Stahlschmidt Zachary R, Heulin Benoit, DeNardo Dale F
School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA.
Physiol Biochem Zool. 2010 Jul-Aug;83(4):576-86. doi: 10.1086/652425.
Parental care is taxonomically widespread because it improves developmental conditions and thus fitness of offspring. Although relatively simplistic compared with parental behaviors of other taxa, python egg-brooding behavior exemplifies parental care because it mediates a trade-off between embryonic respiration and hydration. However, because egg brooding increases gas-exchange resistance between embryonic and nest environments and because female pythons do not adjust their brooding behavior in response to the increasing metabolic requirements of developing offspring, python egg brooding imposes hypoxic costs on embryos during the late stages of incubation. We conducted a series of experiments to determine whether eggshells coadapted with brooding behavior to minimize the negative effects of developmental hypoxia. We tested the hypotheses that python eggshells (1) increase permeability over time to accommodate increasing embryonic respiration and (2) exhibit permeability plasticity in response to chronic hypoxia. Over incubation, we serially measured the atomic and structural components of Children's python (Antaresia childreni) eggshells as well as in vivo and in vitro gas exchange across eggshells. In support of our first hypothesis, A. childreni eggshells exhibited a reduced fibrous layer, became more permeable, and facilitated greater gas exchange as incubation progressed. Our second hypothesis was not supported, as incubation O(2) concentration did not affect the shells' permeabilities to O(2) and H(2)O vapor. Our results suggest that python eggshell permeability changes during incubation but that the alterations over time are fixed and independent of environmental conditions. These findings are of broad evolutionary interest because they demonstrate that, even in relatively simple parental-care models, successful parent-offspring relationships depend on adjustments made by both the parent (i.e., egg-brooding behavioral shifts) and the offspring (i.e., changes in eggshell permeability).
亲代抚育在分类学上分布广泛，因为它能改善发育条件，从而提高后代的适合度。尽管与其他类群的亲代行为相比相对简单，但蟒蛇的孵卵行为体现了亲代抚育，因为它在胚胎呼吸和水合作用之间进行了权衡。然而，由于孵卵增加了胚胎与巢穴环境之间的气体交换阻力，并且雌性蟒蛇不会根据发育中后代不断增加的代谢需求来调整其孵卵行为，所以蟒蛇孵卵在孵化后期会给胚胎带来缺氧成本。我们进行了一系列实验，以确定蛋壳是否与孵卵行为共同适应，以尽量减少发育性缺氧的负面影响。我们检验了以下假设：蟒蛇蛋壳（1）随着时间推移增加通透性，以适应胚胎呼吸增加的需求；（2）对慢性缺氧表现出通透性可塑性。在整个孵化过程中，我们连续测量了儿童蟒（Antaresia childreni）蛋壳的原子和结构成分，以及蛋壳内外的气体交换情况。支持我们的第一个假设的是，随着孵化的进行，儿童蟒蛋壳的纤维层减少，通透性增加，促进了更大的气体交换。我们的第二个假设没有得到支持，因为孵化过程中的氧气浓度并未影响蛋壳对氧气和水蒸气的通透性。我们的结果表明，蟒蛇蛋壳的通透性在孵化过程中会发生变化，但随着时间的改变是固定的，且与环境条件无关。这些发现具有广泛的进化意义，因为它们表明，即使在相对简单的亲代抚育模式中，成功的亲子关系也依赖于亲代（即孵卵行为的转变）和子代（即蛋壳通透性的变化）双方做出的调整。
