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'False head' in certain butterflies found to evolve from multiple traits working in tandem to deflect predators

Animals often evolve to have certain characteristics that help them escape predators more effectively. Some of these characteristics work to deflect predators away from the animal's head. Many butterfly species have evolved such characteristics in the form of a quasi-head on their hindwings. These "false heads" attract predators to a less vital part of the butterfly's body, thus preserving their actual head and allowing them to survive.

Although "false heads" have been observed in many species and studied to some extent, until recently, there was still a lack of comprehensive analysis on how these traits evolved and whether they might be an adaptive constellation—multiple traits evolving together for a common purpose. So, researchers at the Indian Institutes of Science Education and Research (IISER) recently a study in the Proceedings of the Royal Society B: Biological Sciences that delves a little deeper into the evolutionary history of these protective traits.

The researchers analyzed nearly 1,000 images of lycaenid butterfly species to determine the evolutionary relationship of five individual traits that help form the appearance of the species' false heads. These traits consisted of false antennae coming out of the back wings, dark spots resembling eyes, conspicuous coloration in the false head area, false head contour and convergent lines that meet at the false head.

Analysis of the images was performed to assess whether these traits evolved from simple to complex forms, if they evolved in a correlated manner, and if there was a relationship between the size of the butterfly and the presence of a false head.

The results of their analysis showed a correlation between four of the five traits: false antennae, spot, conspicuous coloration and false head contour. The study indicates that these traits evolved together into a more elaborate and head-like pattern over time.

The presence of convergent lines on the butterfly wings was found to have a correlated pattern of evolution with false head contour, but not with the other traits. The results support the idea that the four correlated traits form an adaptive constellation to deflect predators.

The study authors first hypothesized that larger butterflies may have a greater need for a false head due to being more easily detected. Size, however, did not appear to be related to the presence of false head patterns.

They explain, "Visually oriented predators of butterflies, such as birds, lizards, spiders and mantids, may exert similar predation pressures on butterflies of varying sizes, driving the evolution of similar deflective features in varying prey sizes."

The researchers also found that false head traits were sometimes lost and regained by later generations, and believe that this may be due to changes in the predator population.

Despite some limitations related to image quality and diversity of species, this study provides valuable insight into the complex evolution of traits involved in predator deflection and the cause of striking features, like false heads.