Polar light sustains biodiversity over millions of years 

The unique light environment of the Earth’s polar regions creates conditions that foster the formation of circumpolar hybrid zones around both the North and South Poles, according to a new study. 

These extreme conditions synchronize the reproductive phenology of various species, forcing them into a shorter window for reproduction, which may sustain biodiversity in the long term.

Polar light influences biodiversity

In a recent research article, Professor Kari Saikkonen from the University of Turku, Finland, and his colleagues presented a new theory on how the polar light environment influences biodiversity over millions of years. 

The research, published in the journal One Earth, explores the role of the unique light cycles near the poles in shaping long-term biodiversity.

Extreme cycles of polar light

Daylight patterns on Earth vary significantly depending on latitude. At the Equator, day and night are nearly equal year-round, with only minor seasonal variation in day length as one moves away from the Equator. 

However, closer to the poles, there is substantial seasonality, resulting in phenomena like the “midnight sun,” where there is 24-hour daylight in the summer, and the “polar night,” where the sun does not rise for months during the winter in regions within the Arctic and Antarctic circles.

“At the center of our theory is the hypothesis that the extreme light environment of the polar regions creates hybrid zones in both polar regions,” Saikkonen said.

Seasonal changes in day length 

Unlike temperature, which can vary unpredictably with local and global climate, day length is a stable environmental factor that changes consistently with latitude. 

Many organisms, especially photosynthetic ones like plants and some microbes, have adapted to using seasonal changes in day length as signals to time their reproduction.

Since many organisms rely on light as a cue, the polar light environment increases the likelihood that closely related plant species will flower simultaneously.

This creates opportunities for hybridization, where organisms reproduce with individuals from a different species or variety.

Polar light and hybridization 

Saikkonen noted that although hybridization is common in almost all groups of organisms, its role as a force for sustaining biodiversity has not been fully understood. 

“Hybridization may also involve backcrossing, where hybrid individuals mate with members of the original species. This allows genes to be transferred between species, creating new adaptive gene combinations suited to different environmental conditions,” explained Saikkonen.

At lower latitudes, where day length changes only slightly between seasons, the timing of reproduction among distinct populations or subspecies is less likely to overlap, and thus hybridization is less common. 

However, in polar regions, the unique light cycles may promote more frequent hybridization, leading to new biodiversity over long geological periods.

Evolution of biodiversity 

“Species’ range shifts across latitudes during the Earth’s cooler and warmer cycles cause recurrent isolation and contact among species. This results in mixing and differentiation of species, leading to new biodiversity over long periods of time,” said Saikkonen.

Microbes have played a crucial role in the evolution of biodiversity since the origin of life, and they continue to have a significant impact on maintaining and promoting global biodiversity.

“Microbes are ubiquitous, and mounting evidence reveals their high adaptive potential due to their short life cycle. Many microbes are light-sensitive and affect the well-being of virtually all plants and animals. Since all plants and animals have diverse microbiota, they should be treated as a whole,” Saikkonen said.

Polar regions are warming rapidly

In their study, the experts hypothesize that photosensitive microbes may play a role in helping plants adapt to the extreme light conditions of polar regions.

Climate change and biodiversity loss are among the greatest global threats to ecosystems today. The polar regions, in particular, are warming at a much faster rate than the global average – up to 2–4 times faster.

“Climate models predict that Arctic sea ice will melt by the end of this century. Over the same period, Antarctica’s ice-free area will increase from approximately 2% today to almost 25%,” said Saikkonen.

The melting of the western Antarctic glaciers alone could cause sea levels to rise by five meters, threatening 10% of the world’s population and many of the world’s coastal ecosystems over the next decades or centuries.”

Climate-driven biodiversity loss

The researchers argue that the conventional species-focused approach to biodiversity must expand to include the genetic diversity of organisms and the importance of microbial associates in plants and animals.

“We propose that biodiversity can, in the long term, recover after disturbances and mass extinctions, but ecosystems will restructure as novel species assemblages,” said Saikkonen.

“This calls for increased attention to the importance of ensuring sufficient genetic diversity, species diversity, and species interaction potential to support future diversification and ecosystem functions and services. Tackling climate change-driven biodiversity loss is crucial.”

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–