Sears Justine, Hatch Scott A, O'Brien Diane M
Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, AK, 99775, USA.
Oecologia. 2009 Feb;159(1):41-8. doi: 10.1007/s00442-008-1199-3. Epub 2008 Oct 31.
A growing number of studies suggest that an individual's physiology affects its carbon and nitrogen stable isotope signatures, obscuring a signal often assumed to be only a reflection of diet and foraging location. We examined effects of growth and moderate food restriction on red blood cell (RBC) and feather delta(15)N and delta(13)C in rhinoceros auklet chicks (Cerorhinca monocerata), a piscivorous seabird. Chicks were reared in captivity and fed either control (75 g/day; n = 7) or ~40% restricted (40 g/day; n = 6) amounts of high quality forage fish. We quantified effects of growth on isotopic fractionation by comparing delta(15)N and delta(13)C in control chicks to those of captive, non-growing subadult auklets (n = 11) fed the same diet. To estimate natural levels of isotopic variation, we also collected blood from a random sample of free-living rhinoceros auklet adults and chicks in the Gulf of Alaska (n = 15 for each), as well as adult feather samples (n = 13). In the captive experiment, moderate food restriction caused significant depletion in delta(15)N of both RBCs and feathers in treatment chicks compared to control chicks. Growth also induced depletion in RBC delta(15)N, with chicks exhibiting lower delta(15)N when they were growing the fastest. As growth slowed, delta(15)N increased, resulting in an overall pattern of enrichment over the course of the nestling period. Combined effects of growth and restriction depleted delta(15)N in chick RBCs by 0.92 per thousand. We propose that increased nitrogen-use efficiency is responsible for (15)N depletion in both growing and food-restricted chicks. delta(15)N values in RBCs of free-ranging auklets fell within a range of only 1.03 per thousand, while feather delta(15)N varied widely. Together, our captive and field results suggest that both growth and moderate food restriction can affect stable isotope ratios in an ecologically meaningful way in RBCs although not feathers due to greater natural variability in this tissue.
越来越多的研究表明，个体的生理状况会影响其碳和氮稳定同位素特征，从而掩盖了通常被认为仅是饮食和觅食地点反映的信号。我们研究了生长和适度食物限制对犀角海雀雏鸟（Cerorhinca monocerata）红细胞（RBC）和羽毛δ(15)N及δ(13)C的影响，犀角海雀是一种食鱼海鸟。雏鸟在圈养环境中饲养，分别喂食对照量（75克/天；n = 7）或约40%限制量（40克/天；n = 6）的优质饵料鱼。我们通过比较对照雏鸟与喂食相同饮食的圈养、未生长的亚成体海雀（n = 11）的δ(15)N和δ(13)C，来量化生长对同位素分馏的影响。为了估计同位素变化的自然水平，我们还从阿拉斯加湾自由生活的犀角海雀成鸟和雏鸟的随机样本中采集了血液（各n = 15），以及成鸟羽毛样本（n = 13）。在圈养实验中，与对照雏鸟相比，适度食物限制导致处理组雏鸟的红细胞和羽毛中的δ(15)N显著减少。生长也导致红细胞δ(15)N减少，雏鸟生长最快时其δ(15)N较低。随着生长速度减慢，δ(15)N增加，导致雏鸟期内总体呈现富集模式。生长和限制的综合作用使雏鸟红细胞中的δ(15)N减少了0.92‰。我们认为，氮利用效率的提高是生长中和食物受限的雏鸟δ(15)N减少的原因。自由放养海雀红细胞中的δ(15)N值仅在1.03‰的范围内变化，而羽毛δ(15)N变化很大。总之，我们的圈养和野外研究结果表明，生长和适度食物限制都能以一种具有生态意义的方式影响红细胞中的稳定同位素比率，不过对羽毛则无影响，因为该组织的自然变异性更大。
