Koutrouditsou Lydia K, Nudds Robert L
School of Biological Sciences, Faculty of Biology, Medicine and Health University of Manchester Manchester UK.
Ecol Evol. 2021 Mar 17;11(9):4744-4749. doi: 10.1002/ece3.7374. eCollection 2021 May.
The European swallowtail butterfly () is so named, because of the long and narrow prominences extending from the trailing edge of their hindwings and, although not a true tail, they are referred to as such. Despite being a defining feature, an unequivocal function for the tails is yet to be determined, with predator avoidance (diverting an attack from the rest of the body), and enhancement of aerodynamic performance suggested. The swallowtail, however, is sexually size dimorphic with females larger than males, but whether the tail is also sexually dimorphic is unknown. Here, museum specimens were used to determine whether sexual selection has played a role in the evolution of the swallowtail butterfly tails in a similar way to that seen in the tail streamers of the barn swallow (), where the males have longer streamers than those of the females. Previously identified sexual dimorphism in swallowtail butterfly size was replicated, but no evidence for dimorphism in tail length was found. If evolved to mimic antennae and a head to divert a predatory attack, and if an absolute tail size was the most effective for this, then the tail would probably be invariant with butterfly hindwing size. The slope of the relationship between tail length and size, however, although close to zero, was nonetheless statistically significantly above (tail length ∝ hindwing area ). The slope also did not equate to that expected for geometric similarity (tail length ∝ hindwing area) suggesting that tail morphology is not solely driven by aerodynamics. It seems likely then, that tail morphology is primarily determined by, and perhaps a compromise of several, factors associated with predator avoidance (e.g. false head mimicry and a startling function). Of course, experimental data are required to confirm this.
欧洲燕尾蝶（）之所以得名，是因为其后翅后缘延伸出的狭长突出部分，尽管并非真正的尾巴，但仍被如此称呼。尽管这是一个决定性特征，但尾巴的确切功能尚未确定，有人认为其功能是躲避捕食者（将攻击从身体其他部位转移开）以及增强空气动力学性能。然而，燕尾蝶存在性别大小二态性，雌性比雄性大，但尾巴是否也存在性别二态性尚不清楚。在这里，利用博物馆标本确定性选择是否在燕尾蝶尾巴的进化中发挥了作用，其方式类似于家燕（）的尾羽，雄性的尾羽比雌性的更长。之前在燕尾蝶大小方面确定的性别二态性得到了重现，但未发现尾巴长度存在二态性的证据。如果进化是为了模仿触角和头部以转移捕食性攻击，并且如果绝对的尾巴大小对此最为有效，那么尾巴可能会随蝴蝶后翅大小而不变。然而，尾巴长度与大小之间关系的斜率虽然接近零，但在统计学上仍显著高于（尾巴长度 ∝ 后翅面积 ）。该斜率也不等于几何相似性所预期的斜率（尾巴长度 ∝ 后翅面积），这表明尾巴形态并非仅由空气动力学驱动。那么，似乎尾巴形态主要由与躲避捕食者相关的几个因素决定，也许是这些因素的一种折衷（例如假头部模仿和惊吓功能）。当然，需要实验数据来证实这一点。
