How does one kind become two? If you’re a biologist, that’s a loaded question. The consensus is that in most cases the process of speciation occurs when individuals from a single population become geographically isolated. If they are separated long enough, they lose the ability to interbreed.
A new study published in the journal Proceedings of the Royal Society B: Biological Sciences shows what happens when a less common form of speciation occurs. Rather than being separated by a physical barrier, such as a mountain range or an ocean, members of a species can become separated over time.
The researchers focused on two closely related moth species with overlapping ranges in the southeastern United States.
“These two are very similar,” said lead author Yash Sondhi, who conducted research for the study while working at Florida International University and later at the Florida Museum of Natural History. “They’ve differentiated along this one axis, and that’s when they fly.”
Pink maple moths, in the genus Drycampalooks like what you would get if Roald Dahl painted something from a fever dream. They wear a thick lion’s mane over their heads and bellies, and their vibrant scales are the color of strawberry and banana taffy. Both male and female pink moths fly exclusively at night.
Pink-banded oakworm moths, in the genus Anisotaare less striking, with subtle shades of ochre, umber and marl. While females of this species are active at dusk and early evening, the males prefer to fly during the day.
Sondhi knew from previous research that these two groups, Drycampa And Anisotaemerged from a single species about 3.8 million years ago, which is relatively recent on evolutionary timescales. There are a handful of species in the genus Anisotaall of which are active during the day. The nocturnal pink maple moths are the only species in the genus Drycampa.
Sondhi specializes in the biology of insect vision and saw the moth pair as the perfect opportunity to investigate how vision evolves as a species changes its activity patterns.
But things didn’t go as planned.
“I started looking for differences in color vision. Instead we found differences in their clock genes, which makes sense in retrospect,” Sondhi said.
Clock genes control the circadian rhythm of plants and animals. The ebb and flow of the proteins they create causes cells to become active or inactive over a period of about 24 hours. They affect everything from metabolism and cell growth to blood pressure and body temperature.
Any organism that reverses its activity pattern is almost guaranteed to involve clock genes. “It’s a system that’s in everything from fruit flies to mammals to plants. They all have some kind of timekeeping mechanism,” he said.
Sondhi compared the transcriptomes of the two moths. Unlike genomes, which contain the entire DNA of an organism, transcriptomes contain only the subset of genetic material that is actively used to make proteins. This makes them useful for examining differences in protein levels throughout the day.
As expected, Sondhi found a number of genes expressed at different levels in the two moth species. Nocturnal pink maple moths invested more energy in their sense of smell, while the daytime flying oakworm moth produced more genes related to vision.
However, there were no differences in the genes that confer the ability to see color. That doesn’t necessarily mean their color vision is identical, but if differences exist, they likely lie at the level of tuning and sensitivity and not in the structure of the genes themselves.
There was another gene that stood out. Connection lostor discowas expressed at different levels during the day and night in both species. With fruit flies disco It is known to indirectly influence circadian rhythm through the production of neurons that transmit clock enzymes from the brain to the body.
The disco The gene Sondhi found in his moth samples was twice the size of its fruit fly counterpart, and it had extra zinc fingers: active parts of a gene that interact directly with DNA, RNA and proteins. It seemed likely that changes in the disco genes were at least partially responsible for the switch to night flying in pink maple moths.
When he got the disco gene of pink maple moths with that of oak worms, he found 23 mutations that distinguish each from the other. The mutations were also in active parts of the gene, meaning they likely contributed to observable physical differences between the moths. Sondhi looked at evolution in action.
“If this is confirmed functionally, this is a very concrete example of the mechanism behind the way they speciated at the molecular level, which is rare,” he said.
The study is also an important impetus for a better understanding of the different ways in which life sustains and propagates itself. When genetics first became a field of research, researchers focused their efforts mainly on a few representative species, such as fruit flies or laboratory mice. This was done primarily for expediency, but it limits the amount of knowledge we have about broad biological patterns. Just as a human is not a laboratory mouse, a moth is not a fruit fly.
‘As species continue to decline due to climate change and other anthropogenic changes, we will need to genetically engineer a greater number of the species that remain to enable, for example, drought tolerance, or to be active in light-polluted regimes. Consistently, having a broader collection of functionally characterized genes across all organisms is critical DrosophilaSondhi said.
