Moth melanism: From British soot to China’s
tea gardens
Science China Press
image:
In tea gardens (represented as bottom left), tea plants grow as dense branched shrubs, making visual recognition from aerial views difficult. In addition, both color morphs (melanic and grey) are not well-camouflaged against their resting backgrounds of leaves or twigs. Thus, strong selection by visual predators seems to be absent or unclear for the color variations in tea geometrids.
view moreCredit: Photos are from Yongjian Liu and Hongxin Jiang.
Color variation in insects is common, often driven by the advantages of mimicry and camouflage for predator avoidance. A textbook example is industrial melanism in the British peppered moth (Biston betularia), where a rapid phenotypic shift from grey to melanic forms occurred, driven by a camouflage advantage on soot-darkened surfaces during the Industrial Revolution. In Lepidoptera (moths and butterflies), while massive researches have focused on butterflies - often the more colorful members – the color variations of moths, which comprises 90% of the described species, have received much less attentions.
A recent collaborative study, published in National Science Review, investigates the genetics and evolution of melanism in the tea geometrid (Ectropis grisescens), a moth species widely distributed in China’s tea gardens. Like the peppered moths, adult tea geometrids exhibit both melanic and grey forms in nature. However, the ecological scenario in tea gardens, where tea plants typically grow densely with trunks fully sheltered by leaves and twigs, minimizes the potential advantage of color variation for crypsis, if any. This unique setting allowed the authors to trace the parallel evolution of melanism under different geographical, ecological, and selective scenarios, particularly in the absence of predominant selection.
The research team applied genetic and genomic approaches to map the melanism locus to the ‘cortex’ locus, a well-known ‘hotspot’ region that controls industrial melanism in British peppered moths and wing color patterns in many butterflies. Through gene editing experiments, the study functionally verified that the hidden non-coding RNAs within this locus - which had been previously identified in butterflies - serve as the primary effectors of pigmentation in moths as well. The team found distinct mutations around this locus responsible for the independently derived melanism in various tea geometrid populations across China. Field surveys conducted at multiple locations revealed that melanic morphs of the tea geometrid are generally maintained at relatively low frequencies in the wild, especially in northern regions. This pattern may be linked to the reproductive disadvantage observed in the melanic morph, which becomes more pronounced under cooler temperatures.
In conclusion, this study reveals that melanism in moths operates under a highly constrained mechanism but also reveals novel environmental factors other than visual predation that influence its evolution. The findings propose a paradigm: a highly variable genetic hotspot can fuel the repeated evolution of both adaptive and non-adaptive phenotypes, playing a key role in shaping biodiversity.
Journal
National Science Review
Method of Research
Experimental study
NUS study: A simple DNA switch helps tropical butterflies change wing patterns with the seasons
National University of Singapore
image:
A mating pair of dry-season (left) and wet-season (right) B. anynana butterflies
view moreCredit: William Piel
Singapore, 24 October 2025 — Scientists from the National University of Singapore (NUS) have discovered a simple DNA “switch” that helps tropical butterflies adjust the size of their wing eyespots in response to seasonal temperatures, shedding light on the evolution of environmental sensitivity. The findings could inform future efforts to understand and potentially bolster adaptation in a changing climate.
Insects often adapt in surprising ways to their surroundings. Some even change their colours with the seasons. This seasonal flexibility, called plasticity, helps them survive but its evolutionary origins have remained a mystery.
A team led by Professor Antónia Monteiro from the NUS Department of Biological Sciences, identified a stretch of DNA that helps certain butterflies switch their wing patterns between wet and dry seasons.
The research outcome has been published in the journal Nature Ecology & Evolution on 24 October 2025.
Prof Monteiro said, “Many tropical butterflies look strikingly different depending on whether they emerge in the dry or wet season. The African butterfly, Bicyclus anynana, the species we study is one such example.”
In the wet season, these butterflies develop larger eyespots on their wings. During the dry season, these eyespots are smaller. These seasonal changes enhance survival in each environment. Earlier work showed that the temperature at which caterpillars are reared triggers this size change, and that the pronounced temperature response is unique to the satyrid group of butterflies. This group of butterflies is characterised by their predominantly brown wings which are often marked with distinctive eyespots.
In the new study, the team pinpointed a master instruction gene called Antennapedia (Antp), that controls how satyrid butterfly eyespots develop. They found that this gene becomes more or less active depending on the temperatures at which the butterflies were raised. Disrupting the activity of this gene in two different satyrid species reduced eyespot size, especially when the insects were raised at warmer temperatures, confirming Antp’s role in the seasonal size change.
The research team also discovered a previously unknown DNA switch (a “promoter”) that exists only in satyrid butterflies. This switch turns on the Antp gene specifically in eyespot central cells. Disabling the switch reduced the butterflies’ ability to adjust eyespot size with temperature, showing that this genetic element contributed to the evolution of their seasonal flexibility.
Dr Tian Shen, the first author of the paper who conducted the research when he was a graduate student and postdoctoral fellow at NUS, said, “It is striking that a simple genetic switch can underlie complex environmental sensitivity across a broad group of insects. These findings open the door to future research into the roles such switches play in shaping adaptations, and to insights that could inform conservation in a changing climate.”
In B. anynana, when the gene Antp is knocked out (KO), eyespots become smaller, but the effect is stronger under higher temperature conditions.
A simple genetic switch helps a clade of butterflies change their wing eyespot patterns in response to temperature. In satyrid butterflies, eyespots are larger when larvae are reared at higher temperatures (27°C) and smaller at cooler temperatures (17°C). An eyespot-specific promoter (shown in purple) activates the Antp gene in eyespot cells. Butterflies that carry this promoter have more temperature-sensitive eyespots, changing in size more dramatically at higher temperature than at lower temperature. The origin of this Antp promoter, the recruitment of the Antp gene to eyespots, and the evolution of eyespot size plasticity in response to temperature is inferred to have happened at around the same time – 60 million years ago
Credit
Tian Shen
Journal
Nature
Method of Research
Experimental study
Subject of Research
Animals
Article Title
A novel Hox gene promoter fuels the evolution of adaptive phenotypic plasticity in wing eyespots of satyrid butterflies
Article Publication Date
24-Oct-2025
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