Finnish researchers have proposed an interesting theory about the Earth’s poles. They argue that the unique light conditions in these regions create circumpolar hybrid zones around the North and South Poles, which increase the synchrony of reproductive seasons between species. This means that all species are forced into a narrower breeding window, ultimately maintaining biodiversity in the long term.
In a recently published research paper, Professor Kari Saikkonen from the University of Turku and his colleagues present a compelling new theory that Earth’s auroral environments have played a key role in maintaining biodiversity for millions of years. The extreme conditions in these regions, characterized by 24-hour daylight in summer and months of polar night in winter, create an incredible environment that shapes the survival and reproduction of diverse species.
“At the heart of our theory is the hypothesis that extreme light conditions at the poles create hybrid zones at the poles,” Saikkonen says.
The variation in day length with latitude provides a stable environmental signal that is independent of local and global climate and plays an important role in timing the reproduction of many organisms. This phenomenon is particularly important for photosynthetic organisms such as plants and microorganisms, creating unique opportunities for species to interbreed in polar regions.
Hybridization, whether intentional or occurring naturally, can lead to the development of desirable traits in agricultural crops and promote biological compatibility between species.
“Hybridization is common in almost all groups of organisms, but its role as a force maintaining biodiversity is not 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, resulting in new gene combinations that adapt to different environmental conditions,” says Saikkonen.
At low latitudes, subtle changes in photoperiod between seasons do not lead to overlaps in breeding seasons among genetically distinct populations, subspecies, or varieties within a species complex, nor do they promote hybridization.
“Thus, species ranges shift across latitudes during global cooling and warming cycles, resulting in repeated isolation and contact between species, which in turn leads to species mixing and differentiation, generating new biodiversity over long geological periods,” Saikkonen says.
Microorganisms have played a pivotal role in shaping the diverse fabric of life since its creation, and their impact on global biodiversity continues to this day.
“More and more evidence shows that microbes are ubiquitous and have short life cycles that make them highly adaptable. Many microbes are light sensitive and affect the health of virtually all plants and animals. All plants and animals have a diverse microbiome and need to be treated as a whole,” Saikkonen points out.
In their study, Saikkonen and his colleagues put forward a compelling hypothesis that light-sensitive microbes may hold the key to helping plants thrive in polar regions, demonstrating the remarkable adaptability of these tiny organisms.
The threat of climate change and biodiversity loss is one of the most pressing threats to Earth’s ecosystems and the vital services they provide. The Earth’s polar regions are experiencing unprecedented warming, two to four times faster than the global average.
“Climate models predict that Arctic sea ice will melt by the end of the century. Over the same period, Antarctica’s ice-free area will increase from about 2% today to about 25%. Melting West Antarctic glaciers alone would raise sea levels by five metres, threatening 10% of the world’s population and many of the world’s coastal marine ecosystems over the coming decades or centuries,” says Saikkonen.
Researchers are challenging the traditional species-centric approach to biodiversity, emphasizing not only species diversity but also genetic diversity within organisms and the importance of essential microbial partners for plants and animals.
“We propose that biodiversity can recover after disturbances or mass extinctions in the long term, but that ecosystems will reconstitute themselves as new assemblages of species. This calls for greater attention to the importance of ensuring sufficient genes, species and species interactions are available to support future diversification and ecosystem functions and services.”
It is therefore important to address biodiversity loss due to climate change,” emphasizes Saikkonen.
Journal References:
Kari Saikkonen, Tracy Birge, Benjamin Fuchs, Marjo Helander, Janne A. Ihalainen, Riitta Nissinen, and Pelle Pugbu. Towards an integrated understanding of how extreme auroral regimes, hybridization, and light-sensitive microbes shape global biodiversity. One Earth, 2024. DOI: 10.1016/j.oneear.2024.08.002
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