Effect of deuterium on the circadian period and metabolism in wild-type and tau mutant Syrian hamsters

Homozygous tau mutant Syrian hamsters (tau-/-) have a free-running circadian period (τ) around 20 h and a proportionally higher metabolic rate compared with wild-type hamsters (tau+/+) with a period of circa 24 h. In this study, we applied deuterium oxide (D2O) to hamsters to test whether deuteration affects the circadian period of locomotor activity and metabolic rate in both genotypes. Running wheel activity and the metabolic rate were measured in constant illumination before, during, and after administration of 25% deuterium in drinking water. Wild-type hamsters lengthened their circadian period by 1.19 h (SD = 0.29 h) due to D2O application and tau-/- hamsters by 1.20 h (SD = 0.39 h). Deuteration changed neither the amount of activity nor the duration of activity phase (α) in either genotype. The mass specific average metabolic rate (AMR, the oxygen consumption over 24 h) and the mass specific resting metabolic rate (RMR) did not differ during deuteration compared with non-deuteration conditions for either genotype. Both with and without D2O, tau-/- hamsters had higher metabolic rates than tau+/+ hamsters. There was no correlation between changes in the circadian period of locomotor activity and metabolic rates caused by D2O.

Effect of photoperiod on body weight gain, and daily energy intake and energy expenditure in Japanese quail (Coturnix c. Japonica)

Effect of photoperiod and food duration on body weight gain, energy intake, energy expenditure, and sexual development were investigated in two strains of Japanese quail (Coturnix c. japonica), bred for meat (broilers) or egg production (layers), from 7 to 71 days of age. In a first experiment chicks were subjected to 18L:6D, 15L:9D, 12L:12D, 9L:15D, or 6L:18D, with ad lib food during the light period. In a second experiment birds were exposed to a long photoperiod (18L:6D or 15L:9D) with ad lib food during part of the light period (first 6 or 9 h, respectively). Longer photoperiods were associated with larger weight gains. In 18L:6D broilers total body weight gain was 262 g compared to 213 g in 6L:18D broilers. In layers, corresponding values were 182 and 131 g. This effect of photoperiod on weight gain was primarily due to the effect of photoperiod on food availability. The photoperiod below which detrimental effects on weight gain occurred was 9L:15D for both strains. Chicks subjected to 9L:15D or 6L:18D exploited crop filling to enhance energy intake. They also decreased nocturnal metabolic rates to a greater extent compared to levels during the light phase than chicks subjected to light periods of 12 h or more. Sexual maturation was stimulated by photoperiod. At the age of 71 days, eight out of nine females subjected to 18L:6D were producing eggs, but none of the 6L:18D females. It is concluded that changes in feeding behavior and energy expenditure shown under short photoperiods are part of a strategy that allow chicks to gain weight continuously.

Polygamy in the Marsh Harrier, Circus aeruginosus: Individual Variation in Hunting Performance and Number of Mates

1. Theories postulating that sexual task differentiation may lead to polygamy such that the sex investing the least effort in raising the offspring, engages in simultaneous matings, contrast with polygyny in raptors where the male provides most of the food for its females and nestlings. A field study was undertaken to describe parental effort and success in marsh harriers of different mating status to elucidate this controversy. 2. Data on clutch size and laying date were collected on 421 nests in two Dutch land reclamations, Flevoland and Lauwersmeer. 156 nests were known to have monogamous parents, 30 males had two females and nests. Bigamous males raised on average twice as many fledglings (5.7) than monogamous males (3.0). However, their primary females had more success (3.5) than secondary females (2.3), related to increased nestling mortality in secondary nests. Male fledglings were significantly heavier in primary than in secondary nests. 3. Nest observations made on 22 nests (5 of monogamous, 17 of polygamous males) revealed that daily prey deliveries by males were fewer in mono- than in bigamous males. The latter delivered prey by preference to their primary nests. The prey delivered by a trigamous male were consistently larger than those of a bigamous and monogamous male in the same area. 4. Time budget observations revealed that hunting effort was maximal in the nestling phase (ca 8 hrs foraging per day for all three males observed; at other times of year foraging was reduced in early morning and late afternoon. Net hunting yield (prey brought to nests per hour of hunting) increased in three males with their number (1, 2, or 3) of mates. With progress of the breeding season, male hunting ranges extended further outside the breeding territories and had a great measure of overlap, suggesting that territory quality was not a major factor in male hunting yield. 5. Secondary females participated in provisioning for the nestlings more than primary or monogamy-females, thus compensating for reduced male prey deliveries. 6. Classical polygyny theory addresses the question of female choice: which benefits compensate a secondary female for reduced breeding success by mating with an already paired male? Several hypotheses (enhanced offspring survival, offspring genetic quality, parent chances of future reproduction) are discussed, but evidence is nearly completely lacking. 7. An alternative approach stresses the male's role in the decision process. Males may have more interindividual variation in their capacity to bring food than females in their capacity to lay and incubate eggs. Optimal strategies for males would then range with increasing quality from non-breeding via polyandry and monogamy to polygyny. In species like harriers, non-breeding may be optimal for yearling males with submaximal hunting skills, thus creating a skewed sex ratio forcing some females to accept secondary status as mate of older, high quality males. Polygyny is then associated with slower male than female maturation. The evolution of polyandrous traits in species living isolated in poor environments is likewise explained by this model.