The Physiological Cost of Pregnancy in a Tropical Viviparous Snake
During pregnancy, the metabolic rate of females may increase above basal levels to support metabolically active tissues and developing embryos. In mammals, this energetic cost of supporting the pregnancy (MCP) is an important component of reproductive effort, but less is known about the magnitude of this cost in ectothermic vertebrates. We estimated the metabolic cost of supporting pregnancy in a tropical viviparous snake, the Northern Death Adder, Acanthophis praelongus. We measured the metabolic rates of non-gravid and gravid females throughout gestation and following parturition. We also measured the oxygen consumption of a sample of neonates from each clutch within 24 h of birth. The metabolic rate of gravid females rose slowly during pregnancy, but was significantly elevated during the last three weeks of gestation. Considering the late term metabolism of gravid females as 100%, then the baseline metabolism of female Death Adders represented 36.6%, embryo metabolism accounted for 37.0%, and the cost of supporting the pregnancy was 26.4% of the total metabolic rate. Neonate metabolism during the first 24 h of birth was 2.9 times higher than the estimate for embryo metabolism. Thus, our results do not support the assumption that the metabolism of embryos (prior to birth) and neonates is similar in this species. Although gravid female Death Adders maintain high and constant body temperatures during late gestation, the energetic cost of supporting the pregnancy is only a minor component of the total reproductive effort for females of this species.Abstract
Pattern of oxygen consumption during pregnancy in Northern Death Adders, Acanthophis praelongus (n = 7). Graph shows mean values and associated standard errors. The metabolism of females was measured at 30°C, the body temperature that pregnant females select in laboratory thermal gradients and in the field during the day.
Partitioning of oxygen consumption in female Northern Death Adders. For each female, the graph shows maternal oxygen consumption during late pregnancy (V˙O2 pregnant, black bar) and one week after parturition (V˙O2 non-pregnant, gray bar), and the estimated oxygen consumption of the litter (V˙O2 embryos, white bar). In six of seven females, the sum of V˙O2 non-pregnant + V˙O2 embryos exceeded the total oxygen consumption of the gravid female (V˙O2 pregnant). Hence, neonate metabolism cannot be used to estimate embryo metabolism in this species (see text for details).
Litter size versus ΔV˙O2 ( = V˙O2 pregnant − V˙O2 non-pregnant) for Northern Death Adders (n = 7). The solid line shows the line of best fit from an exponential regression (y = 0.1172 e0.0396x, r2 = 0.82). The intercept of the exponential regression (0.121 ml min−1) is an estimate of the maintenance cost of pregnancy.
Contributor Notes
Associate Editor: R. Mason.