Mate preferences act independently on different elements of visual signals in Heliconius butterflies

Mating cues are often comprised of several elements, which can act
independently, or in concert to attract a suitable partner. Individual
elements may also function in other contexts, such as predator defence or
camouflage. In Heliconius butterflies, wing patterns comprise several
individual colour pattern elements, which advertise the butterflies’
toxicity to predators. These wing patterns are also mating cues and males
predominantly court females that possess the same wing pattern as their
own. However, it is not known whether male preference is based on the full
wing pattern or only individual pattern elements. We compared preferences
of male H. erato lativitta between female models with the full wing
pattern and those with some pattern elements removed. We found no
differences in preference between the full wing pattern model and a model
with pattern elements removed, indicating that the complete composition of
all elements is not essential to the mating signal. Wing pattern
preferences also contribute to pre-mating isolation between two other
Heliconius taxa, H. erato cyrbia and H. himera, therefore, we next
compared preferences for the same models in these species. H. erato cyrbia
and H. himera strongly differed in preferences for the models, potentially
providing a mechanism for how pre-mating isolation acts between these
species. These findings suggest that contrasting levels of selective
constraint act on elements across the wing pattern.

求偶信号通常由多种元素构成，这些元素既可独立发挥功能，也可协同配合以吸引合适的交配对象。单个元素还可在其他场景中承担作用，例如用于天敌防御或伪装。在袖蝶属（Heliconius）蝴蝶中，翅纹由多种独立的色彩图案元素组成，这些元素可向天敌传递该物种具有毒性的警示信号。这类翅纹同时兼具求偶信号的功能，雄性袖蝶多会向与自身翅纹一致的雌性展开求偶行为。然而目前学界仍不清楚，雄性的择偶偏好是基于完整翅纹，还是仅针对单个图案元素。为此，我们对比了H. erato lativitta雄性个体对两类雌性翅纹模型的偏好：一类保留完整翅纹，另一组则移除了部分图案元素。实验结果显示，雄性个体对两类模型的偏好并无显著差异，这表明所有图案元素的完整组合并非求偶信号的必要构成要件。翅纹偏好同样有助于另外两类袖蝶类群——H. erato cyrbia与H. himera之间建立交配前生殖隔离。据此，我们接下来对比了这两个物种种雄性对同款实验模型的择偶偏好。结果发现，H. erato cyrbia与H. himera对实验模型的偏好存在显著差异，这或许为阐释这两个物种种间交配前生殖隔离的作用机制提供了潜在路径。上述研究结果表明，翅纹各图案元素所承受的选择约束强度存在显著分化。