Krijgsveld K L, Olson J M, Ricklefs R E
Zoological Laboratory, Biological Centre, University of Groningen, P.O. Box 14, 9750 AA Haren, The Netherlands.
Physiol Biochem Zool. 2001 Mar-Apr;74(2):250-60. doi: 10.1086/319655.
Newly hatched precocial chicks of arctic shorebirds are able to walk and regulate their body temperatures to a limited extent. Yet, they must also grow rapidly to achieve independence before the end of the short arctic growing season. A rapid growth rate may conflict with development of mature function, and because of the allometric scaling of thermal relationships, this trade-off might be resolved differently in large and small species. We assessed growth (mass) and functional maturity (catabolic enzyme activity) in leg and pectoral muscles of chicks aged 1-16 d and adults of two scolopacid shorebirds, the smaller dunlin (Calidris alpina: neonate mass 8 g, adult mass 50 g) and larger whimbrel (Numenius phaeopus; neonate mass 34 g, adult mass 380 g). Enzyme activity indicates maximum catabolic capacity, which is one aspect of the development of functional maturity of muscle. The growth rate-maturity hypothesis predicts that the development of catabolic capacity should be delayed in faster-growing muscle masses. Leg muscles of both species were a larger proportion of adult size at hatching and grew faster than pectoral muscles. Pectoral muscles grew more rapidly in the dunlin than in the whimbrel, whereas leg muscles grew more rapidly in the whimbrel. In both species and in both leg and pectoral muscles, enzyme activities generally increased with age, suggesting increasing functional maturity. Levels of citrate synthase activity were similar to those reported for other species, but l-3-hydroxyacyl-CoA-dehydrogenase and pyruvate kinase (PK) activities were comparatively high. Catabolic capacities of leg muscles were initially high compared to those of pectoral muscles, but with the exception of glycolytic (PK) capacities, these subsequently increased only modestly or even decreased as chicks grew. The earlier functional maturity of the more rapidly growing leg muscles, as well as the generally higher functional maturity in muscles of the more rapidly growing dunlin chicks, contradicts the growth rate-maturity function trade-off and suggests that birds have considerable latitude to modify this relationship. Whimbrel chicks, apparently, can rely on allometric scaling of power requirements for locomotion and the thermal inertia of their larger mass to reduce demands on their muscles, whereas dunlin chicks require muscles with higher metabolic capacity from an earlier age. Thus, larger and smaller species may adopt different strategies of growth and tissue maturation.
北极滨鸟刚孵化出的早成雏能够行走，并在一定程度上调节体温。然而，它们还必须快速生长，以便在北极短暂的生长季节结束前实现独立。快速的生长速度可能与成熟功能的发育相冲突，并且由于热关系的异速生长缩放，这种权衡在大型和小型物种中可能会以不同的方式得到解决。我们评估了1至16日龄雏鸟以及两种鹬科滨鸟成鸟腿部和胸肌的生长（体重）和功能成熟度（分解代谢酶活性），这两种滨鸟分别是体型较小的黑腹滨鹬（Calidris alpina：幼雏体重8克，成鸟体重50克）和体型较大的斑尾塍鹬（Numenius phaeopus；幼雏体重34克，成鸟体重380克）。酶活性表明最大分解代谢能力，这是肌肉功能成熟发育的一个方面。生长速率 - 成熟度假说预测，在生长较快的肌肉质量中，分解代谢能力的发育应该会延迟。两种物种的腿部肌肉在孵化时占成体大小的比例更大，并且比胸肌生长得更快。黑腹滨鹬胸肌的生长速度比斑尾塍鹬更快，而斑尾塍鹬腿部肌肉的生长速度更快。在这两种物种以及腿部和胸肌中，酶活性通常随着年龄的增长而增加，表明功能成熟度在提高。柠檬酸合酶活性水平与其他物种报道的相似，但l - 3 - 羟酰基辅酶A脱氢酶和丙酮酸激酶（PK）活性相对较高。与胸肌相比，腿部肌肉的分解代谢能力最初较高，但随着雏鸟的生长，除了糖酵解（PK）能力外，这些能力随后仅适度增加甚至下降。生长较快的腿部肌肉更早的功能成熟，以及生长较快的黑腹滨鹬雏鸟肌肉中普遍较高的功能成熟度，与生长速率 - 成熟功能的权衡相矛盾，这表明鸟类在改变这种关系方面有相当大的自由度。显然，斑尾塍鹬雏鸟可以依靠运动能量需求的异速生长缩放以及其较大体重的热惯性来降低对肌肉的需求，而黑腹滨鹬雏鸟从更早的年龄起就需要具有更高代谢能力的肌肉。因此，大型和小型物种可能采用不同的生长和组织成熟策略。
