Incubation

About: Incubation is a research topic. Over the lifetime, 5748 publications have been published within this topic receiving 126541 citations.

Scrapie infections initiated at varying doses: an analysis of 117 titration experiments

Abstract: An analysis of 117 titration experiments in the murine scrapie model is presented. The experiments encompass 30 years' work and a wide range of experimental conditions. To check that the experimental designs were reasonably consistent over time, comparisons were made of size, duration, source of inoculum, etc., in each experiment. These comparisons revealed no systematic trends that would render invalid comparisons across experiments. For 114 of the experiments it was possible to calculate the dose at which half of the challenged animals were infected (the ID50). These 114 experiments were then combined on the basis of relative dose (i.e. tenfold dilution relative to the ID50). This created a data set in which over 4000 animals were challenged with doses of scrapie ranging from four orders of magnitude below to five orders of magnitude above the ID50. Analysis of this data reveals that mean incubation periods rise linearly with logarithmic decreases in dose. A one unit increase in relative dose (i.e. a tenfold increase in actual dose) will, on average, decrease the incubation period by 25 days. At ID50 the average incubation period in this data set is 300 days. Within a single dose, in a single experimental model, incubation periods have a distribution close to normal. Variability in incubation period also rises linearly as dose decreases. There is no age or sex effect upon the probability of infection, but female mice have incubation periods that are, on average, nine days shorter than their male counterparts and young mice have incubation periods that are longer by seven days. Although many of these patterns are apparent in the results of single titration curves, they can be more rigorously investigated by considering the outcome for thousands of mice.

Body size, locomotor speed and antipredator behaviour in a tropical snake (Tropidonophis mairii, colubridae): The influence of incubation environments and genetic factors

Abstract: 1. The physical conditions experienced by reptile embryos inside natural nests can influence the size, shape and behaviour of the resultant hatchlings. Although most reptiles are tropical, the effects of incubation temperatures on offspring phenotypes have received little attention in tropical species. 2. The consequences of differences in thermal variance during incubation on offspring were studied in a tropical natricine snake (the Keelback Tropidonophis mairii), which lays eggs in soil cracks of varying depths. Some 253 eggs from 19 clutches were incubated under two thermal regimes with identical mean temperatures (25.6 degreesC), but temperatures in the 'variable' treatment fluctuated more (21.8-29.6 degreesC) than those in the 'constant' temperature treatment (25.2-26.5 degreesC). These thermal regimes were similar to those of shallow (20 cm deep) and deep (40 cm deep) soil cracks, respectively, and represent thermal conditions inside natural nests and potential nest sites. 3. Incubation temperatures affected body size, shape and antipredator behaviour of hatchling snakes. Snakes from constant temperature incubation were longer and thinner than snakes from high variance incubation. Clutch effects influenced all offspring traits, with significant interactions between clutch of origin and incubation treatment for body size, but not swimming speed or behaviour. 4. There was a significant interaction between incubation treatment and offspring sex on neonate swimming speed. Incubation under cycling thermal regimes significantly increased swimming speeds of females, but had little effect on males. Such sex differences in phenotypic responses of hatchling snakes support a major assumption of the Charnov-Bull hypothesis for the evolution of temperature-dependent sex determination.

Does the cost of incubation set limits to clutch size in common eiders Somateria mollissima

Abstract: We examined the effect of natural clutch size on the cost of incubation in a population of common eiders Somateria mollissima nesting in Tromso, northern Norway. The body condition of females at day 5 in the incubation period was not related to clutch size (3–6 eggs), but females incubating large clutches lost more mass and had a lower body condition at day 20 in the incubation period than females incubating small clutches. Females incubating large clutches had a slightly shorter incubation period and a lower egg predation rate. The results do not support the hypothesis that the female's ability to produce eggs is the only ultimate control of clutch size in eider. Instead the results suggest that there may be an interaction between the allocation of body reserves to eggs and incubation, and that females producing large clutches allocate more of their body reserves to incubation than females producing small clutches, in order to shorten the incubation period and to minimise the risk of predation on eggs.

Adaptive sex differences in growth of pre-ovulation oocytes in a passerine bird

Abstract: Maternal modification of offspring sex in birds has strong fitness consequences, however the mechanisms by which female birds can bias sex of their progeny in close concordance with the environment of breeding are not known. In recently established populations of house finches (Carpodacus mexicanus), breeding females lay a sex-biased sequence of eggs when ambient temperature causes early onset of incubation. We studied the mechanisms behind close association of incubation and sex-determination strategies in this species and discovered that pre-ovulation oocytes that produce males and females differed strongly in the temporal patterns of proliferation and growth. In turn, sex-specific exposure of oocytes to maternal secretion of prolactin and androgens produced distinct accumulation of maternal steroids in oocyte yolks in relation to oocyte proliferation order. These findings suggest that sex difference in oocyte growth and egg-laying sequence is an adaptive outcome of hormonal constraints imposed by the overlap of early incubation and oogenesis in this population, and that the close integration of maternal incubation, oocytes' sex-determination and growth might be under control of the same hormonal mechanism. We further document that population establishment and the evolution of these maternal strategies is facilitated by their strong effects on female and offspring fitness in a recently established part of the species range.