The biology and ecology of calcarean sponges are not as well understood as they are for demosponges. Here, in order to gain new insights, particularly about symbiotic relationships, the calcarean sponge Leucetta prolifera was sampled from south-western Australia and examined for its assumed photosymbionts. Pulse amplitude modulated fluorometry and extraction of photopigments established that the sponge was photosynthetic. Molecular analysis of the bacterial symbionts via sequencing of the V1–V3 region of the 16S rDNA gene confirmed that between 5 and 22% of all sequences belonged to the phylum Cyanobacteria, depending on the individual sample, with the most dominant strain aligning with Hormoscilla spongeliae, a widely distributed sponge symbiont. Analysis of fatty acids suggested that the sponge obtains nutrition through photosynthates from its symbionts. The relationship is assumed to be mutualistic, with the sponge receiving dietary support and the cyanobacteria sheltering in the sponge tissues. We list all Calcarea presently known to harbour photosymbionts.

Dietary fish oil (FO) modulates muscle O2 consumption and contractile function, predictive of effects on muscle fatigue. High doses unattainable through human diet and muscle stimulation parameters used engender uncertainty in their physiological relevance. We tested the hypothesis that nutritionally relevant FO doses can modulate membrane fatty acid composition and muscle fatigue. Male Sprague–Dawley rats were randomised to control (10 % olive oil (OO) by weight) or low or moderate FO diet (LowFO and ModFO) (HiDHA tuna fish oil) for 15 weeks (LowFO: 0·3 % FO, 9·7 % OO, 0·25 % energy as EPA+DHA; ModFO: 1·25 % FO, 8·75 % OO, 1·0 % energy as EPA+DHA). Hindlimb muscle function was assessed under anaesthesia in vivo using repetitive 5 s burst sciatic nerve stimulation (0·05 ms, 7–12 V, 5 Hz, 10 s duty cycle, 300 s). There were no dietary differences in maximum developed muscle force. Repetitive peak developed force fell to 50 % within 62 (sem 10) s in controls and took longer to decline in FO-fed rats (LowFO 110 (sem 15) s; ModFO 117 (sem 14) s) (P<0·05). Force within bursts was better sustained with FO and maximum rates of force development and relaxation declined more slowly. The FO-fed rats incorporated higher muscle phospholipid DHA-relative percentages than controls (P<0·001). Incorporation of DHA was greater in the fast-twitch gastrocnemius (Control 9·3 (sem 0·8) %, LowFO 19·9 (sem 0·4), ModFO 24·3 (sem 1·0)) than in the slow-twitch soleus muscle (Control 5·1 (sem 0·2), LowFO 14·3 (sem 0·7), ModFO 18·0 (sem 1·4)) (P<0·001), which was comparable with the myocardium, in line with muscle fibre characteristics. The LowFO and ModFO diets, emulating human dietary and therapeutic supplement intake, respectively, both elicited muscle membrane DHA enrichment and fatigue resistance, providing a foundation for translating these physiological effects to humans.

The effects of dietary lipids on the fatty acid composition of rat pancreatic membranes and acinar cell function were investigated. Weaning rats were fed for 8 weeks on one of two diets which contained 100 g virgin olive oil (OO) or sunflowerseed oil (SO)/kg. Pancreatic plasma membranes were isolated and fatty acids determined. Amylase secretion and cytosolic concentrations of Ca2+ and Mg2+ were measured in pancreatic acini. Membrane fatty acids were profoundly affected by the diets; the rats fed OO had higher levels of 18:1n-9 (42·86 (sem 1·99) %) and total MUFA compared with the animals fed SO (25·37 (sem 1·11) %). Reciprocally, the SO diet resulted in greater levels of total and n-6 PUFA than the OO diet. The most striking effect was observed for 18:2n-6 (SO 17·88 (sem 1·32) %; OO 4·45 (sem 0·60) %), although the levels of 20:4n-6 were also different. The proportion of total saturated fatty acids was similar in both groups, and there was only a slight, not significant (P=0·098), effect on the unsaturation index. Compared with the OO group, acinar cells from the rats fed SO secreted more amylase at rest but less in response to cholecystokinin octapeptide, and this was paralleled by reduced Ca2+ responses to the secretagogue. The results confirm that rat pancreatic cell membranes are strongly influenced by the type of dietary fat consumed and this is accompanied by a modulation of the secretory activity of pancreatic acinar cells that involves, at least in part, Ca2+ signalling.