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Seasonal variation in body composition in an Afrotropical passerine bird: increases in pectoral muscle mass are, unexpectedly, associated with lower thermogenic capacity
Journal of Comparative Physiology B ( IF 2 ) Pub Date : 2020-03-18 , DOI: 10.1007/s00360-020-01273-6
Matthew J Noakes 1 , William H Karasov 2 , Andrew E McKechnie 1, 3
Affiliation  

Phenotypic flexibility in avian metabolic rates and body composition have been well-studied in high-latitude species, which typically increase basal metabolic rate (BMR) and summit metabolism ( M sum ) when acclimatized to winter conditions. Patterns of seasonal metabolic acclimatization are more variable in lower-latitude birds that experience milder winters, with fewer studies investigating adjustments in avian organ and muscle masses in the context of metabolic flexibility in these regions. We quantified seasonal variation (summer vs winter) in the masses of organs and muscles frequently associated with changes in BMR (gizzard, intestines and liver) and M sum (heart and pectoral muscles), in white-browed sparrow-weavers ( Plocepasser mahali ). We also measured pectoral muscle thickness using a portable ultrasound system to determine whether we could non-lethally estimate muscle size. A concurrent study measured seasonal changes in BMR and M sum in the same population of sparrow-weavers, but different individuals. There was no seasonal variation in the dry masses of the gizzard, intestines or liver of sparrow-weavers, and during the same period, BMR did not vary seasonally. We found significantly higher heart (~ 18% higher) and pectoral muscle (~ 9% higher) dry mass during winter, although ultrasound measurements did not detect seasonal changes in pectoral muscle size. Despite winter increases in pectoral muscle mass, M sum was ~ 26% lower in winter compared to summer. To the best of our knowledge, this is the first study to report an increase in avian pectoral muscle mass but a concomitant decrease in thermogenic capacity.

中文翻译:

非洲热带雀形目鸟类身体成分的季节性变化:出乎意料的是,胸肌质量的增加与较低的产热能力有关

鸟类代谢率和身体成分的表型灵活性已在高纬度物种中得到充分研究,当适应冬季条件时,它们通常会增加基础代谢率 (BMR) 和最高代谢率 (M sum )。在冬季较温和的低纬度鸟类中,季节性代谢适应的模式变化更大,在这些地区代谢灵活性的背景下调查鸟类器官和肌肉质量调整的研究较少。我们量化了白眉麻雀(Plocepasser mahali)中经常与 BMR(胃、肠和肝脏)和 M sum(心脏和胸肌)变化相关的大量器官和肌肉的季节性变化(夏季与冬季) . 我们还使用便携式超声系统测量了胸肌厚度,以确定我们是否可以非致命地估计肌肉大小。一项同时进行的研究测量了同一麻雀编织者群体但不同个体的 BMR 和 M 总和的季节性变化。麻雀的胼胝、肠或肝脏的干质量没有季节性变化,同期BMR也没有季节性变化。我们发现冬季心脏干重(高约 18%)和胸肌干重(高约 9%),尽管超声测量未检测到胸肌大小的季节性变化。尽管冬季胸肌质量增加,但与夏季相比,冬季的 M sum 降低了约 26%。据我们所知,
更新日期:2020-03-18
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