Apparent absorption efficiency and gut morphometry of wood mice, Apodemus sylvaticus, from two distinct populations with different diets.

Interpopulation variation in the diet of the wood mouse, Apodemus sylvaticus, is well documented. In this study, we examined the gut morphology and apparent absorption efficiencies of two populations of wood mice whose diet in the field was known to differ. One population inhabited sand dunes, where food availability was relatively low and the diet was dominated by invertebrates. The other population lived in deciduous woodland, with greater food availability and a diet consisting primarily of seeds. Wood mice from the woodland had longer small intestines and total digestive tract lengths than mice from the sand dunes. However, these differences had no effect on the apparent absorption efficiencies of dry mass or energy when the mice were fed mealworms, wheat grain, or All-Bran diets (apparent energy absorption efficiencies of 88%, 89%, and 65%, respectively). The population differences in gut morphometry may be linked to different resource availabilities at the two field sites.

Seasonal variation in the resting metabolic rate of male wood mice Apodemus sylvaticus from two contrasting habitats 15 km apart.

Diurnal and nocturnal resting metabolic rates of winter- and summer-acclimatized adult male wood mice Apodemus sylvaticus from two adjacent populations, 15 km apart, were measured. One population lived in deciduous woodland, and experienced a narrower daily range of temperatures than the second population, which inhabited maritime sand-dunes. Ambient temperature and body mass had significant effects on the resting metabolism of mice, excluding winter-acclimatized sand-dune animals where only temperature explained significant amounts of the observed variation. Only in this latter group could a thermoneutral zone be determined, with a lower critical temperature of ca. 25 degrees C and resting metabolism of 0.155 W. Nocturnal resting metabolic rates were significantly greater than diurnal levels. Winter acclimatization was associated with reductions in thermal conductance and resting metabolism, thus minimizing energy expenditure at rest. Site differences in thermoregulatory strategies were only found in winter, thermal conductances remained similar but mice from the sand-dunes had significantly lower metabolic rates than those from the woodland. Winter acclimatization in wood mice was influenced by factors in addition to photoperiod. Intra-specific and individual variations in resting metabolism, as shown in this study, potentially have a pronounced effect on the daily energy expenditure of a free-living animal.

Elevated platelet-derived growth factor production by aortic grafts implanted on a long-term basis in a canine model.

An endothelial cell lining in a prosthetic vascular graft has been shown to decrease graft thrombogenicity. However, previous studies in our laboratory demonstrated that grafts seeded with endothelial cells produced platelet-derived growth factor, a potent smooth muscle cell mitogen that may promote intimal hyperplasia. This study was undertaken to assess temporal changes in platelet-derived growth factor production by grafts seeded with endothelial cells and unseeded grafts and adjacent arteries. Adult beagles underwent placement of 20 to 22 cm long, 8 mm inner diameter, expanded polytetrafluoroethylene thoracoabdominal aortic grafts that were either seeded with autologous jugular vein endothelial cells or were unseeded controls. Grafts and adjacent arteries were removed at times up to 2 years after implantation. The tissue was studied in organ culture and platelet-derived growth factor production was measured after 72 hours with use of a radioreceptor assay. Platelet-derived growth factor production by endothelialized grafts increased significantly over the period studied, especially at the anastomoses, whereas that by arterial segments did not change significantly. The increase in platelet-derived growth factor production was greater in the distal than the proximal anastomotic segment suggesting a possible explanation for the clinical finding of more severe intimal hyperplasia at the distal anastomosis.

Sexual behavior and plasma androgen concentrations in the male eider duck (Somateria mollissima).

Eider ducks showed clear tidal and seasonal cycles of display when involved in pair-formation behaviour. Plasma androgen (testosterone and dihydrotestosterone) concentrations did not follow similar tidal cycles but there was a 4-fold increase of androgen in spring when rates of display increased 2-fold. There was no difference in androgen levels in blood samples taken from paired birds before and after coitus. Androgens therefore appear to be essential for the expression of sexual behaviour, but there is no apparent quantitative correlation between overt sexual activity and androgen concentrations.