Fruit hardness, size, and weight for wild fruits in Uganda and Madagascar

Fleshy fruits have evolved to be attractive to frugivorous seed dispersers. As a result, many fruit traits like size, color, scent and nutritional content are assumed to be the result of selective pressures exerted by frugivores. At the same time, fruit traits are also subjected to a set of other selective pressures and constraints. One such trait is fruit hardness. On one hand, haptic cues have been suggested to play a role in frugivore behavior, potentially driving selection on fruit skin traits, including hardness. On the other hand, fruit skin traits also interact with antagonists, e.g., seed predators and microbes, which can also impose selective pressures, particularly with respect to fruit hardness.  Yet skin hardness may also be driven not by adaptive response to biotic pressures, but rather a mechanical constraint: fruits are packed with water-rich pulp and seeds which exert mechanical pressure on the skin. Skin hardness may simply result from the need for fruits to withhold in...

肉质果实经演化后，具备吸引果食性种子传播者的特性。据此，诸多果实性状——包括大小、色泽、气味与营养成分——均被认为是果食性动物施加的选择压力所塑造的结果。与此同时，果实性状亦受到一系列其他选择压力与约束条件的制约。果实硬度便是这类受影响的性状之一。一方面，有研究表明触觉线索会影响果食性动物的行为，进而可能对包括硬度在内的果皮性状产生选择压力。另一方面，果皮性状还会与各类生物拮抗因子（如种子捕食者与微生物）发生相互作用，后者同样可施加选择压力，尤其针对果实硬度。然而，果皮硬度的形成未必源于对生物压力的适应性响应，也可能源自一项机械约束：果实内部充满富含水分的果肉与种子，会对果皮施加机械压力。果皮硬度或许仅仅源于果实需要维持自身结构以……