The roles of colour change and behaviour in the hygrothermal balance of a littoral isopod,Ligia oceanica

Summary Ligia oceanica can change its colour using melanophores, the animal's reflectance varying between about 2 and 10%. Darker individuals heat up more quickly, and to higher body temperatures, than do pale ones. Colour change shows an underlying circadian rhythm, though the pattern of this rhythm varies with temperature, humidity, background and time of year. In general the rhythm is such as to ensure maximum camouflage at the critical dusk period, but in some conditions hygrothermal needs are overriding and the animals are paler (to stay cool) or darker (to warm up). In addition, animals show short term colour modification; when transferred to differing backgrounds and temperatures their colours initially reflect background matching, but after 30–45 min are modified into thermally appropriate shades, dark at 5° C and pale at 20° C. Field-caught specimens showed body temperatures that varied with colouration, and modification of colour in relation to thermal needs, particularly by being paler than expected when forced into the open by daytime high tides, and darker than expected when active prior to dusk. Animals invariably selected dark backgrounds in choice chambers. However, choice of humidity depended on previous experience; saturated air was normally preferred, but warm animals chose drier air (to allow evaporative cooling) unless also water-stressed. They also tended to disperse to facilitate cooling, whereas aggregation increased with increasing RH and with decreasing temperature. The interactions of colour changes, behavioural choices, and activity patterns in controlling the hygrothermal belance of Ligia in the intertidal environment are discussed in the light of these results.     

Carbon dioxide assimilation in some aerial plant organs and tissues

Summary CO₂ fixation characteristics of a number of mature (but not senescing) tissues and organs (the outer layers of green pod and the seed testa of Vicia faba L.; the outer layers of green pod and seeds of Trigonella foenum-graecum L.; the outer layers of the green fruit of Lycopersicon esculentum Mill.) were studied and compared with their respective C₃ leaf characteristics. On a chlorophyll basis phosphoenolpyruvate carboxylase, malic enzyme (NADP) and malate dehydrogenase (NAD and NADP) acitivites were much higher in the non-leaf tissues (except for V. faba seed testa) than the leaf tissues. Generally, on a protein basis the differences were less significant. All tissues possessed ribulose-1.5-diphosphate carboxylase activity though there was great variation in activities both on a protein and chlorophyll basis. Protein: chlorophyll ratios varied greatly from tissue to tissue being lowest in the leaf tissue (11.5–14.0) and highest in V. faba seed testa (805.5). Chlorophyll a:b ratios were all between 2 and 3. ¹⁴CO₂ uptake in the dark by L. esculentum fruit slices was about 1/3 that in the light and the major, initially labelled product was malate both in the light and dark. Neither typical C₄-photosynthesis or crassulacean acid metabolism were exhibited by the non-leaf tissues and it was considered that the increased levels of certain enzyme activities were present to refix and recycle respired CO₂.Abbreviations PEP phosphoenolpyruvate - RuDP ribulose -1,5-, diphosphate - MDH malate dehydrogenase - CAM Crassulacean acid metabolism - OAA oxaloacetic acid