When it comes to the brain, bigger is generally considered better in terms of cognitive performance. While this notion is supported by studies of birds and primates showing that larger brains improve learning capacity, similar evidence is surprisingly lacking for invertebrates. Although the brain of invertebrates is smaller and simpler than that of vertebrates, recent work in insects has revealed enormous variation in size across species. Here, we ask whether bee species that have larger brains also have higher learning abilities. We conducted an experiment in which field-collected individuals had to associate an unconditioned stimulus (sucrose) with a conditioned stimulus (coloured strip). We found that most species can learn to associate a colour with a reward, yet some do so better than others. These differences in learning were related to brain size: species with larger brains—both absolute and relative to body size—exhibited enhanced performance to learn the reward-colour association. Our finding highlights the functional significance of brain size in insects, filling a major gap in our understanding of brain evolution and opening new opportunities for future research.

就大脑而言，通常认为越大的认知能力越好。虽然这一观点得到了鸟类和灵长类动物研究的支持，表明较大的大脑可以提高学习能力，但令人惊讶的是，无脊椎动物却缺乏类似的证据。尽管无脊椎动物的大脑比脊椎动物的大脑更小、更简单，但最近对昆虫的研究表明，不同物种的大脑大小存在巨大差异。在这里，我们想知道大脑较大的蜜蜂物种是否也具有较高的学习能力。我们进行了一项实验，其中现场收集的个体必须将无条件刺激（蔗糖）与条件刺激（彩色条）联系起来。我们发现大多数物种都能学会将颜色与奖励联系起来，但有些物种比其他物种做得更好。这些学习上的差异与大脑尺寸有关：具有较大大脑（无论是绝对尺寸还是相对于身体尺寸）的物种在学习奖励与颜色关联方面表现出更强的表现。我们的发现强调了昆虫大脑大小的功能意义，填补了我们对大脑进化理解的重大空白，并为未来的研究开辟了新的机会。