angular velocity register, and their ecological significance is discussed.
Addresses of the authors:
Felicita Scapini, Dipartimento di Biologia Animale e Genetica “Leo Pardi”, Università di Firenze, via Romana 17, 50125 Firenze, Italy
Claudia Rossano, Dipartimento di Biologia Animale e Genetica “Leo Pardi”, Università di Firenze, via Romana 17, 50125 Firenze, Italy
Giovanni Maria Marchetti, Dipartimento di Statistica “G. Parenti”, Università di Firenze, viale Morgagni 56, 50134 Firenze, Italy
Elfed Morgan, School of Biosciences, University of Birmingham, Edgbaston, UK