The ultimate goal of evolution is always the same, survival. That is, everything that has shaped our bodies and instinctive behaviors is designed for the survival of the species as a whole. The same happens with other beings that have developed the most intricate ways to survive, however, how is not entirely clear. This is precisely the case with the secret of the dry leaf butterfly, which has raised the greatest debates throughout history and which now seems to have been revealed.
How the closed wings of the Kallima butterflies came to perfectly resemble a brown, intricately patterned dry tree leaf is not exactly known. In fact, this data has generated the most heated debates among naturalists who have launched various hypotheses to explain the beautiful mimetic pattern of butterflies.
Sudden or gradual onset?
In 1800, Alfred Russel Wallace collected butterflies of the genus Kallima in Southeast Asia and studied them in depth to advance famed naturalist Charles Darwin’s theory of natural selection. Darwin himself had previously suggested that the pattern on the wings of this genus of butterflies had a gradual origin in the mimesis of dry tree leaves.
But the lack of direct experimental evidence has caused many other Lepidoptera scholars to stubbornly refute this hypothesis. It has even been said that the gradual evolution of leaf mimicry is improbable. Proof of this are the writings of the American geneticist Richard Goldschmidt who in the 1940s stipulated that such mimicry must have originated suddenly, as a ‘hopeful monster’ and without intermediate forms.
*Kallima butterfly with wings fully open.
Since then, the controversial debate has generated that the little evidence and the opinions found, keep the secret of the dry leaf butterflies in the unknown. But a recent investigation seems to find light on this unknown and as expected, it seems that Darwin was once again right.
Darwin was right once again
The research published in BMC Ecology and Evolution used the comparative method based on phylogenetic homology. In other words, by observing different species evolutionarily related to the Kallima butterfly, they achieved a «powerful tool to explore the evolutionary origins and the processes of camouflage and mimicry.»
Thanks to this, they were able to reveal that the mimicry of the leaf gradually evolved from the non-mimicry pattern without a sudden transition. A completely contradictory finding to Goldschmidt’s hypothesis and concordant, on the other hand, with Charles Darwin’s theory of natural selection.
And although the study made use of the phenotypic components of the butterfly species, that is, in the appearance of the Kallima and other related butterfly species, the authors are almost certain that the gradual changes in the mimetic patterns of tree leaves , brings about changes in the genotype of the species.
This finding could shed light on the camouflage processes of other species such as moths that imitate the bark of trees, a secret that no one has yet been able to reveal.
References: Suzuki, TK, Tomita, S. & Sezutsu, H. Gradual and contingent evolutionary emergence of leaf mimicry in butterfly wing patterns. BMC Evol Biol 14, 229. DOI
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