Researchers in Finland have proposed a new theory on how the unique light conditions of Earth’s polar regions sustain biodiversity over millions of years. Led by Professor Kari Saikkonen from the University of Turku, the team suggests that the extreme seasonal variations in light—characterized by the months-long “midnight sun” in summer and the prolonged darkness of the “Polar Night” in winter—create conditions for the formation of hybrid zones around the poles. These hybrid zones promote biodiversity by synchronizing the reproductive cycles of species, forcing them into a narrower window for reproduction. The researchers highlight the role of day length as a stable environmental factor, unlike temperature, which fluctuates with climate changes. Because many organisms, particularly plants and microbes, use day length to time their reproductive cycles, the extreme light environment of the polar regions increases the likelihood of reproductive overlap between closely related species. This synchronization leads to hybridization, where different species interbreed, thereby exchanging genetic material and creating new adaptive gene combinations. Hybridization, though common across many groups of organisms, has been underappreciated as a force for sustaining biodiversity. At lower latitudes, where day length varies less across seasons, reproductive overlap and hybridization are much less likely to occur. However, in polar regions, where day length changes dramatically, this overlap is frequent, fostering genetic mixing and differentiation of species over time, especially as species migrate across latitudes during Earth’s cooling and warming cycles.
The research also emphasizes the critical role of microbes in promoting and sustaining biodiversity. Light-sensitive microbes, which are highly adaptable due to their short life cycle, are thought to help plants and other organisms adapt to light conditions. Microbes are an important part of biodiversity that interact with plants and animals to influence their health and development. Saikonen and his team argue that even if biodiversity recovers from problems such as mass extinction, the structure of ecosystems will change, creating a new set of species. As climate change continues to affect the polar regions, with the Arctic warming at a rate two to four times faster than the global average, scientists emphasize the importance of maintaining genetic diversity and species interactions to support ecosystems and services.