Infant mortality across species. A global probe of congenital abnormalities

Abstract

Infant mortality, by which we understand the postnatal stage during which mortality is declining, is a manifestation and embodiment of congenital abnormalities. Severe defects will translate into death occurring shortly after birth whereas slighter anomalies may contribute to death much later, possibly only in adult age. While for many species birth defects would be nearly impossible to identify, infant mortality provides a convenient global assessment. In the present paper we examine a broad range of species from mammals to fish to gastropods to insects. One of the objectives of our comparative analysis is to test a conjecture suggested by reliability engineering according to which the frequency of defects tends to increase together with the complexity of organisms. For that purpose, we set up experiments specially designed to measure infant mortality. In particular, we two species commonly used as model species in biological laboratories, namely the zebrafish Danio rerio and the rotifer Brachionus plicatilis. For the second, whose number of cells is about hundred times smaller than for the first, we find as expected that the screening effect of the infant phase is of much smaller amplitude. Our analysis also raises a number of challenging questions for which further investigation is necessary. For instance, why is the infant death rate of beetles and molluscs falling off exponentially rather than as a power law as observed for most other species? A possible research agenda is discussed in the conclusion of the paper. Main observations and questions Agenda for future comparative research Appendix A: Previous studies of the mortality of rotifers Main features Comments about variability What conclusions can one draw with respect to infant mortality? Appendix B: Methodology of the rotifer experiment Procedures Operational definition of death Appendix C: Correct estimate of the initial death rateThis paper is the second leg of an exploration in three parts; the two others are Bois et al. (2019a,b). Despite the connections, the three papers can be read independently from each other.

On the Mortality of Companies

“…This law can be summarized for by saying that the death rate doubles approximately every 10 years of age. Even the mortality of small animals such as rotifers [ 3 ] exhibit similar behaviour as is shown within the inset in Figure 1 .…”

“…In a series of recent papers [ 1 , 2 , 3 ] the present authors have studied human mortality demonstrating how the shape of the mortality function has a bathtub type of shape where the infant mortality decreases with age whereas in old age it increases ( Figure 1 ). In medical terminology infancy refers to new born under one year of age.…”

Physical models of infant mortality: implications for defects in biological systems

“…As noted at the outset, the major focus of this and previous papers [2,3] is to study the connection between initial abnormalities (whether from manufacturing or congenital anomalies) and subsequent death rates. Of importance is the determination of the delay between introduction of a defect and the resulting failure which may occur after a substantial time lag.…”

“…The age-dependent mortality rates for humans and other animal species have a declining part, corresponding to infant mortality, which is followed by a rising part, corresponding to the ageing process [1][2][3]. Technical systems are said to show a similar pattern, although little published empirical evidence appears to exist to support the point.…”

“…Such assays would take many years and are likely to be expensive. Therefore they are usually limited to crucial devices, such as items destined for the space industry, and the results are not normally made public 2 . An exception appear to be computer hard drives, for which failure data is now available online 3 .…”