The Mystery of Insect Wings

There is a gap in fossil records of about 50 million years between when insects did not have wings and when they did have wings. This gap creates a breeding ground for theories of the origin of how insects evolved to acquire their modified limbs. Many of the theories contradict one another in critical ways, however, scientists have recently started to combine differing theories to help understand the answer to this mystery. For example, the Dual Origin Hypothesis combines the Paranotal Hypothesis with the Pleural Hypothesis. The Paranotal Hypothesis states that wings started out as an extension of the paranotal lobe. This theory gained popularity due to the morphological similarities and the lobe’s proximity to where the wing is attached today. The Pleural Hypothesis argues that wings evolved from either an extension of the pleuron plate or the modification of exites found on the legs of early insects. This theory was convincing due to the level of articulation these areas of the pleuron had already developed. First introduced by Niwa et al. in 2010, the Dual Origin Hypothesis combines the two, stating that the paranotal lobe and areas of the pleuron evolved and consequently merged together to form the wing structure we are familiar with today (Niwa, 2010)

The extension of the paranotal lobe can be defended by a 325-million-year-old fossil, Delitzschala bitterfeldensis, belonging to the Palaeodictyoptera order. The fossil reveals two pairs of wings as well as two paranotal lobes containing veins. It also showed, paired with various other fossils, that they drank from tall tree ferns and clubmosses (Ross, 2017). Genetic evidence supports the Pleural Hypothesis. Patterns found in wing-specific genetic markers found in Hexapods indicate that wings evolved from the appendages of insect ancestors (Averof, 1997). Though both hypotheses have evidence to support them, they also have many flaws. The Dual Origin Hypothesis aims to limit these flaws by combining the two. Recent analysis of an integral gene in wing transformation (vestigial or vg) in the Red Flour Beetle (Tribolium castaneum) indicates that tissue of both the paranotum and legs in the first section of the thorax could be the same tissue involved in ancestral insects (Clark-Hachtel et al., 2013). The method of relating the evolution of extinct insects and the development of extant insects (evo-devo) has opened up the doors to a growing amount of evidence to support the Dual Origin Hypothesis.

It is believed that insects had preadaptations prior to wings. One argument for why the paranotal lobe would have extended is that the lobe was used for thermoregulation. With this advancement, insects were able to become more active. This increase in activity would lead to more opportunity and more flexibility in lifestyle. For example, like the Delitzschala bitterfeldensis, insects were able to go higher in altitude to locations, such as clubmosses, with not as much competition for resources. This may have contributed to an environment that allowed insects to have continual paranotal lobe growth as well as an opportunity to advance their pleural appendages and the eventual merging of the two into a wing.

Though combining two theories may lead to a stronger story of the origin of how insects gained wings, the Dual Origin Hypothesis still is not without its flaws. The Dual Origin Hypothesis still does not explain why insects evolved to grow wings (Clark-Hachtel and Tomoyasu, 2016). Instead, the circumstances and preadaptations are up to speculation. The hypothesis also does not explain how the extended paranotal lobe and articulated pleural appendage merged, whereas the Paranotal Hypothesis does a better job at explaining how the wing took its form. This will likely remain the case until new paleontological evidence surfaces.  

Averof, Michalis, and Stephen M. Cohen. “Evolutionary Origin of Insect Wings from Ancestral Gills.” Nature, vol. 385, no. 6617, 1997, pp. 627–630.

Clark-Hachtel, Courtney M, and Yoshinori Tomoyasu. “Exploring the Origin of Insect Wings from an Evo-Devo Perspective.” Current Opinion in Insect Science, vol. 13, 2016, pp. 77–85.

Clark-Hachtel, C. M., et al. “Insights into Insect Wing Origin Provided by Functional Analysis of Vestigial in the Red Flour Beetle, Tribolium Castaneum.” Proceedings of the National Academy of Sciences, vol. 110, no. 42, 2013, pp. 16951–16956.

Niwa, Nao, et al. “Evolutionary Origin of the Insect Wing via Integration of Two Developmental Modules.” Evolution & Development, vol. 12, no. 2, 2010, pp. 168–176.

Ross, Andrew. “Insect Evolution: The Origin of Wings.” Current Biology, Cell Press, 6 Feb. 2017.