Data from: How chimpanzees integrate sensory information to select figs

Figs are keystone resources that sustain chimpanzees when preferred fruits are scarce. Many figs retain a green(ish) colour throughout development, a pattern that causes chimpanzees to evaluate edibility on the basis of achromatic accessory cues. Such behaviour is conspicuous because it entails a succession of discrete sensory assessments, including the deliberate palpation of individual figs, a task that requires advanced visuomotor control. These actions are strongly suggestive of domain-specific information processing and decision-making, and they call attention to a potential selective force on the origin of advanced manual prehension and digital dexterity during primate evolution. To explore this concept, we report on the foraging behaviours of chimpanzees and the spectral, chemical and mechanical properties of figs, with cutting tests revealing ease of fracture in the mouth. By integrating the ability of different sensory cues to predict fructose content in a Bayesian updating framework, we quantified the amount of information gained when a chimpanzee successively observes, palpates and bites the green figs of Ficus sansibarica. We found that the cue eliciting ingestion was not colour or size, but fig mechanics (including toughness estimates from wedge tests), which relays higher-quality information on fructose concentrations than colour vision. This result explains why chimpanzees evaluate green figs by palpation and dental incision, actions that could explain the adaptive origins of advanced manual prehension.

无花果（fig）是在偏好果实匮乏时支撑黑猩猩生存的关键资源（keystone resources）。多数无花果在整个发育周期中均保持偏绿色外观，这一特征使得黑猩猩需借助非彩色辅助线索来判断其可食用性。这类行为十分显著，因为它包含一系列独立的感官评估流程，其中包括对单个无花果的刻意触摸探查——该过程需要先进的视觉运动控制能力。此类行为强烈暗示了领域特异性的信息处理与决策过程，同时也让学界关注到灵长类演化历程中，先进手动抓握（manual prehension）与手指灵活性（digital dexterity）起源背后的潜在选择压力。为探究这一观点，本研究记录了黑猩猩的觅食行为，以及无花果的光谱、化学与力学特性，并通过剪切试验揭示了其在口腔内的断裂难易程度。研究在贝叶斯更新框架（Bayesian updating framework）中整合不同感官线索预测果糖含量的能力，量化了黑猩猩依次观察、触摸探查并啃咬桑给巴尔榕（Ficus sansibarica）绿色无花果时所获得的信息增益量。结果显示，触发进食行为的线索并非颜色或体型大小，而是无花果的力学特性（包括通过楔入测试（wedge tests）得出的韧性评估值）；相较于色觉，这类线索能传递更高质量的果糖浓度信息。这一结果解释了为何黑猩猩会通过触摸探查与牙齿啃咬来评估绿色无花果的可食用性，而此类行为或可阐明灵长类演化中先进手动抓握能力的适应性起源。