Trees that colonise isolated islands often develop bigger seeds. No species demonstrates this evolutionary pattern more than the coco-de-mer, a native of the Seychelles, whose record-breaking seeds can reach a whopping 40-50cm in diameter.
When the Seychelles split from the mainland, these trees became cut off from the animals they relied upon for seed dispersal. Seeds that fell thus stayed put, growing close to – and competing with – their parents, siblings and cousins.
“This exerted pressure on seed size: the larger the seed, the higher the chance of establishment and survival,” says Christopher Kaiser-Bunbury, a scientist at the Technical University of Darmstadt in Germany. Christopher and colleagues have discovered how the coco-de-mer, which grows in very poor soil, is able to sustain such colossal seeds: it uses its leaves as a funnel-and-gutter system that harvests rainwater and diverts it to the base of the trunk.
As the liquid descends, it collects a host of phosphorus-rich material, creating a nutritious soup that feeds the soil immediately around the tree.