Waters James S, Ochs Alison, Fewell Jennifer H, Harrison Jon F
Department of Biology, Providence College, Providence, RI 02918, USA
Mount Holyoke College, South Hadley, MA 01075, USA.
Proc Biol Sci. 2017 Feb 22;284(1849). doi: 10.1098/rspb.2016.2582.
Metabolic rates of individual animals and social insect colonies generally scale hypometrically, with mass-specific metabolic rates decreasing with increasing size. Although this allometry has wide ranging effects on social behaviour, ecology and evolution, its causes remain controversial. Because it is difficult to experimentally manipulate body size of organisms, most studies of metabolic scaling depend on correlative data, limiting their ability to determine causation. To overcome this limitation, we experimentally reduced the size of harvester ant colonies () and quantified the consequent increase in mass-specific metabolic rates. Our results clearly demonstrate a causal relationship between colony size and hypometric changes in metabolic rate that could not be explained by changes in physical density. These findings provide evidence against prominent models arguing that the hypometric scaling of metabolic rate is primarily driven by constraints on resource delivery or surface area/volume ratios, because colonies were provided with excess food and colony size does not affect individual oxygen or nutrient transport. We found that larger colonies had lower median walking speeds and relatively more stationary ants and including walking speed as a variable in the mass-scaling allometry greatly reduced the amount of residual variation in the model, reinforcing the role of behaviour in metabolic allometry. Following the experimental size reduction, however, the proportion of stationary ants increased, demonstrating that variation in locomotory activity cannot solely explain hypometric scaling of metabolic rates in these colonies. Based on prior studies of this species, the increase in metabolic rate in size-reduced colonies could be due to increased anabolic processes associated with brood care and colony growth.
单个动物和社会性昆虫群体的代谢率通常呈亚比例缩放，即质量特异性代谢率随体型增大而降低。尽管这种异速生长对社会行为、生态学和进化有着广泛影响，但其成因仍存在争议。由于难以通过实验操纵生物体的体型，大多数代谢缩放研究依赖于相关数据，这限制了它们确定因果关系的能力。为克服这一限制，我们通过实验减小了收获蚁群体的规模（），并量化了由此导致的质量特异性代谢率的增加。我们的结果清楚地证明了群体规模与代谢率的亚比例变化之间存在因果关系，而这种关系无法用物理密度的变化来解释。这些发现为一些著名模型提供了反证，这些模型认为代谢率的亚比例缩放主要是由资源输送限制或表面积/体积比驱动的，因为为群体提供了过量食物，且群体规模并不影响个体的氧气或营养物质运输。我们发现较大的群体中位行走速度较低，静止不动的蚂蚁相对较多，并且将行走速度作为质量缩放异速生长模型中的一个变量，大大减少了模型中的残差变异量，这强化了行为在代谢异速生长中的作用。然而，在实验性减小规模后，静止不动的蚂蚁比例增加，这表明运动活动的变化不能单独解释这些群体中代谢率的亚比例缩放。根据对该物种的先前研究，规模减小的群体中代谢率的增加可能是由于与育幼和群体生长相关的合成代谢过程增加所致。
