Voigt Christian C, Matt Felix, Michener Robert, Kunz Thomas H
Institute for Zoo and Wildlife Research, Alfred-Kowalke-Str. 17, 10315 Berlin, Germany.
J Exp Biol. 2003 Apr;206(Pt 8):1419-27. doi: 10.1242/jeb.00274.
Stable isotopes of carbon are commonly used to characterize dietary preferences in animals. Because turnover rates of carbon isotopes are related to metabolic rate, we wanted to determine the rates at which carbon isotopes are exchanged in tissues of two species of nectar-feeding bats (Leptonycteris curasoae and Glossophaga soricina), both of which have relatively high mass-specific metabolic rates. To test the hypothesis that isotope turnover is higher in nectar-feeding bats, because of their high mass-specific metabolic rates, than in other eutherian mammals, we conducted diet-switching experiments and chose three target tissues (hair, wing membrane and blood) to evaluate the isotopic turnover rates. We made the following predictions: (1) isotopic composition should change towards higher delta(13)C-values due to the turnover of carbon isotopes of C(3) origin with those of C(4)/CAM origin; (2) the turnover rates of carbon isotopes would differ between the three types of tissues in the following order of decreasing turnover rates: blood>wing membrane>hair; and (3) turnover rates of nectar-feeding bats should exceed those reported for other small mammals because of the high mass-specific metabolic rate of nectar-feeding bats. Compared to the initial diet, target tissues were enriched in heavy carbon isotopes by 2.8 per thousand in L. curasoae and by 2.6 per thousand in G. soricina. After changing the diet from C(3) to C(4)/CAM origin we found an increase in abundance of (13)C in blood and wing membrane in all experimental subjects. The estimated half life of carbon isotope turnover ranged from 100 to 134 days and did not differ significantly between blood and wing membrane, nor did it differ between the two species. The low turnover rate in wing membrane may reflect its specific composition and the relatively low temperature of this tissue, and long-lived erythrocytes in bat blood may be responsible for the low turnover rate of carbon isotopes in blood. The turnover rate of stable carbon isotopes in hair was low in L. curasoae and undetectable in G. soricina, which may be explained by the seasonal growth of the hair in these two species. Because both species are small (10 and 25 g, respectively) and nectar-feeding bats have higher mass-specific metabolic rates than bats in temperate regions or similar sized terrestrial mammals, our findings of low turnover rates were unexpected.
碳的稳定同位素通常用于表征动物的饮食偏好。由于碳同位素的周转率与代谢率相关，我们想确定两种食蜜蝙蝠（库拉索长舌蝠和索氏长舌蝠）组织中碳同位素的交换速率，这两种蝙蝠都具有相对较高的质量比代谢率。为了验证由于食蜜蝙蝠具有较高的质量比代谢率，其同位素周转率高于其他真兽类哺乳动物这一假设，我们进行了饮食转换实验，并选择了三种目标组织（毛发、翼膜和血液）来评估同位素周转率。我们做出了以下预测：（1）由于源自C3的碳同位素与源自C4/CAM的碳同位素的周转，同位素组成应朝着更高的δ(13)C值变化；（2）碳同位素的周转率在三种组织类型之间会有所不同，周转率从高到低的顺序为：血液>翼膜>毛发；（3）由于食蜜蝙蝠具有较高的质量比代谢率，其周转率应超过其他小型哺乳动物的报道值。与初始饮食相比，库拉索长舌蝠的目标组织中重碳同位素富集了2.8‰，索氏长舌蝠中富集了2.6‰。在将饮食从C3改为C4/CAM来源后，我们发现所有实验对象的血液和翼膜中(13)C的丰度都有所增加。碳同位素周转的估计半衰期在100至134天之间，血液和翼膜之间没有显著差异，两种蝙蝠之间也没有差异。翼膜中周转率较低可能反映了其特殊的组成以及该组织相对较低的温度，而蝙蝠血液中长寿的红细胞可能是血液中碳同位素周转率较低的原因。库拉索长舌蝠毛发中稳定碳同位素的周转率较低，索氏长舌蝠中则无法检测到，这可能由这两个物种毛发的季节性生长来解释。由于这两个物种都体型较小（分别为10克和25克），且食蜜蝙蝠的质量比代谢率高于温带地区的蝙蝠或体型相似的陆生哺乳动物，我们关于低周转率的研究结果出乎意料。
