Circadian rhythms of locomotor activity and temperature selection in sleepy lizards, Tiliqua rugosa

This study examined whether the daily rhythms of locomotor activity and behavioural thermoregulation that have previously been observed in Australian sleepy lizards (Tiliqua rugosa) under field conditions are true circadian rhythms that persist in constant darkness (DD) and whether these rhythms show similar characteristics. Lizards held on laboratory thermal gradients in the Australian spring under the prevailing 12-hour light : dark (LD) cycle for 14 days displayed robust daily rhythms of behavioural thermoregulation and locomotor activity. In the 13-day period of DD that followed LD, most lizards exhibited free-running circadian rhythms of locomotor activity and behavioural thermoregulation. The predominant activity pattern displayed in LD was unimodal and this was retained in DD. While mean levels of skin temperature and locomotor activity were found to decrease from LD to DD, activity duration remained unchanged. The present results demonstrate for the first time that this species’ daily rhythm of locomotor activity is an endogenous circadian rhythm. Our results also demonstrate a close correlation between the circadian activity and thermoregulatory rhythms in this species indicating that the two rhythms are controlled by the same master oscillator(s). Future examination of seasonal aspects of these rhythms, may, however, cause this hypothesis to be modified.David J. Ellis, Bruce T. Firth and Ingrid Bela

Role of the epididymis in sperm competition

The definitive version is available at www.blackwell-synergy.comAlthough it is generally understood that the testes recruited kidney ducts for reproductive function during the evolution of vertebrates, little is understood of the biological significance of the adaptation. In the context of the evolution of the mammalian epididymis, this report provides evidence that a major role of the epididymis is to enhance a male's chance of achieving paternity in a competitive mating system. A unique example of sperm cooperation in monotremes is used as evidence that the epididymis produces sperm competition proteins to form groups of 100 sperm into bundles that have a forward motility nearly thrice that of individual spermatozoa. As it required 3-h incubation in vitro under capacitation conditions to release motile sperm from the bundles, it is suggested that the monotremes provide an example of capacitation that is quite different from capacitation in higher mammals. It is suggested that variation between species in the intensity of sperm competition could explain the variation that occurs between species in the amount of post-testicular sperm maturation and storage in the epididymis, an explanation of why the human epididymis does not play as important a role in reproduction as the epididymis of most mammals.Russell C. Jones, Jean-Louis Dacheux, Brett Nixon, Heath W. Ecroy