Lin Susan M, Nieves-Puigdoller Katherine, Brown Alexandria C, McGraw Kevin J, Clotfelter Ethan D
Department of Biology, Amherst College, Amherst, Massachusetts 01002, USA.
Physiol Biochem Zool. 2010 Mar-Apr;83(2):333-42. doi: 10.1086/649965.
Many animals use carotenoid pigments derived from their diet for coloration and immunity. The carotenoid trade-off hypothesis predicts that, under conditions of carotenoid scarcity, individuals may be forced to allocate limited carotenoids to either coloration or immunity. In polychromatic species, the pattern of allocation may differ among individuals. We tested the carotenoid trade-off hypothesis in the Midas cichlid, Amphilophus citrinellus, a species with two ontogenetic color morphs, barred and gold, the latter of which is the result of carotenoid expression. We performed a diet-supplementation experiment in which cichlids of both color morphs were assigned to one of two diet treatments that differed only in carotenoid content (beta-carotene, lutein, and zeaxanthin). We measured integument color using spectrometry, quantified carotenoid concentrations in tissue and plasma, and assessed innate immunity using lysozyme activity and alternative complement pathway assays. In both color morphs, dietary carotenoid supplementation elevated plasma carotenoid circulation but failed to affect skin coloration. Consistent with observable differences in integument coloration, we found that gold fish sequestered more carotenoids in skin tissue than barred fish, but barred fish had higher concentrations of carotenoids in plasma than gold fish. Neither measure of innate immunity differed between gold and barred fish, or as a function of dietary carotenoid supplementation. Lysozyme activity, but not complement activity, was strongly affected by body condition. Our data show that a diet low in carotenoids is sufficient to maintain both coloration and innate immunity in Midas cichlids. Our data also suggest that the developmental transition from the barred to gold morph is not accompanied by a decrease in innate immunity in this species.
许多动物利用从食物中获取的类胡萝卜素色素来进行体色呈现和维持免疫功能。类胡萝卜素权衡假说预测，在类胡萝卜素稀缺的情况下，个体可能被迫将有限的类胡萝卜素分配到体色呈现或免疫功能二者之一。在多色物种中，分配模式可能因个体而异。我们在迈达斯丽鱼（Amphilophus citrinellus）中测试了类胡萝卜素权衡假说，该物种有两种个体发育阶段的体色形态，即条纹色和金色，后者是类胡萝卜素表达的结果。我们进行了一项饮食补充实验，将两种体色形态的丽鱼分配到两种仅在类胡萝卜素含量（β-胡萝卜素、叶黄素和玉米黄质）上不同的饮食处理之一中。我们使用光谱法测量体表颜色，量化组织和血浆中的类胡萝卜素浓度，并通过溶菌酶活性和替代补体途径测定来评估先天免疫。在两种体色形态中，饮食中补充类胡萝卜素提高了血浆中类胡萝卜素的循环水平，但未能影响皮肤颜色。与体表颜色的可观察差异一致，我们发现金色鱼在皮肤组织中积累的类胡萝卜素比条纹色鱼多，但条纹色鱼血浆中的类胡萝卜素浓度比金色鱼高。金色鱼和条纹色鱼在先天免疫的测量指标上均无差异，也不受饮食中类胡萝卜素补充的影响。溶菌酶活性而非补体活性受身体状况的强烈影响。我们的数据表明，低类胡萝卜素饮食足以维持迈达斯丽鱼的体色呈现和先天免疫。我们的数据还表明，该物种从条纹色形态到金色形态的发育转变并未伴随着先天免疫的下降。
