Researchers in Finland have proposed a fascinating theory about the Earth’s Polar regions. They suggest that the unique light environment in these areas creates circumpolar hybrid zones around the North and South Poles, leading to increased synchrony of reproductive phenology among species. This means that all species are forced into a smaller window for reproduction, ultimately sustaining biodiversity in the long term.
In a recently published research article, Professor Kari Saikkonen and his colleagues from the University of Turku present a compelling new theory about how the Earth’s polar light environment has played a crucial role in maintaining biodiversity for millions of years. The extreme conditions in these regions, characterized by 24-hour daylight in the summer and months-long Polar Nights in winter, create a remarkable environment that shapes the survival and reproduction of diverse species.
“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,” says Saikkonen.
The changing day length across latitudes serves as a stable environmental cue, unaffected by local or global climate, and plays a crucial role in the timing of reproduction for many organisms. This phenomenon, especially crucial for photosynthetic organisms like plants and microbes, creates unique opportunities for species to hybridize in polar regions.
Hybridization, whether intentional or naturally occurring, can lead to the development of desirable traits in agricultural crops and promote biological compatibility between species.
“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 individuals of the original species. This allows genes to be transferred from one species to another while creating new adaptive gene combinations to different environmental conditions,” says Saikkonen.
At lower latitudes, subtle shifts in day length between seasons do not lead to overlapping reproduction timing among genetically distinct populations, subspecies, or varieties within a species complex, nor do they encourage hybridization.
“Therefore, species’ range shifts across latitudes during the cycles of the Earth’s cooler and warmer periods cause recurrent isolation and contact among species. This results in mixing and differentiation of species and creates new biodiversity over long periods of geological time,” says Saikkonen.
Microbes have been pivotal in shaping the diverse tapestry of life since its inception, and their influence on global biodiversity persists to this day.
“Microbes are ubiquitous, and mounting evidence continues to reveal that they have 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 a diverse microbiota, they should be treated as a whole,” notes Saikkonen.
In a study, Saikkonen and colleagues propose a compelling hypothesis: photosensitive microbes may hold the key to helping plants thrive in polar regions, showcasing the remarkable adaptability of these tiny organisms.
The looming specter of climate change and biodiversity loss presents one of the most pressing threats to our planet’s ecosystems and the essential services they provide. The polar regions of our planet are experiencing unprecedented warming at a rate of 2–4 times faster than the global average.
“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 two percent today to almost 25 percent. The melting of the western Antarctic glaciers alone would cause sea levels to rise by five meters, threatening 10 percent of the world’s population and many of the world’s coastal ocean ecosystems over the next decades or centuries,” says Saikkonen.
In challenging the traditional species-centric approach to biodiversity, researchers are emphasizing the critical importance of not only species diversity but also genetic diversity within organisms and the essential microbial partners of 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. This calls for increased attention to the importance of ensuring sufficient genetic, species, and species interaction potential to support future diversification and ecosystem functions and services.
Thus, tackling climate change-driven biodiversity loss is important”, stresses Saikkonen.
Journal reference:
- Kari Saikkonen, Traci Birge, Benjamin Fuchs, Marjo Helander, Janne A. Ihalainen, Riitta Nissinen, Pere Puigb�. Toward an integrated understanding of how extreme polar light regimes, hybridization, and light-sensitive microbes shape global biodiversity. One Earth, 2024; DOI: 10.1016/j.oneear.2024.08.002
