School of Geography and Environmental Studies, University of Tasmania, Private Bag 78, Hobart 7001, Australia.
J Insect Sci. 2013;13:51. doi: 10.1673/031.013.5101.
Altitudinal clines in melanism are generally assumed to reflect the fitness benefits resulting from thermal differences between colour morphs, yet differences in thermal quality are not always discernible. The intra-specific application of the thermal melanism hypothesis was tested in the wingless grasshopper Phaulacridium vittatum (Sjöstedt) (Orthoptera: Acrididae) first by measuring the thermal properties of the different colour morphs in the laboratory, and second by testing for differences in average reflectance and spectral characteristics of populations along 14 altitudinal gradients. Correlations between reflectance, body size, and climatic variables were also tested to investigate the underlying causes of clines in melanism. Melanism in P. vittatum represents a gradation in colour rather than distinct colour morphs, with reflectance ranging from 2.49 to 5.65%. In unstriped grasshoppers, darker morphs warmed more rapidly than lighter morphs and reached a higher maximum temperature (lower temperature excess). In contrast, significant differences in thermal quality were not found between the colour morphs of striped grasshoppers. In support of the thermal melanism hypothesis, grasshoppers were, on average, darker at higher altitudes, there were differences in the spectral properties of brightness and chroma between high and low altitudes, and temperature variables were significant influences on the average reflectance of female grasshoppers. However, altitudinal gradients do not represent predictable variation in temperature, and the relationship between melanism and altitude was not consistent across all gradients. Grasshoppers generally became darker at altitudes above 800 m a.s.l., but on several gradients reflectance declined with altitude and then increased at the highest altitude.
海拔导致的黑化梯度通常被认为反映了不同颜色形态之间因热差异而产生的适应优势，但热致黑化假说在种内的应用并不总是能辨别出热质量的差异。首先，通过在实验室测量不同颜色形态的热特性，其次通过测试 14 个海拔梯度上种群的平均反射率和光谱特征差异，来检验无翅蚱蜢 Phaulacridium vittatum（Sjöstedt）（直翅目：蝗科）中种内的热致黑化假说。还测试了反射率、体型大小和气候变量之间的相关性，以研究黑化梯度的潜在原因。P. vittatum 的黑化代表了颜色的渐变，而不是明显的颜色形态，反射率范围为 2.49 到 5.65%。在无条纹蚱蜢中，较暗的形态比较浅的形态升温更快，达到更高的最高温度（较低的温度过剩）。相比之下，条纹蚱蜢的颜色形态之间没有发现热质量的显著差异。支持热致黑化假说，平均而言，海拔较高的蚱蜢颜色更深，高海拔和低海拔之间的亮度和色度光谱特性存在差异，温度变量对雌性蚱蜢的平均反射率有显著影响。然而，海拔梯度并不能代表温度的可预测变化，而且黑化和海拔之间的关系在所有梯度上并不一致。一般来说，在海拔 800 米以上的地方，蚱蜢的颜色会变得更深，但在几个梯度上，反射率随海拔升高而下降，然后在最高海拔处再次升高。
