The primary conclusion drawn from the study was that, while body size does have some influence on the maximum growth rate of diatom populations, temperature and genome size were found to be more significant factors. Nonetheless, in colder regions, body size still retained its importance, supporting the principles outlined in Bergmann’s Rule.
In species abundance prediction, body size is a crucial and consistent indicator, indicating that smaller creatures tend to be more numerous than larger ones. An exception to this is Bergmann’s Rule, which states that in polar areas, larger organisms are more common. Additional influences on species abundance include factors like light and food availability, competition, and predation.
Recent research by a team from the University of Alberta’s biological sciences department has introduced a genetic aspect to our understanding of species abundance.
Genome size, defined as the total DNA contained in a single copy of a complete genome, can serve as a strong indicator of species abundance. The study focused on diatoms, which are single-celled algae essential to both freshwater and marine food chains. They generate long-chain fatty acids, including fish oil and other lipids that provide energy. These energy-rich molecules created by diatoms are passed up through the food chain, affecting zooplankton, aquatic insects, fish, and ultimately humans.
Diatoms are also vital for photosynthesis, the process that transforms carbon dioxide into oxygen. It is believed that diatoms contribute 20-25 percent of the oxygen in Earth’s atmosphere, surpassing contributions from rainforests and terrestrial plants.
The essential finding revealed that temperature and genome size were the most significant factors affecting the maximum growth rate of diatom populations, with body size still playing a role in colder regions, thereby upholding Bergmann’s Rule.
The research paper titled “Diatom abundance in the polar oceans is predicted by genome size” was published in PLoS Biology. The authors include Wade Roberts, a postdoctoral researcher in the Alverson Lab; Adam Siepielski, an associate professor; and Andrew Alverson, a professor and lab director.
Roberts highlighted the importance of genome size in determining cell function and its capacity to adapt to environmental changes.
“In phytoplankton, there’s a strong correlation between cell size and genome size,” Roberts explained. “We’ve acknowledged this for some time. However, the question remained whether cell size influenced genome size or the other way around. We conducted a path analysis to examine this relationship and discovered that an increase in genome size results in a larger cell size—confirming that genome size indeed drives cell size.”
Diatom genome sizes can vary greatly—by as much as 50 times among different species—yet much of this difference consists of repeated DNA sequences. While DNA encodes proteins that are fundamental to life, the function of this repetitive DNA within the cell remains unclear. It is estimated that only around 2 percent of the human genome is made up of functional genes.
This study enhances our understanding of species abundance by demonstrating that genome size, a fundamental trait across all life, can be a global predictor of species abundance.
“In polar regions, larger organisms tend to be more abundant,” Roberts stated. “This is evident in mammals and other multicellular life forms, but we were uncertain whether this was the same for phytoplankton. Now, we can predict community composition based on temperature, allowing us to assess whether larger diatoms will survive in warming waters.”
This could indicate that larger-celled diatoms may decline in number on a warming Earth, possibly resulting in a decrease in oxygen production.
