Embryo growth rates in birds and mammals

Abstract

Summary1. Embryo mass growth curves of 36 species of bird and 18 species of mammal were fitted by sigmoidal Gompertz functions, in which k (days )1 ) describes the rate at which the embryo approaches an asymptotic mass A (g).2. The parameters of the Gompertz function were uncorrelated with parameters of power functions fitted to the same growth data, indicating that the two models describe different aspects of growth.3. Asymptotes of the Gompertz functions for embryonic growth averaged 2AE5 times neonate size, but were well below adult mass. Thus, the pre-and postnatal phases of growth are distinct and have different target sizes. 4. Embryo growth rate (k) decreases as the )1 ⁄ 4 power of neonate size; values for mammals were 63% of those of birds, on average. 5. Embryo growth rate can be predicted solely by the length of the incubation or gestation period, regardless of the size of the neonate, with the same relationship for birds and mammals. 6. Postnatal growth rate (k G ) scales linearly with embryonic growth rate (k), but is nearly fivetimes more rapid, on average, in birds than in mammals. k G and k have similar magnitude in birds, but k G is relatively much slower than k in mammals. 7. Rate of actuarial senescence x (year )1 ), measured by the increase in mortality rate with age, is positively related to the rate of embryo growth in both birds and mammals, but is higher in the latter. Moreover, rate of ageing in birds is uniquely related to embryo growth while that in mammals is uniquely related to postnatal growth rate. Thus, development and ageing appear to be differently connected in birds and mammals, although the basis for these relationships is not known.

Life-history connections to rates of aging in terrestrial vertebrates

“…When flight is removed from the regression, incubation/gestation period becomes nonsignificant, because flight serves as a proxy for the difference between mammals and birds. The incubation or gestation periods differ substantially between birds and mammals (39), and therefore, without distinguishing these observations taxonomically, the influence of embryo growth rate on the rate of aging evaporates, although the statistical effect is strong within each class.…”

“…Rates of actuarial senescence for mammals (168 species), birds (207), reptiles (39), and amphibians (12) were estimated from the parameters of Weibull functions fitted to the relationship between survival and age in captive and wild populations (Appendix S4). The Weibull function is (Eq.…”

A quantitative analysis of growth control in theDrosophilaeye disc

“…Previously, exponentially declining growth rates, known as Gompertz law, which have been studied extensively in ecological models (Capocelli and Ricciardi, 1974;Gamito, 1998;Nobile et al, 1982), have been found appropriate to describe the growth kinetics of entire embryos (Ricklefs, 2010). We therefore also considered the possibility that the area growth rate may decline exponentially with developmental time:…”

Immediate and delayed effects of growth conditions on ageing parameters in nestling zebra finches

“…However, the accumulation of counterintuitive data underlines that individuals presenting a more rapid juvenile growth rate tend to have a reduced adult lifespan (Metcalfe and Monaghan, 2001;Olsson and Shine, 2002;Rollo, 2002;Dmitriew, 2011;Lee et al, 2012). Consequently, one can conclude that, even if fast growth rates should be the norm and individual fitness decreases as a function of developmental time (Roff, 1980;Ricklefs, 2010), growth remains a flexible life history trait that can change quickly both up and down in response to environmental variations (such as resource availability and foraging risk), with potential costs (Dmitriew, 2011). …”