What the egg can tell about its hen: embryo development on the basis of Dynamic Energy Budgets.

The energy cost of offspring is important in the conversion of resources allocated to reproduction to numbers of offspring, and in obtaining energy budget parameters from quantities that are easy to measure. An efficient numerical procedure is presented to obtain this cost for eggs and foetusses in the context of the dynamic energy budget theory, which specifies that birth occurs when maturity exceeds a threshold value and maternal effects determine the reserve density at birth. This paper extends previous work to arbitrary values of the ratio of the maturity and somatic maintenance costs. I discuss the body size scaling implications for the relative size and age at birth and conclude that the size at birth, contrary to the age at birth, covaries with the maintenance ratio. Apart from evolutionary adaptation of the maturity at birth, this covariation might explain some of the observed scatter in the relative length at birth. The theory can be used to evaluate the effects of the separation of cells in e.g. the two-cell stage of embryonic development, and of the removal of initial egg mass. If cell separation hardly affects energy parameters, body size scaling relationships imply that cell separation can only occur successfully in species with sufficiently large maximum body length (as adult); i.e. some two times that of Daphnia magna. Toxic compounds that increase the cost of synthesis of structure, decrease the allocation to reproduction indirectly via the life cycle, because food uptake is linked to size. They can also decrease the egg size, however, such that the reproduction rate is stimulated at low concentrations. The present theory offers a possible explanation for this well-known phenomenon. © 2008 Springer-Verlag

Allometry of egg and hatchling mass in birds and reptiles: roles of developmental maturity, eggshell structure and phylogeny

The factors determining hatchling mass (HM) are investigated in a wide range of birds and reptiles using regression analysis, analysis of covariance and comparative analysis by independent contrasts. In birds, initial egg mass (IEM) at laying is the most important factor affecting HM and phylogenetic relatedness has no significant effects on HM. Developmental maturity of the avian neonates did not affect the proportion of IEM converted into HM. For all reptile species, IEM also significantly affected HM but phylogenetic relatedness did not. By contrast, allometric relationships between IEM and HM in the different orders of reptiles were affected by shell type. The robustness of allometric relationships across taxa in birds and reptiles suggests that there is a physiological link between IEM and HM, which contrasts with that observed for the relationship between egg mass and incubation period. This result has significant implications for the inter-relationships between IEM and embryonic growth, which are discussed for birds and reptiles

Systematic review of economic aspects of alternative modes of delivery

Objective To carry out a systematic review of the literature relating to economic aspects of alternative modes of delivery. Methods A comprehensive literature search of the years 1990–1999 was conducted of electronic and non-electronic sources using a tested search strategy. Papers considered to contain useful cost or resource use data were read in full and classified according to their relevance to the review and their methodological quality. Relevant cost and resource use data were converted to £ sterling and inflated to 1998-1999 price levels. Results The literature search resulted in 975 papers, 49 of which met criteria for the review. Thirty-two papers were from the USA where the organisation, structure and costs of health care are significantly different from that of other industrialised countries. The aggregate costs of different modes of delivery reported in these American studies were between four and five times higher than costs reported in other studies. The majority of included studies were of poor quality. Data from the better quality studies demonstrated that caesarean section costs a health service substantially more than other modes of delivery. The range of costs of an uncomplicated vaginal delivery were £629-£1298 compared with £1238-£3551 for a caesarean section. However, papers have so far only considered short term health service costs. Conclusions Research is required to estimate the cost and resource use attributable to alternative modes of delivery. Future research should investigate the long term health service costs and the costs that arise outside the health service which are likely to vary according to mode of delivery