How does one species split into two? Recent research reveals the effects of temporal separation among individuals in a moth species.
How does one species evolve into two? For biologists, this question carries significant weight. Generally, it is understood that speciation typically occurs when organisms from one population become separated geographically. If they remain apart for an extended period, they may lose the capability to interbreed.
A recent study featured in the journal Proceedings of the Royal Society B: Biological Sciences illustrates a less common mode of speciation. Instead of being divided by a geographical barrier like a mountain range or an ocean, members of a species can experience separation across time.
The researchers concentrated on two closely related moth species that inhabit overlapping areas in the southeastern United States.
“These two are remarkably similar,” stated lead author Yash Sondhi, who conducted this research while at Florida International University and later at the Florida Museum of Natural History. “They’ve developed differences primarily in their flying times.”
The rosy maple moths, belonging to the genus Dryocampa, resemble a whimsical creation from a Roald Dahl tale. They flaunt a thick mane that resembles a lion’s, and their vivid, colorful scales remind one of strawberry and banana taffy. Both male and female rosy moths are exclusively nocturnal.
In contrast, pink-striped oakworm moths, classified under the genus Anisota, are more subdued in appearance, displaying subtle hues of ochre, umber, and marl. Females of this species are active at dusk and early evening, while males prefer daytime flights.
According to Sondhi, previous studies indicated that these two groups, Dryocampa and Anisota, diverged from a single ancestor about 3.8 million years ago, which is relatively recent in evolutionary terms. The genus Anisota includes several species, all of which are active during the day, while the rosy maple moth is the sole species within Dryocampa that is nocturnal.
Sondhi specializes in insect vision biology and viewed this moth pair as an excellent opportunity to investigate how vision adapts when species alter their activity patterns.
However, his research took an unexpected turn.
“I initially aimed to examine differences in color vision, but we stumbled upon differences in their clock genes, which makes sense in retrospect,” Sondhi explained.
Clock genes regulate the circadian rhythms of plants and animals, influencing the cycles of activity and dormancy over a roughly 24-hour span. They play crucial roles in metabolism, cell growth, blood pressure, and body temperature.
In any organism undergoing a shift in activity pattern, clock genes are bound to be involved. “This system has been preserved across all living organisms, from fruit flies to mammals and plants. They all possess some form of time-keeping system,” he noted.
Sondhi compared the transcriptomes of the two moths. Unlike genomes, which encompass the entirety of an organism’s DNA, transcriptomes include only the genes actively utilized to produce proteins. This makes them effective for studying variations in protein expression throughout the day.
As anticipated, Sondhi identified several genes with differing expressions in the two moth species. The nocturnal rosy maple moths devoted more energy to their sense of smell, while the day-active oakworm moths expressed more genes related to vision.
However, there were no detected differences in genes responsible for color vision. This does not necessarily imply their color vision is identical; any differences likely pertain to sensitivity and tuning rather than the genes’ structural components.
One particular gene stood out: Disconnected, or disco, showcased varying expression levels in both species during day and night. In fruit flies, disco is known to play an indirect role in regulating circadian rhythms by helping produce neurons that convey clock enzymes between the brain and body.
The disco gene Sondhi identified was twice the size of its fruit fly equivalent and featured additional zinc fingers—functional parts of a gene that interact directly with DNA, RNA, and proteins. This suggests that alterations in the disco gene may have contributed to the rosy maple moth’s shift to nocturnal activity.
Upon examining the disco gene across both moth types, Sondhi discovered 23 mutations distinguishing them. These mutations were found in the gene’s active portions, implying they may play a part in observable characteristics of the moths. Sondhi observed evolution in real-time.
“If this is functionally verified, it represents a significant example of the molecular mechanisms underlying speciation, which is quite rare to document,” he remarked.
This research is also a vital step towards enhancing our understanding of the diverse means by which life evolves and sustains itself. Initially, when genetics emerged as a field, researchers often narrowed their focus to a few representative species, such as fruit flies or lab mice, for simplicity. However, this approach limited our comprehension of broader biological trends. Just as humans differ fundamentally from lab mice, moths are not comparable to fruit flies.
“As species continue to decline due to climate change and other human-induced factors, we will need to genetically modify more of the remaining species to enable traits like drought resistance or adaptation to light-polluted environments. Consistently achieving this will necessitate a wider array of functionally characterized genes across different organisms. We cannot solely rely on Drosophila,” Sondhi concluded.
