Tall tree species tend to produce larger seeds, a new study confirms, though scientists are unsure why.
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Dr. Angela Moles (Photo: bio.mq.edu) |
This research was conducted by Australian scientist Dr. Angela Moles from Macquarie University in Sydney and her colleagues, published in the journal Science.
In nature, tree seeds vary significantly in size, from tiny orchid seeds to the enormous double coconut fruits found in the Maldives. Scientists have always wondered what evolutionary forces determine their size.
The enormous double coconuts of the Maldives.
In the largest study of its kind, Moles and her international team examined a representative sample of 13,000 plant species worldwide. They charted based on existing knowledge of the evolutionary relationships among species to identify the most significant changes in seed size over time.
The research team then compared these changes with other variations in the plants, such as whether they grew near the tropics or dispersed seeds via wind or other methods. Previously, scientists believed that these factors influenced seed size.
However, the research team was surprised to discover that the strongest indicator of seed size was the size of the tree: the larger the tree, the bigger its seeds, and as the tree shrank, its seeds tended to shrink as well.
“What’s surprising is that there is no obvious mechanical reason suggesting they need to do this,” remarked co-author Professor Mark Westoby. “So, in this sense, it’s a new question we need to focus on.”
One of the oddities about tree seeds is that while smaller seeds tend to exist in large numbers, this does not confer any evolutionary advantage to the tree. This is because there is a balance between size and survivability; smaller seeds are not equipped as well to survive as their larger counterparts.
