Ricklefs Robert E, Shea Russell E, Choi In-Ho
Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania, 19104-6018.
Department of Biology, Randolph-Macon College, Ashland, Virginia, 23005.
Evolution. 1994 Aug;48(4):1080-1088. doi: 10.1111/j.1558-5646.1994.tb05295.x.
In this study, we investigate whether a tissue-level constraint can explain the general inverse relationship between growth rate and precocity of development in birds. On the whole, altricial (dependent) chicks grow three to four times faster than the less dependent, more able chicks of precocial species of similar adult mass. We suggest that an antagonism between growth and acquisition of mature function in skeletal muscle constrains postnatal growth and development in most species of birds. Altricial species, represented by European starlings in this study, hatch with skeletal muscle having low capacity for generating force but grow rapidly. Conversely, precocial species (northern bobwhite quail and Japanese quail), hatch with relatively mature skeletal muscle, especially in their legs, but grow more slowly. As development proceeds in all species, exponential growth rates decrease as muscles acquire adult levels of function. Among four variables associated with muscle function, exponential growth rate (EGR) was negatively correlated with pyruvate kinase activity (glycolysis), potassium concentration (electrical potential), and dry weight fraction (contractile proteins) in both pectoral and leg muscles but not with citrate synthase activity (aerobic metabolism) in either set of muscles. For pectoral muscle, these variables accounted for 87% of the total variation in EGR in all three species combined despite a twofold difference in growth rates between the starling and quail. EGRs of leg muscle (51% of variation accounted for) were less than predicted by the pectoral-muscle equation in quail during the early part of the postnatal period and in starlings during the late postnatal period. This result would not contradict a growth rate/maturity constraint hypothesis if EGRs were down-regulated for allometric or other considerations.
在本研究中，我们探究了一种组织水平的限制因素是否能够解释鸟类生长速率与发育早熟之间普遍存在的负相关关系。总体而言，晚成雏（依赖型）雏鸟的生长速度比成年体重相似的早成雏物种中依赖性较小、能力更强的雏鸟快三到四倍。我们认为，骨骼肌中生长与成熟功能获得之间的拮抗作用限制了大多数鸟类出生后的生长和发育。以本研究中的欧洲椋鸟为代表的晚成雏物种孵化时骨骼肌产生力量的能力较低，但生长迅速。相反，早成雏物种（北美鹑和日本鹌鹑）孵化时骨骼肌相对成熟，尤其是腿部，但生长较慢。随着所有物种发育的进行，随着肌肉获得成年水平的功能，指数生长速率会下降。在与肌肉功能相关的四个变量中，指数生长速率（EGR）与胸肌和腿部肌肉中的丙酮酸激酶活性（糖酵解）、钾浓度（电势）和干重分数（收缩蛋白）呈负相关，但与两组肌肉中的柠檬酸合酶活性（有氧代谢）均无相关性。对于胸肌，尽管椋鸟和鹌鹑的生长速率相差两倍，但这些变量在所有三个物种中共同解释了EGR总变异的87%。在出生后早期，鹌鹑腿部肌肉的EGR（解释了51%的变异）低于胸肌方程的预测值，而在出生后期，椋鸟腿部肌肉的EGR也低于预测值。如果EGR因异速生长或其他因素而下调，这一结果将与生长速率/成熟度限制假说不矛盾。
