Search

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2004.08.008 Byline: Felicita Scapini, Claudia Rossano, Giovanni M. Marchetti, Elfed Morgan Abstract: We used a 'variable-drift' paradigm to investigate the relation between the angle of solar orientation and the circadian rhythm of locomotor activity in Talitrus saltator. We recorded the circadian rhythms of individual sandhoppers in constant darkness before testing them at a set time during the day. Because of differences in the free-running period between individuals, they were thus tested at different phase points in their circadian cycle, so that the angular measurements were distributed across the subjective scotophase and photophase. To investigate the association between sun orientation angle and circadian time we used circular correlation statistics, and constructed circular-circular regression models 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 was a sinusoidal one, and the distribution of angular orientation predicted on this basis followed closely that of the nonparametrically smoothed data. During the day this followed the arc of movement of the sun, with a phase delay of about 90[degrees] and the sign of the angle of orientation reversed around 1200 and 2400 hours. We interpret the data in terms of a mean angular velocity register and discuss their ecological significance. Author Affiliation: (*) Dipartimento di Biologia Animale e Genetica 'Leo Pardi', Universita degli Studi di Firenze, Italy (a ) Dipartimento di Statistica 'G. Parenti', Universita degli Studi di Firenze, Italy (a ) School of Biosciences, University of Birmingham, U.K. Article Note: (miscellaneous) MS. number: 8144

Management of invasive alien crayfish is challenging, as once established their eradication or control is difficult, even impossible in some areas. Sterile male release technique has been previously assessed in crayfish with encouraging results, however, the methods have not demonstrated the complete sterility of released competitive males. The present study explores whether manual removal of male gonopods, i.e. the appendages responsible for sperm transfer, as a sterilisation technique, might affect male competitiveness and sexual behaviour as well as reproductive potential in the red swamp crayfish Procambarus clarkii.Under controlled laboratory conditions, we analysed the agonistic and sexual behaviour of 64 treated and 64 control males both coupled with a female in single pairs, and 40 treated and 40 control males together with 80 females in a natural‐like social context.Removal of gonopods partly altered sexual behaviour, affecting duration of copulation and competitiveness in treated males. However, male readiness to initiate sexual interaction with females was not affected by the treatment. Treated males needed to invest more in agonistic interactions with females to successfully dominate a female for the copulation to take place. Females coupled with treated males did not produce any offspring, compared to females coupled with control males. Treated males were able to regenerate removed gonopods, even if sometimes only partially or malformed. Females that mated with 11 treated males with regenerated gonopods did not produce any juveniles.Although treated males managed to mate with females and impair their reproductive capability under the laboratory conditions, shorter copulation and elevated number of abdominal extensions were observed in treated couples. This indicates that males and/or females are able to sense the lack of gonopods and/or lack of the contact. We believe that female receptivity after an initial mating requires further investigation. Assessment of receptivity in an experimental setting where females are provided with refuges (e.g. burrows) would help us to elucidate whether there is a compensation for unsuccessful copulation. More research is needed on underlying biological mechanisms to better assess male competitiveness, technique effectiveness and limits of technique application. [ABSTRACT FROM AUTHOR]