Too cold is better than too hot: Preferred temperatures and basking behaviour in a tropical freshwater turtle

Thermoregulation is critical to the survival of animals. Tropical environments can be particularly thermally challenging as they reach very high, even lethal, temperatures. The thermoregulatory responses of tropical freshwater turtles to these challenges are poorly known. One common thermoregulatory behaviour is diurnal basking, which, for many species, facilitates heat gain. Recently, however, a north-eastern Australian population of Krefft's river turtles (Emydura macquarii krefftii) has been observed basking nocturnally, possibly to allow cooling. To test this, we determined the thermal preference (central 50% of temperatures selected) of E. m. krefftii in an aquatic thermal gradient in the laboratory. We then conducted a manipulative experiment to test the effects of water temperatures, both lower and higher than preferred temperature, on diurnal and nocturnal basking. The preferred temperature range fell between 25.3°C (±SD: 1.5) and 27.6°C (±1.4) during the day, and 25.3°C (±2.4) and 26.8°C (±2.5) at night. Based on this, we exposed turtles to three 24 h water temperature treatments (‘cool’ [23°C], ‘preferred’ [26°C] and ‘warm’ [29°C]) while air temperature remained constant at 26°C. Turtles basked more frequently and for longer periods during both the day and night when water temperatures were above their preferred range (the ‘warm’ treatment). This population frequently encounters aquatic temperatures above the preferred thermal range, and our results support the hypothesis that nocturnal basking is a mechanism for escaping unfavourably warm water. Targeted field studies would be a valuable next step in understanding the seasonal scope of this behaviour in a natural environment.     

Development of the vertebrate small intestine and mechanisms of cell differentiation

The intestinal epithelium represents an attractive biological model of differentiation from stem cells to highly differentiated epithelial cells, not only during particular developmental events depending upon the vertebrate species considered but also throughout adult life. The ontogenic maturation of the intestinal epithelium arises from both a programmed expression of specific genes and epigenetic influences mainly due to epithelial and mesenchymal interactions and hormonal participation. In the present paper we review the structural and functional changes that occur in the amphibian, avian and mammalian intestine during embryonic and/or post-embryonic development. Furthermore, we review the data concerning the mechanisms which control the cytodifferentiation of the intestinal epithelium.     

On the relation between absorption and fluorescence emission spectra of photosystems: Derivation of a Stepanov relation for pigment culsters

Stepanov (1957a, Soviet Physics-Doklady 2: 81–84) obtained an equation which relates the absorption spectrum and the fluorescence emission spectrum of a single dye molecule. Here, a similar equation is derived for a cluster of interacting pigments, e.g. the antenna pigments of a photosystem. This relation can be used to assess the possibility of occurrence of rapid exciton equilibration (Dau and Sauer, 1996, Biochim. Biophys. Acta, 1273: 175–190). The excited state potential of a pigment cluster is discussed and compared to the excited state potential of a single pigment.Abbreviations Chl chlorophyll - EE exciton equilibrium - PS photosystem - RC reaction center - REE rapid exciton equilibration